OpenvSwitch详解与入门指南

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"OpenvSwitch 是一款开源的虚拟交换机软件，主要应用于软件定义网络（SDN）环境。这份文档详细介绍了OpenvSwitch的基本操作方法和原理，包括其组织结构、项目背景、获取帮助的方式、安装教程以及相关的实践教程，如OVS与Faucet集成和OVS IPsec配置等。" OpenvSwitch是一款广泛使用的开源虚拟交换机软件，适用于构建和支持SDN（Software-Defined Networking）网络架构。文档首先介绍OpenvSwitch的文档组织结构，包括引导用户快速入门的部分和深入探讨的章节，旨在帮助读者理解项目的整体布局。 OpenvSwitch项目的目标是提供一个可移植、高性能的二层和三层网络交换机，具备丰富的特性，例如支持多租户、QoS策略、VLAN、MPLS、GRE隧道、OpenFlow协议等。项目还强调了网络状态的移动性、对网络动态的响应、逻辑标签的维护和硬件的集成，以满足现代数据中心和云环境的需求。文档中的"Getting Started"部分详细阐述了OpenvSwitch是什么。它概述了OpenvSwitch的功能和组成，强调其在处理网络状态变化、适应网络动态、保持逻辑标签以及与硬件的无缝对接方面的优势。此外，还提供了安装OpenvSwitch的指南，包括从源代码编译安装和使用预编译包安装两种方式，并涵盖了升级和其它安装选项。教程部分提供了两个实例，以帮助用户更好地掌握OpenvSwitch的使用。第一个教程是关于OVS与Faucet的集成，Faucet是一个开放源码的SDN控制器，用于管理OpenvSwitch。这个教程涵盖了设置OVS、配置Faucet、了解基本工作原理、实现交换和路由功能，以及应用访问控制列表（ACLs）等步骤。第二个教程是OVS IPsec配置，详细说明了所需的软件需求、安装过程、配置IPsec隧道的方法，以及故障排查和错误报告的指南。通过这些教程，读者不仅可以学习到OpenvSwitch的基本操作，还能深入理解如何在实际环境中利用OpenvSwitch构建安全、灵活的网络解决方案。对于网络管理员、开发者和SDN研究者来说，这份文档是一份宝贵的参考资料。

Open vSwitch, Release 2.11.90

Build Requirements

To compile the userspace programs in the Open vSwitch distribution, you will need the following software:

• GNU make

• A C compiler, such as:

– GCC 4.6 or later.

– Clang 3.4 or later.

– MSVC 2013. Refer to Open vSwitch on Windows for additional Windows build instructions.

While OVS may be compatible with other compilers, optimal support for atomic operations may be missing,

making OVS very slow (see lib/ovs-atomic.h).

• libssl, from OpenSSL, is optional but recommended if you plan to connect the Open vSwitch to an OpenFlow

controller. libssl is required to establish conﬁdentiality and authenticity in the connections from an Open vSwitch

to an OpenFlow controller. If libssl is installed, then Open vSwitch will automatically build with support for it.

• libcap-ng, written by Steve Grubb, is optional but recommended. It is required to run OVS daemons as a non-

root user with dropped root privileges. If libcap-ng is installed, then Open vSwitch will automatically build with

support for it.

• Python 2.7. You must also have the Python six library version 1.4.0 or later.

• Unbound library, from http://www.unbound.net, is optional but recommended if you want to enable ovs-

vswitchd and other utilities to use DNS names when specifying OpenFlow and OVSDB remotes. If unbound

library is already installed, then Open vSwitch will automatically build with support for it. The environment

variable OVS_RESOLV_CONF can be used to specify DNS server conﬁguration ﬁle (the default ﬁle on Linux

is /etc/resolv.conf).

On Linux, you may choose to compile the kernel module that comes with the Open vSwitch distribution or to use the

kernel module built into the Linux kernel (version 3.3 or later). See the Open vSwitch FAQ question “What features

are not available in the Open vSwitch kernel datapath that ships as part of the upstream Linux kernel?” for more

information on this trade-off. You may also use the userspace-only implementation, at some cost in features and

performance. Refer to Open vSwitch without Kernel Support for details.

To compile the kernel module on Linux, you must also install the following:

• A supported Linux kernel version.

For optional support of ingress policing, you must enable kernel conﬁguration options NET_CLS_BASIC,

NET_SCH_INGRESS, and NET_ACT_POLICE, either built-in or as modules. NET_CLS_POLICE is obsolete

and not needed.)

On kernels before 3.11, the ip_gre module, for GRE tunnels over IP (NET_IPGRE), must not be loaded or

compiled in.

To conﬁgure HTB or HFSC quality of service with Open vSwitch, you must enable the respective conﬁguration

options.

To use Open vSwitch support for TAP devices, you must enable CONFIG_TUN.

• To build a kernel module, you need the same version of GCC that was used to build that kernel.

• A kernel build directory corresponding to the Linux kernel image the module is to run on. Under Debian and

Ubuntu, for example, each linux-image package containing a kernel binary has a corresponding linux-headers

package with the required build infrastructure.

If you are working from a Git tree or snapshot (instead of from a distribution tarball), or if you modify the Open

vSwitch build system or the database schema, you will also need the following software:

8 Chapter 2. Getting Started

Open vSwitch, Release 2.11.90

• Autoconf version 2.63 or later.

• Automake version 1.10 or later.

• libtool version 2.4 or later. (Older versions might work too.)

The datapath tests for userspace and Linux datapaths also rely upon:

• pyftpdlib. Version 1.2.0 is known to work. Earlier versions should also work.

• GNU wget. Version 1.16 is known to work. Earlier versions should also work.

• netcat. Several common implementations are known to work.

• curl. Version 7.47.0 is known to work. Earlier versions should also work.

• tftpy. Version 0.6.2 is known to work. Earlier versions should also work.

• netstat. Available from various distro speciﬁc packages

The ovs-vswitchd.conf.db(5) manpage will include an E-R diagram, in formats other than plain text, only if you have

the following:

• dot from graphviz (http://www.graphviz.org/).

If you are going to extensively modify Open vSwitch, consider installing the following to obtain better warnings:

• “sparse” version 0.5.1 or later (https://git.kernel.org/pub/scm/devel/sparse/sparse.git/).

• GNU make.

• clang, version 3.4 or later

• ﬂake8 along with the hacking ﬂake8 plugin (for Python code). The automatic ﬂake8 check that runs against

Python code has some warnings enabled that come from the “hacking” ﬂake8 plugin. If it’s not installed, the

warnings just won’t occur until it’s run on a system with “hacking” installed.

You may ﬁnd the ovs-dev script found in utilities/ovs-dev.py useful.

Installation Requirements

The machine you build Open vSwitch on may not be the one you run it on. To simply install and run Open vSwitch

you require the following software:

• Shared libraries compatible with those used for the build.

• On Linux, if you want to use the kernel-based datapath (which is the most common use case), then a kernel with

a compatible kernel module. This can be a kernel module built with Open vSwitch (e.g. in the previous step),

or the kernel module that accompanies Linux 3.3 and later. Open vSwitch features and performance can vary

based on the module and the kernel. Refer to Releases for more information.

• For optional support of ingress policing on Linux, the “tc” program from iproute2 (part of all major distributions

and available at https://wiki.linuxfoundation.org/networking/iproute2).

• Python 2.7. You must also have the Python six library version 1.4.0 or later.

On Linux you should ensure that /dev/urandom exists. To support TAP devices, you must also ensure that /dev/

net/tun exists.

Bootstrapping

This step is not needed if you have downloaded a released tarball. If you pulled the sources directly from an Open

vSwitch Git tree or got a Git tree snapshot, then run boot.sh in the top source directory to build the “conﬁgure” script:

2.3. Installing Open vSwitch 9

Open vSwitch, Release 2.11.90

$ ./boot.sh

Conﬁguring

Conﬁgure the package by running the conﬁgure script. You can usually invoke conﬁgure without any arguments. For

example:

$ ./configure

By default all ﬁles are installed under /usr/local. Open vSwitch also expects to ﬁnd its database in /usr/

local/etc/openvswitch by default. If you want to install all ﬁles into, e.g., /usr and /var instead of /

usr/local and /usr/local/var and expect to use /etc/openvswitch as the default database directory,

add options as shown here:

$ ./configure --prefix=/usr --localstatedir=/var --sysconfdir=/etc

Note: Open vSwitch installed with packages like .rpm (e.g. via yum install or rpm -ivh) and .deb (e.g. via

apt-get install or dpkg -i) use the above conﬁgure options.

By default, static libraries are built and linked against. If you want to use shared libraries instead:

$ ./configure --enable-shared

To use a speciﬁc C compiler for compiling Open vSwitch user programs, also specify it on the conﬁgure command

line, like so:

$ ./configure CC=gcc-4.2

To use ‘clang’ compiler:

$ ./configure CC=clang

To supply special ﬂags to the C compiler, specify them as CFLAGS on the conﬁgure command line. If you want the

default CFLAGS, which include -g to build debug symbols and -O2 to enable optimizations, you must include them

yourself. For example, to build with the default CFLAGS plus -mssse3, you might run conﬁgure as follows:

$ ./configure CFLAGS="-g -O2 -mssse3"

For efﬁcient hash computation special ﬂags can be passed to leverage built-in intrinsics. For example on X86_64 with

SSE4.2 instruction set support, CRC32 intrinsics can be used by passing -msse4.2:

$ ./configure CFLAGS="-g -O2 -msse4.2"`

Also builtin popcnt instruction can be used to speedup the counting of the bits set in an integer. For example on

X86_64 with POPCNT support, it can be enabled by passing -mpopcnt:

$ ./configure CFLAGS="-g -O2 -mpopcnt"`

If you are on a different processor and don’t know what ﬂags to choose, it is recommended to use -march=native

settings:

$ ./configure CFLAGS="-g -O2 -march=native"

10 Chapter 2. Getting Started

Open vSwitch, Release 2.11.90

With this, GCC will detect the processor and automatically set appropriate ﬂags for it. This should not be used if you

are compiling OVS outside the target machine.

Note: CFLAGS are not applied when building the Linux kernel module. Custom CFLAGS for the kernel module are

supplied using the EXTRA_CFLAGS variable when running make. For example:

$ make EXTRA_CFLAGS="-Wno-error=date-time"

If you are a developer and want to enable Address Sanitizer for debugging purposes, at about a 2x runtime cost, you

can add -fsanitize=address -fno-omit-frame-pointer -fno-common to CFLAGS. For example:

$ ./configure CFLAGS="-g -O2 -fsanitize=address -fno-omit-frame-pointer -fno-common"

To build the Linux kernel module, so that you can run the kernel-based switch, pass the location of the kernel build

directory on --with-linux. For example, to build for a running instance of Linux:

$ ./configure --with-linux=/lib/modules/$(uname -r)/build

Note: If --with-linux requests building for an unsupported version of Linux, then configure will fail with

an error message. Refer to the Open vSwitch FAQ for advice in that case.

If you wish to build the kernel module for an architecture other than the architecture of the machine used for the build,

you may specify the kernel architecture string using the KARCH variable when invoking the conﬁgure script. For

example, to build for MIPS with Linux:

$ ./configure --with-linux=/path/to/linux KARCH=mips

If you plan to do much Open vSwitch development, you might want to add --enable-Werror, which adds the

-Werror option to the compiler command line, turning warnings into errors. That makes it impossible to miss

warnings generated by the build. For example:

$ ./configure --enable-Werror

If you’re building with GCC, then, for improved warnings, install sparse (see “Prerequisites”) and enable it for

the build by adding --enable-sparse. Use this with --enable-Werror to avoid missing both compiler and

sparse warnings, e.g.:

$ ./configure --enable-Werror --enable-sparse

To build with gcov code coverage support, add --enable-coverage:

$ ./configure --enable-coverage

The conﬁgure script accepts a number of other options and honors additional environment variables. For a full list,

invoke conﬁgure with the --help option:

$ ./configure --help

You can also run conﬁgure from a separate build directory. This is helpful if you want to build Open vSwitch in more

than one way from a single source directory, e.g. to try out both GCC and Clang builds, or to build kernel modules for

more than one Linux version. For example:

2.3. Installing Open vSwitch 11

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