linux tmp文件
tmp是temporary的缩写，这个目录是用来存放一些临时文件。/tmp是Linux下的临时文件夹。
该文件夹中的内容一般不会删除，以redhat为例，系统自动清理/tmp文件夹的默认时限是30天。30天不访问的/tmp下的文件会被系统自动删除。
/tmp-临时文件目录，能够被任何用户，任何程序访问，一般用来存放程序的临时文件，所以应该定期清理一下。FHS甚至建议在开机时，应该要将/tmp下的数据都删除，临时目录还有/var/tmp。
Linux有两个公认的临时目录：/tmp与/var/tmp，这两个目录被用户用于存储临时性的文件，亦经常被程序读写用户存储临时性数据。
两个目录没有本质上的区别，最根本的区别仅仅是系统对其中文件清理的默认时间配置不一致。
/tmp：目录默认清理10天未用的文件，系统重启会清理目录;/var/tmp：目录默认清理30天未用的文件。
linux_lldptool
[root@localhost ~]# lldptool set-lldp -i eno2 adminStatus=rxtx;
[root@localhost ~]# lldptool -T -i eno2 -V sysName enableTx=yes;
[root@localhost ~]# lldptool -T -i eno2 -V portDesc enableTx=yes;
[root@localhost ~]# lldptool -T -i eno2 -V sysDesc enableTx=yes;
[root@localhost ~]# lldptool -T -i eno2 -V sysCap enableTx=yes;
linux修改系统语言
/etc/locale.conf 修改：LANG=“zh_CN.UTF-8” ==> LANG=“en_US.UTF-8” ，然后重启生效
linux用户态与内核态
一. 概念
- 操作系统 － 管理计算机硬件与软件资源的软件.是用户与系统交互的操作接口.为它上面运行的程序提供服务.
- 操作系统内核 － 操作系统的核心.负责管理系统的进程.内存.设备驱动程序.文件和网络系统.一个内核不是一套完整的操作系统.如Linux.
- Linux操作系统 － 基于Linux 内核的操作系统.通常由Linux内核.shell(特殊的应用程序.提供运行其他程序的接口).文件系统和应用程序.
linux体系结构
参考图:
linux的运行空间=内核空间+用户空间
- 内核空间:存放的是整个内核代码和所有内核模块,以及内核维护的数据
- 用户空间:用户程序的代码和数据
由上图可知,用户态的应用程序可以通过三种方式来访问内核态资源:
- shell
- 系统调用
- 公共函数库
操作系统需要两种CPU状态
内核态(kernel mode):运行操作系统程序,操作硬件 用户态(user mode):运行用户程序
指令划分
特权指令:只能由操作系统使用,用户不能使用的指令.例如:启动I/O,内存清零,修改程序状态字,设置时钟,允许/禁止中段,停机等 非特权指令:用户程序可以使用的指令.举例:控制转移,算数运算,取数指令,访管指令(使用户程序从用户态陷入内核态)
CPU状态之间的切换
用户态—>内核态：唯一途径是通过中断、异常、陷入机制（访管指令）
内核态—>用户态：设置程序状态字PSW
二. linux系统调用
操作系统提供给用户程序调用系统服务(硬件设备)的一组"特殊"的接口.
为什么要设置系统调用
- 把用户从底层的硬件编程中解放出来: 与具体的硬件完全隔离,用户不需要面向具体的硬件编码,降低了开发的复杂性和难度
- 极大的提高了系统的安全性: 将用户进程隔离实现内核"保护",用户进程不允许访问内核数据,也无法使用内核函数.用户访问内核的路径是事先搞定好的,只能从规定位置进入内核,而不允许肆意跳入内核,用了这样的陷入内核的统一访问路径限制才能保证内核安全无误.
- 使用户程序具有可移植性: 不同平台,不同硬件
系统调用表与系统调用号
系统调用号:
每个系统调用被赋予一个系统调用号,与具体的系统调用相关联,且预先在系统文件中定义,用相应的宏表示.
系统调用表:
内核维护系统调用表,保存系统调用函数的起始地址,系统调用号对应系统调用在调用表中的偏移量.
如何切换
从用户态到内核态切换可以通过三种方式:
- 系统调用:用户进程主动切换到内核态的方式,用户态进程通过系统调用申请使用操作系统提供的程序完成操作,系统调用本身就是中断.
- 异常:当cpu在执行运行在用户态下的程序时,发生了某些事先不可知的异常,这时会触发由当前运行进程切换到处理此异常的内核相关程序中,也就转到了内核态,比如缺页异常
- 外设中断:当外设完成用户的请求时,会向cpu发送中断信号.
mysql巡检脚本
#!/bin/bash
# MySQL巡检脚本
# 设置MySQL用户名和密码（请将它们设置为适当的值）
MYSQL_USER="root"
MYSQL_PASSWORD="123456"
# 获取MySQL版本信息
MYSQL_VERSION=$(mysql -u ${MYSQL_USER} -p${MYSQL_PASSWORD} -e "SELECT VERSION();" | awk 'NR==2{print $1}')
# 获取MySQL运行状态信息
STATUS=$(systemctl status mysql.service)
# 获取MySQL进程列表
PROCESS_LIST=$(mysql -u ${MYSQL_USER} -p${MYSQL_PASSWORD} -e "SHOW PROCESSLIST;" | awk '{print $1,$2,$3,$4,$5,$6}')
# 检查MySQL是否在运行
if [[ "$STATUS" =~ "active (running)" ]]; then
MYSQL_RUNNING="YES"
else
MYSQL_RUNNING="NO"
fi
# 检查MySQL进程是否存在
if [[ -z "$PROCESS_LIST" ]]; then
MYSQL_PROCESS="NO"
else
MYSQL_PROCESS="YES"
fi
# 生成报告
echo "MySQL巡检报告"
echo "----------------"
echo "MySQL版本: $MYSQL_VERSION"
echo "MySQL运行状态: $MYSQL_RUNNING"
echo "MySQL进程存在: $MYSQL_PROCESS"
echo ""
echo "MySQL进程列表"
echo "----------------"
echo "$PROCESS_LIST"
ovs-fields
ovs-fields(7) Open vSwitch Manual ovs-fields(7)
NAME
ovs-fields - protocol header fields in OpenFlow and Open vSwitch
INTRODUCTION
This document aims to comprehensively document all of the fields, both
standard and non-standard, supported by OpenFlow or Open vSwitch, re‐
gardless of origin.
Fields
A field is a property of a packet. Most familiarly, data fields are
fields that can be extracted from a packet. Most data fields are copied
directly from protocol headers, e.g. at layer 2, the Ethernet source
and destination addresses, or the VLAN ID; at layer 3, the IPv4 or IPv6
source and destination; and at layer 4, the TCP or UDP ports. Other
data fields are computed, e.g. ip_frag describes whether a packet is a
fragment but it is not copied directly from the IP header.
Data fields that are always present as a consequence of the basic net‐
working technology in use are called called root fields. Open vSwitch
2.7 and earlier considered Ethernet fields to be root fields, and this
remains the default mode of operation for Open vSwitch bridges. When a
packet is received from a non-Ethernet interfaces, such as a layer-3
LISP tunnel, Open vSwitch 2.7 and earlier force-fit the packet to this
Ethernet-centric point of view by pretending that an Ethernet header is
present whose Ethernet type that indicates the packet’s actual type
(and whose source and destination addresses are all-zero).
Open vSwitch 2.8 and later implement the ``packet type-aware pipeline’’
concept introduced in OpenFlow 1.5. Such a pipeline does not have any
root fields. Instead, a new metadata field, packet_type, indicates the
basic type of the packet, which can be Ethernet, IPv4, IPv6, or another
type. For backward compatibility, by default Open vSwitch 2.8 imitates
the behavior of Open vSwitch 2.7 and earlier. Later versions of Open
vSwitch may change the default, and in the meantime controllers can
turn off this legacy behavior, on a port-by-port basis, by setting op‐
tions:packet_type to ptap in the Interface table. This is significant
only for ports that can handle non-Ethernet packets, which is currently
just LISP, VXLAN-GPE, and GRE tunnel ports. See ovs-vwitchd.conf.db(5)
for more information.
Non-root data fields are not always present. A packet contains ARP
fields, for example, only when its packet type is ARP or when it is an
Ethernet packet whose Ethernet header indicates the Ethertype for ARP,
0x0806. In this documentation, we say that a field is applicable when
it is present in a packet, and inapplicable when it is not. (These are
not standard terms.) We refer to the conditions that determine whether
a field is applicable as prerequisites. Some VLAN-related fields are a
special case: these fields are always applicable for Ethernet packets,
but have a designated value or bit that indicates whether a VLAN header
is present, with the remaining values or bits indicating the VLAN
header’s content (if it is present).
An inapplicable field does not have a value, not even a nominal
``value’’ such as all-zero-bits. In many circumstances, OpenFlow and
Open vSwitch allow references only to applicable fields. For example,
one may match (see Matching, below) a given field only if the match in‐
cludes the field’s prerequisite, e.g. matching an ARP field is only al‐
lowed if one also matches on Ethertype 0x0806 or the packet_type for
ARP in a packet type-aware bridge.
Sometimes a packet may contain multiple instances of a header. For ex‐
ample, a packet may contain multiple VLAN or MPLS headers, and tunnels
can cause any data field to recur. OpenFlow and Open vSwitch do not ad‐
dress these cases uniformly. For VLAN and MPLS headers, only the outer‐
most header is accessible, so that inner headers may be accessed only
by ``popping’’ (removing) the outer header. (Open vSwitch supports only
a single VLAN header in any case.) For tunnels, e.g. GRE or VXLAN, the
outer header and inner headers are treated as different data fields.
Many network protocols are built in layers as a stack of concatenated
headers. Each header typically contains a ``next type’’ field that in‐
dicates the type of the protocol header that follows, e.g. Ethernet
contains an Ethertype and IPv4 contains a IP protocol type. The excep‐
tional cases, where protocols are layered but an outer layer does not
indicate the protocol type for the inner layer, or gives only an am‐
biguous indication, are troublesome. An MPLS header, for example, only
indicates whether another MPLS header or some other protocol follows,
and in the latter case the inner protocol must be known from the con‐
text. In these exceptional cases, OpenFlow and Open vSwitch cannot pro‐
vide insight into the inner protocol data fields without additional
context, and thus they treat all later data fields as inapplicable un‐
til an OpenFlow action explicitly specifies what protocol follows. In
the case of MPLS, the OpenFlow ``pop MPLS’’ action that removes the
last MPLS header from a packet provides this context, as the Ethertype
of the payload. See Layer 2.5: MPLS for more information.
OpenFlow and Open vSwitch support some fields other than data fields.
Metadata fields relate to the origin or treatment of a packet, but they
are not extracted from the packet data itself. One example is the phys‐
ical port on which a packet arrived at the switch. Register fields act
like variables: they give an OpenFlow switch space for temporary stor‐
age while processing a packet. Existing metadata and register fields
have no prerequisites.
A field’s value consists of an integral number of bytes. For data
fields, sometimes those bytes are taken directly from the packet. Other
data fields are copied from a packet with padding (usually with zeros
and in the most significant positions). The remaining data fields are
transformed in other ways as they are copied from the packets, to make
them more useful for matching.
Matching
The most important use of fields in OpenFlow is matching, to determine
whether particular field values agree with a set of constraints called
a match. A match consists of zero or more constraints on individual
fields, all of which must be met to satisfy the match. (A match that
contains no constraints is always satisfied.) OpenFlow and Open vSwitch
support a number of forms of matching on individual fields:
Exact match, e.g. nw_src=10.1.2.3
Only a particular value of the field is matched; for ex‐
ample, only one particular source IP address. Exact
matches are written as field=value. The forms accepted
for value depend on the field.
All fields support exact matches.
Bitwise match, e.g. nw_src=10.1.0.0/255.255.0.0
Specific bits in the field must have specified values;
for example, only source IP addresses in a particular
subnet. Bitwise matches are written as field=value/mask,
where value and mask take one of the forms accepted for
an exact match on field. Some fields accept other forms
for bitwise matches; for example,
nw_src=10.1.0.0/255.255.0.0 may also be written
nw_src=10.1.0.0/16.
Most OpenFlow switches do not allow every bitwise match‐
ing on every field (and before OpenFlow 1.2, the protocol
did not even provide for the possibility for most
fields). Even switches that do allow bitwise matching on
a given field may restrict the masks that are allowed,
e.g. by allowing matches only on contiguous sets of bits
starting from the most significant bit, that is, ``CIDR’’
masks [RFC 4632]. Open vSwitch does not allows bitwise
matching on every field, but it allows arbitrary bitwise
masks on any field that does support bitwise matching.
(Older versions had some restrictions, as documented in
the descriptions of individual fields.)
Wildcard, e.g. ``any nw_src’’
The value of the field is not constrained. Wildcarded
fields may be written as field=*, although it is unusual
to mention them at all. (When specifying a wildcard ex‐
plicitly in a command invocation, be sure to using quot‐
ing to protect against shell expansion.)
There is a tiny difference between wildcarding a field
and not specifying any match on a field: wildcarding a
field requires satisfying the field’s prerequisites.
Some types of matches on individual fields cannot be expressed directly
with OpenFlow and Open vSwitch. These can be expressed indirectly:
Set match, e.g. ``tcp_dst ∈ {80, 443, 8080}’’
The value of a field is one of a specified set of values;
for example, the TCP destination port is 80, 443, or
8080.
For matches used in flows (see Flows, below), multiple
flows can simulate set matches.
Range match, e.g. ``1000 ≤ tcp_dst ≤ 1999’’
The value of the field must lie within a numerical range,
for example, TCP destination ports between 1000 and 1999.
Range matches can be expressed as a collection of bitwise
matches. For example, suppose that the goal is to match
TCP source ports 1000 to 1999, inclusive. The binary rep‐
resentations of 1000 and 1999 are:
01111101000
11111001111
The following series of bitwise matches will match 1000
and 1999 and all the values in between:
01111101xxx
0111111xxxx
10xxxxxxxxx
110xxxxxxxx
1110xxxxxxx
11110xxxxxx
1111100xxxx
which can be written as the following matches:
tcp,tp_src=0x03e8/0xfff8
tcp,tp_src=0x03f0/0xfff0
tcp,tp_src=0x0400/0xfe00
tcp,tp_src=0x0600/0xff00
tcp,tp_src=0x0700/0xff80
tcp,tp_src=0x0780/0xffc0
tcp,tp_src=0x07c0/0xfff0
Inequality match, e.g. ``tcp_dst ≠ 80’’
The value of the field differs from a specified value,
for example, all TCP destination ports except 80.
An inequality match on an n-bit field can be expressed as
a disjunction of n 1-bit matches. For example, the in‐
equality match ``vlan_pcp ≠ 5’’ can be expressed as
``vlan_pcp = 0/4 or vlan_pcp = 2/2 or vlan_pcp = 0/1.’’
For matches used in flows (see Flows, below), sometimes
one can more compactly express inequality as a higher-
priority flow that matches the exceptional case paired
with a lower-priority flow that matches the general case.
Alternatively, an inequality match may be converted to a
pair of range matches, e.g. tcp_src ≠ 80 may be expressed
as ``0 ≤ tcp_src < 80 or 80 < tcp_src ≤ 65535’’, and then
each range match may in turn be converted to a bitwise
match.
Conjunctive match, e.g. ``tcp_src ∈ {80, 443, 8080} and tcp_dst
∈ {80, 443, 8080}’’
As an OpenFlow extension, Open vSwitch supports matching
on conditions on conjunctions of the previously mentioned
forms of matching. See the documentation for conj_id for
more information.
All of these supported forms of matching are special cases of bitwise
matching. In some cases this influences the design of field values.
ip_frag is the most prominent example: it is designed to make all of
the practically useful checks for IP fragmentation possible as a single
bitwise match.
Shorthands
Some matches are very commonly used, so Open vSwitch accepts shorthand
notations. In some cases, Open vSwitch also uses shorthand notations
when it displays matches. The following shorthands are defined, with
their long forms shown on the right side:
eth packet_type=(0,0) (Open vSwitch 2.8 and later)
ip eth_type=0x0800
ipv6 eth_type=0x86dd
icmp eth_type=0x0800,ip_proto=1
icmp6 eth_type=0x86dd,ip_proto=58
tcp eth_type=0x0800,ip_proto=6
tcp6 eth_type=0x86dd,ip_proto=6
udp eth_type=0x0800,ip_proto=17
udp6 eth_type=0x86dd,ip_proto=17
sctp eth_type=0x0800,ip_proto=132
sctp6 eth_type=0x86dd,ip_proto=132
arp eth_type=0x0806
rarp eth_type=0x8035
mpls eth_type=0x8847
mplsm eth_type=0x8848
Evolution of OpenFlow Fields
The discussion so far applies to all OpenFlow and Open vSwitch ver‐
sions. This section starts to draw in specific information by explain‐
ing, in broad terms, the treatment of fields and matches in each Open‐
Flow version.
OpenFlow 1.0
OpenFlow 1.0 defined the OpenFlow protocol format of a match as a
fixed-length data structure that could match on the following fields:
• Ingress port.
• Ethernet source and destination MAC.
• Ethertype (with a special value to match frames that lack
an Ethertype).
• VLAN ID and priority.
• IPv4 source, destination, protocol, and DSCP.
• TCP source and destination port.
• UDP source and destination port.
• ICMPv4 type and code.
• ARP IPv4 addresses (SPA and TPA) and opcode.
Each supported field corresponded to some member of the data structure.
Some members represented multiple fields, in the case of the TCP, UDP,
ICMPv4, and ARP fields whose presence is mutually exclusive. This also
meant that some members were poor fits for their fields: only the low 8
bits of the 16-bit ARP opcode could be represented, and the ICMPv4 type
and code were padded with 8 bits of zeros to fit in the 16-bit members
primarily meant for TCP and UDP ports. An additional bitmap member in‐
dicated, for each member, whether its field should be an ``exact’’ or
``wildcarded’’ match (see Matching), with additional support for CIDR
prefix matching on the IPv4 source and destination fields.
Simplicity was recognized early on as the main virtue of this approach.
Obviously, any fixed-length data structure cannot support matching new
protocols that do not fit. There was no room, for example, for matching
IPv6 fields, which was not a priority at the time. Lack of room to sup‐
port matching the Ethernet addresses inside ARP packets actually caused
more of a design problem later, leading to an Open vSwitch extension
action specialized for dropping ``spoofed’’ ARP packets in which the
frame and ARP Ethernet source addressed differed. (This extension was
never standardized. Open vSwitch dropped support for it a few releases
after it added support for full ARP matching.)
The design of the OpenFlow fixed-length matches also illustrates com‐
promises, in both directions, between the strengths and weaknesses of
software and hardware that have always influenced the design of Open‐
Flow. Support for matching ARP fields that do fit in the data structure
was only added late in the design process (and remained optional in
OpenFlow 1.0), for example, because common switch ASICs did not support
matching these fields.
The compromises in favor of software occurred for more complicated rea‐
sons. The OpenFlow designers did not know how to implement matching in
software that was fast, dynamic, and general. (A way was later found
[Srinivasan].) Thus, the designers sought to support dynamic, general
matching that would be fast in realistic special cases, in particular
when all of the matches were microflows, that is, matches that specify
every field present in a packet, because such matches can be imple‐
mented as a single hash table lookup. Contemporary research supported
the feasibility of this approach: the number of microflows in a campus
network had been measured to peak at about 10,000 [Casado, section
3.2]. (Calculations show that this can only be true in a lightly loaded
network [Pepelnjak].)
As a result, OpenFlow 1.0 required switches to treat microflow matches
as the highest possible priority. This let software switches perform
the microflow hash table lookup first. Only on failure to match a mi‐
croflow did the switch need to fall back to checking the more general
and presumed slower matches. Also, the OpenFlow 1.0 flow match was min‐
imally flexible, with no support for general bitwise matching, partly
on the basis that this seemed more likely amenable to relatively effi‐
cient software implementation. (CIDR masking for IPv4 addresses was
added relatively late in the OpenFlow 1.0 design process.)
Microflow matching was later discovered to aid some hardware implemen‐
tations. The TCAM chips used for matching in hardware do not support
priority in the same way as OpenFlow but instead tie priority to order‐
ing [Pagiamtzis]. Thus, adding a new match with a priority between the
priorities of existing matches can require reordering an arbitrary num‐
ber of TCAM entries. On the other hand, when microflows are highest
priority, they can be managed as a set-aside portion of the TCAM en‐
tries.
The emphasis on matching microflows also led designers to carefully
consider the bandwidth requirements between switch and controller: to
maximize the number of microflow setups per second, one must minimize
the size of each flow’s description. This favored the fixed-length for‐
mat in use, because it expressed common TCP and UDP microflows in fewer
bytes than more flexible ``type-length-value’’ (TLV) formats. (Early
versions of OpenFlow also avoided TLVs in general to head off protocol
fragmentation.)
Inapplicable Fields
OpenFlow 1.0 does not clearly specify how to treat inapplicable fields.
The members for inapplicable fields are always present in the match
data structure, as are the bits that indicate whether the fields are
matched, and the ``correct’’ member and bit values for inapplicable
fields is unclear. OpenFlow 1.0 implementations changed their behavior
over time as priorities shifted. The early OpenFlow reference implemen‐
tation, motivated to make every flow a microflow to enable hashing,
treated inapplicable fields as exact matches on a value of 0. Ini‐
tially, this behavior was implemented in the reference controller only.
Later, the reference switch was also changed to actually force any
wildcarded inapplicable fields into exact matches on 0. The latter be‐
havior sometimes caused problems, because the modified flow was the one
reported back to the controller later when it queried the flow table,
and the modifications sometimes meant that the controller could not
properly recognize the flow that it had added. In retrospect, perhaps
this problem should have alerted the designers to a design error, but
the ability to use a single hash table was held to be more important
than almost every other consideration at the time.
When more flexible match formats were introduced much later, they dis‐
allowed any mention of inapplicable fields as part of a match. This
raised the question of how to translate between this new format and the
OpenFlow 1.0 fixed format. It seemed somewhat inconsistent and backward
to treat fields as exact-match in one format and forbid matching them
in the other, so instead the treatment of inapplicable fields in the
fixed-length format was changed from exact match on 0 to wildcarding.
(A better classifier had by now eliminated software performance prob‐
lems with wildcards.)
The OpenFlow 1.0.1 errata (released only in 2012) added some additional
explanation [OpenFlow 1.0.1, section 3.4], but it did not mandate spe‐
cific behavior because of variation among implementations.
OpenFlow 1.1
The OpenFlow 1.1 protocol match format was designed as a
type/length/value (TLV) format to allow for future flexibility. The
specification standardized only a single type OFPMT_STANDARD (0) with a
fixed-size payload, described here. The additional fields and bitwise
masks in OpenFlow 1.1 cause this match structure to be over twice as
large as in OpenFlow 1.0, 88 bytes versus 40.
OpenFlow 1.1 added support for the following fields:
• SCTP source and destination port.
• MPLS label and traffic control (TC) fields.
• One 64-bit register (named ``metadata’’).
OpenFlow 1.1 increased the width of the ingress port number field (and
all other port numbers in the protocol) from 16 bits to 32 bits.
OpenFlow 1.1 increased matching flexibility by introducing arbitrary
bitwise matching on Ethernet and IPv4 address fields and on the new
``metadata’’ register field. Switches were not required to support all
possible masks [OpenFlow 1.1, section 4.3].
By a strict reading of the specification, OpenFlow 1.1 removed support
for matching ICMPv4 type and code [OpenFlow 1.1, section A.2.3], but
this is likely an editing error because ICMP matching is described
elsewhere [OpenFlow 1.1, Table 3, Table 4, Figure 4]. Open vSwitch does
support ICMPv4 type and code matching with OpenFlow 1.1.
OpenFlow 1.1 avoided the pitfalls of inapplicable fields that OpenFlow
1.0 encountered, by requiring the switch to ignore the specified field
values [OpenFlow 1.1, section A.2.3]. It also implied that the switch
should ignore the bits that indicate whether to match inapplicable
fields.
Physical Ingress Port
OpenFlow 1.1 introduced a new pseudo-field, the physical ingress port.
The physical ingress port is only a pseudo-field because it cannot be
used for matching. It appears only one place in the protocol, in the
``packet-in’’ message that passes a packet received at the switch to an
OpenFlow controller.
A packet’s ingress port and physical ingress port are identical except
for packets processed by a switch feature such as bonding or tunneling
that makes a packet appear to arrive on a ``virtual’’ port associated
with the bond or the tunnel. For such packets, the ingress port is the
virtual port and the physical ingress port is, naturally, the physical
port. Open vSwitch implements both bonding and tunneling, but its bond‐
ing implementation does not use virtual ports and its tunnels are typi‐
cally not on the same OpenFlow switch as their physical ingress ports
(which need not be part of any switch), so the ingress port and physi‐
cal ingress port are always the same in Open vSwitch.
OpenFlow 1.2
OpenFlow 1.2 abandoned the fixed-length approach to matching. One rea‐
son was size, since adding support for IPv6 address matching (now seen
as important), with bitwise masks, would have added 64 bytes to the
match length, increasing it from 88 bytes in OpenFlow 1.1 to over 150
bytes. Extensibility had also become important as controller writers
increasingly wanted support for new fields without having to change
messages throughout the OpenFlow protocol. The challenges of carefully
defining fixed-length matches to avoid problems with inapplicable
fields had also become clear over time.
Therefore, OpenFlow 1.2 adopted a flow format using a flexible type-
length-value (TLV) representation, in which each TLV expresses a match
on one field. These TLVs were in turn encapsulated inside the outer TLV
wrapper introduced in OpenFlow 1.1 with the new identifier OFPMT_OXM
(1). (This wrapper fulfilled its intended purpose of reducing the
amount of churn in the protocol when changing match formats; some mes‐
sages that included matches remained unchanged from OpenFlow 1.1 to 1.2
and later versions.)
OpenFlow 1.2 added support for the following fields:
• ARP hardware addresses (SHA and THA).
• IPv4 ECN.
• IPv6 source and destination addresses, flow label, DSCP,
ECN, and protocol.
• TCP, UDP, and SCTP port numbers when encapsulated inside
IPv6.
• ICMPv6 type and code.
• ICMPv6 Neighbor Discovery target address and source and
target Ethernet addresses.
The OpenFlow 1.2 format, called OXM (OpenFlow Extensible Match), was
modeled closely on an extension to OpenFlow 1.0 introduced in Open
vSwitch 1.1 called NXM (Nicira Extended Match). Each OXM or NXM TLV has
the following format:
type
<---------------->
16 7 1 8 length bytes
+------------+-----+--+------+ +------------+
|vendor/class|field|HM|length| | body |
+------------+-----+--+------+ +------------+
The most significant 16 bits of the NXM or OXM header, called vendor by
NXM and class by OXM, identify an organization permitted to allocate
identifiers for fields. NXM allocates only two vendors, 0x0000 for
fields supported by OpenFlow 1.0 and 0x0001 for fields implemented as
an Open vSwitch extension. OXM assigns classes as follows:
0x0000 (OFPXMC_NXM_0).
0x0001 (OFPXMC_NXM_1).
Reserved for NXM compatibility.
0x0002 to 0x7fff
Reserved for allocation to ONF members, but none yet as‐
signed.
0x8000 (OFPXMC_OPENFLOW_BASIC)
Used for most standard OpenFlow fields.
0x8001 (OFPXMC_PACKET_REGS)
Used for packet register fields in OpenFlow 1.5 and later.
0x8002 to 0xfffe
Reserved for the OpenFlow specification.
0xffff (OFPXMC_EXPERIMENTER)
Experimental use.
When class is 0xffff, the OXM header is extended to 64 bits by using
the first 32 bits of the body as an experimenter field whose most sig‐
nificant byte is zero and whose remaining bytes are an Organizationally
Unique Identifier (OUI) assigned by the IEEE [IEEE OUI], as shown be‐
low.
type experimenter
<----------> <---------->
16 7 1 8 8 24 (length - 4) bytes
+------+-----+--+------+ +------+-----+ +------------------+
|class |field|HM|length| | zero | OUI | | body |
+------+-----+--+------+ +------+-----+ +------------------+
0xffff 0x00
OpenFlow says that support for experimenter fields is optional. Open
vSwitch 2.4 and later does support them, so that it can support the
following experimenter classes:
0x4f4e4600 (ONFOXM_ET)
Used by official Open Networking Foundation extensions in
OpenFlow 1.3 and later. e.g. [TCP Flags Match Field Ex‐
tension].
0x005ad650 (NXOXM_NSH)
Used by Open vSwitch for NSH extensions, in the absence
of an official ONF-assigned class. (This OUI is randomly
generated.)
Taken as a unit, class (or vendor), field, and experimenter (when
present) uniquely identify a particular field.
When hasmask (abbreviated HM above) is 0, the OXM is an exact match on
an entire field. In this case, the body (excluding the experimenter
field, if present) is a single value to be matched.
When hasmask is 1, the OXM is a bitwise match. The body (excluding the
experimenter field) consists of a value to match, followed by the bit‐
wise mask to apply. A 1-bit in the mask indicates that the correspond‐
ing bit in the value should be matched and a 0-bit that it should be
ignored. For example, for an IP address field, a value of 192.168.0.0
followed by a mask of 255.255.0.0 would match addresses in the
196.168.0.0/16 subnet.
• Some fields might not support masking at all, and some
fields that do support masking might restrict it to cer‐
tain patterns. For example, fields that have IP address
values might be restricted to CIDR masks. The descrip‐
tions of individual fields note these restrictions.
• An OXM TLV with a mask that is all zeros is not useful
(although it is not forbidden), because it is has the
same effect as omitting the TLV entirely.
• It is not meaningful to pair a 0-bit in an OXM mask with
a 1-bit in its value, and Open vSwitch rejects such an
OXM with the error OFPBMC_BAD_WILDCARDS, as required by
OpenFlow 1.3 and later.
The length identifies the number of bytes in the body, including the
4-byte experimenter header, if it is present. Each OXM TLV has a fixed
length; that is, given class, field, experimenter (if present), and
hasmask, length is a constant. The length is included explicitly to al‐
low software to minimally parse OXM TLVs of unknown types.
OXM TLVs must be ordered so that a field’s prerequisites are satisfied
before it is parsed. For example, an OXM TLV that matches on the IPv4
source address field is only allowed following an OXM TLV that matches
on the Ethertype for IPv4. Similarly, an OXM TLV that matches on the
TCP source port must follow a TLV that matches an Ethertype of IPv4 or
IPv6 and one that matches an IP protocol of TCP (in that order). The
order of OXM TLVs is not otherwise restricted; no canonical ordering is
defined.
A given field may be matched only once in a series of OXM TLVs.
OpenFlow 1.3
OpenFlow 1.3 showed OXM to be largely successful, by adding new fields
without making any changes to how flow matches otherwise worked. It
added OXMs for the following fields supported by Open vSwitch:
• Tunnel ID for ports associated with e.g. VXLAN or keyed
GRE.
• MPLS ``bottom of stack’’ (BOS) bit.
OpenFlow 1.3 also added OXMs for the following fields not documented
here and not yet implemented by Open vSwitch:
• IPv6 extension header handling.
• PBB I-SID.
OpenFlow 1.4
OpenFlow 1.4 added OXMs for the following fields not documented here
and not yet implemented by Open vSwitch:
• PBB UCA.
OpenFlow 1.5
OpenFlow 1.5 added OXMs for the following fields supported by Open
vSwitch:
• Packet type.
• TCP flags.
• Packet registers.
• The output port in the OpenFlow action set.
FIELDS REFERENCE
The following sections document the fields that Open vSwitch supports.
Each section provides introductory material on a group of related
fields, followed by information on each individual field. In addition
to field-specific information, each field begins with a table with en‐
tries for the following important properties:
Name The field’s name, used for parsing and formatting the
field, e.g. in ovs-ofctl commands. For historical rea‐
sons, some fields have an additional name that is ac‐
cepted as an alternative in parsing. This name, when
there is one, is listed as well, e.g. ``tun (aka tun‐
nel_id).’’
Width The field’s width, always a multiple of 8 bits. Some
fields don’t use all of the bits, so this may be accompa‐
nied by an explanation. For example, OpenFlow embeds the
2-bit IP ECN field as as the low bits in an 8-bit byte,
and so its width is expressed as ``8 bits (only the
least-significant 2 bits may be nonzero).’’
Format How a value for the field is formatted or parsed by,
e.g., ovs-ofctl. Some possibilities are generic:
decimal
Formats as a decimal number. On input, accepts
decimal numbers or hexadecimal numbers prefixed by
0x.
hexadecimal
Formats as a hexadecimal number prefixed by 0x. On
input, accepts decimal numbers or hexadecimal num‐
bers prefixed by 0x. (The default for parsing is
not hexadecimal: only a 0x prefix causes input to
be treated as hexadecimal.)
Ethernet
Formats and accepts the common Ethernet address
format xx:xx:xx:xx:xx:xx.
IPv4 Formats and accepts the dotted-quad format
a.b.c.d. For bitwise matches, formats and accepts
address/length CIDR notation in addition to ad‐
dress/mask.
IPv6 Formats and accepts the common IPv6 address for‐
mats, plus CIDR notation for bitwise matches.
OpenFlow 1.0 port
Accepts 16-bit port numbers in decimal, plus Open‐
Flow well-known port names (e.g. IN_PORT) in up‐
percase or lowercase.
OpenFlow 1.1+ port
Same syntax as OpenFlow 1.0 ports but for 32-bit
OpenFlow 1.1+ port number fields.
Other, field-specific formats are explained along with
their fields.
Masking
For most fields, this says ``arbitrary bitwise masks,’’
meaning that a flow may match any combination of bits in
the field. Some fields instead say ``exact match only,’’
which means that a flow that matches on this field must
match on the whole field instead of just certain bits.
Either way, this reports masking support for the latest
version of Open vSwitch using OXM or NXM (that is, either
OpenFlow 1.2+ or OpenFlow 1.0 plus Open vSwitch NXM ex‐
tensions). In particular, OpenFlow 1.0 (without NXM) and
1.1 don’t always support masking even if Open vSwitch it‐
self does; refer to the OpenFlow 1.0 and OpenFlow 1.1
rows to learn about masking with these protocol versions.
Prerequisites
Requirements that must be met to match on this field. For
example, ip_src has IPv4 as a prerequisite, meaning that
a match must include eth_type=0x0800 to match on the IPv4
source address. The following prerequisites, with their
requirements, are currently in use:
none (no requirements)
VLAN VID
vlan_tci=0x1000/0x1000 (i.e. a VLAN header is
present)
ARP eth_type=0x0806 (ARP) or eth_type=0x8035 (RARP)
IPv4 eth_type=0x0800
IPv6 eth_type=0x86dd
IPv4/IPv6
IPv4 or IPv6
MPLS eth_type=0x8847 or eth_type=0x8848
TCP IPv4/IPv6 and ip_proto=6
UDP IPv4/IPv6 and ip_proto=17
SCTP IPv4/IPv6 and ip_proto=132
ICMPv4 IPv4 and ip_proto=1
ICMPv6 IPv6 and ip_proto=58
ND solicit
ICMPv6 and icmp_type=135 and icmp_code=0
ND advert
ICMPv6 and icmp_type=136 and icmp_code=0
ND ND solicit or ND advert
The TCP, UDP, and SCTP prerequisites also have the spe‐
cial requirement that nw_frag is not being used to select
``later fragments.’’ This is because only the first frag‐
ment of a fragmented IPv4 or IPv6 datagram contains the
TCP or UDP header.
Access Most fields are ``read/write,’’ which means that common
OpenFlow actions like set_field can modify them. Fields
that are ``read-only’’ cannot be modified in these gen‐
eral-purpose ways, although there may be other ways that
actions can modify them.
OpenFlow 1.0
OpenFlow 1.1
These rows report the level of support that OpenFlow 1.0 or
OpenFlow 1.1, respectively, has for a field. For OpenFlow
1.0, supported fields are reported as either ``yes (exact
match only)’’ for fields that do not support any bitwise
masking or ``yes (CIDR match only)’’ for fields that sup‐
port CIDR masking. OpenFlow 1.1 supported fields report ei‐
ther ``yes (exact match only)’’ or simply ``yes’’ for
fields that do support arbitrary masks. These OpenFlow ver‐
sions supported a fixed collection of fields that cannot be
extended, so many more fields are reported as ``not sup‐
ported.’’
OXM
NXM These rows report the OXM and NXM code points that corre‐
spond to a given field. Either or both may be ``none.’’
A field that has only an OXM code point is usually one that
was standardized before it was added to Open vSwitch. A
field that has only an NXM code point is usually one that
is not yet standardized. When a field has both OXM and NXM
code points, it usually indicates that it was introduced as
an Open vSwitch extension under the NXM code point, then
later standardized under the OXM code point. A field can
have more than one OXM code point if it was standardized in
OpenFlow 1.4 or later and additionally introduced as an of‐
ficial ONF extension for OpenFlow 1.3. (A field that has
neither OXM nor NXM code point is typically an obsolete
field that is supported in some other form using OXM or
NXM.)
Each code point in these rows is described in the form
``NAME (number) since OpenFlow spec and Open vSwitch ver‐
sion,’’ e.g. ``OXM_OF_ETH_TYPE (5) since OpenFlow 1.2 and
Open vSwitch 1.7.’’ First, NAME, which specifies a name for
the code point, starts with a prefix that designates a
class and, in some cases, a vendor, as listed in the fol‐
lowing table:
Prefix Vendor Class
─────────────── ─────────── ───────
NXM_OF (none) 0x0000
NXM_NX (none) 0x0001
ERICOXM_OF (none) 0x1000
OXM_OF (none) 0x8000
OXM_OF_PKT_REG (none) 0x8001
NXOXM_ET 0x00002320 0xffff
NXOXM_NSH 0x005ad650 0xffff
ONFOXM_ET 0x4f4e4600 0xffff
For more information on OXM/NXM classes and vendors, refer
back to OpenFlow 1.2 under Evolution of OpenFlow Fields.
The number is the field number within the class and vendor.
The OpenFlow spec is the version of OpenFlow that standard‐
ized the code point. It is omitted for NXM code points be‐
cause they are nonstandard. The version is the version of
Open vSwitch that first supported the code point.
CONJUNCTIVE MATCH FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────── ────── ───── ──── ──────── ────────────────
conj_id 4 no no none OVS 2.4+
An individual OpenFlow flow can match only a single value for each
field. However, situations often arise where one wants to match one of
a set of values within a field or fields. For matching a single field
against a set, it is straightforward and efficient to add multiple
flows to the flow table, one for each value in the set. For example,
one might use the following flows to send packets with IP source ad‐
dress a, b, c, or d to the OpenFlow controller:
ip,ip_src=a actions=controller
ip,ip_src=b actions=controller
ip,ip_src=c actions=controller
ip,ip_src=d actions=controller
Similarly, these flows send packets with IP destination address e, f,
g, or h to the OpenFlow controller:
ip,ip_dst=e actions=controller
ip,ip_dst=f actions=controller
ip,ip_dst=g actions=controller
ip,ip_dst=h actions=controller
Installing all of the above flows in a single flow table yields a dis‐
junctive effect: a packet is sent to the controller if ip_src ∈
{a,b,c,d} or ip_dst ∈ {e,f,g,h} (or both). (Pedantically, if both of
the above sets of flows are present in the flow table, they should have
different priorities, because OpenFlow says that the results are unde‐
fined when two flows with same priority can both match a single
packet.)
Suppose, on the other hand, one wishes to match conjunctively, that is,
to send a packet to the controller only if both ip_src ∈ {a,b,c,d} and
ip_dst ∈ {e,f,g,h}. This requires 4 × 4 = 16 flows, one for each possi‐
ble pairing of ip_src and ip_dst. That is acceptable for our small ex‐
ample, but it does not gracefully extend to larger sets or greater num‐
bers of dimensions.
The conjunction action is a solution for conjunctive matches that is
built into Open vSwitch. A conjunction action ties groups of individual
OpenFlow flows into higher-level ``conjunctive flows’’. Each group cor‐
responds to one dimension, and each flow within the group matches one
possible value for the dimension. A packet that matches one flow from
each group matches the conjunctive flow.
To implement a conjunctive flow with conjunction, assign the conjunc‐
tive flow a 32-bit id, which must be unique within an OpenFlow table.
Assign each of the n ≥ 2 dimensions a unique number from 1 to n; the
ordering is unimportant. Add one flow to the OpenFlow flow table for
each possible value of each dimension with conjunction(id, k/n) as the
flow’s actions, where k is the number assigned to the flow’s dimension.
Together, these flows specify the conjunctive flow’s match condition.
When the conjunctive match condition is met, Open vSwitch looks up one
more flow that specifies the conjunctive flow’s actions and receives
its statistics. This flow is found by setting conj_id to the specified
id and then again searching the flow table.
The following flows provide an example. Whenever the IP source is one
of the values in the flows that match on the IP source (dimension 1 of
2), and the IP destination is one of the values in the flows that match
on IP destination (dimension 2 of 2), Open vSwitch searches for a flow
that matches conj_id against the conjunction ID (1234), finding the
first flow listed below.
conj_id=1234 actions=controller
ip,ip_src=10.0.0.1 actions=conjunction(1234, 1/2)
ip,ip_src=10.0.0.4 actions=conjunction(1234, 1/2)
ip,ip_src=10.0.0.6 actions=conjunction(1234, 1/2)
ip,ip_src=10.0.0.7 actions=conjunction(1234, 1/2)
ip,ip_dst=10.0.0.2 actions=conjunction(1234, 2/2)
ip,ip_dst=10.0.0.5 actions=conjunction(1234, 2/2)
ip,ip_dst=10.0.0.7 actions=conjunction(1234, 2/2)
ip,ip_dst=10.0.0.8 actions=conjunction(1234, 2/2)
Many subtleties exist:
• In the example above, every flow in a single dimension
has the same form, that is, dimension 1 matches on ip_src
and dimension 2 on ip_dst, but this is not a requirement.
Different flows within a dimension may match on different
bits within a field (e.g. IP network prefixes of differ‐
ent lengths, or TCP/UDP port ranges as bitwise matches),
or even on entirely different fields (e.g. to match pack‐
ets for TCP source port 80 or TCP destination port 80).
• The flows within a dimension can vary their matches
across more than one field, e.g. to match only specific
pairs of IP source and destination addresses or L4 port
numbers.
• A flow may have multiple conjunction actions, with dif‐
ferent id values. This is useful for multiple conjunctive
flows with overlapping sets. If one conjunctive flow
matches packets with both ip_src ∈ {a,b} and ip_dst ∈
{d,e} and a second conjunctive flow matches ip_src ∈
{b,c} and ip_dst ∈ {f,g}, for example, then the flow that
matches ip_src=b would have two conjunction actions, one
for each conjunctive flow. The order of conjunction ac‐
tions within a list of actions is not significant.
• A flow with conjunction actions may also include note ac‐
tions for annotations, but not any other kind of actions.
(They would not be useful because they would never be ex‐
ecuted.)
• All of the flows that constitute a conjunctive flow with
a given id must have the same priority. (Flows with the
same id but different priorities are currently treated as
different conjunctive flows, that is, currently id values
need only be unique within an OpenFlow table at a given
priority. This behavior isn’t guaranteed to stay the same
in later releases, so please use id values unique within
an OpenFlow table.)
• Conjunctive flows must not overlap with each other, at a
given priority, that is, any given packet must be able to
match at most one conjunctive flow at a given priority.
Overlapping conjunctive flows yield unpredictable re‐
sults. (The flows that constitute a conjunctive flow may
overlap with those that constitute the same or another
conjunctive flow.)
• Following a conjunctive flow match, the search for the
flow with conj_id=id is done in the same general-purpose
way as other flow table searches, so one can use flows
with conj_id=id to act differently depending on circum‐
stances. (One exception is that the search for the
conj_id=id flow itself ignores conjunctive flows, to
avoid recursion.) If the search with conj_id=id fails,
Open vSwitch acts as if the conjunctive flow had not
matched at all, and continues searching the flow table
for other matching flows.
• OpenFlow prerequisite checking occurs for the flow with
conj_id=id in the same way as any other flow, e.g. in an
OpenFlow 1.1+ context, putting a mod_nw_src action into
the example above would require adding an ip match, like
this:
conj_id=1234,ip actions=mod_nw_src:1.2.3.4,controller
• OpenFlow prerequisite checking also occurs for the indi‐
vidual flows that comprise a conjunctive match in the
same way as any other flow.
• The flows that constitute a conjunctive flow do not have
useful statistics. They are never updated with byte or
packet counts, and so on. (For such a flow, therefore,
the idle and hard timeouts work much the same way.)
• Sometimes there is a choice of which flows include a par‐
ticular match. For example, suppose that we added an ex‐
tra constraint to our example, to match on ip_src ∈
{a,b,c,d} and ip_dst ∈ {e,f,g,h} and tcp_dst = i. One way
to implement this is to add the new constraint to the
conj_id flow, like this:
conj_id=1234,tcp,tcp_dst=i actions=mod_nw_src:1.2.3.4,controller
but this is not recommended because of the cost of the
extra flow table lookup. Instead, add the constraint to
the individual flows, either in one of the dimensions or
(slightly better) all of them.
• A conjunctive match must have n ≥ 2 dimensions (otherwise
a conjunctive match is not necessary). Open vSwitch en‐
forces this.
• Each dimension within a conjunctive match should ordinar‐
ily have more than one flow. Open vSwitch does not en‐
force this.
Conjunction ID Field
Name: conj_id
Width: 32 bits
Format: decimal
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CONJ_ID (37) since Open vSwitch 2.4
Used for conjunctive matching. See above for more information.
TUNNEL FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────────────────── ──────────────── ───── ──── ──────── ─────────────────────
tun_id aka tunnel_id 8 yes yes none OF 1.3+ and OVS 1.1+
tun_src 4 yes yes none OVS 2.0+
tun_dst 4 yes yes none OVS 2.0+
tun_ipv6_src 16 yes yes none OVS 2.5+
tun_ipv6_dst 16 yes yes none OVS 2.5+
tun_gbp_id 2 yes yes none OVS 2.4+
tun_gbp_flags 1 yes yes none OVS 2.4+
tun_erspan_ver 1 (low 4 bits) yes yes none OVS 2.10+
tun_erspan_idx 4 (low 20 bits) yes yes none OVS 2.10+
tun_erspan_dir 1 (low 1 bits) yes yes none OVS 2.10+
tun_erspan_hwid 1 (low 6 bits) yes yes none OVS 2.10+
tun_gtpu_flags 1 yes no none OVS 2.13+
tun_gtpu_msgtype 1 yes no none OVS 2.13+
tun_metadata0 124 yes yes none OVS 2.5+
tun_metadata1 124 yes yes none OVS 2.5+
tun_metadata2 124 yes yes none OVS 2.5+
tun_metadata3 124 yes yes none OVS 2.5+
tun_metadata4 124 yes yes none OVS 2.5+
tun_metadata5 124 yes yes none OVS 2.5+
tun_metadata6 124 yes yes none OVS 2.5+
tun_metadata7 124 yes yes none OVS 2.5+
tun_metadata8 124 yes yes none OVS 2.5+
tun_metadata9 124 yes yes none OVS 2.5+
tun_metadata10 124 yes yes none OVS 2.5+
tun_metadata11 124 yes yes none OVS 2.5+
tun_metadata12 124 yes yes none OVS 2.5+
tun_metadata13 124 yes yes none OVS 2.5+
tun_metadata14 124 yes yes none OVS 2.5+
tun_metadata15 124 yes yes none OVS 2.5+
tun_metadata16 124 yes yes none OVS 2.5+
tun_metadata17 124 yes yes none OVS 2.5+
tun_metadata18 124 yes yes none OVS 2.5+
tun_metadata19 124 yes yes none OVS 2.5+
tun_metadata20 124 yes yes none OVS 2.5+
tun_metadata21 124 yes yes none OVS 2.5+
tun_metadata22 124 yes yes none OVS 2.5+
tun_metadata23 124 yes yes none OVS 2.5+
tun_metadata24 124 yes yes none OVS 2.5+
tun_metadata25 124 yes yes none OVS 2.5+
tun_metadata26 124 yes yes none OVS 2.5+
tun_metadata27 124 yes yes none OVS 2.5+
tun_metadata28 124 yes yes none OVS 2.5+
tun_metadata29 124 yes yes none OVS 2.5+
tun_metadata30 124 yes yes none OVS 2.5+
tun_metadata31 124 yes yes none OVS 2.5+
tun_metadata32 124 yes yes none OVS 2.5+
tun_metadata33 124 yes yes none OVS 2.5+
tun_metadata34 124 yes yes none OVS 2.5+
tun_metadata35 124 yes yes none OVS 2.5+
tun_metadata36 124 yes yes none OVS 2.5+
tun_metadata37 124 yes yes none OVS 2.5+
tun_metadata38 124 yes yes none OVS 2.5+
tun_metadata39 124 yes yes none OVS 2.5+
tun_metadata40 124 yes yes none OVS 2.5+
tun_metadata41 124 yes yes none OVS 2.5+
tun_metadata42 124 yes yes none OVS 2.5+
tun_metadata43 124 yes yes none OVS 2.5+
tun_metadata44 124 yes yes none OVS 2.5+
tun_metadata45 124 yes yes none OVS 2.5+
tun_metadata46 124 yes yes none OVS 2.5+
tun_metadata47 124 yes yes none OVS 2.5+
tun_metadata48 124 yes yes none OVS 2.5+
tun_metadata49 124 yes yes none OVS 2.5+
tun_metadata50 124 yes yes none OVS 2.5+
tun_metadata51 124 yes yes none OVS 2.5+
tun_metadata52 124 yes yes none OVS 2.5+
tun_metadata53 124 yes yes none OVS 2.5+
tun_metadata54 124 yes yes none OVS 2.5+
tun_metadata55 124 yes yes none OVS 2.5+
tun_metadata56 124 yes yes none OVS 2.5+
tun_metadata57 124 yes yes none OVS 2.5+
tun_metadata58 124 yes yes none OVS 2.5+
tun_metadata59 124 yes yes none OVS 2.5+
tun_metadata60 124 yes yes none OVS 2.5+
tun_metadata61 124 yes yes none OVS 2.5+
tun_metadata62 124 yes yes none OVS 2.5+
tun_metadata63 124 yes yes none OVS 2.5+
tun_flags 2 (low 1 bits) yes yes none OVS 2.5+
The fields in this group relate to tunnels, which Open vSwitch supports
in several forms (GRE, VXLAN, and so on). Most of these fields do ap‐
pear in the wire format of a packet, so they are data fields from that
point of view, but they are metadata from an OpenFlow flow table point
of view because they do not appear in packets that are forwarded to the
controller or to ordinary (non-tunnel) output ports.
Open vSwitch supports a spectrum of usage models for mapping tunnels to
OpenFlow ports:
``Port-based’’ tunnels
In this model, an OpenFlow port represents one tunnel: it
matches a particular type of tunnel traffic between two
IP endpoints, with a particular tunnel key (if keys are
in use). In this situation, in_port suffices to distin‐
guish one tunnel from another, so the tunnel header
fields have little importance for OpenFlow processing.
(They are still populated and may be used if it is conve‐
nient.) The tunnel header fields play no role in sending
packets out such an OpenFlow port, either, because the
OpenFlow port itself fully specifies the tunnel headers.
The following Open vSwitch commands create a bridge
br-int, add port tap0 to the bridge as OpenFlow port 1,
establish a port-based GRE tunnel between the local host
and remote IP 192.168.1.1 using GRE key 5001 as OpenFlow
port 2, and arranges to forward all traffic from tap0 to
the tunnel and vice versa:
ovs-vsctl add-br br-int
ovs-vsctl add-port br-int tap0 -- set interface tap0 ofport_request=1
ovs-vsctl add-port br-int gre0 -- \
set interface gre0 ofport_request=2 type=gre \
options:remote_ip=192.168.1.1 options:key=5001
ovs-ofctl add-flow br-int in_port=1,actions=2
ovs-ofctl add-flow br-int in_port=2,actions=1
``Flow-based’’ tunnels
In this model, one OpenFlow port represents all possible
tunnels of a given type with an endpoint on the current
host, for example, all GRE tunnels. In this situation,
in_port only indicates that traffic was received on the
particular kind of tunnel. This is where the tunnel
header fields are most important: they allow the OpenFlow
tables to discriminate among tunnels based on their IP
endpoints or keys. Tunnel header fields also determine
the IP endpoints and keys of packets sent out such a tun‐
nel port.
The following Open vSwitch commands create a bridge
br-int, add port tap0 to the bridge as OpenFlow port 1,
establish a flow-based GRE tunnel port 3, and arranges to
forward all traffic from tap0 to remote IP 192.168.1.1
over a GRE tunnel with key 5001 and vice versa:
ovs-vsctl add-br br-int
ovs-vsctl add-port br-int tap0 -- set interface tap0 ofport_request=1
ovs-vsctl add-port br-int allgre -- \
set interface allgre ofport_request=3 type=gre \
options:remote_ip=flow options:key=flow
ovs-ofctl add-flow br-int \
’in_port=1 actions=set_tunnel:5001,set_field:192.168.1.1->tun_dst,3’
ovs-ofctl add-flow br-int ’in_port=3,tun_src=192.168.1.1,tun_id=5001 actions=1’
Mixed models.
One may define both flow-based and port-based tunnels at
the same time. For example, it is valid and possibly use‐
ful to create and configure both gre0 and allgre tunnel
ports described above.
Traffic is attributed on ingress to the most specific
matching tunnel. For example, gre0 is more specific than
allgre. Therefore, if both exist, then gre0 will be the
ingress port for any GRE traffic received from
192.168.1.1 with key 5001.
On egress, traffic may be directed to any appropriate
tunnel port. If both gre0 and allgre are configured as
already described, then the actions 2 and set_tun‐
nel:5001,set_field:192.168.1.1->tun_dst,3 send the same
tunnel traffic.
Intermediate models.
Ports may be configured as partially flow-based. For ex‐
ample, one may define an OpenFlow port that represents
tunnels between a pair of endpoints but leaves the flow
table to discriminate on the flow key.
ovs-vswitchd.conf.db(5) describes all the details of tunnel configura‐
tion.
These fields do not have any prerequisites, which means that a flow may
match on any or all of them, in any combination.
These fields are zeros for packets that did not arrive on a tunnel.
Tunnel ID Field
Name: tun_id (aka tunnel_id)
Width: 64 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_TUNNEL_ID (38) since OpenFlow 1.3 and Open
vSwitch 1.10
NXM: NXM_NX_TUN_ID (16) since Open vSwitch 1.1
Many kinds of tunnels support a tunnel ID:
• VXLAN and Geneve have a 24-bit virtual network identifier
(VNI).
• LISP has a 24-bit instance ID.
• GRE has an optional 32-bit key.
• STT has a 64-bit key.
• ERSPAN has a 10-bit key (Session ID).
• GTPU has a 32-bit key (Tunnel Endpoint ID).
When a packet is received from a tunnel, this field holds the tunnel ID
in its least significant bits, zero-extended to fit. This field is zero
if the tunnel does not support an ID, or if no ID is in use for a tun‐
nel type that has an optional ID, or if an ID of zero received, or if
the packet was not received over a tunnel.
When a packet is output to a tunnel port, the tunnel configuration de‐
termines whether the tunnel ID is taken from this field or bound to a
fixed value. See the earlier description of ``port-based’’ and ``flow-
based’’ tunnels for more information.
The following diagram shows the origin of this field in a typical keyed
GRE tunnel:
Ethernet IPv4 GRE Ethernet
<-----------> <---------------> <------------> <---------->
48 48 16 8 32 32 16 16 32 48 48 16
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
|dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
0x800 47 0x6558
Tunnel IPv4 Source Field
Name: tun_src
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV4_SRC (31) since Open vSwitch 2.0
When a packet is received from a tunnel, this field is the source ad‐
dress in the outer IP header of the tunneled packet. This field is zero
if the packet was not received over a tunnel.
When a packet is output to a flow-based tunnel port, this field influ‐
ences the IPv4 source address used to send the packet. If it is zero,
then the kernel chooses an appropriate IP address based using the rout‐
ing table.
The following diagram shows the origin of this field in a typical keyed
GRE tunnel:
Ethernet IPv4 GRE Ethernet
<-----------> <---------------> <------------> <---------->
48 48 16 8 32 32 16 16 32 48 48 16
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
|dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
0x800 47 0x6558
Tunnel IPv4 Destination Field
Name: tun_dst
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV4_DST (32) since Open vSwitch 2.0
When a packet is received from a tunnel, this field is the destination
address in the outer IP header of the tunneled packet. This field is
zero if the packet was not received over a tunnel.
When a packet is output to a flow-based tunnel port, this field speci‐
fies the destination to which the tunnel packet is sent.
The following diagram shows the origin of this field in a typical keyed
GRE tunnel:
Ethernet IPv4 GRE Ethernet
<-----------> <---------------> <------------> <---------->
48 48 16 8 32 32 16 16 32 48 48 16
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
|dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
+---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
0x800 47 0x6558
Tunnel IPv6 Source Field
Name: tun_ipv6_src
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV6_SRC (109) since Open vSwitch 2.5
Similar to tun_src, but for tunnels over IPv6.
Tunnel IPv6 Destination Field
Name: tun_ipv6_dst
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_IPV6_DST (110) since Open vSwitch 2.5
Similar to tun_dst, but for tunnels over IPv6.
VXLAN Group-Based Policy Fields
The VXLAN header is defined as follows [RFC 7348], where the I bit must
be set to 1, unlabeled bits or those labeled reserved must be set to 0,
and Open vSwitch makes the VNI available via tun_id:
VXLAN flags
<------------->
1 1 1 1 1 1 1 1 24 24 8
+-+-+-+-+-+-+-+-+--------+---+--------+
| | | | |I| | | |reserved|VNI|reserved|
+-+-+-+-+-+-+-+-+--------+---+--------+
VXLAN Group-Based Policy [VXLAN Group Policy Option] adds new interpre‐
tations to existing bits in the VXLAN header, reinterpreting it as fol‐
lows, with changes highlighted:
GBP flags
<------------->
1 1 1 1 1 1 1 1 24 24 8
+-+-+-+-+-+-+-+-+---------------+---+--------+
| |D| | |A| | | |group policy ID|VNI|reserved|
+-+-+-+-+-+-+-+-+---------------+---+--------+
Open vSwitch makes GBP fields and flags available through the following
fields. Only packets that arrive over a VXLAN tunnel with the GBP ex‐
tension enabled have these fields set. In other packets they are zero
on receive and ignored on transmit.
VXLAN Group-Based Policy ID Field
Name: tun_gbp_id
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_GBP_ID (38) since Open vSwitch 2.4
For a packet tunneled over VXLAN with the Group-Based Policy (GBP) ex‐
tension, this field represents the GBP policy ID, as shown above.
VXLAN Group-Based Policy Flags Field
Name: tun_gbp_flags
Width: 8 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_GBP_FLAGS (39) since Open vSwitch 2.4
For a packet tunneled over VXLAN with the Group-Based Policy (GBP) ex‐
tension, this field represents the GBP policy flags, as shown above.
The field has the format shown below:
GBP Flags
<------------->
1 1 1 1 1 1 1 1
+-+-+-+-+-+-+-+-+
| |D| | |A| | | |
+-+-+-+-+-+-+-+-+
Unlabeled bits are reserved and must be transmitted as 0. The VXLAN GBP
draft defines the other bits’ meanings as:
D (Don’t Learn)
When set, this bit indicates that the egress tunnel end‐
point must not learn the source address of the encapsu‐
lated frame.
A (Applied)
When set, indicates that the group policy has already
been applied to this packet. Devices must not apply poli‐
cies when the A bit is set.
ERSPAN Metadata Fields
These fields provide access to features in the ERSPAN tunneling proto‐
col [ERSPAN], which has two major versions: version 1 (aka type II) and
version 2 (aka type III).
Regardless of version, ERSPAN is encapsulated within a fixed 8-byte GRE
header that consists of a 4-byte GRE base header and a 4-byte sequence
number. The ERSPAN version 1 header format is:
GRE ERSPAN v1 Ethernet
<------------> <---------------------> <---------->
16 16 32 4 18 10 12 20 48 48 16
+---+------+---+ +---+---+-------+---+---+ +---+---+----+
|...| type |seq| |ver|...|session|...|idx| |dst|src|type| ...
+---+------+---+ +---+---+-------+---+---+ +---+---+----+
0x88be 1 tun_id
The ERSPAN version 2 header format is:
GRE ERSPAN v2 Ethernet
<------------> <----------------------------------------> <---------->
16 16 32 4 18 10 32 22 6 1 3 48 48 16
+---+------+---+ +---+---+-------+---------+---+----+---+---+ +---+---+----+
|...| type |seq| |ver|...|session|timestamp|...|hwid|dir|...| |dst|src|type| ...
+---+------+---+ +---+---+-------+---------+---+----+---+---+ +---+---+----+
0x22eb 2 tun_id 0/1
ERSPAN Version Field
Name: tun_erspan_ver
Width: 8 bits (only the least-significant 4 bits may be nonzero)
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_VER (12) since Open vSwitch 2.10
ERSPAN version number: 1 for version 1, or 2 for version 2.
ERSPAN Index Field
Name: tun_erspan_idx
Width: 32 bits (only the least-significant 20 bits may be nonzero)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_IDX (11) since Open vSwitch 2.10
This field is a 20-bit index/port number associated with the ERSPAN
traffic’s source port and direction (ingress/egress). This field is
platform dependent.
ERSPAN Direction Field
Name: tun_erspan_dir
Width: 8 bits (only the least-significant 1 bits may be nonzero)
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_DIR (13) since Open vSwitch 2.10
For ERSPAN v2, the mirrored traffic’s direction: 0 for ingress traffic,
1 for egress traffic.
ERSPAN Hardware ID Field
Name: tun_erspan_hwid
Width: 8 bits (only the least-significant 6 bits may be nonzero)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_ERSPAN_HWID (14) since Open vSwitch 2.10
A 6-bit unique identifier of an ERSPAN v2 engine within a system.
GTP-U Metadata Fields
These fields provide access to set-up GPRS Tunnelling Protocol for User
Plane (GTPv1-U), based on 3GPP TS 29.281. A GTP-U header has the fol‐
lowing format:
8 8 16 32
+-----+--------+------+----+
|flags|msg type|length|TEID| ...
+-----+--------+------+----+
The flags and message type have the Open vSwitch GTP-U specific fields
described below. Open vSwitch makes the TEID (Tunnel Endpoint Identi‐
fier), which identifies a tunnel endpoint in the receiving GTP-U proto‐
col entity, available via tun_id.
GTP-U Flags Field
Name: tun_gtpu_flags
Width: 8 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_GTPU_FLAGS (15) since Open vSwitch 2.13
This field holds the 8-bit GTP-U flags, encoded as:
GTP-U Tunnel Flags
<------------------->
3 1 1 1 1 1
+-------+--+---+-+-+--+
|version|PT|rsv|E|S|PN|
+-------+--+---+-+-+--+
1 0
The flags are:
version
Used to determine the version of the GTP-U protocol,
which should be set to 1.
PT Protocol type, used as a protocol discriminator between
GTP (1) and GTP’ (0).
rsv Reserved. Must be zero.
E If 1, indicates the presence of a meaningful value of the
Next Extension Header field.
S If 1, indicates the presence of a meaningful value of the
Sequence Number field.
PN If 1, indicates the presence of a meaningful value of the
N-PDU Number field.
GTP-U Message Type Field
Name: tun_gtpu_msgtype
Width: 8 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_ET_GTPU_MSGTYPE (16) since Open vSwitch 2.13
This field indicates whether it’s a signalling message used for path
management, or a user plane message which carries the original packet.
The complete range of message types can be referred to [3GPP TS
29.281].
Geneve Fields
These fields provide access to additional features in the Geneve tun‐
neling protocol [Geneve]. Their names are somewhat generic in the hope
that the same fields could be reused for other protocols in the future;
for example, the NSH protocol [NSH] supports TLV options whose form is
identical to that for Geneve options.
Generic Tunnel Option 0 Field
Name: tun_metadata0
Width: 992 bits (124 bytes)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_METADATA0 (40) since Open vSwitch 2.5
The above information specifically covers generic tunnel option 0, but
Open vSwitch supports 64 options, numbered 0 through 63, whose NXM
field numbers are 40 through 103.
These fields provide OpenFlow access to the generic type-length-value
options defined by the Geneve tunneling protocol or other protocols
with options in the same TLV format as Geneve options. Each of these
options has the following wire format:
header body
<-------------------> <------------------>
16 8 3 5 4×(length - 1) bytes
+-----+----+---+------+--------------------+
|class|type|res|length| value |
+-----+----+---+------+--------------------+
0
Taken together, the class and type in the option format mean that there
are about 16 million distinct kinds of TLV options, too many to give
individual OXM code points. Thus, Open vSwitch requires the user to de‐
fine the TLV options of interest, by binding up to 64 TLV options to
generic tunnel option NXM code points. Each option may have up to 124
bytes in its body, the maximum allowed by the TLV format, but bound op‐
tions may total at most 252 bytes of body.
Open vSwitch extensions to the OpenFlow protocol bind TLV options to
NXM code points. The ovs-ofctl(8) program offers one way to use these
extensions, e.g. to configure a mapping from a TLV option with class
0xffff, type 0, and a body length of 4 bytes:
ovs-ofctl add-tlv-map br0 "{class=0xffff,type=0,len=4}->tun_metadata0"
Once a TLV option is properly bound, it can be accessed and modified
like any other field, e.g. to send packets that have value 1234 for the
option described above to the controller:
ovs-ofctl add-flow br0 tun_metadata0=1234,actions=controller
An option not received or not bound is matched as all zeros.
Tunnel Flags Field
Name: tun_flags
Width: 16 bits (only the least-significant 1 bits may be nonzero)
Format: tunnel flags
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_TUN_FLAGS (104) since Open vSwitch 2.5
Flags indicating various aspects of the tunnel encapsulation.
Matches on this field are most conveniently written in terms of sym‐
bolic names (given in the diagram below), each preceded by either + for
a flag that must be set, or - for a flag that must be unset, without
any other delimiters between the flags. Flags not mentioned are wild‐
carded. For example, tun_flags=+oam matches only OAM packets. Matches
can also be written as flags/mask, where flags and mask are 16-bit num‐
bers in decimal or in hexadecimal prefixed by 0x.
Currently, only one flag is defined:
oam The tunnel protocol indicated that this is an OAM (Opera‐
tions and Management) control packet.
The switch may reject matches against unknown flags.
Newer versions of Open vSwitch may introduce additional flags with new
meanings. It is therefore not recommended to use an exact match on this
field since the behavior of these new flags is unknown and should be
ignored.
For non-tunneled packets, the value is 0.
METADATA FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
────────────── ────── ───── ──── ──────── ─────────────────────
in_port 2 no yes none OVS 1.1+
in_port_oxm 4 no yes none OF 1.2+ and OVS 1.7+
skb_priority 4 no no none
pkt_mark 4 yes yes none OVS 2.0+
actset_output 4 no no none OF 1.3+ and OVS 2.4+
packet_type 4 no no none OF 1.5+ and OVS 2.8+
These fields relate to the origin or treatment of a packet, but they
are not extracted from the packet data itself.
Ingress Port Field
Name: in_port
Width: 16 bits
Format: OpenFlow 1.0 port
Masking: not maskable
Prerequisites: none
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: none
NXM: NXM_OF_IN_PORT (0) since Open vSwitch 1.1
The OpenFlow port on which the packet being processed arrived. This is
a 16-bit field that holds an OpenFlow 1.0 port number. For receiving a
packet, the only values that appear in this field are:
1 through 0xfeff (65,279), inclusive.
Conventional OpenFlow port numbers.
OFPP_LOCAL (0xfffe or 65,534).
The ``local’’ port, which in Open vSwitch is always named
the same as the bridge itself. This represents a connec‐
tion between the switch and the local TCP/IP stack. This
port is where an IP address is most commonly configured
on an Open vSwitch switch.
OpenFlow does not require a switch to have a local port,
but all existing versions of Open vSwitch have always in‐
cluded a local port. Future Directions: Future versions
of Open vSwitch might be able to optionally omit the lo‐
cal port, if someone submits code to implement such a
feature.
OFPP_NONE (OpenFlow 1.0) or OFPP_ANY (OpenFlow 1.1+) (0xffff or
65,535).
OFPP_CONTROLLER (0xfffd or 65,533).
When a controller injects a packet into an OpenFlow switch
with a ``packet-out’’ request, it can specify one of these
ingress ports to indicate that the packet was generated in‐
ternally rather than having been received on some port.
OpenFlow 1.0 specified OFPP_NONE for this purpose. Despite
that, some controllers used OFPP_CONTROLLER, and some
switches only accepted OFPP_CONTROLLER, so OpenFlow 1.0.2
required support for both ports. OpenFlow 1.1 and later
were more clearly drafted to allow only OFPP_CONTROLLER.
For maximum compatibility, Open vSwitch allows both ports
with all OpenFlow versions.
Values not mentioned above will never appear when receiving a packet,
including the following notable values:
0 Zero is not a valid OpenFlow port number.
OFPP_MAX (0xff00 or 65,280).
This value has only been clearly specified as a valid
port number as of OpenFlow 1.3.3. Before that, its status
was unclear, and so Open vSwitch has never allowed
OFPP_MAX to be used as a port number, so packets will
never be received on this port. (Other OpenFlow switches,
of course, might use it.)
OFPP_UNSET (0xfff7 or 65,527)
OFPP_IN_PORT (0xfff8 or 65,528)
OFPP_TABLE (0xfff9 or 65,529)
OFPP_NORMAL (0xfffa or 65,530)
OFPP_FLOOD (0xfffb or 65,531)
OFPP_ALL (0xfffc or 65,532)
These port numbers are used only in output actions and
never appear as ingress ports.
Most of these port numbers were defined in OpenFlow 1.0,
but OFPP_UNSET was only introduced in OpenFlow 1.5.
Values that will never appear when receiving a packet may still be
matched against in the flow table. There are still circumstances in
which those flows can be matched:
• The resubmit Open vSwitch extension action allows a flow
table lookup with an arbitrary ingress port.
• An action that modifies the ingress port field (see be‐
low), such as e.g. load or set_field, followed by an ac‐
tion or instruction that performs another flow table
lookup, such as resubmit or goto_table.
This field is heavily used for matching in OpenFlow tables, but for
packet egress, it has only very limited roles:
• OpenFlow requires suppressing output actions to in_port.
That is, the following two flows both drop all packets
that arrive on port 1:
in_port=1,actions=1
in_port=1,actions=drop
(This behavior is occasionally useful for flooding to a
subset of ports. Specifying actions=1,2,3,4, for example,
outputs to ports 1, 2, 3, and 4, omitting the ingress
port.)
• OpenFlow has a special port OFPP_IN_PORT (with value
0xfff8) that outputs to the ingress port. For example, in
a switch that has four ports numbered 1 through 4, ac‐
tions=1,2,3,4,in_port outputs to ports 1, 2, 3, and 4,
including the ingress port.
Because the ingress port field has so little influence on packet pro‐
cessing, it does not ordinarily make sense to modify the ingress port
field. The field is writable only to support the occasional use case
where the ingress port’s roles in packet egress, described above, be‐
come troublesome. For example, actions=load:0->NXM_OF_IN_PORT[],out‐
put:123 will output to port 123 regardless of whether it is in the
ingress port. If the ingress port is important, then one may save and
restore it on the stack:
actions=push:NXM_OF_IN_PORT[],load:0->NXM_OF_IN_PORT[],output:123,pop:NXM_OF_IN_PORT[]
or, in Open vSwitch 2.7 or later, use the clone action to save and re‐
store it:
actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
The ability to modify the ingress port is an Open vSwitch extension to
OpenFlow.
OXM Ingress Port Field
Name: in_port_oxm
Width: 32 bits
Format: OpenFlow 1.1+ port
Masking: not maskable
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IN_PORT (0) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: none
OpenFlow 1.1 and later use a 32-bit port number, so this field supplies
a 32-bit view of the ingress port. Current versions of Open vSwitch
support only a 16-bit range of ports:
• OpenFlow 1.0 ports 0x0000 to 0xfeff, inclusive, map to
OpenFlow 1.1 port numbers with the same values.
• OpenFlow 1.0 ports 0xff00 to 0xffff, inclusive, map to
OpenFlow 1.1 port numbers 0xffffff00 to 0xffffffff.
• OpenFlow 1.1 ports 0x0000ff00 to 0xfffffeff are not
mapped and not supported.
in_port and in_port_oxm are two views of the same information, so all
of the comments on in_port apply to in_port_oxm too. Modifying in_port
changes in_port_oxm, and vice versa.
Setting in_port_oxm to an unsupported value yields unspecified behav‐
ior.
Output Queue Field
Name: skb_priority
Width: 32 bits
Format: hexadecimal
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: none
Future Directions: Open vSwitch implements the output queue as a field,
but does not currently expose it through OXM or NXM for matching pur‐
poses. If this turns out to be a useful feature, it could be imple‐
mented in future versions. Only the set_queue, enqueue, and pop_queue
actions currently influence the output queue.
This field influences how packets in the flow will be queued, for qual‐
ity of service (QoS) purposes, when they egress the switch. Its range
of meaningful values, and their meanings, varies greatly from one Open‐
Flow implementation to another. Even within a single implementation,
there is no guarantee that all OpenFlow ports have the same queues con‐
figured or that all OpenFlow ports in an implementation can be config‐
ured the same way queue-wise.
Configuring queues on OpenFlow is not well standardized. On Linux, Open
vSwitch supports queue configuration via OVSDB, specifically the QoS
and Queue tables (see ovs-vswitchd.conf.db(5) for details). Ports of
Open vSwitch to other platforms might require queue configuration
through some separate protocol (such as a CLI). Even on Linux, Open
vSwitch exposes only a fraction of the kernel’s queuing features
through OVSDB, so advanced or unusual uses might require use of sepa‐
rate utilities (e.g. tc). OpenFlow switches other than Open vSwitch
might use OF-CONFIG or any of the configuration methods mentioned
above. Finally, some OpenFlow switches have a fixed number of fixed-
function queues (e.g. eight queues with strictly defined priorities)
and others do not support any control over queuing.
The only output queue that all OpenFlow implementations must support is
zero, to identify a default queue, whose properties are implementation-
defined. Outputting a packet to a queue that does not exist on the out‐
put port yields unpredictable behavior: among the possibilities are
that the packet might be dropped or transmitted with a very high or
very low priority.
OpenFlow 1.0 only allowed output queues to be specified as part of an
enqueue action that specified both a queue and an output port. That is,
OpenFlow 1.0 treats the queue as an argument to an action, not as a
field.
To increase flexibility, OpenFlow 1.1 added an action to set the output
queue. This model was carried forward, without change, through OpenFlow
1.5.
Open vSwitch implements the native queuing model of each OpenFlow ver‐
sion it supports. Open vSwitch also includes an extension for setting
the output queue as an action in OpenFlow 1.0.
When a packet ingresses into an OpenFlow switch, the output queue is
ordinarily set to 0, indicating the default queue. However, Open
vSwitch supports various ways to forward a packet from one OpenFlow
switch to another within a single host. In these cases, Open vSwitch
maintains the output queue across the forwarding step. For example:
• A hop across an Open vSwitch ``patch port’’ (which does
not actually involve queuing) preserves the output queue.
• When a flow sets the output queue then outputs to an
OpenFlow tunnel port, the encapsulation preserves the
output queue. If the kernel TCP/IP stack routes the en‐
capsulated packet directly to a physical interface, then
that output honors the output queue. Alternatively, if
the kernel routes the encapsulated packet to another Open
vSwitch bridge, then the output queue set previously be‐
comes the initial output queue on ingress to the second
bridge and will thus be used for further output actions
(unless overridden by a new ``set queue’’ action).
(This description reflects the current behavior of Open
vSwitch on Linux. This behavior relies on details of the
Linux TCP/IP stack. It could be difficult to make ports
to other operating systems behave the same way.)
Packet Mark Field
Name: pkt_mark
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_PKT_MARK (33) since Open vSwitch 2.0
Packet mark comes to Open vSwitch from the Linux kernel, in which the
sk_buff data structure that represents a packet contains a 32-bit mem‐
ber named skb_mark. The value of skb_mark propagates along with the
packet it accompanies wherever the packet goes in the kernel. It has no
predefined semantics but various kernel-user interfaces can set and
match on it, which makes it suitable for ``marking’’ packets at one
point in their handling and then acting on the mark later. With ipta‐
bles, for example, one can mark some traffic specially at ingress and
then handle that traffic differently at egress based on the marked
value.
Packet mark is an attempt at a generalization of the skb_mark concept
beyond Linux, at least through more generic naming. Like skb_priority,
packet mark is preserved across forwarding steps within a machine. Un‐
like skb_priority, packet mark has no direct effect on packet forward‐
ing: the value set in packet mark does not matter unless some later
OpenFlow table or switch matches on packet mark, or unless the packet
passes through some other kernel subsystem that has been configured to
interpret packet mark in specific ways, e.g. through iptables configu‐
ration mentioned above.
Preserving packet mark across kernel forwarding steps relies heavily on
kernel support, which ports to non-Linux operating systems may not
have. Regardless of operating system support, Open vSwitch supports
packet mark within a single bridge and across patch ports.
The value of packet mark when a packet ingresses into the first Open
vSwich bridge is typically zero, but it could be nonzero if its value
was previously set by some kernel subsystem.
Action Set Output Port Field
Name: actset_output
Width: 32 bits
Format: OpenFlow 1.1+ port
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: ONFOXM_ET_ACTSET_OUTPUT (43) since OpenFlow 1.3 and
Open vSwitch 2.4; OXM_OF_ACTSET_OUTPUT (43) since
OpenFlow 1.5 and Open vSwitch 2.4
NXM: none
Holds the output port currently in the OpenFlow action set (i.e. from
an output action within a write_actions instruction). Its value is an
OpenFlow port number. If there is no output port in the OpenFlow action
set, or if the output port will be ignored (e.g. because there is an
output group in the OpenFlow action set), then the value will be
OFPP_UNSET.
Open vSwitch allows any table to match this field. OpenFlow, however,
only requires this field to be matchable from within an OpenFlow egress
table (a feature that Open vSwitch does not yet implement).
Packet Type Field
Name: packet_type
Width: 32 bits
Format: packet type
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_PACKET_TYPE (44) since OpenFlow 1.5 and Open
vSwitch 2.8
NXM: none
The type of the packet in the format specified in OpenFlow 1.5:
Packet type
<--------->
16 16
+---+-------+
|ns |ns_type| ...
+---+-------+
The upper 16 bits, ns, are a namespace. The meaning of ns_type depends
on the namespace. The packet type field is specified and displayed in
the format (ns,ns_type).
Open vSwitch currently supports the following classes of packet types
for matching:
(0,0) Ethernet.
(1,ethertype)
The specified ethertype. Open vSwitch can forward packets
with any ethertype, but it can only match on and process
data fields for the following supported packet types:
(1,0x800)
IPv4
(1,0x806)
ARP
(1,0x86dd)
IPv6
(1,0x8847)
MPLS
(1,0x8848)
MPLS multicast
(1,0x8035)
RARP
(1,0x894f)
NSH
Consider the distinction between a packet with packet_type=(0,0),
dl_type=0x800 and one with packet_type=(1,0x800). The former is an Eth‐
ernet frame that contains an IPv4 packet, like this:
Ethernet IPv4
<-----------> <--------------->
48 48 16 8 32 32
+---+---+-----+ +---+-----+---+---+
|dst|src|type | |...|proto|src|dst| ...
+---+---+-----+ +---+-----+---+---+
0x800
The latter is an IPv4 packet not encapsulated inside any outer frame,
like this:
IPv4
<--------------->
8 32 32
+---+-----+---+---+
|...|proto|src|dst| ...
+---+-----+---+---+
Matching on packet_type is a pre-requisite for matching on any data
field, but for backward compatibility, when a match on a data field is
present without a packet_type match, Open vSwitch acts as though a
match on (0,0) (Ethernet) had been supplied. Similarly, when Open
vSwitch sends flow match information to a controller, e.g. in a reply
to a request to dump the flow table, Open vSwitch omits a match on
packet type (0,0) if it would be implied by a data field match.
CONNECTION TRACKING FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────────── ────── ───── ──── ──────── ────────────────
ct_state 4 yes no none OVS 2.5+
ct_zone 2 no no none OVS 2.5+
ct_mark 4 yes yes none OVS 2.5+
ct_label 16 yes yes none OVS 2.5+
ct_nw_src 4 yes no CT OVS 2.8+
ct_nw_dst 4 yes no CT OVS 2.8+
ct_ipv6_src 16 yes no CT OVS 2.8+
ct_ipv6_dst 16 yes no CT OVS 2.8+
ct_nw_proto 1 no no CT OVS 2.8+
ct_tp_src 2 yes no CT OVS 2.8+
ct_tp_dst 2 yes no CT OVS 2.8+
Open vSwitch supports ``connection tracking,’’ which allows bidirec‐
tional streams of packets to be statefully grouped into connections.
Open vSwitch connection tracking, for example, identifies the patterns
of TCP packets that indicates a successfully initiated connection, as
well as those that indicate that a connection has been torn down. Open
vSwitch connection tracking can also identify related connections, such
as FTP data connections spawned from FTP control connections.
An individual packet passing through the pipeline may be in one of two
states, ``untracked’’ or ``tracked,’’ which may be distinguished via
the ``trk’’ flag in ct_state. A packet is untracked at the beginning of
the Open vSwitch pipeline and continues to be untracked until the pipe‐
line invokes the ct action. The connection tracking fields are all ze‐
roes in an untracked packet. When a flow in the Open vSwitch pipeline
invokes the ct action, the action initializes the connection tracking
fields and the packet becomes tracked for the remainder of its process‐
ing.
The connection tracker stores connection state in an internal table,
but it only adds a new entry to this table when a ct action for a new
connection invokes ct with the commit parameter. For a given connec‐
tion, when a pipeline has executed ct, but not yet with commit, the
connection is said to be uncommitted. State for an uncommitted connec‐
tion is ephemeral and does not persist past the end of the pipeline, so
some features are only available to committed connections. A connection
would typically be left uncommitted as a way to drop its packets.
Connection tracking is an Open vSwitch extension to OpenFlow. Open
vSwitch 2.5 added the initial support for connection tracking. Subse‐
quent versions of Open vSwitch added many refinements and extensions to
the initial support. Many of these capabilities depend on the Open
vSwitch datapath rather than simply the userspace version. The capabil‐
ities column in the Datapath table (see ovs-vswitchd.conf.db(5)) re‐
ports the detailed capabilities of a particular Open vSwitch datapath.
Connection Tracking State Field
Name: ct_state
Width: 32 bits
Format: ct state
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_STATE (105) since Open vSwitch 2.5
This field holds several flags that can be used to determine the state
of the connection to which the packet belongs.
Matches on this field are most conveniently written in terms of sym‐
bolic names (listed below), each preceded by either + for a flag that
must be set, or - for a flag that must be unset, without any other de‐
limiters between the flags. Flags not mentioned are wildcarded. For ex‐
ample, tcp,ct_state=+trk-new matches TCP packets that have been run
through the connection tracker and do not establish a new connection.
Matches can also be written as flags/mask, where flags and mask are
32-bit numbers in decimal or in hexadecimal prefixed by 0x.
The following flags are defined:
new (0x01)
A new connection. Set to 1 if this is an uncommitted con‐
nection.
est (0x02)
Part of an existing connection. Set to 1 if packets of a
committed connection have been seen by conntrack from
both directions.
rel (0x04)
Related to an existing connection, e.g. an ICMP ``desti‐
nation unreachable’’ message or an FTP data connections.
This flag will only be 1 if the connection to which this
one is related is committed.
Connections identified as rel are separate from the orig‐
inating connection and must be committed separately. All
packets for a related connection will have the rel flag
set, not just the initial packet.
rpl (0x08)
This packet is in the reply direction, meaning that it is
in the opposite direction from the packet that initiated
the connection. This flag will only be 1 if the connec‐
tion is committed.
inv (0x10)
The state is invalid, meaning that the connection tracker
couldn’t identify the connection. This flag is a catch-
all for problems in the connection or the connection
tracker, such as:
• L3/L4 protocol handler is not loaded/unavailable.
With the Linux kernel datapath, this may mean that
the nf_conntrack_ipv4 or nf_conntrack_ipv6 modules
are not loaded.
• L3/L4 protocol handler determines that the packet
is malformed.
• Packets are unexpected length for protocol.
trk (0x20)
This packet is tracked, meaning that it has previously
traversed the connection tracker. If this flag is not
set, then no other flags will be set. If this flag is
set, then the packet is tracked and other flags may also
be set.
snat (0x40)
This packet was transformed by source address/port trans‐
lation by a preceding ct action. Open vSwitch 2.6 added
this flag.
dnat (0x80)
This packet was transformed by destination address/port
translation by a preceding ct action. Open vSwitch 2.6
added this flag.
There are additional constraints on these flags, listed in decreasing
order of precedence below:
1. If trk is unset, no other flags are set.
2. If trk is set, one or more other flags may be set.
3. If inv is set, only the trk flag is also set.
4. new and est are mutually exclusive.
5. new and rpl are mutually exclusive.
6. rel may be set in conjunction with any other flags.
Future versions of Open vSwitch may define new flags.
Connection Tracking Zone Field
Name: ct_zone
Width: 16 bits
Format: hexadecimal
Masking: not maskable
Prerequisites: none
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_ZONE (106) since Open vSwitch 2.5
A connection tracking zone, the zone value passed to the most recent ct
action. Each zone is an independent connection tracking context, so
tracking the same packet in multiple contexts requires using the ct ac‐
tion multiple times.
Connection Tracking Mark Field
Name: ct_mark
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_MARK (107) since Open vSwitch 2.5
The metadata committed, by an action within the exec parameter to the
ct action, to the connection to which the current packet belongs.
Connection Tracking Label Field
Name: ct_label
Width: 128 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_LABEL (108) since Open vSwitch 2.5
The label committed, by an action within the exec parameter to the ct
action, to the connection to which the current packet belongs.
Open vSwitch 2.8 introduced the matching support for connection tracker
original direction 5-tuple fields.
For non-committed non-related connections the conntrack original direc‐
tion tuple fields always have the same values as the corresponding
headers in the packet itself. For any other packets of a committed con‐
nection the conntrack original direction tuple fields reflect the val‐
ues from that initial non-committed non-related packet, and thus may be
different from the actual packet headers, as the actual packet headers
may be in reverse direction (for reply packets), transformed by NAT
(when nat option was applied to the connection), or be of different
protocol (i.e., when an ICMP response is sent to an UDP packet). In
case of related connections, e.g., an FTP data connection, the original
direction tuple contains the original direction headers from the parent
connection, e.g., an FTP control connection.
The following fields are populated by the ct action, and require a
match to a valid connection tracking state as a prerequisite, in addi‐
tion to the IP or IPv6 ethertype match. Examples of valid connection
tracking state matches include ct_state=+new, ct_state=+est,
ct_state=+rel, and ct_state=+trk-inv.
Connection Tracking Original Direction IPv4 Source Address Field
Name: ct_nw_src
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_NW_SRC (120) since Open vSwitch 2.8
Matches IPv4 conntrack original direction tuple source address. See the
paragraphs above for general description to the conntrack original di‐
rection tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IPv4 Destination Address Field
Name: ct_nw_dst
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_NW_DST (121) since Open vSwitch 2.8
Matches IPv4 conntrack original direction tuple destination address.
See the paragraphs above for general description to the conntrack orig‐
inal direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IPv6 Source Address Field
Name: ct_ipv6_src
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_IPV6_SRC (122) since Open vSwitch 2.8
Matches IPv6 conntrack original direction tuple source address. See the
paragraphs above for general description to the conntrack original di‐
rection tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IPv6 Destination Address Field
Name: ct_ipv6_dst
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_IPV6_DST (123) since Open vSwitch 2.8
Matches IPv6 conntrack original direction tuple destination address.
See the paragraphs above for general description to the conntrack orig‐
inal direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction IP Protocol Field
Name: ct_nw_proto
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_NW_PROTO (119) since Open vSwitch 2.8
Matches conntrack original direction tuple IP protocol type, which is
specified as a decimal number between 0 and 255, inclusive (e.g. 1 to
match ICMP packets or 6 to match TCP packets). In case of, for example,
an ICMP response to an UDP packet, this may be different from the IP
protocol type of the packet itself. See the paragraphs above for gen‐
eral description to the conntrack original direction tuple. Introduced
in Open vSwitch 2.8.
Connection Tracking Original Direction Transport Layer Source Port
Field
Name: ct_tp_src
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_TP_SRC (124) since Open vSwitch 2.8
Bitwise match on the conntrack original direction tuple transport
source, when MFF_CT_NW_PROTO has value 6 for TCP, 17 for UDP, or 132
for SCTP. When MFF_CT_NW_PROTO has value 1 for ICMP, or 58 for ICMPv6,
the lower 8 bits of MFF_CT_TP_SRC matches the conntrack original direc‐
tion ICMP type. See the paragraphs above for general description to the
conntrack original direction tuple. Introduced in Open vSwitch 2.8.
Connection Tracking Original Direction Transport Layer Source Port
Field
Name: ct_tp_dst
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: CT
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_CT_TP_DST (125) since Open vSwitch 2.8
Bitwise match on the conntrack original direction tuple transport des‐
tination port, when MFF_CT_NW_PROTO has value 6 for TCP, 17 for UDP, or
132 for SCTP. When MFF_CT_NW_PROTO has value 1 for ICMP, or 58 for
ICMPv6, the lower 8 bits of MFF_CT_TP_DST matches the conntrack origi‐
nal direction ICMP code. See the paragraphs above for general descrip‐
tion to the conntrack original direction tuple. Introduced in Open
vSwitch 2.8.
REGISTER FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────── ────── ───── ──── ──────── ─────────────────────
metadata 8 yes yes none OF 1.2+ and OVS 1.8+
reg0 4 yes yes none OVS 1.1+
reg1 4 yes yes none OVS 1.1+
reg2 4 yes yes none OVS 1.1+
reg3 4 yes yes none OVS 1.1+
reg4 4 yes yes none OVS 1.3+
reg5 4 yes yes none OVS 1.7+
reg6 4 yes yes none OVS 1.7+
reg7 4 yes yes none OVS 1.7+
reg8 4 yes yes none OVS 2.6+
reg9 4 yes yes none OVS 2.6+
reg10 4 yes yes none OVS 2.6+
reg11 4 yes yes none OVS 2.6+
reg12 4 yes yes none OVS 2.6+
reg13 4 yes yes none OVS 2.6+
reg14 4 yes yes none OVS 2.6+
reg15 4 yes yes none OVS 2.6+
xreg0 8 yes yes none OF 1.3+ and OVS 2.4+
xreg1 8 yes yes none OF 1.3+ and OVS 2.4+
xreg2 8 yes yes none OF 1.3+ and OVS 2.4+
xreg3 8 yes yes none OF 1.3+ and OVS 2.4+
xreg4 8 yes yes none OF 1.3+ and OVS 2.4+
xreg5 8 yes yes none OF 1.3+ and OVS 2.4+
xreg6 8 yes yes none OF 1.3+ and OVS 2.4+
xreg7 8 yes yes none OF 1.3+ and OVS 2.4+
xxreg0 16 yes yes none OVS 2.6+
xxreg1 16 yes yes none OVS 2.6+
xxreg2 16 yes yes none OVS 2.6+
xxreg3 16 yes yes none OVS 2.6+
These fields give an OpenFlow switch space for temporary storage while
the pipeline is running. Whereas metadata fields can have a meaningful
initial value and can persist across some hops across OpenFlow
switches, registers are always initially 0 and their values never per‐
sist across inter-switch hops (not even across patch ports).
OpenFlow Metadata Field
Name: metadata
Width: 64 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes
OXM: OXM_OF_METADATA (2) since OpenFlow 1.2 and Open
vSwitch 1.8
NXM: none
This field is the oldest standardized OpenFlow register field, intro‐
duced in OpenFlow 1.1. It was introduced to model the limited number of
user-defined bits that some ASIC-based switches can carry through their
pipelines. Because of hardware limitations, OpenFlow allows switches to
support writing and masking only an implementation-defined subset of
bits, even no bits at all. The Open vSwitch software switch always sup‐
ports all 64 bits, but of course an Open vSwitch port to an ASIC would
have the same restriction as the ASIC itself.
This field has an OXM code point, but OpenFlow 1.4 and earlier allow it
to be modified only with a specialized instruction, not with a ``set-
field’’ action. OpenFlow 1.5 removes this restriction. Open vSwitch
does not enforce this restriction, regardless of OpenFlow version.
Register 0 Field
Name: reg0
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_REG0 (0) since Open vSwitch 1.1
This is the first of several Open vSwitch registers, all of which have
the same properties. Open vSwitch 1.1 introduced registers 0, 1, 2, and
3, version 1.3 added register 4, version 1.7 added registers 5, 6, and
7, and version 2.6 added registers 8 through 15.
Extended Register 0 Field
Name: xreg0
Width: 64 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_PKT_REG0 (0) since OpenFlow 1.3 and Open
vSwitch 2.4
NXM: none
This is the first of the registers introduced in OpenFlow 1.5. OpenFlow
1.5 calls these fields just the ``packet registers,’’ but Open vSwitch
already had 32-bit registers by that name, so Open vSwitch uses the
name ``extended registers’’ in an attempt to reduce confusion. The
standard allows for up to 128 registers, each 64 bits wide, but Open
vSwitch only implements 4 (in versions 2.4 and 2.5) or 8 (in version
2.6 and later).
Each of the 64-bit extended registers overlays two of the 32-bit regis‐
ters: xreg0 overlays reg0 and reg1, with reg0 supplying the most-sig‐
nificant bits of xreg0 and reg1 the least-significant. Similarly, xreg1
overlays reg2 and reg3, and so on.
The OpenFlow specification says, ``In most cases, the packet registers
can not be matched in tables, i.e. they usually can not be used in the
flow entry match structure’’ [OpenFlow 1.5, section 7.2.3.10], but
there is no reason for a software switch to impose such a restriction,
and Open vSwitch does not.
Double-Extended Register 0 Field
Name: xxreg0
Width: 128 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: none
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_XXREG0 (111) since Open vSwitch 2.6
This is the first of the double-extended registers introduce in Open
vSwitch 2.6. Each of the 128-bit extended registers overlays four of
the 32-bit registers: xxreg0 overlays reg0 through reg3, with reg0 sup‐
plying the most-significant bits of xxreg0 and reg3 the least-signifi‐
cant. xxreg1 similarly overlays reg4 through reg7, and so on.
LAYER 2 (ETHERNET) FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────────────────── ────── ───── ──── ───────── ─────────────────────
eth_src aka dl_src 6 yes yes Ethernet OF 1.2+ and OVS 1.1+
eth_dst aka dl_dst 6 yes yes Ethernet OF 1.2+ and OVS 1.1+
eth_type aka dl_type 2 no no Ethernet OF 1.2+ and OVS 1.1+
Ethernet is the only layer-2 protocol that Open vSwitch supports. As
with most software, Open vSwitch and OpenFlow regard an Ethernet frame
to begin with the 14-byte header and end with the final byte of the
payload; that is, the frame check sequence is not considered part of
the frame.
Ethernet Source Field
Name: eth_src (aka dl_src)
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ETH_SRC (4) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: NXM_OF_ETH_SRC (2) since Open vSwitch 1.1
The Ethernet source address:
Ethernet
<---------->
48 48 16
+---+---+----+
|dst|src|type| ...
+---+---+----+
Ethernet Destination Field
Name: eth_dst (aka dl_dst)
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ETH_DST (3) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: NXM_OF_ETH_DST (1) since Open vSwitch 1.1
The Ethernet destination address:
Ethernet
<---------->
48 48 16
+---+---+----+
|dst|src|type| ...
+---+---+----+
Open vSwitch 1.8 and later support arbitrary masks for source and/or
destination. Earlier versions only support masking the destination with
the following masks:
01:00:00:00:00:00
Match only the multicast bit. Thus,
dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 matches all
multicast (including broadcast) Ethernet packets, and
dl_dst=00:00:00:00:00:00/01:00:00:00:00:00 matches all
unicast Ethernet packets.
fe:ff:ff:ff:ff:ff
Match all bits except the multicast bit. This is probably
not useful.
ff:ff:ff:ff:ff:ff
Exact match (equivalent to omitting the mask).
00:00:00:00:00:00
Wildcard all bits (equivalent to dl_dst=*).
Ethernet Type Field
Name: eth_type (aka dl_type)
Width: 16 bits
Format: hexadecimal
Masking: not maskable
Prerequisites: Ethernet
Access: read-only
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ETH_TYPE (5) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_ETH_TYPE (3) since Open vSwitch 1.1
The most commonly seen Ethernet frames today use a format called ``Eth‐
ernet II,’’ in which the last two bytes of the Ethernet header specify
the Ethertype. For such a frame, this field is copied from those bytes
of the header, like so:
Ethernet
<---------------->
48 48 16
+---+---+----------+
|dst|src| type | ...
+---+---+----------+
≥0x600
Every Ethernet type has a value 0x600 (1,536) or greater. When the last
two bytes of the Ethernet header have a value too small to be an Ether‐
net type, then the value found there is the total length of the frame
in bytes, excluding the Ethernet header. An 802.2 LLC header typically
follows the Ethernet header. OpenFlow and Open vSwitch only support LLC
headers with DSAP and SSAP 0xaa and control byte 0x03, which indicate
that a SNAP header follows the LLC header. In turn, OpenFlow and Open
vSwitch only support a SNAP header with organization 0x000000. In such
a case, this field is copied from the type field in the SNAP header,
like this:
Ethernet LLC SNAP
<------------> <------------> <----------------->
48 48 16 8 8 8 24 16
+---+---+------+ +----+----+----+ +--------+----------+
|dst|src| type | |DSAP|SSAP|cntl| | org | type | ...
+---+---+------+ +----+----+----+ +--------+----------+
<0x600 0xaa 0xaa 0x03 0x000000 ≥0x600
When an 802.1Q header is inserted after the Ethernet source and desti‐
nation, this field is populated with the encapsulated Ethertype, not
the 802.1Q Ethertype. With an Ethernet II inner frame, the result looks
like this:
Ethernet 802.1Q Ethertype
<------> <--------> <-------->
48 48 16 16 16
+----+---+ +------+---+ +----------+
|dst |src| | TPID |TCI| | type | ...
+----+---+ +------+---+ +----------+
0x8100 ≥0x600
LLC and SNAP encapsulation look like this with an 802.1Q header:
Ethernet 802.1Q Ethertype LLC SNAP
<------> <--------> <-------> <------------> <----------------->
48 48 16 16 16 8 8 8 24 16
+----+---+ +------+---+ +---------+ +----+----+----+ +--------+----------+
|dst |src| | TPID |TCI| | type | |DSAP|SSAP|cntl| | org | type | ...
+----+---+ +------+---+ +---------+ +----+----+----+ +--------+----------+
0x8100 <0x600 0xaa 0xaa 0x03 0x000000 ≥0x600
When a packet doesn’t match any of the header formats described above,
Open vSwitch and OpenFlow set this field to 0x5ff
(OFP_DL_TYPE_NOT_ETH_TYPE).
VLAN FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────────── ──────────────── ───── ──── ───────── ─────────────────────
dl_vlan 2 (low 12 bits) no yes Ethernet
dl_vlan_pcp 1 (low 3 bits) no yes Ethernet
vlan_vid 2 (low 12 bits) yes yes Ethernet OF 1.2+ and OVS 1.7+
vlan_pcp 1 (low 3 bits) no yes VLAN VID OF 1.2+ and OVS 1.7+
vlan_tci 2 yes yes Ethernet OVS 1.1+
The 802.1Q VLAN header causes more trouble than any other 4 bytes in
networking. OpenFlow 1.0, 1.1, and 1.2+ all treat VLANs differently.
Open vSwitch extensions add another variant to the mix. Open vSwitch
reconciles all four treatments as best it can.
VLAN Header Format
An 802.1Q VLAN header consists of two 16-bit fields:
TPID TCI
<-------> <--------->
16 3 1 12
+---------+---+---+---+
|Ethertype|PCP|CFI|VID|
+---------+---+---+---+
0x8100 0
The first 16 bits of the VLAN header, the TPID (Tag Protocol IDenti‐
fier), is an Ethertype. When the VLAN header is inserted just after the
source and destination MAC addresses in a Ethertype frame, the TPID
serves to identify the presence of the VLAN. The standard TPID, the
only one that Open vSwitch supports, is 0x8100. OpenFlow 1.0 explicitly
supports only TPID 0x8100. OpenFlow 1.1, but not earlier or later ver‐
sions, also requires support for TPID 0x88a8 (Open vSwitch does not
support this). OpenFlow 1.2 through 1.5 do not require support for spe‐
cific TPIDs (the ``push vlan header’’ action does say that only 0x8100
and 0x88a8 should be pushed). No version of OpenFlow provides a way to
distinguish or match on the TPID.
The remaining 16 bits of the VLAN header, the TCI (Tag Control Informa‐
tion), is subdivided into three subfields:
• PCP (Priority Control Point), is a 3-bit 802.1p priority.
The lowest priority is value 1, the second-lowest is
value 0, and priority increases from 2 up to highest pri‐
ority 7.
• CFI (Canonical Format Indicator), is a 1-bit field. On an
Ethernet network, its value is always 0. This led to it
later being repurposed under the name DEI (Drop Eligibil‐
ity Indicator). By either name, OpenFlow and Open vSwitch
don’t provide any way to match or set this bit.
• VID (VLAN IDentifier), is a 12-bit VLAN. If the VID is 0,
then the frame is not part of a VLAN. In that case, the
VLAN header is called a priority tag because it is only
meaningful for assigning the frame a priority. VID 0xfff
(4,095) is reserved.
See eth_type for illustrations of a complete Ethernet frame with 802.1Q
tag included.
Multiple VLANs
Open vSwitch can match only a single VLAN header. If more than one VLAN
header is present, then eth_type holds the TPID of the inner VLAN
header. Open vSwitch stops parsing the packet after the inner TPID, so
matching further into the packet (e.g. on the inner TCI or L3 fields)
is not possible.
OpenFlow only directly supports matching a single VLAN header. In Open‐
Flow 1.1 or later, one OpenFlow table can match on the outermost VLAN
header and pop it off, and a later OpenFlow table can match on the next
outermost header. Open vSwitch does not support this.
VLAN Field Details
The four variants have three different levels of expressiveness: Open‐
Flow 1.0 and 1.1 VLAN matching are less powerful than OpenFlow 1.2+
VLAN matching, which is less powerful than Open vSwitch extension VLAN
matching.
OpenFlow 1.0 VLAN Fields
OpenFlow 1.0 uses two fields, called dl_vlan and dl_vlan_pcp, each of
which can be either exact-matched or wildcarded, to specify VLAN
matches:
• When both dl_vlan and dl_vlan_pcp are wildcarded, the
flow matches packets without an 802.1Q header or with any
802.1Q header.
• The match dl_vlan=0xffff causes a flow to match only
packets without an 802.1Q header. Such a flow should also
wildcard dl_vlan_pcp, since a packet without an 802.1Q
header does not have a PCP. OpenFlow does not specify
what to do if a match on PCP is actually present, but
Open vSwitch ignores it.
• Otherwise, the flow matches only packets with an 802.1Q
header. If dl_vlan is not wildcarded, then the flow only
matches packets with the VLAN ID specified in dl_vlan’s
low 12 bits. If dl_vlan_pcp is not wildcarded, then the
flow only matches packets with the priority specified in
dl_vlan_pcp’s low 3 bits.
OpenFlow does not specify how to interpret the high 4
bits of dl_vlan or the high 5 bits of dl_vlan_pcp. Open
vSwitch ignores them.
OpenFlow 1.1 VLAN Fields
VLAN matching in OpenFlow 1.1 is similar to OpenFlow 1.0. The one re‐
finement is that when dl_vlan matches on 0xfffe (OFVPID_ANY), the flow
matches only packets with an 802.1Q header, with any VLAN ID. If
dl_vlan_pcp is wildcarded, the flow matches any packet with an 802.1Q
header, regardless of VLAN ID or priority. If dl_vlan_pcp is not wild‐
carded, then the flow only matches packets with the priority specified
in dl_vlan_pcp’s low 3 bits.
OpenFlow 1.1 uses the name OFPVID_NONE, instead of OFP_VLAN_NONE, for a
dl_vlan of 0xffff, but it has the same meaning.
In OpenFlow 1.1, Open vSwitch reports error OFPBMC_BAD_VALUE for an at‐
tempt to match on dl_vlan between 4,096 and 0xfffd, inclusive, or
dl_vlan_pcp greater than 7.
OpenFlow 1.2 VLAN Fields
OpenFlow 1.2+ VLAN ID Field
Name: vlan_vid
Width: 16 bits (only the least-significant 12 bits may be nonzero)
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_VLAN_VID (6) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: none
The OpenFlow standard describes this field as consisting of ``12+1’’
bits. On ingress, its value is 0 if no 802.1Q header is present, and
otherwise it holds the VLAN VID in its least significant 12 bits, with
bit 12 (0x1000 aka OFPVID_PRESENT) also set to 1. The three most sig‐
nificant bits are always zero:
OXM_OF_VLAN_VID
<------------->
3 1 12
+---+--+--------+
| |P |VLAN ID |
+---+--+--------+
0
As a consequence of this field’s format, one may use it to match the
VLAN ID in all of the ways available with the OpenFlow 1.0 and 1.1 for‐
mats, and a few new ways:
Fully wildcarded
Matches any packet, that is, one without an 802.1Q header
or with an 802.1Q header with any TCI value.
Value 0x0000 (OFPVID_NONE), mask 0xffff (or no mask)
Matches only packets without an 802.1Q header.
Value 0x1000, mask 0x1000
Matches any packet with an 802.1Q header, regardless of
VLAN ID.
Value 0x1009, mask 0xffff (or no mask)
Match only packets with an 802.1Q header with VLAN ID 9.
Value 0x1001, mask 0x1001
Matches only packets that have an 802.1Q header with an
odd-numbered VLAN ID. (This is just an example; one can
match on any desired VLAN ID bit pattern.)
OpenFlow 1.2+ VLAN Priority Field
Name: vlan_pcp
Width: 8 bits (only the least-significant 3 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: VLAN VID
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_VLAN_PCP (7) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: none
The 3 least significant bits may be used to match the PCP bits in an
802.1Q header. Other bits are always zero:
OXM_OF_VLAN_VID
<------------->
5 3
+--------+------+
| zero | PCP |
+--------+------+
0
This field may only be used when vlan_vid is not wildcarded and does
not exact match on 0 (which only matches when there is no 802.1Q
header).
See VLAN Comparison Chart, below, for some examples.
Open vSwitch Extension VLAN Field
The vlan_tci extension can describe more kinds of VLAN matches than the
other variants. It is also simpler than the other variants.
VLAN TCI Field
Name: vlan_tci
Width: 16 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: Ethernet
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: none
NXM: NXM_OF_VLAN_TCI (4) since Open vSwitch 1.1
For a packet without an 802.1Q header, this field is zero. For a packet
with an 802.1Q header, this field is the TCI with the bit in CFI’s po‐
sition (marked P for ``present’’ below) forced to 1. Thus, for a packet
in VLAN 9 with priority 7, it has the value 0xf009:
NXM_VLAN_TCI
<---------->
3 1 12
+----+--+----+
|PCP |P |VID |
+----+--+----+
7 1 9
Usage examples:
vlan_tci=0
Match packets without an 802.1Q header.
vlan_tci=0x1000/0x1000
Match packets with an 802.1Q header, regardless of VLAN
and priority values.
vlan_tci=0xf123
Match packets tagged with priority 7 in VLAN 0x123.
vlan_tci=0x1123/0x1fff
Match packets tagged with VLAN 0x123 (and any priority).
vlan_tci=0x5000/0xf000
Match packets tagged with priority 2 (in any VLAN).
vlan_tci=0/0xfff
Match packets with no 802.1Q header or tagged with VLAN 0
(and any priority).
vlan_tci=0x5000/0xe000
Match packets with no 802.1Q header or tagged with prior‐
ity 2 (in any VLAN).
vlan_tci=0/0xefff
Match packets with no 802.1Q header or tagged with VLAN 0
and priority 0.
See VLAN Comparison Chart, below, for more examples.
VLAN Comparison Chart
The following table describes each of several possible matching crite‐
ria on 802.1Q header may be expressed with each variation of the VLAN
matching fields:
Criteria OpenFlow 1.0 OpenFlow 1.1 OpenFlow 1.2+ NXM
_ _ _ _ _
[1] ????/1,??/? ????/1,??/? 0000/0000,-- 0000/0000
[2] ffff/0,??/? ffff/0,??/? 0000/ffff,-- 0000/ffff
[3] 0xxx/0,??/1 0xxx/0,??/1 1xxx/ffff,-- 1xxx/1fff
[4] ????/1,0y/0 fffe/0,0y/0 1000/1000,0y z000/f000
[5] 0xxx/0,0y/0 0xxx/0,0y/0 1xxx/ffff,0y zxxx/ffff
[6] (none) (none) 1001/1001,-- 1001/1001
[7] (none) (none) (none) 3000/3000
[8] (none) (none) (none) 0000/0fff
[9] (none) (none) (none) 0000/f000
[10] (none) (none) (none) 0000/efff
All numbers in the table are expressed in hexadecimal. The columns in
the table are interpreted as follows:
Criteria
See the list below.
OpenFlow 1.0
OpenFlow 1.1
wwww/x,yy/z means VLAN ID match value wwww with wildcard
bit x and VLAN PCP match value yy with wildcard bit z. ?
means that the given bits are ignored (and conventionally 0
for wwww or yy, conventionally 1 for x or z). ``(none)’’
means that OpenFlow 1.0 (or 1.1) cannot match with these
criteria.
OpenFlow 1.2+
xxxx/yyyy,zz means vlan_vid with value xxxx and mask yyyy,
and vlan_pcp (which is not maskable) with value zz. --
means that vlan_pcp is omitted. ``(none)’’ means that Open‐
Flow 1.2 cannot match with these criteria.
NXM xxxx/yyyy means vlan_tci with value xxxx and mask yyyy.
The matching criteria described by the table are:
[1] Matches any packet, that is, one without an 802.1Q header
or with an 802.1Q header with any TCI value.
[2] Matches only packets without an 802.1Q header.
OpenFlow 1.0 doesn’t define the behavior if dl_vlan is
set to 0xffff and dl_vlan_pcp is not wildcarded. (Open
vSwitch always ignores dl_vlan_pcp when dl_vlan is set to
0xffff.)
OpenFlow 1.1 says explicitly to ignore dl_vlan_pcp when
dl_vlan is set to 0xffff.
OpenFlow 1.2 doesn’t say how to interpret a match with
vlan_vid value 0 and a mask with OFPVID_PRESENT (0x1000)
set to 1 and some other bits in the mask set to 1 also.
Open vSwitch interprets it the same way as a mask of
0x1000.
Any NXM match with vlan_tci value 0 and the CFI bit set
to 1 in the mask is equivalent to the one listed in the
table.
[3] Matches only packets that have an 802.1Q header with VID
xxx (and any PCP).
[4] Matches only packets that have an 802.1Q header with PCP
y (and any VID).
OpenFlow 1.0 doesn’t clearly define the behavior for this
case. Open vSwitch implements it this way.
In the NXM value, z equals (y << 1) | 1.
[5] Matches only packets that have an 802.1Q header with VID
xxx and PCP y.
In the NXM value, z equals (y << 1) | 1.
[6] Matches only packets that have an 802.1Q header with an
odd-numbered VID (and any PCP). Only possible with Open‐
Flow 1.2 and NXM. (This is just an example; one can match
on any desired VID bit pattern.)
[7] Matches only packets that have an 802.1Q header with an
odd-numbered PCP (and any VID). Only possible with NXM.
(This is just an example; one can match on any desired
VID bit pattern.)
[8] Matches packets with no 802.1Q header or with an 802.1Q
header with a VID of 0. Only possible with NXM.
[9] Matches packets with no 802.1Q header or with an 802.1Q
header with a PCP of 0. Only possible with NXM.
[10] Matches packets with no 802.1Q header or with an 802.1Q
header with both VID and PCP of 0. Only possible with
NXM.
LAYER 2.5: MPLS FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
─────────── ──────────────── ───── ──── ──────── ──────────────────────
mpls_label 4 (low 20 bits) no yes MPLS OF 1.2+ and OVS 1.11+
mpls_tc 1 (low 3 bits) no yes MPLS OF 1.2+ and OVS 1.11+
mpls_bos 1 (low 1 bits) no no MPLS OF 1.3+ and OVS 1.11+
mpls_ttl 1 no yes MPLS OVS 2.6+
One or more MPLS headers (more commonly called MPLS labels) follow an
Ethernet type field that specifies an MPLS Ethernet type [RFC 3032].
Ethertype 0x8847 is used for all unicast. Multicast MPLS is divided
into two specific classes, one of which uses Ethertype 0x8847 and the
other 0x8848 [RFC 5332].
The most common overall packet format is Ethernet II, shown below (SNAP
encapsulation may be used but is not ordinarily seen in Ethernet net‐
works):
Ethernet MPLS
<------------> <------------>
48 48 16 20 3 1 8
+---+---+------+ +-----+--+-+---+
|dst|src| type | |label|TC|S|TTL| ...
+---+---+------+ +-----+--+-+---+
0x8847
MPLS can be encapsulated inside an 802.1Q header, in which case the
combination looks like this:
Ethernet 802.1Q Ethertype MPLS
<------> <--------> <-------> <------------>
48 48 16 16 16 20 3 1 8
+----+---+ +------+---+ +---------+ +-----+--+-+---+
|dst |src| | TPID |TCI| | type | |label|TC|S|TTL| ...
+----+---+ +------+---+ +---------+ +-----+--+-+---+
0x8100 0x8847
The fields within an MPLS label are:
Label, 20 bits.
An identifier.
Traffic control (TC), 3 bits.
Used for quality of service.
Bottom of stack (BOS), 1 bit (labeled just ``S’’ above).
0 indicates that another MPLS label follows this one.
1 indicates that this MPLS label is the last one in the
stack, so that some other protocol follows this one.
Time to live (TTL), 8 bits.
Each hop across an MPLS network decrements the TTL by 1.
If it reaches 0, the packet is discarded.
OpenFlow does not make the MPLS TTL available as a match
field, but actions are available to set and decrement the
TTL. Open vSwitch 2.6 and later makes the MPLS TTL avail‐
able as an extension.
MPLS Label Stacks
Unlike the other encapsulations supported by OpenFlow and Open vSwitch,
MPLS labels are routinely used in ``stacks’’ two or three deep and
sometimes even deeper. Open vSwitch currently supports up to three la‐
bels.
The OpenFlow specification only supports matching on the outermost MPLS
label at any given time. To match on the second label, one must first
``pop’’ the outer label and advance to another OpenFlow table, where
the inner label may be matched. To match on the third label, one must
pop the two outer labels, and so on.
MPLS Inner Protocol
Unlike all other forms of encapsulation that Open vSwitch and OpenFlow
support, an MPLS label does not indicate what inner protocol it encap‐
sulates. Different deployments determine the inner protocol in differ‐
ent ways [RFC 3032]:
• A few reserved label values do indicate an inner proto‐
col. Label 0, the ``IPv4 Explicit NULL Label,’’ indicates
inner IPv4. Label 2, the ``IPv6 Explicit NULL Label,’’
indicates inner IPv6.
• Some deployments use a single inner protocol consis‐
tently.
• In some deployments, the inner protocol must be inferred
from the innermost label.
• In some deployments, the inner protocol must be inferred
from the innermost label and the encapsulated data, e.g.
to distinguish between inner IPv4 and IPv6 based on
whether the first nibble of the inner protocol data are 4
or 6. OpenFlow and Open vSwitch do not currently support
these cases.
Open vSwitch and OpenFlow do not infer the inner protocol, even if re‐
served label values are in use. Instead, the flow table must specify
the inner protocol at the time it pops the bottommost MPLS label, using
the Ethertype argument to the pop_mpls action.
Field Details
MPLS Label Field
Name: mpls_label
Width: 32 bits (only the least-significant 20 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_MPLS_LABEL (34) since OpenFlow 1.2 and Open vSwitch
1.11
NXM: none
The least significant 20 bits hold the ``label’’ field from the MPLS
label. Other bits are zero:
OXM_OF_MPLS_LABEL
<--------------->
12 20
+--------+--------+
| zero | label |
+--------+--------+
0
Most label values are available for any use by deployments. Values un‐
der 16 are reserved.
MPLS Traffic Class Field
Name: mpls_tc
Width: 8 bits (only the least-significant 3 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_MPLS_TC (35) since OpenFlow 1.2 and Open vSwitch
1.11
NXM: none
The least significant 3 bits hold the TC field from the MPLS label.
Other bits are zero:
OXM_OF_MPLS_TC
<------------>
5 3
+--------+-----+
| zero | TC |
+--------+-----+
0
This field is intended for use for Quality of Service (QoS) and Ex‐
plicit Congestion Notification purposes, but its particular interpreta‐
tion is deployment specific.
Before 2009, this field was named EXP and reserved for experimental use
[RFC 5462].
MPLS Bottom of Stack Field
Name: mpls_bos
Width: 8 bits (only the least-significant 1 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_MPLS_BOS (36) since OpenFlow 1.3 and Open vSwitch
1.11
NXM: none
The least significant bit holds the BOS field from the MPLS label.
Other bits are zero:
OXM_OF_MPLS_BOS
<------------->
7 1
+--------+------+
| zero | BOS |
+--------+------+
0
This field is useful as part of processing a series of incoming MPLS
labels. A flow that includes a pop_mpls action should generally match
on mpls_bos:
• When mpls_bos is 0, there is another MPLS label following
this one, so the Ethertype passed to pop_mpls should be
an MPLS Ethertype. For example: table=0, dl_type=0x8847,
mpls_bos=0, actions=pop_mpls:0x8847, goto_table:1
• When mpls_bos is 1, this MPLS label is the last one, so
the Ethertype passed to pop_mpls should be a non-MPLS
Ethertype such as IPv4. For example: table=1,
dl_type=0x8847, mpls_bos=1, actions=pop_mpls:0x0800,
goto_table:2
MPLS Time-to-Live Field
Name: mpls_ttl
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: MPLS
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_MPLS_TTL (30) since Open vSwitch 2.6
Holds the 8-bit time-to-live field from the MPLS label:
NXM_NX_MPLS_TTL
<------------->
8
+---------------+
| TTL |
+---------------+
LAYER 3: IPV4 AND IPV6 FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
────────────────────── ──────────────── ───── ──── ────────── ─────────────────────
ip_src aka nw_src 4 yes yes IPv4 OF 1.2+ and OVS 1.1+
ip_dst aka nw_dst 4 yes yes IPv4 OF 1.2+ and OVS 1.1+
ipv6_src 16 yes yes IPv6 OF 1.2+ and OVS 1.1+
ipv6_dst 16 yes yes IPv6 OF 1.2+ and OVS 1.1+
ipv6_label 4 (low 20 bits) yes yes IPv6 OF 1.2+ and OVS 1.4+
nw_proto aka ip_proto 1 no no IPv4/IPv6 OF 1.2+ and OVS 1.1+
nw_ttl 1 no yes IPv4/IPv6 OVS 1.4+
ip_frag aka nw_frag 1 (low 2 bits) yes no IPv4/IPv6 OVS 1.3+
nw_tos 1 no yes IPv4/IPv6 OVS 1.1+
ip_dscp 1 (low 6 bits) no yes IPv4/IPv6 OF 1.2+ and OVS 1.7+
nw_ecn aka ip_ecn 1 (low 2 bits) no yes IPv4/IPv6 OF 1.2+ and OVS 1.4+
IPv4 Specific Fields
These fields are applicable only to IPv4 flows, that is, flows that
match on the IPv4 Ethertype 0x0800.
IPv4 Source Address Field
Name: ip_src (aka nw_src)
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: IPv4
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_IPV4_SRC (11) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_IP_SRC (7) since Open vSwitch 1.1
The source address from the IPv4 header:
Ethernet IPv4
<-----------> <--------------->
48 48 16 8 32 32
+---+---+-----+ +---+-----+---+---+
|dst|src|type | |...|proto|src|dst| ...
+---+---+-----+ +---+-----+---+---+
0x800
For historical reasons, in an ARP or RARP flow, Open vSwitch interprets
matches on nw_src as actually referring to the ARP SPA.
IPv4 Destination Address Field
Name: ip_dst (aka nw_dst)
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: IPv4
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_IPV4_DST (12) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_IP_DST (8) since Open vSwitch 1.1
The destination address from the IPv4 header:
Ethernet IPv4
<-----------> <--------------->
48 48 16 8 32 32
+---+---+-----+ +---+-----+---+---+
|dst|src|type | |...|proto|src|dst| ...
+---+---+-----+ +---+-----+---+---+
0x800
For historical reasons, in an ARP or RARP flow, Open vSwitch interprets
matches on nw_dst as actually referring to the ARP TPA.
IPv6 Specific Fields
These fields apply only to IPv6 flows, that is, flows that match on the
IPv6 Ethertype 0x86dd.
IPv6 Source Address Field
Name: ipv6_src
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_SRC (26) since OpenFlow 1.2 and Open
vSwitch 1.1
NXM: NXM_NX_IPV6_SRC (19) since Open vSwitch 1.1
The source address from the IPv6 header:
Ethernet IPv6
<------------> <-------------->
48 48 16 8 128 128
+---+---+------+ +---+----+---+---+
|dst|src| type | |...|next|src|dst| ...
+---+---+------+ +---+----+---+---+
0x86dd
Open vSwitch 1.8 added support for bitwise matching; earlier versions
supported only CIDR masks.
IPv6 Destination Address Field
Name: ipv6_dst
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_DST (27) since OpenFlow 1.2 and Open
vSwitch 1.1
NXM: NXM_NX_IPV6_DST (20) since Open vSwitch 1.1
The destination address from the IPv6 header:
Ethernet IPv6
<------------> <-------------->
48 48 16 8 128 128
+---+---+------+ +---+----+---+---+
|dst|src| type | |...|next|src|dst| ...
+---+---+------+ +---+----+---+---+
0x86dd
Open vSwitch 1.8 added support for bitwise matching; earlier versions
supported only CIDR masks.
IPv6 Flow Label Field
Name: ipv6_label
Width: 32 bits (only the least-significant 20 bits may be nonzero)
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_FLABEL (28) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: NXM_NX_IPV6_LABEL (27) since Open vSwitch 1.4
The least significant 20 bits hold the flow label field from the IPv6
header. Other bits are zero:
OXM_OF_IPV6_FLABEL
<---------------->
12 20
+--------+---------+
| zero | label |
+--------+---------+
0
IPv4/IPv6 Fields
These fields exist with at least approximately the same meaning in both
IPv4 and IPv6, so they are treated as a single field for matching pur‐
poses. Any flow that matches on the IPv4 Ethertype 0x0800 or the IPv6
Ethertype 0x86dd may match on these fields.
IPv4/v6 Protocol Field
Name: nw_proto (aka ip_proto)
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read-only
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IP_PROTO (10) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_IP_PROTO (6) since Open vSwitch 1.1
Matches the IPv4 or IPv6 protocol type.
For historical reasons, in an ARP or RARP flow, Open vSwitch interprets
matches on nw_proto as actually referring to the ARP opcode. The ARP
opcode is a 16-bit field, so for matching purposes ARP opcodes greater
than 255 are treated as 0; this works adequately because in practice
ARP and RARP only use opcodes 1 through 4.
In the case of fragmented traffic, a difference exists in the way the
field acts for IPv4 and IPv6 later fragments. For IPv6 fragments with
nonzero offset, nw_proto is set to the IPv6 protocol type for fragments
(44). Conversely, for IPv4 later fragments, the field is set based on
the protocol type present in the header.
IPv4/v6 TTL/Hop Limit Field
Name: nw_ttl
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_IP_TTL (29) since Open vSwitch 1.4
The main reason to match on the TTL or hop limit field is to detect
whether a dec_ttl action will fail due to a TTL exceeded error. Another
way that a controller can detect TTL exceeded is to listen for OFPR_IN‐
VALID_TTL ``packet-in’’ messages via OpenFlow.
IPv4/v6 Fragment Bitmask Field
Name: ip_frag (aka nw_frag)
Width: 8 bits (only the least-significant 2 bits may be nonzero)
Format: frag
Masking: arbitrary bitwise masks
Prerequisites: IPv4/IPv6
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXM_NX_IP_FRAG (26) since Open vSwitch 1.3
Specifies what kinds of IP fragments or non-fragments to match. The
value for this field is most conveniently specified as one of the fol‐
lowing:
no Match only non-fragmented packets.
yes Matches all fragments.
first Matches only fragments with offset 0.
later Matches only fragments with nonzero offset.
not_later
Matches non-fragmented packets and fragments with zero
offset.
The field is internally formatted as 2 bits: bit 0 is 1 for an IP frag‐
ment with any offset (and otherwise 0), and bit 1 is 1 for an IP frag‐
ment with nonzero offset (and otherwise 0), like so:
NXM_NX_IP_FRAG
<------------>
6 1 1
+----+-----+---+
|zero|later|any|
+----+-----+---+
0
Even though 2 bits have 4 possible values, this field only uses 3 of
them:
• A packet that is not an IP fragment has value 0.
• A packet that is an IP fragment with offset 0 (the first
fragment) has bit 0 set and thus value 1.
• A packet that is an IP fragment with nonzero offset has
bits 0 and 1 set and thus value 3.
The switch may reject matches against values that can never appear.
It is important to understand how this field interacts with the Open‐
Flow fragment handling mode:
• In OFPC_FRAG_DROP mode, the OpenFlow switch drops all IP
fragments before they reach the flow table, so every
packet that is available for matching will have value 0
in this field.
• Open vSwitch does not implement OFPC_FRAG_REASM mode, but
if it did then IP fragments would be reassembled before
they reached the flow table and again every packet avail‐
able for matching would always have value 0.
• In OFPC_FRAG_NORMAL mode, all three values are possible,
but OpenFlow 1.0 says that fragments’ transport ports are
always 0, even for the first fragment, so this does not
provide much extra information.
• In OFPC_FRAG_NX_MATCH mode, all three values are possi‐
ble. For fragments with offset 0, Open vSwitch makes L4
header information available.
Thus, this field is likely to be most useful for an Open vSwitch switch
configured in OFPC_FRAG_NX_MATCH mode. See the description of the
set-frags command in ovs-ofctl(8), for more details.
IPv4/IPv6 TOS Fields
IPv4 and IPv6 contain a one-byte ``type of service’’ or TOS field that
has the following format:
type of service
<------------->
6 2
+--------+------+
| DSCP | ECN |
+--------+------+
IPv4/v6 DSCP (Bits 2-7) Field
Name: nw_tos
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: none
NXM: NXM_OF_IP_TOS (5) since Open vSwitch 1.1
This field is the TOS byte with the two ECN bits cleared to 0:
NXM_OF_IP_TOS
<----------->
6 2
+------+------+
| DSCP | zero |
+------+------+
0
IPv4/v6 DSCP (Bits 0-5) Field
Name: ip_dscp
Width: 8 bits (only the least-significant 6 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IP_DSCP (8) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: none
This field is the TOS byte shifted right to put the DSCP bits in the 6
least-significant bits:
OXM_OF_IP_DSCP
<------------>
2 6
+-------+------+
| zero | DSCP |
+-------+------+
0
IPv4/v6 ECN Field
Name: nw_ecn (aka ip_ecn)
Width: 8 bits (only the least-significant 2 bits may be nonzero)
Format: decimal
Masking: not maskable
Prerequisites: IPv4/IPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_IP_ECN (9) since OpenFlow 1.2 and Open vSwitch 1.7
NXM: NXM_NX_IP_ECN (28) since Open vSwitch 1.4
This field is the TOS byte with the DSCP bits cleared to 0:
OXM_OF_IP_ECN
<----------->
6 2
+-------+-----+
| zero | ECN |
+-------+-----+
0
LAYER 3: ARP FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────── ────── ───── ──── ──────── ─────────────────────
arp_op 2 no yes ARP OF 1.2+ and OVS 1.1+
arp_spa 4 yes yes ARP OF 1.2+ and OVS 1.1+
arp_tpa 4 yes yes ARP OF 1.2+ and OVS 1.1+
arp_sha 6 yes yes ARP OF 1.2+ and OVS 1.1+
arp_tha 6 yes yes ARP OF 1.2+ and OVS 1.1+
In theory, Address Resolution Protocol, or ARP, is a generic protocol
generic protocol that can be used to obtain the hardware address that
corresponds to any higher-level protocol address. In contemporary us‐
age, ARP is used only in Ethernet networks to obtain the Ethernet ad‐
dress for a given IPv4 address. OpenFlow and Open vSwitch only support
this usage of ARP. For this use case, an ARP packet has the following
format, with the ARP fields exposed as Open vSwitch fields highlighted:
Ethernet ARP
<-----------> <---------------------------------->
48 48 16 16 16 8 8 16 48 16 48 16
+---+---+-----+ +---+-----+---+---+--+---+---+---+---+
|dst|src|type | |hrd| pro |hln|pln|op|sha|spa|tha|tpa|
+---+---+-----+ +---+-----+---+---+--+---+---+---+---+
0x806 1 0x800 6 4
The ARP fields are also used for RARP, the Reverse Address Resolution
Protocol, which shares ARP’s wire format.
ARP Opcode Field
Name: arp_op
Width: 16 bits
Format: decimal
Masking: not maskable
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ARP_OP (21) since OpenFlow 1.2 and Open vSwitch
1.7
NXM: NXM_OF_ARP_OP (15) since Open vSwitch 1.1
Even though this is a 16-bit field, Open vSwitch does not support ARP
opcodes greater than 255; it treats them to zero. This works adequately
because in practice ARP and RARP only use opcodes 1 through 4.
ARP Source IPv4 Address Field
Name: arp_spa
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ARP_SPA (22) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_ARP_SPA (16) since Open vSwitch 1.1
ARP Target IPv4 Address Field
Name: arp_tpa
Width: 32 bits
Format: IPv4
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: yes (CIDR match only)
OpenFlow 1.1: yes
OXM: OXM_OF_ARP_TPA (23) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_ARP_TPA (17) since Open vSwitch 1.1
ARP Source Ethernet Address Field
Name: arp_sha
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ARP_SHA (24) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ARP_SHA (17) since Open vSwitch 1.1
ARP Target Ethernet Address Field
Name: arp_tha
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ARP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ARP_THA (25) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ARP_THA (18) since Open vSwitch 1.1
LAYER 3: NSH FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
───────────────── ──────────────── ───── ──── ──────── ────────────────
nsh_flags 1 yes yes NSH OVS 2.8+
nsh_ttl 1 no yes NSH OVS 2.9+
nsh_mdtype 1 no no NSH OVS 2.8+
nsh_np 1 no no NSH OVS 2.8+
nsh_spi aka nsp 4 (low 24 bits) no yes NSH OVS 2.8+
nsh_si aka nsi 1 no yes NSH OVS 2.8+
nsh_c1 aka nshc1 4 yes yes NSH OVS 2.8+
nsh_c2 aka nshc2 4 yes yes NSH OVS 2.8+
nsh_c3 aka nshc3 4 yes yes NSH OVS 2.8+
nsh_c4 aka nshc4 4 yes yes NSH OVS 2.8+
Service functions are widely deployed and essential in many networks.
These service functions provide a range of features such as security,
WAN acceleration, and server load balancing. Service functions may be
instantiated at different points in the network infrastructure such as
the wide area network, data center, and so forth.
Prior to development of the SFC architecture [RFC 7665] and the proto‐
col specified in this document, current service function deployment
models have been relatively static and bound to topology for insertion
and policy selection. Furthermore, they do not adapt well to elastic
service environments enabled by virtualization.
New data center network and cloud architectures require more flexible
service function deployment models. Additionally, the transition to
virtual platforms demands an agile service insertion model that sup‐
ports dynamic and elastic service delivery. Specifically, the following
functions are necessary:
1. The movement of service functions and application workloads
in the network.
2. The ability to easily bind service policy to granular infor‐
mation, such as per-subscriber state.
3. The capability to steer traffic to the requisite service
function(s).
The Network Service Header (NSH) specification defines a new data plane
protocol, which is an encapsulation for service function chains. The
NSH is designed to encapsulate an original packet or frame, and in turn
be encapsulated by an outer transport encapsulation (which is used to
deliver the NSH to NSH-aware network elements), as shown below:
+-----------------------+----------------------------+---------------------+
|Transport Encapsulation|Network Service Header (NSH)|Original Packet/Frame|
+-----------------------+----------------------------+---------------------+
The NSH is composed of the following elements:
1. Service Function Path identification.
2. Indication of location within a Service Function Path.
3. Optional, per packet metadata (fixed length or variable).
[RFC 7665] provides an overview of a service chaining architecture that
clearly defines the roles of the various elements and the scope of a
service function chaining encapsulation. Figure 3 of [RFC 7665] depicts
the SFC architectural components after classification. The NSH is the
SFC encapsulation referenced in [RFC 7665].
flags field (2 bits) Field
Name: nsh_flags
Width: 8 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_FLAGS (1) since Open vSwitch 2.8
TTL field (6 bits) Field
Name: nsh_ttl
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_TTL (10) since Open vSwitch 2.9
mdtype field (8 bits) Field
Name: nsh_mdtype
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_MDTYPE (2) since Open vSwitch 2.8
np (next protocol) field (8 bits) Field
Name: nsh_np
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_NP (3) since Open vSwitch 2.8
spi (service path identifier) field (24 bits) Field
Name: nsh_spi (aka nsp)
Width: 32 bits (only the least-significant 24 bits may be nonzero)
Format: hexadecimal
Masking: not maskable
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_SPI (4) since Open vSwitch 2.8
si (service index) field (8 bits) Field
Name: nsh_si (aka nsi)
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_SI (5) since Open vSwitch 2.8
c1 (Network Platform Context) field (32 bits) Field
Name: nsh_c1 (aka nshc1)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C1 (6) since Open vSwitch 2.8
c2 (Network Shared Context) field (32 bits) Field
Name: nsh_c2 (aka nshc2)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C2 (7) since Open vSwitch 2.8
c3 (Service Platform Context) field (32 bits) Field
Name: nsh_c3 (aka nshc3)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C3 (8) since Open vSwitch 2.8
c4 (Service Shared Context) field (32 bits) Field
Name: nsh_c4 (aka nshc4)
Width: 32 bits
Format: hexadecimal
Masking: arbitrary bitwise masks
Prerequisites: NSH
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: NXOXM_NSH_C4 (9) since Open vSwitch 2.8
LAYER 4: TCP, UDP, AND SCTP FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
─────────────────── ──────────────── ───── ──── ──────── ─────────────────────
tcp_src aka tp_src 2 yes yes TCP OF 1.2+ and OVS 1.1+
tcp_dst aka tp_dst 2 yes yes TCP OF 1.2+ and OVS 1.1+
tcp_flags 2 (low 12 bits) yes no TCP OF 1.3+ and OVS 2.1+
udp_src 2 yes yes UDP OF 1.2+ and OVS 1.1+
udp_dst 2 yes yes UDP OF 1.2+ and OVS 1.1+
sctp_src 2 yes yes SCTP OF 1.2+ and OVS 2.0+
sctp_dst 2 yes yes SCTP OF 1.2+ and OVS 2.0+
For matching purposes, no distinction is made whether these protocols
are encapsulated within IPv4 or IPv6.
TCP
The following diagram shows TCP within IPv4. Open vSwitch also supports
TCP in IPv6. Only TCP fields implemented as Open vSwitch fields are
shown:
Ethernet IPv4 TCP
<-----------> <---------------> <------------------->
48 48 16 8 32 32 16 16 12
+---+---+-----+ +---+-----+---+---+ +---+---+---+-----+---+
|dst|src|type | |...|proto|src|dst| |src|dst|...|flags|...| ...
+---+---+-----+ +---+-----+---+---+ +---+---+---+-----+---+
0x800 6
TCP Source Port Field
Name: tcp_src (aka tp_src)
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: TCP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_TCP_SRC (13) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_TCP_SRC (9) since Open vSwitch 1.1
Open vSwitch 1.6 added support for bitwise matching.
TCP Destination Port Field
Name: tcp_dst (aka tp_dst)
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: TCP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_TCP_DST (14) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_TCP_DST (10) since Open vSwitch 1.1
Open vSwitch 1.6 added support for bitwise matching.
TCP Flags Field
Name: tcp_flags
Width: 16 bits (only the least-significant 12 bits may be nonzero)
Format: TCP flags
Masking: arbitrary bitwise masks
Prerequisites: TCP
Access: read-only
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: ONFOXM_ET_TCP_FLAGS (42) since OpenFlow 1.3 and Open
vSwitch 2.4; OXM_OF_TCP_FLAGS (42) since OpenFlow 1.5 and
Open vSwitch 2.3
NXM: NXM_NX_TCP_FLAGS (34) since Open vSwitch 2.1
This field holds the TCP flags. TCP currently defines 9 flag bits. An
additional 3 bits are reserved. For more information, see [RFC 793],
[RFC 3168], and [RFC 3540].
Matches on this field are most conveniently written in terms of sym‐
bolic names (given in the diagram below), each preceded by either + for
a flag that must be set, or - for a flag that must be unset, without
any other delimiters between the flags. Flags not mentioned are wild‐
carded. For example, tcp,tcp_flags=+syn-ack matches TCP SYNs that are
not ACKs, and tcp,tcp_flags=+[200] matches TCP packets with the re‐
served [200] flag set. Matches can also be written as flags/mask, where
flags and mask are 16-bit numbers in decimal or in hexadecimal prefixed
by 0x.
The flag bits are:
reserved later RFCs RFC 793
<---------------> <--------> <--------------------->
4 1 1 1 1 1 1 1 1 1 1 1 1
+----+-----+-----+-----+--+---+---+---+---+---+---+---+---+
|zero|[800]|[400]|[200]|NS|CWR|ECE|URG|ACK|PSH|RST|SYN|FIN|
+----+-----+-----+-----+--+---+---+---+---+---+---+---+---+
0
UDP
The following diagram shows UDP within IPv4. Open vSwitch also supports
UDP in IPv6. Only UDP fields that Open vSwitch exposes as fields are
shown:
Ethernet IPv4 UDP
<-----------> <---------------> <--------->
48 48 16 8 32 32 16 16
+---+---+-----+ +---+-----+---+---+ +---+---+---+
|dst|src|type | |...|proto|src|dst| |src|dst|...| ...
+---+---+-----+ +---+-----+---+---+ +---+---+---+
0x800 17
UDP Source Port Field
Name: udp_src
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: UDP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_UDP_SRC (15) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_UDP_SRC (11) since Open vSwitch 1.1
UDP Destination Port Field
Name: udp_dst
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: UDP
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_UDP_DST (16) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_UDP_DST (12) since Open vSwitch 1.1
SCTP
The following diagram shows SCTP within IPv4. Open vSwitch also sup‐
ports SCTP in IPv6. Only SCTP fields that Open vSwitch exposes as
fields are shown:
Ethernet IPv4 SCTP
<-----------> <---------------> <--------->
48 48 16 8 32 32 16 16
+---+---+-----+ +---+-----+---+---+ +---+---+---+
|dst|src|type | |...|proto|src|dst| |src|dst|...| ...
+---+---+-----+ +---+-----+---+---+ +---+---+---+
0x800 132
SCTP Source Port Field
Name: sctp_src
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: SCTP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_SCTP_SRC (17) since OpenFlow 1.2 and Open
vSwitch 2.0
NXM: none
SCTP Destination Port Field
Name: sctp_dst
Width: 16 bits
Format: decimal
Masking: arbitrary bitwise masks
Prerequisites: SCTP
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_SCTP_DST (18) since OpenFlow 1.2 and Open
vSwitch 2.0
NXM: none
LAYER 4: ICMPV4 AND ICMPV6 FIELDS
Summary:
Name Bytes Mask RW? Prereqs NXM/OXM Support
──────────────── ────── ───── ──── ─────────── ─────────────────────
icmp_type 1 no yes ICMPv4 OF 1.2+ and OVS 1.1+
icmp_code 1 no yes ICMPv4 OF 1.2+ and OVS 1.1+
icmpv6_type 1 no yes ICMPv6 OF 1.2+ and OVS 1.1+
icmpv6_code 1 no yes ICMPv6 OF 1.2+ and OVS 1.1+
nd_target 16 yes yes ND OF 1.2+ and OVS 1.1+
nd_sll 6 yes yes ND solicit OF 1.2+ and OVS 1.1+
nd_tll 6 yes yes ND advert OF 1.2+ and OVS 1.1+
nd_reserved 4 no yes ND OVS 2.11+
nd_options_type 1 no yes ND OVS 2.11+
ICMPv4
Ethernet IPv4 ICMPv4
<-----------> <---------------> <----------->
48 48 16 8 32 32 8 8
+---+---+-----+ +---+-----+---+---+ +----+----+---+
|dst|src|type | |...|proto|src|dst| |type|code|...| ...
+---+---+-----+ +---+-----+---+---+ +----+----+---+
0x800 1
ICMPv4 Type Field
Name: icmp_type
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv4
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ICMPV4_TYPE (19) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_ICMP_TYPE (13) since Open vSwitch 1.1
For historical reasons, in an ICMPv4 flow, Open vSwitch interprets
matches on tp_src as actually referring to the ICMP type.
ICMPv4 Code Field
Name: icmp_code
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv4
Access: read/write
OpenFlow 1.0: yes (exact match only)
OpenFlow 1.1: yes (exact match only)
OXM: OXM_OF_ICMPV4_CODE (20) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_OF_ICMP_CODE (14) since Open vSwitch 1.1
For historical reasons, in an ICMPv4 flow, Open vSwitch interprets
matches on tp_dst as actually referring to the ICMP code.
ICMPv6
Ethernet IPv6 ICMPv6
<------------> <--------------> <----------->
48 48 16 8 128 128 8 8
+---+---+------+ +---+----+---+---+ +----+----+---+
|dst|src| type | |...|next|src|dst| |type|code|...| ...
+---+---+------+ +---+----+---+---+ +----+----+---+
0x86dd 58
ICMPv6 Type Field
Name: icmpv6_type
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ICMPV6_TYPE (29) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ICMPV6_TYPE (21) since Open vSwitch 1.1
ICMPv6 Code Field
Name: icmpv6_code
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ICMPv6
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_ICMPV6_CODE (30) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ICMPV6_CODE (22) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery
Ethernet IPv6 ICMPv6 ICMPv6 ND
<------------> <--------------> <--------------> <--------------->
48 48 16 8 128 128 8 8 128
+---+---+------+ +---+----+---+---+ +-------+----+---+ +------+----------+
|dst|src| type | |...|next|src|dst| | type |code|...| |target|option ...|
+---+---+------+ +---+----+---+---+ +-------+----+---+ +------+----------+
0x86dd 58 135/136 0
ICMPv6 Neighbor Discovery Target IPv6 Field
Name: nd_target
Width: 128 bits
Format: IPv6
Masking: arbitrary bitwise masks
Prerequisites: ND
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_ND_TARGET (31) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ND_TARGET (23) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery Source Ethernet Address Field
Name: nd_sll
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ND solicit
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_ND_SLL (32) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ND_SLL (24) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery Target Ethernet Address Field
Name: nd_tll
Width: 48 bits
Format: Ethernet
Masking: arbitrary bitwise masks
Prerequisites: ND advert
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: OXM_OF_IPV6_ND_TLL (33) since OpenFlow 1.2 and Open
vSwitch 1.7
NXM: NXM_NX_ND_TLL (25) since Open vSwitch 1.1
ICMPv6 Neighbor Discovery Reserved Field Field
Name: nd_reserved
Width: 32 bits
Format: decimal
Masking: not maskable
Prerequisites: ND
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: ERICOXM_OF_ICMPV6_ND_RESERVED (1) since Open vSwitch
2.11
This is used to set the R,S,O bits in Neighbor Advertisement Messages
ICMPv6 Neighbor Discovery Options Type Field Field
Name: nd_options_type
Width: 8 bits
Format: decimal
Masking: not maskable
Prerequisites: ND
Access: read/write
OpenFlow 1.0: not supported
OpenFlow 1.1: not supported
OXM: none
NXM: ERICOXM_OF_ICMPV6_ND_OPTIONS_TYPE (2) since Open
vSwitch 2.11
A value of 1 indicates that the option is Source Link Layer. A value of
2 indicates that the options is Target Link Layer. See RFC 4861 for
further details.
REFERENCES
Casado M. Casado, M. J. Freedman, J. Pettit, J. Luo, N. McKeown,
and S. Shenker, ``Ethane: Taking Control of the Enter‐
prise,’’ Computer Communications Review, October 2007.
ERSPAN M. Foschiano, K. Ghosh, M. Mehta, ``Cisco Systems’ Encap‐
sulated Remote Switch Port Analyzer (ERSPAN),’’ ⟨https://
tools.ietf.org/html/draft-foschiano-erspan-03⟩ .
EXT-56 J. Tonsing, ``Permit one of a set of prerequisites to ap‐
ply, e.g. don’t preclude non-Ethernet media,’’ ⟨https://
rs.opennetworking.org/bugs/browse/EXT-56⟩ (ONF members
only).
EXT-112
J. Tourrilhes, ``Support non-Ethernet packets throughout
the pipeline,’’ ⟨https://rs.opennetworking.org/bugs/
browse/EXT-112⟩ (ONF members only).
EXT-134
J. Tourrilhes, ``Match first nibble of the MPLS pay‐
load,’’ ⟨https://rs.opennetworking.org/bugs/browse/
EXT-134⟩ (ONF members only).
Geneve J. Gross, I. Ganga, and T. Sridhar, editors, ``Geneve:
Generic Network Virtualization Encapsulation,’’ ⟨https://
datatracker.ietf.org/doc/draft-ietf-nvo3-geneve/⟩ .
IEEE OUI
IEEE Standards Association, ``MAC Address Block Large
(MA-L),’’ ⟨https://standards.ieee.org/develop/regauth/
oui/index.html⟩ .
NSH P. Quinn and U. Elzur, editors, ``Network Service
Header,’’ ⟨https://datatracker.ietf.org/doc/
draft-ietf-sfc-nsh/⟩ .
OpenFlow 1.0.1
Open Networking Foundation, ``OpenFlow Switch Errata,
Version 1.0.1,’’ June 2012.
OpenFlow 1.1
OpenFlow Consortium, ``OpenFlow Switch Specification Ver‐
sion 1.1.0 Implemented (Wire Protocol 0x02),’’ February
2011.
OpenFlow 1.5
Open Networking Foundation, ``OpenFlow Switch Specifica‐
tion Version 1.5.0 (Protocol version 0x06),’’ December
2014.
OpenFlow Extensions 1.3.x Package 2
Open Networking Foundation, ``OpenFlow Extensions 1.3.x
Package 2,’’ December 2013.
TCP Flags Match Field Extension
Open Networking Foundation, ``TCP flags match field Ex‐
tension,’’ December 2014. In [OpenFlow Extensions 1.3.x
Package 2].
Pepelnjak
I. Pepelnjak, ``OpenFlow and Fermi Estimates,’’ ⟨http://
blog.ipspace.net/2013/09/openflow-and-fermi-esti‐
mates.html⟩ .
RFC 793
``Transmission Control Protocol,’’ ⟨http://www.ietf.org/
rfc/rfc793.txt⟩ .
RFC 3032
E. Rosen, D. Tappan, G. Fedorkow, Y. Rekhter, D. Fari‐
nacci, T. Li, and A. Conta, ``MPLS Label Stack Encod‐
ing,’’ ⟨http://www.ietf.org/rfc/rfc3032.txt⟩ .
RFC 3168
K. Ramakrishnan, S. Floyd, and D. Black, ``The Addition
of Explicit Congestion Notification (ECN) to IP,’’
⟨https://tools.ietf.org/html/rfc3168⟩ .
RFC 3540
N. Spring, D. Wetherall, and D. Ely, ``Robust Explicit
Congestion Notification (ECN) Signaling with Nonces,’’
⟨https://tools.ietf.org/html/rfc3540⟩ .
RFC 4632
V. Fuller and T. Li, ``Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan,’’ ⟨https://tools.ietf.org/html/rfc4632⟩ .
RFC 5462
L. Andersson and R. Asati, ``Multiprotocol Label Switch‐
ing (MPLS) Label Stack Entry: ``EXP’’ Field Renamed to
``Traffic Class’’ Field,’’ ⟨http://www.ietf.org/rfc/
rfc5462.txt⟩ .
RFC 6830
D. Farinacci, V. Fuller, D. Meyer, and D. Lewis, ``The
Locator/ID Separation Protocol (LISP),’’ ⟨http://
www.ietf.org/rfc/rfc6830.txt⟩ .
RFC 7348
M. Mahalingam, D. Dutt, K. Duda, P. Agarwal, L. Kreeger,
T. Sridhar, M. Bursell, and C. Wright, ``Virtual eXtensi‐
ble Local Area Network (VXLAN): A Framework for Overlay‐
ing Virtualized Layer 2 Networks over Layer 3 Networks,
’’ ⟨https://tools.ietf.org/html/rfc7348⟩ .
RFC 7665
J. Halpern, Ed. and C. Pignataro, Ed., ``Service Function
Chaining (SFC) Architecture,’’ ⟨https://tools.ietf.org/
html/rfc7665⟩ .
Srinivasan
V. Srinivasan, S. Suriy, and G. Varghese, ``Packet Clas‐
sification using Tuple Space Search,’’ SIGCOMM 1999.
Pagiamtzis
K. Pagiamtzis and A. Sheikholeslami, ``Content-address‐
able memory (CAM) circuits and architectures: A tutorial
and survey,’’ IEEE Journal of Solid-State Circuits, vol.
41, no. 3, pp. 712-727, March 2006.
VXLAN Group Policy Option
M. Smith and L. Kreeger, `` VXLAN Group Policy Option.’’
Internet-Draft. ⟨https://tools.ietf.org/html/
draft-smith-vxlan-group-policy⟩ .
AUTHORS
Ben Pfaff, with advice from Justin Pettit and Jean Tourrilhes.
Open vSwitch 3.0.0 ovs-fields(7)
qemu
qemu概述
https://blog.csdn.net/weixin_38387929/article/details/120121636
qemu的几个特点:
- qemu可以被当做模拟器,也可以被当做虚拟机
- 当qemu被当做模拟器时,我们可以在一台设备上通过模拟设备,运行针对不同于本机上CPU的程序或者操作系统
- 当qemu被当做虚拟机使用时,qemu必须基于Xen Hypervisor或者kvm内核模块才能支持虚拟化.在这种条件下qemu虚拟机可以直接在本机CPU上运行客户机代码获得接近本机的性能.
Qemu和KVM的关系
- 当qemu在模拟器模式下,运行操作系统时,我们可以认为这是一种软件实现的虚拟化技术,它的效率比真机差很多,用户可以明显的感觉出来
- 当qemu在虚拟机模式下,qemu必须在linux上运行,并且需要借助kvm或者xen,利用intel或者AMD提供的硬件辅助虚拟化技术,才能使虚拟机达到接近真机的性能.
- qemu与kvm内核模块协同工作,在虚拟机进程中,各司其职,又相互配合,最终实现高效的虚拟机应用
qemu与kvm的关系如下
- kvm在物理机启动时创建/dev/kvm设备文件,当创建虚拟机时,kvm为该虚拟机进程创建一个vm的文件描述符,当创建vCPU时,kvm为每个vCPU创建一个文件描述符.
- 同时,kvm向用户空间提供了一系列针对特殊设备文件的ioctl系统调用.qemu主要通过ioctl系统调用与kvm进行交互的.
qemu与kvm等虚拟化的关系
qemu有几种虚拟化模式
首先,它可以使用基于内核的虚拟机(kvm)执行x86处理器硬件虚拟化,以几乎比拟硬件本机的速度执行运算任务. 其次,他可以通过机器点啊的实时转换来模拟其他处理器以用于虚拟机运行在不同平台的操作系统. 最后,他可以实时转换为其他架构运行简单的程序,类似于linux的wine.
因为QEMU没有图形用户界面（GUI），而其提供的核心能力又是关键而重要的，因此通常用作更复杂的虚拟化管理器的一部分。比如，我们经常使用的开源VirtualBox、Xen虚拟化产品，其核心底层的虚拟化部分就有集成和使用QEMU，此外，主流的KVM虚拟化也是集成和使用QEMU的主力虚拟化管理器系统。
从KVM的角度来说，KVM（Kernel Virtual Machine）是Linux的一个内核驱动模块，它能够让Linux主机成为一个Hypervisor（虚拟机监控器）。在支持VMX（Virtual Machine Extension）功能的x86处理器中，Linux在原有的用户模式和内核模式中新增加了客户模式，并且客户模式也拥有自己的内核模式和用户模式，虚拟机就是运行在客户模式中。KVM模块的职责就是打开并初始化VMX功能，提供相应的接口以支持虚拟机的运行。KVM通过调用Linux本身内核功能，实现对CPU的底层虚拟化和内存的虚拟化，使Linux内核成为虚拟化层。KVM在2007年2月被导入Linux 2.6.20内核中。从存在形式来看，它包括两个内核模块：kvm.ko和kvm_intel.ko（或kvm_amd.ko），本质上，KVM是管理虚拟硬件设备的驱动，该驱动使用字符设备/dev/kvm（由KVM本身创建）作为管理接口，主要负责vCPU的创建、虚拟内存的分配、vCPU寄存器的读写以及vCPU的运行。
从QEMU的角度来说，QEMU（Quick Emulator)本身并不包含或依赖KVM模块，而是一套由Fabrice Bellard编写的模拟计算机的自由软件。QEMU虚拟机是一个纯软件的实现，可以在没有KVM模块的情况下独立运行，但是性能比较低。QEMU有整套的虚拟机实现，包括处理器虚拟化、内存虚拟化以及I/O设备的虚拟化。在不需要KVM加速的情况下，QEMU通过一个特殊的“重编译器”对特定的处理器的二进制代码进行翻译，从而具有了跨平台的通用性。QEMU有两种工作模式：系统模式，可以模拟出整个电脑系统，另一种是用户模式，可以运行不同与当前硬件平台的其他平台上的程序（比如在x86平台上运行跑在ARM平台上的程序）。目前最新版本是4.x。从QEMU角度来看，虚拟机运行期间，QEMU通过KVM模块提供的系统调用接口进行内核设置，由KVM模块负责将虚拟机置于处理器的VMX模式运行。QEMU使用了KVM模块的虚拟化功能，为自己的虚拟机提供硬件虚拟化加速以提高虚拟机的性能。
而现在流行的KVM虚拟化平台，就是在修改了QEMU代码，把他模拟CPU、内存的代码换成KVM，而网卡、显示器等留着，因此QEMU+KVM就成了一个完整的虚拟化平台。由于KVM运行在内核空间，只是内核模块，QEMU运行在用户空间，实际模拟创建，管理各种虚拟硬件（磁盘，网卡，显卡等）。从KVM的角度来说，用户没法直接跟内核模块交互，需要借助用户空间的管理工具，因此需要借助QEMU这个运行在用户空间的工具。KVM和QEMU相辅相成，QEMU通过KVM达到了硬件虚拟化的速度，而KVM则通过QEMU来模拟设备并实现和内核空间的KVM的交互，虽然这个交互并不仅仅只有QEMU能够办到。此外，由于QEMU模拟IO设备效率不高的原因，现在常常采用半虚拟化的virtio方式来虚拟IO设备。
综上，理解了QEMU和KVM的关系，也就理解了VirtualBox、Xen等虚拟化产品集成和使用QEMU的关系。
硬件设备
在qemu中,存在两种使用硬件设备的方式:
- 直通模式使用主机实际物理设备
- qemu的设备驱动仿真实现的模拟虚拟设备.
如果采用直通方式使用实际的物理设备,那么就会抢占主机的设备使用权,并且其他虚拟机也将无法使用该物理设备. 在直通模式中,虚拟机可以直接访问usb总线或pci总线,并可以直接与设备通信. 一般情况下,采用直通模式的物理设备都是很难进行qemu仿真的设备,比如网络摄像头,串行和并行端口等. 其他设备因为大部分虚拟机都会使用,并且很难与主机共享,例如网络设备,因此大部分都会使用qemu模拟仿真的虚拟设备.比如在虚拟机的网络设备中,可以通过模拟网卡来解决,从而在网络堆栈上添加额外的层. 此外,qemu可以选择连接到linux内核中的"virto"半虚拟化驱动程序,这意味着linux内核处理虚拟机和硬件设备之间的输入/输出,而不采用qemu的模拟设备进行中转和传输(仅用作中介).
磁盘映像
qemu可以处理几种不同的磁盘映像格式. 首选为raw或qcow2 Raw是一种非常简单的格式，它将文件系统中的字节逐字节存储在文件中。大多数其他仿真器都支持此格式。 Qcow2是QEMU自己的图像格式，对小图像很有用，并且支持磁盘映像压缩以及捕获磁盘映像状态的快照。 还支持另外两种格式：在VirtualBox中使用的vdi和在VMWare中使用的vmdk。
shell中=和～的用法
shell 中 =~ 的用法
我们先看一个脚本，该脚本的功能是搜索当前目录下文件中的指定字符串
#!/bin/bash
apath=$1;acontent=$2;aexp=$3;
if [[ $aexp =~ all ]] ;then
atype=''
else
atype=".$aexp"
fi
find $apath -name "*"$atype -type f -print0 | xargs -0 grep --color -rn "$acontent"
if [[ $aexp =~ all ]]
其中 ~是对后面的正则表达式匹配的意思，如果匹配就输出1，不匹配就输出0
SNAT和DNAT
SNAT
In Source Network Address Translation (SNAT), the NAT router modifies the IP address of the sender in IP packets. SNAT is commonly used to enable hosts with private addresses to communicate with servers on the public Internet.
RFC 1918 reserves the following three subnets as private addresses:
10.0.0.0/8
172.16.0.0/12
192.168.0.0/16
DNAT
In Destination Network Address Translation (DNAT), the NAT router modifies the IP address of the destination in IP packet headers.