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Open vSwitch <http://openvswitch.org>
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Frequently Asked Questions
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==========================
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Q: What is Open vSwitch?
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A: Open vSwitch is a production quality open source software switch
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designed to be used as a vswitch in virtualized server
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environments. A vswitch forwards traffic between different VMs on
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the same physical host and also forwards traffic between VMs and
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the physical network. Open vSwitch supports standard management
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interfaces (e.g. sFlow, NetFlow, IPFIX, RSPAN, CLI), and is open to
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programmatic extension and control using OpenFlow and the OVSDB
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Open vSwitch as designed to be compatible with modern switching
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chipsets. This means that it can be ported to existing high-fanout
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switches allowing the same flexible control of the physical
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infrastructure as the virtual infrastructure. It also means that
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Open vSwitch will be able to take advantage of on-NIC switching
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chipsets as their functionality matures.
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Q: What virtualization platforms can use Open vSwitch?
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A: Open vSwitch can currently run on any Linux-based virtualization
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platform (kernel 2.6.32 and newer), including: KVM, VirtualBox, Xen,
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Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the
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mainline kernel. The bulk of the code is written in platform-
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independent C and is easily ported to other environments. We welcome
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inquires about integrating Open vSwitch with other virtualization
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Q: How can I try Open vSwitch?
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A: The Open vSwitch source code can be built on a Linux system. You can
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build and experiment with Open vSwitch on any Linux machine.
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Packages for various Linux distributions are available on many
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platforms, including: Debian, Ubuntu, Fedora.
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You may also download and run a virtualization platform that already
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has Open vSwitch integrated. For example, download a recent ISO for
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XenServer or Xen Cloud Platform. Be aware that the version
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integrated with a particular platform may not be the most recent Open
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Q: Does Open vSwitch only work on Linux?
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A: No, Open vSwitch has been ported to a number of different operating
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systems and hardware platforms. Most of the development work occurs
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on Linux, but the code should be portable to any POSIX system. We've
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seen Open vSwitch ported to a number of different platforms,
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including FreeBSD, Windows, and even non-POSIX embedded systems.
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By definition, the Open vSwitch Linux kernel module only works on
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Linux and will provide the highest performance. However, a userspace
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datapath is available that should be very portable.
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Q: What's involved with porting Open vSwitch to a new platform or
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A: The PORTING document describes how one would go about porting Open
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vSwitch to a new operating system or hardware platform.
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Q: Why would I use Open vSwitch instead of the Linux bridge?
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A: Open vSwitch is specially designed to make it easier to manage VM
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network configuration and monitor state spread across many physical
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hosts in dynamic virtualized environments. Please see WHY-OVS for a
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more detailed description of how Open vSwitch relates to the Linux
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Q: How is Open vSwitch related to distributed virtual switches like the
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VMware vNetwork distributed switch or the Cisco Nexus 1000V?
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A: Distributed vswitch applications (e.g., VMware vNetwork distributed
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switch, Cisco Nexus 1000V) provide a centralized way to configure and
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monitor the network state of VMs that are spread across many physical
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hosts. Open vSwitch is not a distributed vswitch itself, rather it
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runs on each physical host and supports remote management in a way
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that makes it easier for developers of virtualization/cloud
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management platforms to offer distributed vswitch capabilities.
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To aid in distribution, Open vSwitch provides two open protocols that
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are specially designed for remote management in virtualized network
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environments: OpenFlow, which exposes flow-based forwarding state,
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and the OVSDB management protocol, which exposes switch port state.
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In addition to the switch implementation itself, Open vSwitch
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includes tools (ovs-ofctl, ovs-vsctl) that developers can script and
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extend to provide distributed vswitch capabilities that are closely
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integrated with their virtualization management platform.
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Q: Why doesn't Open vSwitch support distribution?
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A: Open vSwitch is intended to be a useful component for building
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flexible network infrastructure. There are many different approaches
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to distribution which balance trade-offs between simplicity,
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scalability, hardware compatibility, convergence times, logical
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forwarding model, etc. The goal of Open vSwitch is to be able to
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support all as a primitive building block rather than choose a
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particular point in the distributed design space.
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Q: How can I contribute to the Open vSwitch Community?
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A: You can start by joining the mailing lists and helping to answer
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questions. You can also suggest improvements to documentation. If
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you have a feature or bug you would like to work on, send a mail to
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one of the mailing lists:
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http://openvswitch.org/mlists/
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Q: What does it mean for an Open vSwitch release to be LTS (long-term
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A: All official releases have been through a comprehensive testing
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process and are suitable for production use. Planned releases will
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occur several times a year. If a significant bug is identified in an
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LTS release, we will provide an updated release that includes the
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fix. Releases that are not LTS may not be fixed and may just be
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supplanted by the next major release. The current LTS release is
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Q: What Linux kernel versions does each Open vSwitch release work with?
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A: The following table lists the Linux kernel versions against which the
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given versions of the Open vSwitch kernel module will successfully
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build. The Linux kernel versions are upstream kernel versions, so
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Linux kernels modified from the upstream sources may not build in
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some cases even if they are based on a supported version. This is
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most notably true of Red Hat Enterprise Linux (RHEL) kernels, which
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are extensively modified from upstream.
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Open vSwitch Linux kernel
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------------ -------------
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Open vSwitch userspace should also work with the Linux kernel module
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built into Linux 3.3 and later.
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Open vSwitch userspace is not sensitive to the Linux kernel version.
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It should build against almost any kernel, certainly against 2.6.32
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Q: I get an error like this when I configure Open vSwitch:
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configure: error: Linux kernel in <dir> is version <x>, but
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version newer than <y> is not supported (please refer to the
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A: If there is a newer version of Open vSwitch, consider building that
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one, because it may support the kernel that you are building
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against. (To find out, consult the table in the previous answer.)
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Otherwise, use the Linux kernel module supplied with the kernel
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that you are using. All versions of Open vSwitch userspace are
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compatible with all versions of the Open vSwitch kernel module, so
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this will also work. See also the following question.
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Q: What features are not available in the Open vSwitch kernel datapath
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that ships as part of the upstream Linux kernel?
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A: The kernel module in upstream Linux does not include support for
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LISP. Work is in progress to add support for LISP to the upstream
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Linux version of the Open vSwitch kernel module. For now, if you
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need this feature, use the kernel module from the Open vSwitch
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distribution instead of the upstream Linux kernel module.
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Certain features require kernel support to function or to have
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reasonable performance. If the ovs-vswitchd log file indicates that
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a feature is not supported, consider upgrading to a newer upstream
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Linux release or using the kernel module paired with the userspace
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Q: What features are not available when using the userspace datapath?
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A: Tunnel virtual ports are not supported, as described in the
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previous answer. It is also not possible to use queue-related
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actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets
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may not be transmitted.
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Q: What Linux kernel versions does IPFIX flow monitoring work with?
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A: IPFIX flow monitoring requires the Linux kernel module from Open
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vSwitch version 1.10.90 or later.
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Q: Should userspace or kernel be upgraded first to minimize downtime?
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In general, the Open vSwitch userspace should be used with the
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kernel version included in the same release or with the version
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from upstream Linux. However, when upgrading between two releases
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of Open vSwitch it is best to migrate userspace first to reduce
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the possibility of incompatibilities.
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Q: What happened to the bridge compatibility feature?
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A: Bridge compatibility was a feature of Open vSwitch 1.9 and earlier.
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When it was enabled, Open vSwitch imitated the interface of the
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Linux kernel "bridge" module. This allowed users to drop Open
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vSwitch into environments designed to use the Linux kernel bridge
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module without adapting the environment to use Open vSwitch.
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Open vSwitch 1.10 and later do not support bridge compatibility.
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The feature was dropped because version 1.10 adopted a new internal
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architecture that made bridge compatibility difficult to maintain.
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Now that many environments use OVS directly, it would be rarely
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To use bridge compatibility, install OVS 1.9 or earlier, including
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the accompanying kernel modules (both the main and bridge
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compatibility modules), following the instructions that come with
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the release. Be sure to start the ovs-brcompatd daemon.
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Q: I thought Open vSwitch was a virtual Ethernet switch, but the
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documentation keeps talking about bridges. What's a bridge?
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A: In networking, the terms "bridge" and "switch" are synonyms. Open
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vSwitch implements an Ethernet switch, which means that it is also
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A: See the "VLAN" section below.
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Q: How do I configure a port as an access port?
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A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
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the following commands configure br0 with eth0 as a trunk port (the
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default) and tap0 as an access port for VLAN 9:
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 tap0 tag=9
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If you want to configure an already added port as an access port,
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use "ovs-vsctl set", e.g.:
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ovs-vsctl set port tap0 tag=9
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Q: How do I configure a port as a SPAN port, that is, enable mirroring
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of all traffic to that port?
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A: The following commands configure br0 with eth0 and tap0 as trunk
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ports. All traffic coming in or going out on eth0 or tap0 is also
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mirrored to tap1; any traffic arriving on tap1 is dropped:
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 tap0
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ovs-vsctl add-port br0 tap1 \
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-- --id=@p get port tap1 \
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-- --id=@m create mirror name=m0 select-all=true output-port=@p \
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-- set bridge br0 mirrors=@m
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To later disable mirroring, run:
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ovs-vsctl clear bridge br0 mirrors
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Q: Does Open vSwitch support configuring a port in promiscuous mode?
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A: Yes. How you configure it depends on what you mean by "promiscuous
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- Conventionally, "promiscuous mode" is a feature of a network
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interface card. Ordinarily, a NIC passes to the CPU only the
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packets actually destined to its host machine. It discards
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the rest to avoid wasting memory and CPU cycles. When
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promiscuous mode is enabled, however, it passes every packet
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to the CPU. On an old-style shared-media or hub-based
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network, this allows the host to spy on all packets on the
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network. But in the switched networks that are almost
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everywhere these days, promiscuous mode doesn't have much
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effect, because few packets not destined to a host are
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delivered to the host's NIC.
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This form of promiscuous mode is configured in the guest OS of
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the VMs on your bridge, e.g. with "ifconfig".
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- The VMware vSwitch uses a different definition of "promiscuous
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mode". When you configure promiscuous mode on a VMware vNIC,
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the vSwitch sends a copy of every packet received by the
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vSwitch to that vNIC. That has a much bigger effect than just
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enabling promiscuous mode in a guest OS. Rather than getting
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a few stray packets for which the switch does not yet know the
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correct destination, the vNIC gets every packet. The effect
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is similar to replacing the vSwitch by a virtual hub.
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This "promiscuous mode" is what switches normally call "port
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mirroring" or "SPAN". For information on how to configure
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SPAN, see "How do I configure a port as a SPAN port, that is,
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enable mirroring of all traffic to that port?"
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Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
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mirroring of all traffic to that VLAN?
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A: The following commands configure br0 with eth0 as a trunk port and
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tap0 as an access port for VLAN 10. All traffic coming in or going
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out on tap0, as well as traffic coming in or going out on eth0 in
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VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
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VLAN 10, in cases where one is present, is dropped as part of
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 tap0 tag=10
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-- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
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-- set bridge br0 mirrors=@m
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To later disable mirroring, run:
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ovs-vsctl clear bridge br0 mirrors
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Mirroring to a VLAN can disrupt a network that contains unmanaged
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switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
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GRE tunnel has fewer caveats than mirroring to a VLAN and should
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generally be preferred.
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Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
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A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
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of the specified output-vlan. This loss of information may make
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the mirrored traffic too hard to interpret.
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To mirror multiple VLANs, use the commands above, but specify a
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comma-separated list of VLANs as the value for select-vlan. To
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mirror every VLAN, use the commands above, but omit select-vlan and
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When a packet arrives on a VLAN that is used as a mirror output
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VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
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floods the packet across all the ports for which the mirror output
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VLAN is configured. (If an OpenFlow controller is in use, then it
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can override this behavior through the flow table.) If OVS is used
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as an intermediate switch, rather than an edge switch, this ensures
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that the RSPAN traffic is distributed through the network.
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Mirroring to a VLAN can disrupt a network that contains unmanaged
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switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
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GRE tunnel has fewer caveats than mirroring to a VLAN and should
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generally be preferred.
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Q: How do I configure mirroring of all traffic to a GRE tunnel?
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A: The following commands configure br0 with eth0 and tap0 as trunk
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ports. All traffic coming in or going out on eth0 or tap0 is also
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mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
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traffic arriving on gre0 is dropped:
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 tap0
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ovs-vsctl add-port br0 gre0 \
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-- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
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-- --id=@p get port gre0 \
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-- --id=@m create mirror name=m0 select-all=true output-port=@p \
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-- set bridge br0 mirrors=@m
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To later disable mirroring and destroy the GRE tunnel:
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ovs-vsctl clear bridge br0 mirrors
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ovs-vcstl del-port br0 gre0
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Q: Does Open vSwitch support ERSPAN?
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A: No. ERSPAN is an undocumented proprietary protocol. As an
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alternative, Open vSwitch supports mirroring to a GRE tunnel (see
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Q: How do I connect two bridges?
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A: First, why do you want to do this? Two connected bridges are not
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much different from a single bridge, so you might as well just have
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a single bridge with all your ports on it.
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If you still want to connect two bridges, you can use a pair of
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patch ports. The following example creates bridges br0 and br1,
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adds eth0 and tap0 to br0, adds tap1 to br1, and then connects br0
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and br1 with a pair of patch ports.
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 tap0
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ovs-vsctl add-port br1 tap1
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-- add-port br0 patch0 \
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-- set interface patch0 type=patch options:peer=patch1 \
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-- add-port br1 patch1 \
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-- set interface patch1 type=patch options:peer=patch0
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Bridges connected with patch ports are much like a single bridge.
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For instance, if the example above also added eth1 to br1, and both
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eth0 and eth1 happened to be connected to the same next-hop switch,
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then you could loop your network just as you would if you added
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eth0 and eth1 to the same bridge (see the "Configuration Problems"
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section below for more information).
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If you are using Open vSwitch 1.9 or an earlier version, then you
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need to be using the kernel module bundled with Open vSwitch rather
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than the one that is integrated into Linux 3.3 and later, because
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Open vSwitch 1.9 and earlier versions need kernel support for patch
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ports. This also means that in Open vSwitch 1.9 and earlier, patch
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ports will not work with the userspace datapath, only with the
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Q: How do I configure a bridge without an OpenFlow local port?
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(Local port in the sense of OFPP_LOCAL)
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A: Open vSwitch does not support such a configuration.
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Bridges always have their local ports.
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Implementation Details
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----------------------
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Q: I hear OVS has a couple of kinds of flows. Can you tell me about them?
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A: Open vSwitch uses different kinds of flows for different purposes:
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- OpenFlow flows are the most important kind of flow. OpenFlow
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controllers use these flows to define a switch's policy.
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OpenFlow flows support wildcards, priorities, and multiple
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When in-band control is in use, Open vSwitch sets up a few
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"hidden" flows, with priority higher than a controller or the
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user can configure, that are not visible via OpenFlow. (See
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the "Controller" section of the FAQ for more information
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- The Open vSwitch software switch implementation uses a second
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kind of flow internally. These flows, called "datapath" or
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"kernel" flows, do not support priorities and comprise only a
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single table, which makes them suitable for caching. (Like
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OpenFlow flows, datapath flows do support wildcarding, in Open
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vSwitch 1.11 and later.) OpenFlow flows and datapath flows
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also support different actions and number ports differently.
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Datapath flows are an implementation detail that is subject to
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change in future versions of Open vSwitch. Even with the
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current version of Open vSwitch, hardware switch
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implementations do not necessarily use this architecture.
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Users and controllers directly control only the OpenFlow flow
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table. Open vSwitch manages the datapath flow table itself, so
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users should not normally be concerned with it.
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Q: Why are there so many different ways to dump flows?
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A: Open vSwitch has two kinds of flows (see the previous question), so
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it has commands with different purposes for dumping each kind of
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- "ovs-ofctl dump-flows <br>" dumps OpenFlow flows, excluding
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hidden flows. This is the most commonly useful form of flow
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dump. (Unlike the other commands, this should work with any
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OpenFlow switch, not just Open vSwitch.)
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- "ovs-appctl bridge/dump-flows <br>" dumps OpenFlow flows,
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including hidden flows. This is occasionally useful for
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troubleshooting suspected issues with in-band control.
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- "ovs-dpctl dump-flows [dp]" dumps the datapath flow table
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entries for a Linux kernel-based datapath. In Open vSwitch
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1.10 and later, ovs-vswitchd merges multiple switches into a
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single datapath, so it will show all the flows on all your
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kernel-based switches. This command can occasionally be
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useful for debugging.
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- "ovs-appctl dpif/dump-flows <br>", new in Open vSwitch 1.10,
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dumps datapath flows for only the specified bridge, regardless
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Q: I just upgraded and I see a performance drop. Why?
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A: The OVS kernel datapath may have been updated to a newer version than
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the OVS userspace components. Sometimes new versions of OVS kernel
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module add functionality that is backwards compatible with older
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userspace components but may cause a drop in performance with them.
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Especially, if a kernel module from OVS 2.1 or newer is paired with
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OVS userspace 1.10 or older, there will be a performance drop for
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Updating the OVS userspace components to the latest released
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version should fix the performance degradation.
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To get the best possible performance and functionality, it is
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recommended to pair the same versions of the kernel module and OVS
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Configuration Problems
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----------------------
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Q: I created a bridge and added my Ethernet port to it, using commands
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ovs-vsctl add-port br0 eth0
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and as soon as I ran the "add-port" command I lost all connectivity
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A: A physical Ethernet device that is part of an Open vSwitch bridge
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should not have an IP address. If one does, then that IP address
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will not be fully functional.
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You can restore functionality by moving the IP address to an Open
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vSwitch "internal" device, such as the network device named after
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the bridge itself. For example, assuming that eth0's IP address is
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192.168.128.5, you could run the commands below to fix up the
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ifconfig eth0 0.0.0.0
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ifconfig br0 192.168.128.5
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(If your only connection to the machine running OVS is through the
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IP address in question, then you would want to run all of these
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commands on a single command line, or put them into a script.) If
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there were any additional routes assigned to eth0, then you would
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also want to use commands to adjust these routes to go through br0.
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If you use DHCP to obtain an IP address, then you should kill the
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DHCP client that was listening on the physical Ethernet interface
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(e.g. eth0) and start one listening on the internal interface
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(e.g. br0). You might still need to manually clear the IP address
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from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
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There is no compelling reason why Open vSwitch must work this way.
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However, this is the way that the Linux kernel bridge module has
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always worked, so it's a model that those accustomed to Linux
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bridging are already used to. Also, the model that most people
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expect is not implementable without kernel changes on all the
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versions of Linux that Open vSwitch supports.
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By the way, this issue is not specific to physical Ethernet
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devices. It applies to all network devices except Open vswitch
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Q: I created a bridge and added a couple of Ethernet ports to it,
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using commands like these:
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 eth1
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and now my network seems to have melted: connectivity is unreliable
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(even connectivity that doesn't go through Open vSwitch), all the
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LEDs on my physical switches are blinking, wireshark shows
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duplicated packets, and CPU usage is very high.
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A: More than likely, you've looped your network. Probably, eth0 and
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eth1 are connected to the same physical Ethernet switch. This
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yields a scenario where OVS receives a broadcast packet on eth0 and
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sends it out on eth1, then the physical switch connected to eth1
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sends the packet back on eth0, and so on forever. More complicated
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scenarios, involving a loop through multiple switches, are possible
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The solution depends on what you are trying to do:
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- If you added eth0 and eth1 to get higher bandwidth or higher
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reliability between OVS and your physical Ethernet switch,
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use a bond. The following commands create br0 and then add
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eth0 and eth1 as a bond:
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ovs-vsctl add-bond br0 bond0 eth0 eth1
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Bonds have tons of configuration options. Please read the
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documentation on the Port table in ovs-vswitchd.conf.db(5)
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- Perhaps you don't actually need eth0 and eth1 to be on the
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same bridge. For example, if you simply want to be able to
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connect each of them to virtual machines, then you can put
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each of them on a bridge of its own:
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br1 eth1
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and then connect VMs to br0 and br1. (A potential
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disadvantage is that traffic cannot directly pass between br0
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and br1. Instead, it will go out eth0 and come back in eth1,
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- If you have a redundant or complex network topology and you
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want to prevent loops, turn on spanning tree protocol (STP).
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The following commands create br0, enable STP, and add eth0
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and eth1 to the bridge. The order is important because you
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don't want have to have a loop in your network even
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ovs-vsctl set bridge br0 stp_enable=true
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 eth1
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The Open vSwitch implementation of STP is not well tested.
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Please report any bugs you observe, but if you'd rather avoid
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acting as a beta tester then another option might be your
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Q: I can't seem to use Open vSwitch in a wireless network.
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A: Wireless base stations generally only allow packets with the source
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MAC address of NIC that completed the initial handshake.
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Therefore, without MAC rewriting, only a single device can
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communicate over a single wireless link.
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This isn't specific to Open vSwitch, it's enforced by the access
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point, so the same problems will show up with the Linux bridge or
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any other way to do bridging.
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Q: I can't seem to add my PPP interface to an Open vSwitch bridge.
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A: PPP most commonly carries IP packets, but Open vSwitch works only
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with Ethernet frames. The correct way to interface PPP to an
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Ethernet network is usually to use routing instead of switching.
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Q: Is there any documentation on the database tables and fields?
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A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
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Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
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I only see a datapath called "ovs-system". How can I see datapath
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information about a particular bridge?
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A: In version 1.9.0, OVS switched to using a single datapath that is
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shared by all bridges of that type. The "ovs-appctl dpif/*"
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commands provide similar functionality that is scoped by the bridge.
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Q: I created a GRE port using ovs-vsctl so why can't I send traffic or
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see the port in the datapath?
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A: On Linux kernels before 3.11, the OVS GRE module and Linux GRE module
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cannot be loaded at the same time. It is likely that on your system the
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Linux GRE module is already loaded and blocking OVS (to confirm, check
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dmesg for errors regarding GRE registration). To fix this, unload all
675
GRE modules that appear in lsmod as well as the OVS kernel module. You
676
can then reload the OVS module following the directions in INSTALL,
677
which will ensure that dependencies are satisfied.
679
Q: Open vSwitch does not seem to obey my packet filter rules.
681
A: It depends on mechanisms and configurations you want to use.
683
You cannot usefully use typical packet filters, like iptables, on
684
physical Ethernet ports that you add to an Open vSwitch bridge.
685
This is because Open vSwitch captures packets from the interface at
686
a layer lower below where typical packet-filter implementations
687
install their hooks. (This actually applies to any interface of
688
type "system" that you might add to an Open vSwitch bridge.)
690
You can usefully use typical packet filters on Open vSwitch
691
internal ports as they are mostly ordinary interfaces from the point
692
of view of packet filters.
694
For example, suppose you create a bridge br0 and add Ethernet port
695
eth0 to it. Then you can usefully add iptables rules to affect the
696
internal interface br0, but not the physical interface eth0. (br0
697
is also where you would add an IP address, as discussed elsewhere
700
For simple filtering rules, it might be possible to achieve similar
701
results by installing appropriate OpenFlow flows instead.
703
If the use of a particular packet filter setup is essential, Open
704
vSwitch might not be the best choice for you. On Linux, you might
705
want to consider using the Linux Bridge. (This is the only choice if
706
you want to use ebtables rules.) On NetBSD, you might want to
707
consider using the bridge(4) with BRIDGE_IPF option.
710
Quality of Service (QoS)
711
------------------------
713
Q: How do I configure Quality of Service (QoS)?
715
A: Suppose that you want to set up bridge br0 connected to physical
716
Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
717
vif1.0 and vif2.0, and that you want to limit traffic from vif1.0
718
to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps. Then, you
719
could configure the bridge this way:
723
add-port br0 eth0 -- \
724
add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \
725
add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \
726
set port eth0 qos=@newqos -- \
727
--id=@newqos create qos type=linux-htb \
728
other-config:max-rate=1000000000 \
729
queues:123=@vif10queue \
730
queues:234=@vif20queue -- \
731
--id=@vif10queue create queue other-config:max-rate=10000000 -- \
732
--id=@vif20queue create queue other-config:max-rate=20000000
734
At this point, bridge br0 is configured with the ports and eth0 is
735
configured with the queues that you need for QoS, but nothing is
736
actually directing packets from vif1.0 or vif2.0 to the queues that
737
we have set up for them. That means that all of the packets to
738
eth0 are going to the "default queue", which is not what we want.
740
We use OpenFlow to direct packets from vif1.0 and vif2.0 to the
741
queues reserved for them:
743
ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal
744
ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal
746
Each of the above flows matches on the input port, sets up the
747
appropriate queue (123 for vif1.0, 234 for vif2.0), and then
748
executes the "normal" action, which performs the same switching
749
that Open vSwitch would have done without any OpenFlow flows being
750
present. (We know that vif1.0 and vif2.0 have OpenFlow port
751
numbers 5 and 6, respectively, because we set their ofport_request
752
columns above. If we had not done that, then we would have needed
753
to find out their port numbers before setting up these flows.)
755
Now traffic going from vif1.0 or vif2.0 to eth0 should be
758
By the way, if you delete the bridge created by the above commands,
763
then that will leave one unreferenced QoS record and two
764
unreferenced Queue records in the Open vSwich database. One way to
765
clear them out, assuming you don't have other QoS or Queue records
766
that you want to keep, is:
768
ovs-vsctl -- --all destroy QoS -- --all destroy Queue
770
If you do want to keep some QoS or Queue records, or the Open
771
vSwitch you are using is older than version 1.8 (which added the
772
--all option), then you will have to destroy QoS and Queue records
775
Q: I configured Quality of Service (QoS) in my OpenFlow network by
776
adding records to the QoS and Queue table, but the results aren't
779
A: Did you install OpenFlow flows that use your queues? This is the
780
primary way to tell Open vSwitch which queues you want to use. If
781
you don't do this, then the default queue will be used, which will
782
probably not have the effect you want.
784
Refer to the previous question for an example.
786
Q: I'd like to take advantage of some QoS feature that Open vSwitch
787
doesn't yet support. How do I do that?
789
A: Open vSwitch does not implement QoS itself. Instead, it can
790
configure some, but not all, of the QoS features built into the
791
Linux kernel. If you need some QoS feature that OVS cannot
792
configure itself, then the first step is to figure out whether
793
Linux QoS supports that feature. If it does, then you can submit a
794
patch to support Open vSwitch configuration for that feature, or
795
you can use "tc" directly to configure the feature in Linux. (If
796
Linux QoS doesn't support the feature you want, then first you have
797
to add that support to Linux.)
799
Q: I configured QoS, correctly, but my measurements show that it isn't
800
working as well as I expect.
802
A: With the Linux kernel, the Open vSwitch implementation of QoS has
805
- Open vSwitch configures a subset of Linux kernel QoS
806
features, according to what is in OVSDB. It is possible that
807
this code has bugs. If you believe that this is so, then you
808
can configure the Linux traffic control (QoS) stack directly
809
with the "tc" program. If you get better results that way,
810
you can send a detailed bug report to bugs@openvswitch.org.
812
It is certain that Open vSwitch cannot configure every Linux
813
kernel QoS feature. If you need some feature that OVS cannot
814
configure, then you can also use "tc" directly (or add that
817
- The Open vSwitch implementation of OpenFlow allows flows to
818
be directed to particular queues. This is pretty simple and
819
unlikely to have serious bugs at this point.
821
However, most problems with QoS on Linux are not bugs in Open
822
vSwitch at all. They tend to be either configuration errors
823
(please see the earlier questions in this section) or issues with
824
the traffic control (QoS) stack in Linux. The Open vSwitch
825
developers are not experts on Linux traffic control. We suggest
826
that, if you believe you are encountering a problem with Linux
827
traffic control, that you consult the tc manpages (e.g. tc(8),
828
tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or
829
mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev).
831
Q: Does Open vSwitch support OpenFlow meters?
833
A: Since version 2.0, Open vSwitch has OpenFlow protocol support for
834
OpenFlow meters. There is no implementation of meters in the Open
835
vSwitch software switch (neither the kernel-based nor userspace
844
A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
845
partition a single switch into multiple switches. Suppose, for
846
example, that you have two groups of machines, group A and group B.
847
You want the machines in group A to be able to talk to each other,
848
and you want the machine in group B to be able to talk to each
849
other, but you don't want the machines in group A to be able to
850
talk to the machines in group B. You can do this with two
851
switches, by plugging the machines in group A into one switch and
852
the machines in group B into the other switch.
854
If you only have one switch, then you can use VLANs to do the same
855
thing, by configuring the ports for machines in group A as VLAN
856
"access ports" for one VLAN and the ports for group B as "access
857
ports" for a different VLAN. The switch will only forward packets
858
between ports that are assigned to the same VLAN, so this
859
effectively subdivides your single switch into two independent
860
switches, one for each group of machines.
862
So far we haven't said anything about VLAN headers. With access
863
ports, like we've described so far, no VLAN header is present in
864
the Ethernet frame. This means that the machines (or switches)
865
connected to access ports need not be aware that VLANs are
866
involved, just like in the case where we use two different physical
869
Now suppose that you have a whole bunch of switches in your
870
network, instead of just one, and that some machines in group A are
871
connected directly to both switches 1 and 2. To allow these
872
machines to talk to each other, you could add an access port for
873
group A's VLAN to switch 1 and another to switch 2, and then
874
connect an Ethernet cable between those ports. That works fine,
875
but it doesn't scale well as the number of switches and the number
876
of VLANs increases, because you use up a lot of valuable switch
877
ports just connecting together your VLANs.
879
This is where VLAN headers come in. Instead of using one cable and
880
two ports per VLAN to connect a pair of switches, we configure a
881
port on each switch as a VLAN "trunk port". Packets sent and
882
received on a trunk port carry a VLAN header that says what VLAN
883
the packet belongs to, so that only two ports total are required to
884
connect the switches, regardless of the number of VLANs in use.
885
Normally, only switches (either physical or virtual) are connected
886
to a trunk port, not individual hosts, because individual hosts
887
don't expect to see a VLAN header in the traffic that they receive.
889
None of the above discussion says anything about particular VLAN
890
numbers. This is because VLAN numbers are completely arbitrary.
891
One must only ensure that a given VLAN is numbered consistently
892
throughout a network and that different VLANs are given different
893
numbers. (That said, VLAN 0 is usually synonymous with a packet
894
that has no VLAN header, and VLAN 4095 is reserved.)
898
A: Many drivers in Linux kernels before version 3.3 had VLAN-related
899
bugs. If you are having problems with VLANs that you suspect to be
900
driver related, then you have several options:
902
- Upgrade to Linux 3.3 or later.
904
- Build and install a fixed version of the particular driver
905
that is causing trouble, if one is available.
907
- Use a NIC whose driver does not have VLAN problems.
909
- Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
910
that works around bugs in kernel drivers. To enable VLAN
911
splinters on interface eth0, use the command:
913
ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
915
For VLAN splinters to be effective, Open vSwitch must know
916
which VLANs are in use. See the "VLAN splinters" section in
917
the Interface table in ovs-vswitchd.conf.db(5) for details on
918
how Open vSwitch infers in-use VLANs.
920
VLAN splinters increase memory use and reduce performance, so
921
use them only if needed.
923
- Apply the "vlan workaround" patch from the XenServer kernel
924
patch queue, build Open vSwitch against this patched kernel,
925
and then use ovs-vlan-bug-workaround(8) to enable the VLAN
926
workaround for each interface whose driver is buggy.
928
(This is a nontrivial exercise, so this option is included
929
only for completeness.)
931
It is not always easy to tell whether a Linux kernel driver has
932
buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
933
can help you test. See their manpages for details. Of the two
934
utilities, ovs-test(8) is newer and more thorough, but
935
ovs-vlan-test(8) may be easier to use.
937
Q: VLANs still don't work. I've tested the driver so I know that it's OK.
939
A: Do you have VLANs enabled on the physical switch that OVS is
940
attached to? Make sure that the port is configured to trunk the
941
VLAN or VLANs that you are using with OVS.
943
Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
944
and to its destination host, but OVS seems to drop incoming return
947
A: It's possible that you have the VLAN configured on your physical
948
switch as the "native" VLAN. In this mode, the switch treats
949
incoming packets either tagged with the native VLAN or untagged as
950
part of the native VLAN. It may also send outgoing packets in the
951
native VLAN without a VLAN tag.
953
If this is the case, you have two choices:
955
- Change the physical switch port configuration to tag packets
956
it forwards to OVS with the native VLAN instead of forwarding
959
- Change the OVS configuration for the physical port to a
960
native VLAN mode. For example, the following sets up a
961
bridge with port eth0 in "native-tagged" mode in VLAN 9:
964
ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
966
In this situation, "native-untagged" mode will probably work
967
equally well. Refer to the documentation for the Port table
968
in ovs-vswitchd.conf.db(5) for more information.
970
Q: I added a pair of VMs on different VLANs, like this:
973
ovs-vsctl add-port br0 eth0
974
ovs-vsctl add-port br0 tap0 tag=9
975
ovs-vsctl add-port br0 tap1 tag=10
977
but the VMs can't access each other, the external network, or the
980
A: It is to be expected that the VMs can't access each other. VLANs
981
are a means to partition a network. When you configured tap0 and
982
tap1 as access ports for different VLANs, you indicated that they
983
should be isolated from each other.
985
As for the external network and the Internet, it seems likely that
986
the machines you are trying to access are not on VLAN 9 (or 10) and
987
that the Internet is not available on VLAN 9 (or 10).
989
Q: I added a pair of VMs on the same VLAN, like this:
992
ovs-vsctl add-port br0 eth0
993
ovs-vsctl add-port br0 tap0 tag=9
994
ovs-vsctl add-port br0 tap1 tag=9
996
The VMs can access each other, but not the external network or the
999
A: It seems likely that the machines you are trying to access in the
1000
external network are not on VLAN 9 and that the Internet is not
1001
available on VLAN 9. Also, ensure VLAN 9 is set up as an allowed
1002
trunk VLAN on the upstream switch port to which eth0 is connected.
1004
Q: Can I configure an IP address on a VLAN?
1006
A: Yes. Use an "internal port" configured as an access port. For
1007
example, the following configures IP address 192.168.0.7 on VLAN 9.
1008
That is, OVS will forward packets from eth0 to 192.168.0.7 only if
1009
they have an 802.1Q header with VLAN 9. Conversely, traffic
1010
forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
1013
ovs-vsctl add-br br0
1014
ovs-vsctl add-port br0 eth0
1015
ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
1016
ifconfig vlan9 192.168.0.7
1018
See also the following question.
1020
Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
1023
ovs-vsctl add-br br0
1024
ovs-vsctl add-port br0 eth0
1025
ifconfig br0 192.168.0.5
1026
ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
1027
ifconfig vlan9 192.168.0.9
1029
but other hosts that are only on VLAN 0 can reach the IP address
1030
configured on VLAN 9. What's going on?
1032
A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
1033
approaches to IP address handling in Internet hosts:
1035
- In the "Strong ES Model", where an ES is a host ("End
1036
System"), an IP address is primarily associated with a
1037
particular interface. The host discards packets that arrive
1038
on interface A if they are destined for an IP address that is
1039
configured on interface B. The host never sends packets from
1040
interface A using a source address configured on interface B.
1042
- In the "Weak ES Model", an IP address is primarily associated
1043
with a host. The host accepts packets that arrive on any
1044
interface if they are destined for any of the host's IP
1045
addresses, even if the address is configured on some
1046
interface other than the one on which it arrived. The host
1047
does not restrict itself to sending packets from an IP
1048
address associated with the originating interface.
1050
Linux uses the weak ES model. That means that when packets
1051
destined to the VLAN 9 IP address arrive on eth0 and are bridged to
1052
br0, the kernel IP stack accepts them there for the VLAN 9 IP
1053
address, even though they were not received on vlan9, the network
1056
To simulate the strong ES model on Linux, one may add iptables rule
1057
to filter packets based on source and destination address and
1058
adjust ARP configuration with sysctls.
1060
BSD uses the strong ES model.
1062
Q: My OpenFlow controller doesn't see the VLANs that I expect.
1064
A: The configuration for VLANs in the Open vSwitch database (e.g. via
1065
ovs-vsctl) only affects traffic that goes through Open vSwitch's
1066
implementation of the OpenFlow "normal switching" action. By
1067
default, when Open vSwitch isn't connected to a controller and
1068
nothing has been manually configured in the flow table, all traffic
1069
goes through the "normal switching" action. But, if you set up
1070
OpenFlow flows on your own, through a controller or using ovs-ofctl
1071
or through other means, then you have to implement VLAN handling
1074
You can use "normal switching" as a component of your OpenFlow
1075
actions, e.g. by putting "normal" into the lists of actions on
1076
ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
1077
controller. In situations where this is not suitable, you can
1078
implement VLAN handling yourself, e.g.:
1080
- If a packet comes in on an access port, and the flow table
1081
needs to send it out on a trunk port, then the flow can add
1082
the appropriate VLAN tag with the "mod_vlan_vid" action.
1084
- If a packet comes in on a trunk port, and the flow table
1085
needs to send it out on an access port, then the flow can
1086
strip the VLAN tag with the "strip_vlan" action.
1088
Q: I configured ports on a bridge as access ports with different VLAN
1091
ovs-vsctl add-br br0
1092
ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
1093
ovs-vsctl add-port br0 eth0
1094
ovs-vsctl add-port br0 tap0 tag=9
1095
ovs-vsctl add-port br0 tap1 tag=10
1097
but the VMs running behind tap0 and tap1 can still communicate,
1098
that is, they are not isolated from each other even though they are
1101
A: Do you have a controller configured on br0 (as the commands above
1102
do)? If so, then this is a variant on the previous question, "My
1103
OpenFlow controller doesn't see the VLANs that I expect," and you
1104
can refer to the answer there for more information.
1112
A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means
1113
to solve the scaling challenges of VLAN networks in a multi-tenant
1114
environment. VXLAN is an overlay network which transports an L2 network
1115
over an existing L3 network. For more information on VXLAN, please see
1116
the IETF draft available here:
1118
http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-03
1120
Q: How much of the VXLAN protocol does Open vSwitch currently support?
1122
A: Open vSwitch currently supports the framing format for packets on the
1123
wire. There is currently no support for the multicast aspects of VXLAN.
1124
To get around the lack of multicast support, it is possible to
1125
pre-provision MAC to IP address mappings either manually or from a
1128
Q: What destination UDP port does the VXLAN implementation in Open vSwitch
1131
A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which
1132
is 4789. However, it is possible to configure the destination UDP port
1133
manually on a per-VXLAN tunnel basis. An example of this configuration is
1136
ovs-vsctl add-br br0
1137
ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1
1138
type=vxlan options:remote_ip=192.168.1.2 options:key=flow
1139
options:dst_port=8472
1142
Using OpenFlow (Manually or Via Controller)
1143
-------------------------------------------
1145
Q: What versions of OpenFlow does Open vSwitch support?
1147
A: The following table lists the versions of OpenFlow supported by
1148
each version of Open vSwitch:
1150
Open vSwitch OF1.0 OF1.1 OF1.2 OF1.3 OF1.4 OF1.5
1151
=============== ===== ===== ===== ===== ===== =====
1152
1.9 and earlier yes --- --- --- --- ---
1153
1.10 yes --- [*] [*] --- ---
1154
1.11 yes --- [*] [*] --- ---
1155
2.0 yes [*] [*] [*] --- ---
1156
2.1 yes [*] [*] [*] --- ---
1157
2.2 yes [*] [*] [*] [%] [*]
1158
2.3 yes yes yes yes [*] [*]
1160
[*] Supported, with one or more missing features.
1161
[%] Experimental, unsafe implementation.
1163
Open vSwitch 2.3 enables OpenFlow 1.0, 1.1, 1.2, and 1.3 by default
1164
in ovs-vswitchd. In Open vSwitch 1.10 through 2.2, OpenFlow 1.1,
1165
1.2, and 1.3 must be enabled manually in ovs-vswitchd. OpenFlow
1166
1.4 and 1.5 are also supported, with missing features, in Open
1167
vSwitch 2.3 and later, but not enabled by default. In any case,
1168
the user may override the default:
1170
- To enable OpenFlow 1.0, 1.1, 1.2, and 1.3 on bridge br0:
1172
ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
1174
- To enable OpenFlow 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5 on bridge br0:
1176
ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13,OpenFlow14,OpenFlow15
1178
- To enable only OpenFlow 1.0 on bridge br0:
1180
ovs-vsctl set bridge br0 protocols=OpenFlow10
1182
All current versions of ovs-ofctl enable only OpenFlow 1.0 by
1183
default. Use the -O option to enable support for later versions of
1184
OpenFlow in ovs-ofctl. For example:
1186
ovs-ofctl -O OpenFlow13 dump-flows br0
1188
(Open vSwitch 2.2 had an experimental implementation of OpenFlow
1189
1.4 that could cause crashes. We don't recommend enabling it.)
1191
OPENFLOW-1.1+ in the Open vSwitch source tree tracks support for
1192
OpenFlow 1.1 and later features. When support for OpenFlow 1.4 and
1193
1.5 is solidly implemented, Open vSwitch will enable those version
1194
by default. Also, the OpenFlow 1.5 specification is still under
1195
development and thus subject to change.
1197
Q: Does Open vSwitch support MPLS?
1199
A: Before version 1.11, Open vSwitch did not support MPLS. That is,
1200
these versions can match on MPLS Ethernet types, but they cannot
1201
match, push, or pop MPLS labels, nor can they look past MPLS labels
1202
into the encapsulated packet.
1204
Open vSwitch versions 1.11, 2.0, and 2.1 have very minimal support
1205
for MPLS. With the userspace datapath only, these versions can
1206
match, push, or pop a single MPLS label, but they still cannot look
1207
past MPLS labels (even after popping them) into the encapsulated
1208
packet. Kernel datapath support is unchanged from earlier
1211
Open vSwitch version 2.2 will be able to match, push, or pop up to
1212
3 MPLS labels. Looking past MPLS labels into the encapsulated
1213
packet will still be unsupported. Both userspace and kernel
1214
datapaths will be supported, but MPLS processing always happens in
1215
userspace either way, so kernel datapath performance will be
1218
Q: I'm getting "error type 45250 code 0". What's that?
1220
A: This is a Open vSwitch extension to OpenFlow error codes. Open
1221
vSwitch uses this extension when it must report an error to an
1222
OpenFlow controller but no standard OpenFlow error code is
1225
Open vSwitch logs the errors that it sends to controllers, so the
1226
easiest thing to do is probably to look at the ovs-vswitchd log to
1227
find out what the error was.
1229
If you want to dissect the extended error message yourself, the
1230
format is documented in include/openflow/nicira-ext.h in the Open
1231
vSwitch source distribution. The extended error codes are
1232
documented in lib/ofp-errors.h.
1234
Q1: Some of the traffic that I'd expect my OpenFlow controller to see
1235
doesn't actually appear through the OpenFlow connection, even
1236
though I know that it's going through.
1237
Q2: Some of the OpenFlow flows that my controller sets up don't seem
1238
to apply to certain traffic, especially traffic between OVS and
1239
the controller itself.
1241
A: By default, Open vSwitch assumes that OpenFlow controllers are
1242
connected "in-band", that is, that the controllers are actually
1243
part of the network that is being controlled. In in-band mode,
1244
Open vSwitch sets up special "hidden" flows to make sure that
1245
traffic can make it back and forth between OVS and the controllers.
1246
These hidden flows are higher priority than any flows that can be
1247
set up through OpenFlow, and they are not visible through normal
1248
OpenFlow flow table dumps.
1250
Usually, the hidden flows are desirable and helpful, but
1251
occasionally they can cause unexpected behavior. You can view the
1252
full OpenFlow flow table, including hidden flows, on bridge br0
1255
ovs-appctl bridge/dump-flows br0
1257
to help you debug. The hidden flows are those with priorities
1258
greater than 65535 (the maximum priority that can be set with
1261
The DESIGN file at the top level of the Open vSwitch source
1262
distribution describes the in-band model in detail.
1264
If your controllers are not actually in-band (e.g. they are on
1265
localhost via 127.0.0.1, or on a separate network), then you should
1266
configure your controllers in "out-of-band" mode. If you have one
1267
controller on bridge br0, then you can configure out-of-band mode
1270
ovs-vsctl set controller br0 connection-mode=out-of-band
1272
Q: I configured all my controllers for out-of-band control mode but
1273
"ovs-appctl bridge/dump-flows" still shows some hidden flows.
1275
A: You probably have a remote manager configured (e.g. with "ovs-vsctl
1276
set-manager"). By default, Open vSwitch assumes that managers need
1277
in-band rules set up on every bridge. You can disable these rules
1280
ovs-vsctl set bridge br0 other-config:disable-in-band=true
1282
This actually disables in-band control entirely for the bridge, as
1283
if all the bridge's controllers were configured for out-of-band
1286
Q: My OpenFlow controller doesn't see the VLANs that I expect.
1288
A: See answer under "VLANs", above.
1290
Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
1291
but I got a funny message like this:
1293
ofp_util|INFO|normalization changed ofp_match, details:
1294
ofp_util|INFO| pre: nw_dst=192.168.0.1
1297
and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
1298
match had disappeared, so that the flow ends up matching every
1301
A: The term "normalization" in the log message means that a flow
1302
cannot match on an L3 field without saying what L3 protocol is in
1303
use. The "ovs-ofctl" command above didn't specify an L3 protocol,
1304
so the L3 field match was dropped.
1306
In this case, the L3 protocol could be IP or ARP. A correct
1307
command for each possibility is, respectively:
1309
ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
1313
ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
1315
Similarly, a flow cannot match on an L4 field without saying what
1316
L4 protocol is in use. For example, the flow match "tp_src=1234"
1317
is, by itself, meaningless and will be ignored. Instead, to match
1318
TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
1319
source port 1234, write "udp,tp_src=1234".
1321
Q: How can I figure out the OpenFlow port number for a given port?
1323
A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
1324
respond with an OFPT_FEATURES_REPLY that, among other information,
1325
includes a mapping between OpenFlow port names and numbers. From a
1326
command prompt, "ovs-ofctl show br0" makes such a request and
1327
prints the response for switch br0.
1329
The Interface table in the Open vSwitch database also maps OpenFlow
1330
port names to numbers. To print the OpenFlow port number
1331
associated with interface eth0, run:
1333
ovs-vsctl get Interface eth0 ofport
1335
You can print the entire mapping with:
1337
ovs-vsctl -- --columns=name,ofport list Interface
1339
but the output mixes together interfaces from all bridges in the
1340
database, so it may be confusing if more than one bridge exists.
1342
In the Open vSwitch database, ofport value -1 means that the
1343
interface could not be created due to an error. (The Open vSwitch
1344
log should indicate the reason.) ofport value [] (the empty set)
1345
means that the interface hasn't been created yet. The latter is
1346
normally an intermittent condition (unless ovs-vswitchd is not
1349
Q: I added some flows with my controller or with ovs-ofctl, but when I
1350
run "ovs-dpctl dump-flows" I don't see them.
1352
A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
1353
won't display the information that you want. You want to use
1354
"ovs-ofctl dump-flows" instead.
1356
Q: It looks like each of the interfaces in my bonded port shows up
1357
as an individual OpenFlow port. Is that right?
1359
A: Yes, Open vSwitch makes individual bond interfaces visible as
1360
OpenFlow ports, rather than the bond as a whole. The interfaces
1361
are treated together as a bond for only a few purposes:
1363
- Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
1364
controller is not configured, this happens implicitly to
1367
- Mirrors configured for output to a bonded port.
1369
It would make a lot of sense for Open vSwitch to present a bond as
1370
a single OpenFlow port. If you want to contribute an
1371
implementation of such a feature, please bring it up on the Open
1372
vSwitch development mailing list at dev@openvswitch.org.
1374
Q: I have a sophisticated network setup involving Open vSwitch, VMs or
1375
multiple hosts, and other components. The behavior isn't what I
1378
A: To debug network behavior problems, trace the path of a packet,
1379
hop-by-hop, from its origin in one host to a remote host. If
1380
that's correct, then trace the path of the response packet back to
1383
Usually a simple ICMP echo request and reply ("ping") packet is
1384
good enough. Start by initiating an ongoing "ping" from the origin
1385
host to a remote host. If you are tracking down a connectivity
1386
problem, the "ping" will not display any successful output, but
1387
packets are still being sent. (In this case the packets being sent
1388
are likely ARP rather than ICMP.)
1390
Tools available for tracing include the following:
1392
- "tcpdump" and "wireshark" for observing hops across network
1393
devices, such as Open vSwitch internal devices and physical
1396
- "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
1397
later or "ovs-dpctl dump-flows <br>" in earlier versions.
1398
These tools allow one to observe the actions being taken on
1399
packets in ongoing flows.
1401
See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
1402
documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
1403
documentation, and "Why are there so many different ways to
1404
dump flows?" above for some background.
1406
- "ovs-appctl ofproto/trace" to observe the logic behind how
1407
ovs-vswitchd treats packets. See ovs-vswitchd(8) for
1408
documentation. You can out more details about a given flow
1409
that "ovs-dpctl dump-flows" displays, by cutting and pasting
1410
a flow from the output into an "ovs-appctl ofproto/trace"
1413
- SPAN, RSPAN, and ERSPAN features of physical switches, to
1414
observe what goes on at these physical hops.
1416
Starting at the origin of a given packet, observe the packet at
1417
each hop in turn. For example, in one plausible scenario, you
1420
1. "tcpdump" the "eth" interface through which an ARP egresses
1421
a VM, from inside the VM.
1423
2. "tcpdump" the "vif" or "tap" interface through which the ARP
1424
ingresses the host machine.
1426
3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
1427
the host interface through which the ARP egresses the
1428
physical machine. You may need to use "ovs-dpctl show" to
1429
interpret the port numbers. If the output seems surprising,
1430
you can use "ovs-appctl ofproto/trace" to observe details of
1431
how ovs-vswitchd determined the actions in the "ovs-dpctl
1434
4. "tcpdump" the "eth" interface through which the ARP egresses
1435
the physical machine.
1437
5. "tcpdump" the "eth" interface through which the ARP
1438
ingresses the physical machine, at the remote host that
1441
6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
1442
remote host that receives the ARP and observe the VM "vif"
1443
or "tap" interface to which the flow is directed. Again,
1444
"ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
1446
7. "tcpdump" the "vif" or "tap" interface to which the ARP is
1449
8. "tcpdump" the "eth" interface through which the ARP
1450
ingresses a VM, from inside the VM.
1452
It is likely that during one of these steps you will figure out the
1453
problem. If not, then follow the ARP reply back to the origin, in
1456
Q: How do I make a flow drop packets?
1458
A: To drop a packet is to receive it without forwarding it. OpenFlow
1459
explicitly specifies forwarding actions. Thus, a flow with an
1460
empty set of actions does not forward packets anywhere, causing
1461
them to be dropped. You can specify an empty set of actions with
1462
"actions=" on the ovs-ofctl command line. For example:
1464
ovs-ofctl add-flow br0 priority=65535,actions=
1466
would cause every packet entering switch br0 to be dropped.
1468
You can write "drop" explicitly if you like. The effect is the
1469
same. Thus, the following command also causes every packet
1470
entering switch br0 to be dropped:
1472
ovs-ofctl add-flow br0 priority=65535,actions=drop
1474
"drop" is not an action, either in OpenFlow or Open vSwitch.
1475
Rather, it is only a way to say that there are no actions.
1477
Q: I added a flow to send packets out the ingress port, like this:
1479
ovs-ofctl add-flow br0 in_port=2,actions=2
1481
but OVS drops the packets instead.
1483
A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
1484
out its ingress port. The rationale is that dropping these packets
1485
makes it harder to loop the network. Sometimes this behavior can
1486
even be convenient, e.g. it is often the desired behavior in a flow
1487
that forwards a packet to several ports ("floods" the packet).
1489
Sometimes one really needs to send a packet out its ingress port
1490
("hairpin"). In this case, output to OFPP_IN_PORT, which in
1491
ovs-ofctl syntax is expressed as just "in_port", e.g.:
1493
ovs-ofctl add-flow br0 in_port=2,actions=in_port
1495
This also works in some circumstances where the flow doesn't match
1496
on the input port. For example, if you know that your switch has
1497
five ports numbered 2 through 6, then the following will send every
1498
received packet out every port, even its ingress port:
1500
ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
1504
ovs-ofctl add-flow br0 actions=all,in_port
1506
Sometimes, in complicated flow tables with multiple levels of
1507
"resubmit" actions, a flow needs to output to a particular port
1508
that may or may not be the ingress port. It's difficult to take
1509
advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch
1510
provides, as an OpenFlow extension, the ability to modify the
1511
in_port field. Whatever value is currently in the in_port field is
1512
the port to which outputs will be dropped, as well as the
1513
destination for OFPP_IN_PORT. This means that the following will
1514
reliably output to port 2 or to ports 2 through 6, respectively:
1516
ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
1517
ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
1519
If the input port is important, then one may save and restore it on
1522
ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
1523
load:0->NXM_OF_IN_PORT[],\
1525
pop:NXM_OF_IN_PORT[]
1527
Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2
1528
on port 2. I set up flows to forward only traffic destined to the
1529
other host and drop other traffic, like this:
1531
priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2
1532
priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1
1533
priority=0,actions=drop
1535
But it doesn't work--I don't get any connectivity when I do this.
1538
A: These flows drop the ARP packets that IP hosts use to establish IP
1539
connectivity over Ethernet. To solve the problem, add flows to
1540
allow ARP to pass between the hosts:
1542
priority=5,in_port=1,arp,actions=2
1543
priority=5,in_port=2,arp,actions=1
1545
This issue can manifest other ways, too. The following flows that
1546
match on Ethernet addresses instead of IP addresses will also drop
1547
ARP packets, because ARP requests are broadcast instead of being
1548
directed to a specific host:
1550
priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2
1551
priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1
1552
priority=0,actions=drop
1554
The solution already described above will also work in this case.
1555
It may be better to add flows to allow all multicast and broadcast
1558
priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
1559
priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
1565
Q: How do I implement a new OpenFlow message?
1567
A: Add your new message to "enum ofpraw" and "enum ofptype" in
1568
lib/ofp-msgs.h, following the existing pattern. Then recompile and
1569
fix all of the new warnings, implementing new functionality for the
1570
new message as needed. (If you configure with --enable-Werror, as
1571
described in INSTALL, then it is impossible to miss any warnings.)
1573
If you need to add an OpenFlow vendor extension message for a
1574
vendor that doesn't yet have any extension messages, then you will
1575
also need to edit build-aux/extract-ofp-msgs.
1581
bugs@openvswitch.org
1582
http://openvswitch.org/
added
removed
FAQ
