Frequently Asked Questions
==========================
+General
+-------
+
+Q: What is Open vSwitch?
+
+A: Open vSwitch is a production quality open source software switch
+ designed to be used as a vswitch in virtualized server environments. A
+ vswitch forwards traffic between different VMs on the same physical host
+ and also forwards traffic between VMs and the physical network. Open
+ vSwitch supports standard management interfaces (e.g. sFlow, NetFlow,
+ RSPAN, CLI), and is open to programmatic extension and control using
+ OpenFlow and the OVSDB management protocol.
+
+ Open vSwitch as designed to be compatible with modern switching
+ chipsets. This means that it can be ported to existing high-fanout
+ switches allowing the same flexible control of the physical
+ infrastructure as the virtual infrastructure. It also means that
+ Open vSwitch will be able to take advantage of on-NIC switching
+ chipsets as their functionality matures.
+
+Q: What virtualization platforms can use Open vSwitch?
+
+A: Open vSwitch can currently run on any Linux-based virtualization
+ platform (kernel 2.6.18 and newer), including: KVM, VirtualBox, Xen,
+ Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the
+ mainline kernel. The bulk of the code is written in platform-
+ independent C and is easily ported to other environments. We welcome
+ inquires about integrating Open vSwitch with other virtualization
+ platforms.
+
+Q: How can I try Open vSwitch?
+
+A: The Open vSwitch source code can be built on a Linux system. You can
+ build and experiment with Open vSwitch on any Linux machine.
+ Packages for various Linux distributions are available on many
+ platforms, including: Debian, Ubuntu, Fedora.
+
+ You may also download and run a virtualization platform that already
+ has Open vSwitch integrated. For example, download a recent ISO for
+ XenServer or Xen Cloud Platform. Be aware that the version
+ integrated with a particular platform may not be the most recent Open
+ vSwitch release.
+
+Q: Does Open vSwitch only work on Linux?
+
+A: No, Open vSwitch has been ported to a number of different operating
+ systems and hardware platforms. Most of the development work occurs
+ on Linux, but the code should be portable to any POSIX system. We've
+ seen Open vSwitch ported to a number of different platforms,
+ including FreeBSD, Windows, and even non-POSIX embedded systems.
+
+ By definition, the Open vSwitch Linux kernel module only works on
+ Linux and will provide the highest performance. However, a userspace
+ datapath is available that should be very portable.
+
+Q: What's involved with porting Open vSwitch to a new platform or
+ switching ASIC?
+
+A: The PORTING document describes how one would go about porting Open
+ vSwitch to a new operating system or hardware platform.
+
+Q: Why would I use Open vSwitch instead of the Linux bridge?
+
+A: Open vSwitch is specially designed to make it easier to manage VM
+ network configuration and monitor state spread across many physical
+ hosts in dynamic virtualized environments. Please see WHY-OVS for a
+ more detailed description of how Open vSwitch relates to the Linux
+ Bridge.
+
+Q: How is Open vSwitch related to distributed virtual switches like the
+ VMware vNetwork distributed switch or the Cisco Nexus 1000V?
+
+A: Distributed vswitch applications (e.g., VMware vNetwork distributed
+ switch, Cisco Nexus 1000V) provide a centralized way to configure and
+ monitor the network state of VMs that are spread across many physical
+ hosts. Open vSwitch is not a distributed vswitch itself, rather it
+ runs on each physical host and supports remote management in a way
+ that makes it easier for developers of virtualization/cloud
+ management platforms to offer distributed vswitch capabilities.
+
+ To aid in distribution, Open vSwitch provides two open protocols that
+ are specially designed for remote management in virtualized network
+ environments: OpenFlow, which exposes flow-based forwarding state,
+ and the OVSDB management protocol, which exposes switch port state.
+ In addition to the switch implementation itself, Open vSwitch
+ includes tools (ovs-controller, ovs-ofctl, ovs-vsctl) that developers
+ can script and extend to provide distributed vswitch capabilities
+ that are closely integrated with their virtualization management
+ platform.
+
+Q: Why doesn't Open vSwitch support distribution?
+
+A: Open vSwitch is intended to be a useful component for building
+ flexible network infrastructure. There are many different approaches
+ to distribution which balance trade-offs between simplicity,
+ scalability, hardware compatibility, convergence times, logical
+ forwarding model, etc. The goal of Open vSwitch is to be able to
+ support all as a primitive building block rather than choose a
+ particular point in the distributed design space.
+
+Q: How can I contribute to the Open vSwitch Community?
+
+A: You can start by joining the mailing lists and helping to answer
+ questions. You can also suggest improvements to documentation. If
+ you have a feature or bug you would like to work on, send a mail to
+ one of the mailing lists:
+
+ http://openvswitch.org/mlists/
+
+
+
+Releases
+--------
+
+Q: What does it mean for an Open vSwitch release to be LTS (long-term
+ support)?
+
+A: All official releases have been through a comprehensive testing
+ process and are suitable for production use. Planned releases will
+ occur several times a year. If a significant bug is identified in an
+ LTS release, we will provide an updated release that includes the
+ fix. Releases that are not LTS may not be fixed and may just be
+ supplanted by the next major release. The current LTS release is
+ 1.4.x.
+
+Q: What features are not available in the Open vSwitch kernel datapath
+ that ships as part of the upstream Linux kernel?
+
+A: The kernel module in upstream Linux 3.3 and later does not include
+ the following features:
+
+ - Bridge compatibility, that is, support for the ovs-brcompatd
+ daemon that (if you enable it) lets "brctl" and other Linux
+ bridge tools transparently work with Open vSwitch instead.
+
+ We do not expect bridge compatibility to ever be available in
+ upstream Linux. If you need bridge compatibility, use the
+ kernel module from the Open vSwitch distribution instead of the
+ upstream Linux kernel module.
+
+ - Tunnel virtual ports, that is, interfaces with type "gre",
+ "ipsec_gre", "capwap". It is possible to create tunnels in
+ Linux and attach them to Open vSwitch as system devices.
+ However, they cannot be dynamically created through the OVSDB
+ protocol or set the tunnel ids as a flow action.
+
+ Work is in progress in adding these features to the upstream
+ Linux version of the Open vSwitch kernel module. For now, if
+ you need these features, use the kernel module from the Open
+ vSwitch distribution instead of the upstream Linux kernel
+ module.
+
+ - Patch virtual ports, that is, interfaces with type "patch".
+ You can use Linux "veth" devices as a substitute.
+
+ We don't have any plans to add patch ports upstream.
+
+Q: What features are not available when using the userspace datapath?
+
+A: Tunnel and patch virtual ports are not supported, as described in the
+ previous answer. It is also not possible to use queue-related
+ actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets
+ may not be transmitted.
+
+
+Basic Configuration
+-------------------
+
+Q: How do I configure a port as an access port?
+
+A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
+ the following commands configure br0 with eth0 as a trunk port (the
+ default) and tap0 as an access port for VLAN 9:
+
+ ovs-vsctl add-br br0
+ ovs-vsctl add-port br0 eth0
+ ovs-vsctl add-port br0 tap0 tag=9
+
+ If you want to configure an already added port as an access port,
+ use "ovs-vsctl set", e.g.:
+
+ ovs-vsctl set port tap0 tag=9
+
+Q: How do I configure a port as a SPAN port, that is, enable mirroring
+ of all traffic to that port?
+
+A: The following commands configure br0 with eth0 and tap0 as trunk
+ ports. All traffic coming in or going out on eth0 or tap0 is also
+ mirrored to tap1; any traffic arriving on tap1 is dropped:
+
+ ovs-vsctl add-br br0
+ ovs-vsctl add-port br0 eth0
+ ovs-vsctl add-port br0 tap0
+ ovs-vsctl add-port br0 tap1 \
+ -- --id=@p get port tap1 \
+ -- --id=@m create mirror name=m0 select-all=true output-port=@p \
+ -- set bridge br0 mirrors=@m
+
+ To later disable mirroring, run:
+
+ ovs-vsctl clear bridge br0 mirrors
+
+Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
+ mirroring of all traffic to that VLAN?
+
+A: The following commands configure br0 with eth0 as a trunk port and
+ tap0 as an access port for VLAN 10. All traffic coming in or going
+ out on tap0, as well as traffic coming in or going out on eth0 in
+ VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
+ VLAN 10, in cases where one is present, is dropped as part of
+ mirroring:
+
+ ovs-vsctl add-br br0
+ ovs-vsctl add-port br0 eth0
+ ovs-vsctl add-port br0 tap0 tag=10
+ ovs-vsctl \
+ -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
+ output-vlan=15 \
+ -- set bridge br0 mirrors=@m
+
+ To later disable mirroring, run:
+
+ ovs-vsctl clear bridge br0 mirrors
+
+ Mirroring to a VLAN can disrupt a network that contains unmanaged
+ switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
+ GRE tunnel has fewer caveats than mirroring to a VLAN and should
+ generally be preferred.
+
+Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
+
+A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
+ of the specified output-vlan. This loss of information may make
+ the mirrored traffic too hard to interpret.
+
+ To mirror multiple VLANs, use the commands above, but specify a
+ comma-separated list of VLANs as the value for select-vlan. To
+ mirror every VLAN, use the commands above, but omit select-vlan and
+ its value entirely.
+
+ When a packet arrives on a VLAN that is used as a mirror output
+ VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
+ floods the packet across all the ports for which the mirror output
+ VLAN is configured. (If an OpenFlow controller is in use, then it
+ can override this behavior through the flow table.) If OVS is used
+ as an intermediate switch, rather than an edge switch, this ensures
+ that the RSPAN traffic is distributed through the network.
+
+ Mirroring to a VLAN can disrupt a network that contains unmanaged
+ switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
+ GRE tunnel has fewer caveats than mirroring to a VLAN and should
+ generally be preferred.
+
+Q: How do I configure mirroring of all traffic to a GRE tunnel?
+
+A: The following commands configure br0 with eth0 and tap0 as trunk
+ ports. All traffic coming in or going out on eth0 or tap0 is also
+ mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
+ traffic arriving on gre0 is dropped:
+
+ ovs-vsctl add-br br0
+ ovs-vsctl add-port br0 eth0
+ ovs-vsctl add-port br0 tap0
+ ovs-vsctl add-port br0 gre0 \
+ -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
+ -- --id=@p get port gre0 \
+ -- --id=@m create mirror name=m0 select-all=true output-port=@p \
+ -- set bridge br0 mirrors=@m
+
+ To later disable mirroring and destroy the GRE tunnel:
+
+ ovs-vsctl clear bridge br0 mirrors
+ ovs-vcstl del-port br0 gre0
+
+Q: Does Open vSwitch support ERSPAN?
+
+A: No. ERSPAN is an undocumented proprietary protocol. As an
+ alternative, Open vSwitch supports mirroring to a GRE tunnel (see
+ above).
+
+
Configuration Problems
----------------------
point, so the same problems will show up with the Linux bridge or
any other way to do bridging.
+Q: Is there any documentation on the database tables and fields?
+
+A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
+
VLANs
-----
+Q: What's a VLAN?
+
+A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
+ partition a single switch into multiple switches. Suppose, for
+ example, that you have two groups of machines, group A and group B.
+ You want the machines in group A to be able to talk to each other,
+ and you want the machine in group B to be able to talk to each
+ other, but you don't want the machines in group A to be able to
+ talk to the machines in group B. You can do this with two
+ switches, by plugging the machines in group A into one switch and
+ the machines in group B into the other switch.
+
+ If you only have one switch, then you can use VLANs to do the same
+ thing, by configuring the ports for machines in group A as VLAN
+ "access ports" for one VLAN and the ports for group B as "access
+ ports" for a different VLAN. The switch will only forward packets
+ between ports that are assigned to the same VLAN, so this
+ effectively subdivides your single switch into two independent
+ switches, one for each group of machines.
+
+ So far we haven't said anything about VLAN headers. With access
+ ports, like we've described so far, no VLAN header is present in
+ the Ethernet frame. This means that the machines (or switches)
+ connected to access ports need not be aware that VLANs are
+ involved, just like in the case where we use two different physical
+ switches.
+
+ Now suppose that you have a whole bunch of switches in your
+ network, instead of just one, and that some machines in group A are
+ connected directly to both switches 1 and 2. To allow these
+ machines to talk to each other, you could add an access port for
+ group A's VLAN to switch 1 and another to switch 2, and then
+ connect an Ethernet cable between those ports. That works fine,
+ but it doesn't scale well as the number of switches and the number
+ of VLANs increases, because you use up a lot of valuable switch
+ ports just connecting together your VLANs.
+
+ This is where VLAN headers come in. Instead of using one cable and
+ two ports per VLAN to connect a pair of switches, we configure a
+ port on each switch as a VLAN "trunk port". Packets sent and
+ received on a trunk port carry a VLAN header that says what VLAN
+ the packet belongs to, so that only two ports total are required to
+ connect the switches, regardless of the number of VLANs in use.
+ Normally, only switches (either physical or virtual) are connected
+ to a trunk port, not individual hosts, because individual hosts
+ don't expect to see a VLAN header in the traffic that they receive.
+
+ None of the above discussion says anything about particular VLAN
+ numbers. This is because VLAN numbers are completely arbitrary.
+ One must only ensure that a given VLAN is numbered consistently
+ throughout a network and that different VLANs are given different
+ numbers. (That said, VLAN 0 is usually synonymous with a packet
+ that has no VLAN header, and VLAN 4095 is reserved.)
+
Q: VLANs don't work.
A: Many drivers in Linux kernels before version 3.3 had VLAN-related
that works around bugs in kernel drivers. To enable VLAN
splinters on interface eth0, use the command:
- ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
+ ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
For VLAN splinters to be effective, Open vSwitch must know
which VLANs are in use. See the "VLAN splinters" section in
controller. This will only be suitable for some situations,
though.
+Q: I configured ports on a bridge as access ports with different VLAN
+ tags, like this:
+
+ ovs-vsctl add-br br0
+ ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
+ ovs-vsctl add-port br0 eth0
+ ovs-vsctl add-port br0 tap0 tag=9
+ ovs-vsctl add-port br0 tap1 tag=10
+
+ but the VMs running behind tap0 and tap1 can still communicate,
+ that is, they are not isolated from each other even though they are
+ on different VLANs.
+
+A: Do you have a controller configured on br0 (as the commands above
+ do)? If so, then this is a variant on the previous question, "My
+ OpenFlow controller doesn't see the VLANs that I expect," and you
+ can refer to the answer there for more information.
+
Controllers
-----------
+Q: What versions of OpenFlow does Open vSwitch support?
+
+A: Open vSwitch supports OpenFlow 1.0. It also includes a number of
+ extensions that bring many of the features from later versions of
+ OpenFlow. Work is underway to provide support for later versions and
+ can be tracked here:
+
+ http://openvswitch.org/development/openflow-1-x-plan/
+
Q: I'm getting "error type 45250 code 0". What's that?
A: This is a Open vSwitch extension to OpenFlow error codes. Open
A: See answer under "VLANs", above.
+Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
+ but I got a funny message like this:
+
+ ofp_util|INFO|normalization changed ofp_match, details:
+ ofp_util|INFO| pre: nw_dst=192.168.0.1
+ ofp_util|INFO|post:
+
+ and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
+ match had disappeared, so that the flow ends up matching every
+ packet.
+
+A: The term "normalization" in the log message means that a flow
+ cannot match on an L3 field without saying what L3 protocol is in
+ use. The "ovs-ofctl" command above didn't specify an L3 protocol,
+ so the L3 field match was dropped.
+
+ In this case, the L3 protocol could be IP or ARP. A correct
+ command for each possibility is, respectively:
+
+ ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
+
+ and
+
+ ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
+
+ Similarly, a flow cannot match on an L4 field without saying what
+ L4 protocol is in use. For example, the flow match "tp_src=1234"
+ is, by itself, meaningless and will be ignored. Instead, to match
+ TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
+ source port 1234, write "udp,tp_src=1234".
+
+Q: How can I figure out the OpenFlow port number for a given port?
+
+A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
+ respond with an OFPT_FEATURES_REPLY that, among other information,
+ includes a mapping between OpenFlow port names and numbers. From a
+ command prompt, "ovs-ofctl show br0" makes such a request and
+ prints the response for switch br0.
+
+ The Interface table in the Open vSwitch database also maps OpenFlow
+ port names to numbers. To print the OpenFlow port number
+ associated with interface eth0, run:
+
+ ovs-vsctl get Interface eth0 ofport
+
+ You can print the entire mapping with:
+
+ ovs-vsctl -- --columns=name,ofport list Interface
+
+ but the output mixes together interfaces from all bridges in the
+ database, so it may be confusing if more than one bridge exists.
+
+ In the Open vSwitch database, ofport value -1 means that the
+ interface could not be created due to an error. (The Open vSwitch
+ log should indicate the reason.) ofport value [] (the empty set)
+ means that the interface hasn't been created yet. The latter is
+ normally an intermittent condition (unless ovs-vswitchd is not
+ running).
+
+Q: I added some flows with my controller or with ovs-ofctl, but when I
+ run "ovs-dpctl dump-flows" I don't see them.
+
+A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
+ won't display the information that you want. You want to use
+ "ovs-ofctl dump-flows" instead.
+
Contact
-------
git://git.onelab.eu / sliver-openvswitch.git / blobdiff