1 Frequently Asked Questions
2 ==========================
4 Open vSwitch <http://openvswitch.org>
9 ### Q: What is Open vSwitch?
11 A: Open vSwitch is a production quality open source software switch
12 designed to be used as a vswitch in virtualized server
13 environments. A vswitch forwards traffic between different VMs on
14 the same physical host and also forwards traffic between VMs and
15 the physical network. Open vSwitch supports standard management
16 interfaces (e.g. sFlow, NetFlow, IPFIX, RSPAN, CLI), and is open to
17 programmatic extension and control using OpenFlow and the OVSDB
20 Open vSwitch as designed to be compatible with modern switching
21 chipsets. This means that it can be ported to existing high-fanout
22 switches allowing the same flexible control of the physical
23 infrastructure as the virtual infrastructure. It also means that
24 Open vSwitch will be able to take advantage of on-NIC switching
25 chipsets as their functionality matures.
27 ### Q: What virtualization platforms can use Open vSwitch?
29 A: Open vSwitch can currently run on any Linux-based virtualization
30 platform (kernel 2.6.32 and newer), including: KVM, VirtualBox, Xen,
31 Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the
32 mainline kernel. The bulk of the code is written in platform-
33 independent C and is easily ported to other environments. We welcome
34 inquires about integrating Open vSwitch with other virtualization
37 ### Q: How can I try Open vSwitch?
39 A: The Open vSwitch source code can be built on a Linux system. You can
40 build and experiment with Open vSwitch on any Linux machine.
41 Packages for various Linux distributions are available on many
42 platforms, including: Debian, Ubuntu, Fedora.
44 You may also download and run a virtualization platform that already
45 has Open vSwitch integrated. For example, download a recent ISO for
46 XenServer or Xen Cloud Platform. Be aware that the version
47 integrated with a particular platform may not be the most recent Open
50 ### Q: Does Open vSwitch only work on Linux?
52 A: No, Open vSwitch has been ported to a number of different operating
53 systems and hardware platforms. Most of the development work occurs
54 on Linux, but the code should be portable to any POSIX system. We've
55 seen Open vSwitch ported to a number of different platforms,
56 including FreeBSD, Windows, and even non-POSIX embedded systems.
58 By definition, the Open vSwitch Linux kernel module only works on
59 Linux and will provide the highest performance. However, a userspace
60 datapath is available that should be very portable.
62 ### Q: What's involved with porting Open vSwitch to a new platform or switching ASIC?
64 A: The [PORTING.md] document describes how one would go about
65 porting Open vSwitch to a new operating system or hardware platform.
67 ### Q: Why would I use Open vSwitch instead of the Linux bridge?
69 A: Open vSwitch is specially designed to make it easier to manage VM
70 network configuration and monitor state spread across many physical
71 hosts in dynamic virtualized environments. Please see
72 [WHY-OVS.md] for a more detailed description of how Open vSwitch
73 relates to the Linux Bridge.
75 ### Q: How is Open vSwitch related to distributed virtual switches like the VMware vNetwork distributed switch or the Cisco Nexus 1000V?
77 A: Distributed vswitch applications (e.g., VMware vNetwork distributed
78 switch, Cisco Nexus 1000V) provide a centralized way to configure and
79 monitor the network state of VMs that are spread across many physical
80 hosts. Open vSwitch is not a distributed vswitch itself, rather it
81 runs on each physical host and supports remote management in a way
82 that makes it easier for developers of virtualization/cloud
83 management platforms to offer distributed vswitch capabilities.
85 To aid in distribution, Open vSwitch provides two open protocols that
86 are specially designed for remote management in virtualized network
87 environments: OpenFlow, which exposes flow-based forwarding state,
88 and the OVSDB management protocol, which exposes switch port state.
89 In addition to the switch implementation itself, Open vSwitch
90 includes tools (ovs-ofctl, ovs-vsctl) that developers can script and
91 extend to provide distributed vswitch capabilities that are closely
92 integrated with their virtualization management platform.
94 ### Q: Why doesn't Open vSwitch support distribution?
96 A: Open vSwitch is intended to be a useful component for building
97 flexible network infrastructure. There are many different approaches
98 to distribution which balance trade-offs between simplicity,
99 scalability, hardware compatibility, convergence times, logical
100 forwarding model, etc. The goal of Open vSwitch is to be able to
101 support all as a primitive building block rather than choose a
102 particular point in the distributed design space.
104 ### Q: How can I contribute to the Open vSwitch Community?
106 A: You can start by joining the mailing lists and helping to answer
107 questions. You can also suggest improvements to documentation. If
108 you have a feature or bug you would like to work on, send a mail to
109 one of the mailing lists:
111 http://openvswitch.org/mlists/
113 ### Q: Why can I no longer connect to my OpenFlow controller or OVSDB manager?
115 A: Starting in OVS 2.4, we switched the default ports to the
116 IANA-specified port numbers for OpenFlow (6633->6653) and OVSDB
117 (6632->6640). We recommend using these port numbers, but if you
118 cannot, all the programs allow overriding the default port. See the
119 appropriate man page.
125 ### Q: What does it mean for an Open vSwitch release to be LTS (long-term support)?
127 A: All official releases have been through a comprehensive testing
128 process and are suitable for production use. Planned releases will
129 occur several times a year. If a significant bug is identified in an
130 LTS release, we will provide an updated release that includes the
131 fix. Releases that are not LTS may not be fixed and may just be
132 supplanted by the next major release. The current LTS release is
135 ### Q: What Linux kernel versions does each Open vSwitch release work with?
137 A: The following table lists the Linux kernel versions against which the
138 given versions of the Open vSwitch kernel module will successfully
139 build. The Linux kernel versions are upstream kernel versions, so
140 Linux kernels modified from the upstream sources may not build in
141 some cases even if they are based on a supported version. This is
142 most notably true of Red Hat Enterprise Linux (RHEL) kernels, which
143 are extensively modified from upstream.
145 | Open vSwitch | Linux kernel
146 |:------------:|:-------------:
147 | 1.4.x | 2.6.18 to 3.2
148 | 1.5.x | 2.6.18 to 3.2
149 | 1.6.x | 2.6.18 to 3.2
150 | 1.7.x | 2.6.18 to 3.3
151 | 1.8.x | 2.6.18 to 3.4
152 | 1.9.x | 2.6.18 to 3.8
153 | 1.10.x | 2.6.18 to 3.8
154 | 1.11.x | 2.6.18 to 3.8
155 | 2.0.x | 2.6.32 to 3.10
156 | 2.1.x | 2.6.32 to 3.11
157 | 2.3.x | 2.6.32 to 3.14
158 | 2.4.x | 2.6.32 to 4.0
159 | 2.5.x | 2.6.32 to 4.1
161 Open vSwitch userspace should also work with the Linux kernel module
162 built into Linux 3.3 and later.
164 Open vSwitch userspace is not sensitive to the Linux kernel version.
165 It should build against almost any kernel, certainly against 2.6.32
168 ### Q: I get an error like this when I configure Open vSwitch:
170 configure: error: Linux kernel in <dir> is version <x>, but
171 version newer than <y> is not supported (please refer to the
176 A: You have the following options:
178 - Use the Linux kernel module supplied with the kernel that you are
179 using. (See also the following FAQ.)
181 - If there is a newer released version of Open vSwitch, consider
182 building that one, because it may support the kernel that you are
183 building against. (To find out, consult the table in the
186 - The Open vSwitch "master" branch may support the kernel that you
187 are using, so consider building the kernel module from "master".
189 All versions of Open vSwitch userspace are compatible with all
190 versions of the Open vSwitch kernel module, so you do not have to
191 use the kernel module from one source along with the userspace
192 programs from the same source.
194 ### Q: What features are not available in the Open vSwitch kernel datapath that ships as part of the upstream Linux kernel?
196 A: The kernel module in upstream Linux does not include support for
197 LISP. Work is in progress to add support for LISP to the upstream
198 Linux version of the Open vSwitch kernel module. For now, if you
199 need this feature, use the kernel module from the Open vSwitch
200 distribution instead of the upstream Linux kernel module.
202 Certain features require kernel support to function or to have
203 reasonable performance. If the ovs-vswitchd log file indicates that
204 a feature is not supported, consider upgrading to a newer upstream
205 Linux release or using the kernel module paired with the userspace
208 ### Q: Why do tunnels not work when using a kernel module other than the one packaged with Open vSwitch?
210 A: Support for tunnels was added to the upstream Linux kernel module
211 after the rest of Open vSwitch. As a result, some kernels may contain
212 support for Open vSwitch but not tunnels. The minimum kernel version
213 that supports each tunnel protocol is:
215 | Protocol | Linux Kernel
216 |:--------:|:-------------:
220 | LISP | <not upstream>
221 | STT | <not upstream>
223 If you are using a version of the kernel that is older than the one
224 listed above, it is still possible to use that tunnel protocol. However,
225 you must compile and install the kernel module included with the Open
226 vSwitch distribution rather than the one on your machine. If problems
227 persist after doing this, check to make sure that the module that is
228 loaded is the one you expect.
230 ### Q: Why are UDP tunnel checksums not computed for VXLAN or Geneve?
232 A: Generating outer UDP checksums requires kernel support that was not
233 part of the initial implementation of these protocols. If using the
234 upstream Linux Open vSwitch module, you must use kernel 4.0 or
235 newer. The out-of-tree modules from Open vSwitch release 2.4 and later
236 support UDP checksums.
238 ### Q: What features are not available when using the userspace datapath?
240 A: Tunnel virtual ports are not supported, as described in the
241 previous answer. It is also not possible to use queue-related
242 actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets
243 may not be transmitted.
245 ### Q: What Linux kernel versions does IPFIX flow monitoring work with?
247 A: IPFIX flow monitoring requires the Linux kernel module from Linux
248 3.10 or later, or the out-of-tree module from Open vSwitch version
251 ### Q: Should userspace or kernel be upgraded first to minimize downtime?
253 In general, the Open vSwitch userspace should be used with the
254 kernel version included in the same release or with the version
255 from upstream Linux. However, when upgrading between two releases
256 of Open vSwitch it is best to migrate userspace first to reduce
257 the possibility of incompatibilities.
259 ### Q: What happened to the bridge compatibility feature?
261 A: Bridge compatibility was a feature of Open vSwitch 1.9 and earlier.
262 When it was enabled, Open vSwitch imitated the interface of the
263 Linux kernel "bridge" module. This allowed users to drop Open
264 vSwitch into environments designed to use the Linux kernel bridge
265 module without adapting the environment to use Open vSwitch.
267 Open vSwitch 1.10 and later do not support bridge compatibility.
268 The feature was dropped because version 1.10 adopted a new internal
269 architecture that made bridge compatibility difficult to maintain.
270 Now that many environments use OVS directly, it would be rarely
273 To use bridge compatibility, install OVS 1.9 or earlier, including
274 the accompanying kernel modules (both the main and bridge
275 compatibility modules), following the instructions that come with
276 the release. Be sure to start the ovs-brcompatd daemon.
282 ### Q: I thought Open vSwitch was a virtual Ethernet switch, but the documentation keeps talking about bridges. What's a bridge?
284 A: In networking, the terms "bridge" and "switch" are synonyms. Open
285 vSwitch implements an Ethernet switch, which means that it is also
288 ### Q: What's a VLAN?
290 A: See the "VLAN" section below.
296 ### Q: How do I configure a port as an access port?
298 A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
299 the following commands configure br0 with eth0 as a trunk port (the
300 default) and tap0 as an access port for VLAN 9:
303 ovs-vsctl add-port br0 eth0
304 ovs-vsctl add-port br0 tap0 tag=9
306 If you want to configure an already added port as an access port,
307 use "ovs-vsctl set", e.g.:
309 ovs-vsctl set port tap0 tag=9
311 ### Q: How do I configure a port as a SPAN port, that is, enable mirroring of all traffic to that port?
313 A: The following commands configure br0 with eth0 and tap0 as trunk
314 ports. All traffic coming in or going out on eth0 or tap0 is also
315 mirrored to tap1; any traffic arriving on tap1 is dropped:
318 ovs-vsctl add-port br0 eth0
319 ovs-vsctl add-port br0 tap0
320 ovs-vsctl add-port br0 tap1 \
321 -- --id=@p get port tap1 \
322 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
323 -- set bridge br0 mirrors=@m
325 To later disable mirroring, run:
327 ovs-vsctl clear bridge br0 mirrors
329 ### Q: Does Open vSwitch support configuring a port in promiscuous mode?
331 A: Yes. How you configure it depends on what you mean by "promiscuous
334 - Conventionally, "promiscuous mode" is a feature of a network
335 interface card. Ordinarily, a NIC passes to the CPU only the
336 packets actually destined to its host machine. It discards
337 the rest to avoid wasting memory and CPU cycles. When
338 promiscuous mode is enabled, however, it passes every packet
339 to the CPU. On an old-style shared-media or hub-based
340 network, this allows the host to spy on all packets on the
341 network. But in the switched networks that are almost
342 everywhere these days, promiscuous mode doesn't have much
343 effect, because few packets not destined to a host are
344 delivered to the host's NIC.
346 This form of promiscuous mode is configured in the guest OS of
347 the VMs on your bridge, e.g. with "ifconfig".
349 - The VMware vSwitch uses a different definition of "promiscuous
350 mode". When you configure promiscuous mode on a VMware vNIC,
351 the vSwitch sends a copy of every packet received by the
352 vSwitch to that vNIC. That has a much bigger effect than just
353 enabling promiscuous mode in a guest OS. Rather than getting
354 a few stray packets for which the switch does not yet know the
355 correct destination, the vNIC gets every packet. The effect
356 is similar to replacing the vSwitch by a virtual hub.
358 This "promiscuous mode" is what switches normally call "port
359 mirroring" or "SPAN". For information on how to configure
360 SPAN, see "How do I configure a port as a SPAN port, that is,
361 enable mirroring of all traffic to that port?"
363 ### Q: How do I configure a DPDK port as an access port?
365 A: Firstly, you must have a DPDK-enabled version of Open vSwitch.
367 If your version is DPDK-enabled it will support the --dpdk
368 argument on the command line and will display lines with
369 "EAL:..." during startup when --dpdk is supplied.
371 Secondly, when adding a DPDK port, unlike a system port, the
372 type for the interface must be specified. For example;
375 ovs-vsctl add-port br0 dpdk0 -- set Interface dpdk0 type=dpdk
377 Finally, it is required that DPDK port names begin with 'dpdk'.
379 See [INSTALL.DPDK.md] for more information on enabling and using DPDK with
382 ### Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable mirroring of all traffic to that VLAN?
384 A: The following commands configure br0 with eth0 as a trunk port and
385 tap0 as an access port for VLAN 10. All traffic coming in or going
386 out on tap0, as well as traffic coming in or going out on eth0 in
387 VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
388 VLAN 10, in cases where one is present, is dropped as part of
392 ovs-vsctl add-port br0 eth0
393 ovs-vsctl add-port br0 tap0 tag=10
395 -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
397 -- set bridge br0 mirrors=@m
399 To later disable mirroring, run:
401 ovs-vsctl clear bridge br0 mirrors
403 Mirroring to a VLAN can disrupt a network that contains unmanaged
404 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
405 GRE tunnel has fewer caveats than mirroring to a VLAN and should
406 generally be preferred.
408 ### Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
410 A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
411 of the specified output-vlan. This loss of information may make
412 the mirrored traffic too hard to interpret.
414 To mirror multiple VLANs, use the commands above, but specify a
415 comma-separated list of VLANs as the value for select-vlan. To
416 mirror every VLAN, use the commands above, but omit select-vlan and
419 When a packet arrives on a VLAN that is used as a mirror output
420 VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
421 floods the packet across all the ports for which the mirror output
422 VLAN is configured. (If an OpenFlow controller is in use, then it
423 can override this behavior through the flow table.) If OVS is used
424 as an intermediate switch, rather than an edge switch, this ensures
425 that the RSPAN traffic is distributed through the network.
427 Mirroring to a VLAN can disrupt a network that contains unmanaged
428 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
429 GRE tunnel has fewer caveats than mirroring to a VLAN and should
430 generally be preferred.
432 ### Q: How do I configure mirroring of all traffic to a GRE tunnel?
434 A: The following commands configure br0 with eth0 and tap0 as trunk
435 ports. All traffic coming in or going out on eth0 or tap0 is also
436 mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
437 traffic arriving on gre0 is dropped:
440 ovs-vsctl add-port br0 eth0
441 ovs-vsctl add-port br0 tap0
442 ovs-vsctl add-port br0 gre0 \
443 -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
444 -- --id=@p get port gre0 \
445 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
446 -- set bridge br0 mirrors=@m
448 To later disable mirroring and destroy the GRE tunnel:
450 ovs-vsctl clear bridge br0 mirrors
451 ovs-vcstl del-port br0 gre0
453 ### Q: Does Open vSwitch support ERSPAN?
455 A: No. ERSPAN is an undocumented proprietary protocol. As an
456 alternative, Open vSwitch supports mirroring to a GRE tunnel (see
459 ### Q: How do I connect two bridges?
461 A: First, why do you want to do this? Two connected bridges are not
462 much different from a single bridge, so you might as well just have
463 a single bridge with all your ports on it.
465 If you still want to connect two bridges, you can use a pair of
466 patch ports. The following example creates bridges br0 and br1,
467 adds eth0 and tap0 to br0, adds tap1 to br1, and then connects br0
468 and br1 with a pair of patch ports.
471 ovs-vsctl add-port br0 eth0
472 ovs-vsctl add-port br0 tap0
474 ovs-vsctl add-port br1 tap1
476 -- add-port br0 patch0 \
477 -- set interface patch0 type=patch options:peer=patch1 \
478 -- add-port br1 patch1 \
479 -- set interface patch1 type=patch options:peer=patch0
481 Bridges connected with patch ports are much like a single bridge.
482 For instance, if the example above also added eth1 to br1, and both
483 eth0 and eth1 happened to be connected to the same next-hop switch,
484 then you could loop your network just as you would if you added
485 eth0 and eth1 to the same bridge (see the "Configuration Problems"
486 section below for more information).
488 If you are using Open vSwitch 1.9 or an earlier version, then you
489 need to be using the kernel module bundled with Open vSwitch rather
490 than the one that is integrated into Linux 3.3 and later, because
491 Open vSwitch 1.9 and earlier versions need kernel support for patch
492 ports. This also means that in Open vSwitch 1.9 and earlier, patch
493 ports will not work with the userspace datapath, only with the
496 ### Q: How do I configure a bridge without an OpenFlow local port? (Local port in the sense of OFPP_LOCAL)
498 A: Open vSwitch does not support such a configuration.
499 Bridges always have their local ports.
502 Implementation Details
503 ----------------------
505 ### Q: I hear OVS has a couple of kinds of flows. Can you tell me about them?
507 A: Open vSwitch uses different kinds of flows for different purposes:
509 - OpenFlow flows are the most important kind of flow. OpenFlow
510 controllers use these flows to define a switch's policy.
511 OpenFlow flows support wildcards, priorities, and multiple
514 When in-band control is in use, Open vSwitch sets up a few
515 "hidden" flows, with priority higher than a controller or the
516 user can configure, that are not visible via OpenFlow. (See
517 the "Controller" section of the FAQ for more information
520 - The Open vSwitch software switch implementation uses a second
521 kind of flow internally. These flows, called "datapath" or
522 "kernel" flows, do not support priorities and comprise only a
523 single table, which makes them suitable for caching. (Like
524 OpenFlow flows, datapath flows do support wildcarding, in Open
525 vSwitch 1.11 and later.) OpenFlow flows and datapath flows
526 also support different actions and number ports differently.
528 Datapath flows are an implementation detail that is subject to
529 change in future versions of Open vSwitch. Even with the
530 current version of Open vSwitch, hardware switch
531 implementations do not necessarily use this architecture.
533 Users and controllers directly control only the OpenFlow flow
534 table. Open vSwitch manages the datapath flow table itself, so
535 users should not normally be concerned with it.
537 ### Q: Why are there so many different ways to dump flows?
539 A: Open vSwitch has two kinds of flows (see the previous question), so
540 it has commands with different purposes for dumping each kind of
543 - `ovs-ofctl dump-flows <br>` dumps OpenFlow flows, excluding
544 hidden flows. This is the most commonly useful form of flow
545 dump. (Unlike the other commands, this should work with any
546 OpenFlow switch, not just Open vSwitch.)
548 - `ovs-appctl bridge/dump-flows <br>` dumps OpenFlow flows,
549 including hidden flows. This is occasionally useful for
550 troubleshooting suspected issues with in-band control.
552 - `ovs-dpctl dump-flows [dp]` dumps the datapath flow table
553 entries for a Linux kernel-based datapath. In Open vSwitch
554 1.10 and later, ovs-vswitchd merges multiple switches into a
555 single datapath, so it will show all the flows on all your
556 kernel-based switches. This command can occasionally be
557 useful for debugging.
559 - `ovs-appctl dpif/dump-flows <br>`, new in Open vSwitch 1.10,
560 dumps datapath flows for only the specified bridge, regardless
563 ### Q: How does multicast snooping works with VLANs?
565 A: Open vSwitch maintains snooping tables for each VLAN.
571 ### Q: I just upgraded and I see a performance drop. Why?
573 A: The OVS kernel datapath may have been updated to a newer version than
574 the OVS userspace components. Sometimes new versions of OVS kernel
575 module add functionality that is backwards compatible with older
576 userspace components but may cause a drop in performance with them.
577 Especially, if a kernel module from OVS 2.1 or newer is paired with
578 OVS userspace 1.10 or older, there will be a performance drop for
581 Updating the OVS userspace components to the latest released
582 version should fix the performance degradation.
584 To get the best possible performance and functionality, it is
585 recommended to pair the same versions of the kernel module and OVS
589 Configuration Problems
590 ----------------------
592 ### Q: I created a bridge and added my Ethernet port to it, using commands
596 ovs-vsctl add-port br0 eth0
598 and as soon as I ran the "add-port" command I lost all connectivity
601 A: A physical Ethernet device that is part of an Open vSwitch bridge
602 should not have an IP address. If one does, then that IP address
603 will not be fully functional.
605 You can restore functionality by moving the IP address to an Open
606 vSwitch "internal" device, such as the network device named after
607 the bridge itself. For example, assuming that eth0's IP address is
608 192.168.128.5, you could run the commands below to fix up the
611 ifconfig eth0 0.0.0.0
612 ifconfig br0 192.168.128.5
614 (If your only connection to the machine running OVS is through the
615 IP address in question, then you would want to run all of these
616 commands on a single command line, or put them into a script.) If
617 there were any additional routes assigned to eth0, then you would
618 also want to use commands to adjust these routes to go through br0.
620 If you use DHCP to obtain an IP address, then you should kill the
621 DHCP client that was listening on the physical Ethernet interface
622 (e.g. eth0) and start one listening on the internal interface
623 (e.g. br0). You might still need to manually clear the IP address
624 from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
626 There is no compelling reason why Open vSwitch must work this way.
627 However, this is the way that the Linux kernel bridge module has
628 always worked, so it's a model that those accustomed to Linux
629 bridging are already used to. Also, the model that most people
630 expect is not implementable without kernel changes on all the
631 versions of Linux that Open vSwitch supports.
633 By the way, this issue is not specific to physical Ethernet
634 devices. It applies to all network devices except Open vSwitch
637 ### Q: I created a bridge and added a couple of Ethernet ports to it,
638 ### using commands like these:
641 ovs-vsctl add-port br0 eth0
642 ovs-vsctl add-port br0 eth1
644 and now my network seems to have melted: connectivity is unreliable
645 (even connectivity that doesn't go through Open vSwitch), all the
646 LEDs on my physical switches are blinking, wireshark shows
647 duplicated packets, and CPU usage is very high.
649 A: More than likely, you've looped your network. Probably, eth0 and
650 eth1 are connected to the same physical Ethernet switch. This
651 yields a scenario where OVS receives a broadcast packet on eth0 and
652 sends it out on eth1, then the physical switch connected to eth1
653 sends the packet back on eth0, and so on forever. More complicated
654 scenarios, involving a loop through multiple switches, are possible
657 The solution depends on what you are trying to do:
659 - If you added eth0 and eth1 to get higher bandwidth or higher
660 reliability between OVS and your physical Ethernet switch,
661 use a bond. The following commands create br0 and then add
662 eth0 and eth1 as a bond:
665 ovs-vsctl add-bond br0 bond0 eth0 eth1
667 Bonds have tons of configuration options. Please read the
668 documentation on the Port table in ovs-vswitchd.conf.db(5)
671 Configuration for DPDK-enabled interfaces is slightly less
672 straightforward: see [INSTALL.DPDK.md].
674 - Perhaps you don't actually need eth0 and eth1 to be on the
675 same bridge. For example, if you simply want to be able to
676 connect each of them to virtual machines, then you can put
677 each of them on a bridge of its own:
680 ovs-vsctl add-port br0 eth0
683 ovs-vsctl add-port br1 eth1
685 and then connect VMs to br0 and br1. (A potential
686 disadvantage is that traffic cannot directly pass between br0
687 and br1. Instead, it will go out eth0 and come back in eth1,
690 - If you have a redundant or complex network topology and you
691 want to prevent loops, turn on spanning tree protocol (STP).
692 The following commands create br0, enable STP, and add eth0
693 and eth1 to the bridge. The order is important because you
694 don't want have to have a loop in your network even
698 ovs-vsctl set bridge br0 stp_enable=true
699 ovs-vsctl add-port br0 eth0
700 ovs-vsctl add-port br0 eth1
702 The Open vSwitch implementation of STP is not well tested.
703 Please report any bugs you observe, but if you'd rather avoid
704 acting as a beta tester then another option might be your
707 ### Q: I can't seem to use Open vSwitch in a wireless network.
709 A: Wireless base stations generally only allow packets with the source
710 MAC address of NIC that completed the initial handshake.
711 Therefore, without MAC rewriting, only a single device can
712 communicate over a single wireless link.
714 This isn't specific to Open vSwitch, it's enforced by the access
715 point, so the same problems will show up with the Linux bridge or
716 any other way to do bridging.
718 ### Q: I can't seem to add my PPP interface to an Open vSwitch bridge.
720 A: PPP most commonly carries IP packets, but Open vSwitch works only
721 with Ethernet frames. The correct way to interface PPP to an
722 Ethernet network is usually to use routing instead of switching.
724 ### Q: Is there any documentation on the database tables and fields?
726 A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
728 ### Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
729 I only see a datapath called "ovs-system". How can I see datapath
730 information about a particular bridge?
732 A: In version 1.9.0, OVS switched to using a single datapath that is
733 shared by all bridges of that type. The "ovs-appctl dpif/*"
734 commands provide similar functionality that is scoped by the bridge.
736 ### Q: I created a GRE port using ovs-vsctl so why can't I send traffic or
737 see the port in the datapath?
739 A: On Linux kernels before 3.11, the OVS GRE module and Linux GRE module
740 cannot be loaded at the same time. It is likely that on your system the
741 Linux GRE module is already loaded and blocking OVS (to confirm, check
742 dmesg for errors regarding GRE registration). To fix this, unload all
743 GRE modules that appear in lsmod as well as the OVS kernel module. You
744 can then reload the OVS module following the directions in
745 [INSTALL.md], which will ensure that dependencies are satisfied.
747 ### Q: Open vSwitch does not seem to obey my packet filter rules.
749 A: It depends on mechanisms and configurations you want to use.
751 You cannot usefully use typical packet filters, like iptables, on
752 physical Ethernet ports that you add to an Open vSwitch bridge.
753 This is because Open vSwitch captures packets from the interface at
754 a layer lower below where typical packet-filter implementations
755 install their hooks. (This actually applies to any interface of
756 type "system" that you might add to an Open vSwitch bridge.)
758 You can usefully use typical packet filters on Open vSwitch
759 internal ports as they are mostly ordinary interfaces from the point
760 of view of packet filters.
762 For example, suppose you create a bridge br0 and add Ethernet port
763 eth0 to it. Then you can usefully add iptables rules to affect the
764 internal interface br0, but not the physical interface eth0. (br0
765 is also where you would add an IP address, as discussed elsewhere
768 For simple filtering rules, it might be possible to achieve similar
769 results by installing appropriate OpenFlow flows instead.
771 If the use of a particular packet filter setup is essential, Open
772 vSwitch might not be the best choice for you. On Linux, you might
773 want to consider using the Linux Bridge. (This is the only choice if
774 you want to use ebtables rules.) On NetBSD, you might want to
775 consider using the bridge(4) with BRIDGE_IPF option.
777 ### Q: It seems that Open vSwitch does nothing when I removed a port and
778 then immediately put it back. For example, consider that p1 is
779 a port of type=internal:
781 ovs-vsctl del-port br0 p1 -- \
783 set interface p1 type=internal
785 A: It's an expected behaviour.
787 If del-port and add-port happen in a single OVSDB transaction as
788 your example, Open vSwitch always "skips" the intermediate steps.
789 Even if they are done in multiple transactions, it's still allowed
790 for Open vSwitch to skip the intermediate steps and just implement
791 the overall effect. In both cases, your example would be turned
794 If you want to make Open vSwitch actually destroy and then re-create
795 the port for some side effects like resetting kernel setting for the
796 corresponding interface, you need to separate operations into multiple
797 OVSDB transactions and ensure that at least the first one does not have
798 --no-wait. In the following example, the first ovs-vsctl will block
799 until Open vSwitch reloads the new configuration and removes the port:
801 ovs-vsctl del-port br0 p1
802 ovs-vsctl add-port br0 p1 -- \
803 set interface p1 type=internal
805 ### Q: I want to add thousands of ports to an Open vSwitch bridge, but
806 it takes too long (minutes or hours) to do it with ovs-vsctl. How
809 A: If you add them one at a time with ovs-vsctl, it can take a long
810 time to add thousands of ports to an Open vSwitch bridge. This is
811 because every invocation of ovs-vsctl first reads the current
812 configuration from OVSDB. As the number of ports grows, this
813 starts to take an appreciable amount of time, and when it is
814 repeated thousands of times the total time becomes significant.
816 The solution is to add the ports in one invocation of ovs-vsctl (or
817 a small number of them). For example, using bash:
820 cmds=; for i in {1..5000}; do cmds+=" -- add-port br0 p$i"; done
823 takes seconds, not minutes or hours, in the OVS sandbox environment.
825 ### Q: I created a bridge named br0. My bridge shows up in "ovs-vsctl
826 show", but "ovs-ofctl show br0" just prints "br0 is not a bridge
829 A: Open vSwitch wasn't able to create the bridge. Check the
830 ovs-vswitchd log for details (Debian and Red Hat packaging for Open
831 vSwitch put it in /var/log/openvswitch/ovs-vswitchd.log).
833 In general, the Open vSwitch database reflects the desired
834 configuration state. ovs-vswitchd monitors the database and, when
835 it changes, reconfigures the system to reflect the new desired
836 state. This normally happens very quickly. Thus, a discrepancy
837 between the database and the actual state indicates that
838 ovs-vswitchd could not implement the configuration, and so one
839 should check the log to find out why. (Another possible cause is
840 that ovs-vswitchd is not running. This will make "ovs-vsctl"
841 commands hang, if they change the configuration, unless one
842 specifies "--no-wait".)
844 ### Q: I have a bridge br0. I added a new port vif1.0, and it shows
845 up in "ovs-vsctl show", but "ovs-vsctl list port" says that it has
846 OpenFlow port ("ofport") -1, and "ovs-ofctl show br0" doesn't show
849 A: Open vSwitch wasn't able to create the port. Check the
850 ovs-vswitchd log for details (Debian and Red Hat packaging for Open
851 vSwitch put it in /var/log/openvswitch/ovs-vswitchd.log). Please
852 see the previous question for more information.
854 You may want to upgrade to Open vSwitch 2.3 (or later), in which
855 ovs-vsctl will immediately report when there is an issue creating a
858 ### Q: I created a tap device tap0, configured an IP address on it, and
859 added it to a bridge, like this:
862 ifconfig tap0 192.168.0.123
864 ovs-vsctl add-port br0 tap0
866 I expected that I could then use this IP address to contact other
867 hosts on the network, but it doesn't work. Why not?
869 A: The short answer is that this is a misuse of a "tap" device. Use
870 an "internal" device implemented by Open vSwitch, which works
871 differently and is designed for this use. To solve this problem
872 with an internal device, instead run:
875 ovs-vsctl add-port br0 int0 -- set Interface int0 type=internal
876 ifconfig int0 192.168.0.123
878 Even more simply, you can take advantage of the internal port that
879 every bridge has under the name of the bridge:
882 ifconfig br0 192.168.0.123
884 In more detail, a "tap" device is an interface between the Linux
885 (or *BSD) network stack and a user program that opens it as a
886 socket. When the "tap" device transmits a packet, it appears in
887 the socket opened by the userspace program. Conversely, when the
888 userspace program writes to the "tap" socket, the kernel TCP/IP
889 stack processes the packet as if it had been received by the "tap"
892 Consider the configuration above. Given this configuration, if you
893 "ping" an IP address in the 192.168.0.x subnet, the Linux kernel
894 routing stack will transmit an ARP on the tap0 device. Open
895 vSwitch userspace treats "tap" devices just like any other network
896 device; that is, it doesn't open them as "tap" sockets. That means
897 that the ARP packet will simply get dropped.
899 You might wonder why the Open vSwitch kernel module doesn't
900 intercept the ARP packet and bridge it. After all, Open vSwitch
901 intercepts packets on other devices. The answer is that Open
902 vSwitch only intercepts *received* packets, but this is a packet
903 being transmitted. The same thing happens for all other types of
904 network devices, except for Open vSwitch "internal" ports. If you,
905 for example, add a physical Ethernet port to an OVS bridge,
906 configure an IP address on a physical Ethernet port, and then issue
907 a "ping" to an address in that subnet, the same thing happens: an
908 ARP gets transmitted on the physical Ethernet port and Open vSwitch
909 never sees it. (You should not do that, as documented at the
910 beginning of this section.)
912 It can make sense to add a "tap" device to an Open vSwitch bridge,
913 if some userspace program (other than Open vSwitch) has opened the
914 tap socket. This is the case, for example, if the "tap" device was
915 created by KVM (or QEMU) to simulate a virtual NIC. In such a
916 case, when OVS bridges a packet to the "tap" device, the kernel
917 forwards that packet to KVM in userspace, which passes it along to
918 the VM, and in the other direction, when the VM sends a packet, KVM
919 writes it to the "tap" socket, which causes OVS to receive it and
920 bridge it to the other OVS ports. Please note that in such a case
921 no IP address is configured on the "tap" device (there is normally
922 an IP address configured in the virtual NIC inside the VM, but this
923 is not visible to the host Linux kernel or to Open vSwitch).
925 There is one special case in which Open vSwitch does directly read
926 and write "tap" sockets. This is an implementation detail of the
927 Open vSwitch userspace switch, which implements its "internal"
928 ports as Linux (or *BSD) "tap" sockets. In such a userspace
929 switch, OVS receives packets sent on the "tap" device used to
930 implement an "internal" port by reading the associated "tap"
931 socket, and bridges them to the rest of the switch. In the other
932 direction, OVS transmits packets bridged to the "internal" port by
933 writing them to the "tap" socket, causing them to be processed by
934 the kernel TCP/IP stack as if they had been received on the "tap"
935 device. Users should not need to be concerned with this
936 implementation detail.
938 Open vSwitch has a network device type called "tap". This is
939 intended only for implementing "internal" ports in the OVS
940 userspace switch and should not be used otherwise. In particular,
941 users should not configure KVM "tap" devices as type "tap" (use
942 type "system", the default, instead).
945 Quality of Service (QoS)
946 ------------------------
948 ### Q: Does OVS support Quality of Service (QoS)?
950 A: Yes. For traffic that egresses from a switch, OVS supports traffic
951 shaping; for traffic that ingresses into a switch, OVS support
952 policing. Policing is a simple form of quality-of-service that
953 simply drops packets received in excess of the configured rate. Due
954 to its simplicity, policing is usually less accurate and less
955 effective than egress traffic shaping, which queues packets.
957 Keep in mind that ingress and egress are from the perspective of the
958 switch. That means that egress shaping limits the rate at which
959 traffic is allowed to transmit from a physical interface, but the
960 rate at which traffic will be received on a virtual machine's VIF.
961 For ingress policing, the behavior is the opposite.
963 ### Q: How do I configure egress traffic shaping?
965 A: Suppose that you want to set up bridge br0 connected to physical
966 Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
967 vif1.0 and vif2.0, and that you want to limit traffic from vif1.0
968 to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps. Then, you
969 could configure the bridge this way:
973 add-port br0 eth0 -- \
974 add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \
975 add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \
976 set port eth0 qos=@newqos -- \
977 --id=@newqos create qos type=linux-htb \
978 other-config:max-rate=1000000000 \
979 queues:123=@vif10queue \
980 queues:234=@vif20queue -- \
981 --id=@vif10queue create queue other-config:max-rate=10000000 -- \
982 --id=@vif20queue create queue other-config:max-rate=20000000
984 At this point, bridge br0 is configured with the ports and eth0 is
985 configured with the queues that you need for QoS, but nothing is
986 actually directing packets from vif1.0 or vif2.0 to the queues that
987 we have set up for them. That means that all of the packets to
988 eth0 are going to the "default queue", which is not what we want.
990 We use OpenFlow to direct packets from vif1.0 and vif2.0 to the
991 queues reserved for them:
993 ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal
994 ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal
996 Each of the above flows matches on the input port, sets up the
997 appropriate queue (123 for vif1.0, 234 for vif2.0), and then
998 executes the "normal" action, which performs the same switching
999 that Open vSwitch would have done without any OpenFlow flows being
1000 present. (We know that vif1.0 and vif2.0 have OpenFlow port
1001 numbers 5 and 6, respectively, because we set their ofport_request
1002 columns above. If we had not done that, then we would have needed
1003 to find out their port numbers before setting up these flows.)
1005 Now traffic going from vif1.0 or vif2.0 to eth0 should be
1008 By the way, if you delete the bridge created by the above commands,
1011 ovs-vsctl del-br br0
1013 then that will leave one unreferenced QoS record and two
1014 unreferenced Queue records in the Open vSwich database. One way to
1015 clear them out, assuming you don't have other QoS or Queue records
1016 that you want to keep, is:
1018 ovs-vsctl -- --all destroy QoS -- --all destroy Queue
1020 If you do want to keep some QoS or Queue records, or the Open
1021 vSwitch you are using is older than version 1.8 (which added the
1022 --all option), then you will have to destroy QoS and Queue records
1025 ### Q: How do I configure ingress policing?
1027 A: A policing policy can be configured on an interface to drop packets
1028 that arrive at a higher rate than the configured value. For example,
1029 the following commands will rate-limit traffic that vif1.0 may
1032 ovs-vsctl set interface vif1.0 ingress_policing_rate=10000
1033 ovs-vsctl set interface vif1.0 ingress_policing_burst=1000
1035 Traffic policing can interact poorly with some network protocols and
1036 can have surprising results. The "Ingress Policing" section of
1037 ovs-vswitchd.conf.db(5) discusses the issues in greater detail.
1039 ### Q: I configured Quality of Service (QoS) in my OpenFlow network by
1040 adding records to the QoS and Queue table, but the results aren't
1043 A: Did you install OpenFlow flows that use your queues? This is the
1044 primary way to tell Open vSwitch which queues you want to use. If
1045 you don't do this, then the default queue will be used, which will
1046 probably not have the effect you want.
1048 Refer to the previous question for an example.
1050 ### Q: I'd like to take advantage of some QoS feature that Open vSwitch
1051 doesn't yet support. How do I do that?
1053 A: Open vSwitch does not implement QoS itself. Instead, it can
1054 configure some, but not all, of the QoS features built into the
1055 Linux kernel. If you need some QoS feature that OVS cannot
1056 configure itself, then the first step is to figure out whether
1057 Linux QoS supports that feature. If it does, then you can submit a
1058 patch to support Open vSwitch configuration for that feature, or
1059 you can use "tc" directly to configure the feature in Linux. (If
1060 Linux QoS doesn't support the feature you want, then first you have
1061 to add that support to Linux.)
1063 ### Q: I configured QoS, correctly, but my measurements show that it isn't
1064 working as well as I expect.
1066 A: With the Linux kernel, the Open vSwitch implementation of QoS has
1069 - Open vSwitch configures a subset of Linux kernel QoS
1070 features, according to what is in OVSDB. It is possible that
1071 this code has bugs. If you believe that this is so, then you
1072 can configure the Linux traffic control (QoS) stack directly
1073 with the "tc" program. If you get better results that way,
1074 you can send a detailed bug report to bugs@openvswitch.org.
1076 It is certain that Open vSwitch cannot configure every Linux
1077 kernel QoS feature. If you need some feature that OVS cannot
1078 configure, then you can also use "tc" directly (or add that
1081 - The Open vSwitch implementation of OpenFlow allows flows to
1082 be directed to particular queues. This is pretty simple and
1083 unlikely to have serious bugs at this point.
1085 However, most problems with QoS on Linux are not bugs in Open
1086 vSwitch at all. They tend to be either configuration errors
1087 (please see the earlier questions in this section) or issues with
1088 the traffic control (QoS) stack in Linux. The Open vSwitch
1089 developers are not experts on Linux traffic control. We suggest
1090 that, if you believe you are encountering a problem with Linux
1091 traffic control, that you consult the tc manpages (e.g. tc(8),
1092 tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or
1093 mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev).
1095 ### Q: Does Open vSwitch support OpenFlow meters?
1097 A: Since version 2.0, Open vSwitch has OpenFlow protocol support for
1098 OpenFlow meters. There is no implementation of meters in the Open
1099 vSwitch software switch (neither the kernel-based nor userspace
1106 ### Q: What's a VLAN?
1108 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
1109 partition a single switch into multiple switches. Suppose, for
1110 example, that you have two groups of machines, group A and group B.
1111 You want the machines in group A to be able to talk to each other,
1112 and you want the machine in group B to be able to talk to each
1113 other, but you don't want the machines in group A to be able to
1114 talk to the machines in group B. You can do this with two
1115 switches, by plugging the machines in group A into one switch and
1116 the machines in group B into the other switch.
1118 If you only have one switch, then you can use VLANs to do the same
1119 thing, by configuring the ports for machines in group A as VLAN
1120 "access ports" for one VLAN and the ports for group B as "access
1121 ports" for a different VLAN. The switch will only forward packets
1122 between ports that are assigned to the same VLAN, so this
1123 effectively subdivides your single switch into two independent
1124 switches, one for each group of machines.
1126 So far we haven't said anything about VLAN headers. With access
1127 ports, like we've described so far, no VLAN header is present in
1128 the Ethernet frame. This means that the machines (or switches)
1129 connected to access ports need not be aware that VLANs are
1130 involved, just like in the case where we use two different physical
1133 Now suppose that you have a whole bunch of switches in your
1134 network, instead of just one, and that some machines in group A are
1135 connected directly to both switches 1 and 2. To allow these
1136 machines to talk to each other, you could add an access port for
1137 group A's VLAN to switch 1 and another to switch 2, and then
1138 connect an Ethernet cable between those ports. That works fine,
1139 but it doesn't scale well as the number of switches and the number
1140 of VLANs increases, because you use up a lot of valuable switch
1141 ports just connecting together your VLANs.
1143 This is where VLAN headers come in. Instead of using one cable and
1144 two ports per VLAN to connect a pair of switches, we configure a
1145 port on each switch as a VLAN "trunk port". Packets sent and
1146 received on a trunk port carry a VLAN header that says what VLAN
1147 the packet belongs to, so that only two ports total are required to
1148 connect the switches, regardless of the number of VLANs in use.
1149 Normally, only switches (either physical or virtual) are connected
1150 to a trunk port, not individual hosts, because individual hosts
1151 don't expect to see a VLAN header in the traffic that they receive.
1153 None of the above discussion says anything about particular VLAN
1154 numbers. This is because VLAN numbers are completely arbitrary.
1155 One must only ensure that a given VLAN is numbered consistently
1156 throughout a network and that different VLANs are given different
1157 numbers. (That said, VLAN 0 is usually synonymous with a packet
1158 that has no VLAN header, and VLAN 4095 is reserved.)
1160 ### Q: VLANs don't work.
1162 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
1163 bugs. If you are having problems with VLANs that you suspect to be
1164 driver related, then you have several options:
1166 - Upgrade to Linux 3.3 or later.
1168 - Build and install a fixed version of the particular driver
1169 that is causing trouble, if one is available.
1171 - Use a NIC whose driver does not have VLAN problems.
1173 - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
1174 that works around bugs in kernel drivers. To enable VLAN
1175 splinters on interface eth0, use the command:
1177 ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
1179 For VLAN splinters to be effective, Open vSwitch must know
1180 which VLANs are in use. See the "VLAN splinters" section in
1181 the Interface table in ovs-vswitchd.conf.db(5) for details on
1182 how Open vSwitch infers in-use VLANs.
1184 VLAN splinters increase memory use and reduce performance, so
1185 use them only if needed.
1187 - Apply the "vlan workaround" patch from the XenServer kernel
1188 patch queue, build Open vSwitch against this patched kernel,
1189 and then use ovs-vlan-bug-workaround(8) to enable the VLAN
1190 workaround for each interface whose driver is buggy.
1192 (This is a nontrivial exercise, so this option is included
1193 only for completeness.)
1195 It is not always easy to tell whether a Linux kernel driver has
1196 buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
1197 can help you test. See their manpages for details. Of the two
1198 utilities, ovs-test(8) is newer and more thorough, but
1199 ovs-vlan-test(8) may be easier to use.
1201 ### Q: VLANs still don't work. I've tested the driver so I know that it's OK.
1203 A: Do you have VLANs enabled on the physical switch that OVS is
1204 attached to? Make sure that the port is configured to trunk the
1205 VLAN or VLANs that you are using with OVS.
1207 ### Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
1208 and to its destination host, but OVS seems to drop incoming return
1211 A: It's possible that you have the VLAN configured on your physical
1212 switch as the "native" VLAN. In this mode, the switch treats
1213 incoming packets either tagged with the native VLAN or untagged as
1214 part of the native VLAN. It may also send outgoing packets in the
1215 native VLAN without a VLAN tag.
1217 If this is the case, you have two choices:
1219 - Change the physical switch port configuration to tag packets
1220 it forwards to OVS with the native VLAN instead of forwarding
1223 - Change the OVS configuration for the physical port to a
1224 native VLAN mode. For example, the following sets up a
1225 bridge with port eth0 in "native-tagged" mode in VLAN 9:
1227 ovs-vsctl add-br br0
1228 ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
1230 In this situation, "native-untagged" mode will probably work
1231 equally well. Refer to the documentation for the Port table
1232 in ovs-vswitchd.conf.db(5) for more information.
1234 ### Q: I added a pair of VMs on different VLANs, like this:
1236 ovs-vsctl add-br br0
1237 ovs-vsctl add-port br0 eth0
1238 ovs-vsctl add-port br0 tap0 tag=9
1239 ovs-vsctl add-port br0 tap1 tag=10
1241 but the VMs can't access each other, the external network, or the
1244 A: It is to be expected that the VMs can't access each other. VLANs
1245 are a means to partition a network. When you configured tap0 and
1246 tap1 as access ports for different VLANs, you indicated that they
1247 should be isolated from each other.
1249 As for the external network and the Internet, it seems likely that
1250 the machines you are trying to access are not on VLAN 9 (or 10) and
1251 that the Internet is not available on VLAN 9 (or 10).
1253 ### Q: I added a pair of VMs on the same VLAN, like this:
1255 ovs-vsctl add-br br0
1256 ovs-vsctl add-port br0 eth0
1257 ovs-vsctl add-port br0 tap0 tag=9
1258 ovs-vsctl add-port br0 tap1 tag=9
1260 The VMs can access each other, but not the external network or the
1263 A: It seems likely that the machines you are trying to access in the
1264 external network are not on VLAN 9 and that the Internet is not
1265 available on VLAN 9. Also, ensure VLAN 9 is set up as an allowed
1266 trunk VLAN on the upstream switch port to which eth0 is connected.
1268 ### Q: Can I configure an IP address on a VLAN?
1270 A: Yes. Use an "internal port" configured as an access port. For
1271 example, the following configures IP address 192.168.0.7 on VLAN 9.
1272 That is, OVS will forward packets from eth0 to 192.168.0.7 only if
1273 they have an 802.1Q header with VLAN 9. Conversely, traffic
1274 forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
1277 ovs-vsctl add-br br0
1278 ovs-vsctl add-port br0 eth0
1279 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
1280 ifconfig vlan9 192.168.0.7
1282 See also the following question.
1284 ### Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
1287 ovs-vsctl add-br br0
1288 ovs-vsctl add-port br0 eth0
1289 ifconfig br0 192.168.0.5
1290 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
1291 ifconfig vlan9 192.168.0.9
1293 but other hosts that are only on VLAN 0 can reach the IP address
1294 configured on VLAN 9. What's going on?
1296 A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
1297 approaches to IP address handling in Internet hosts:
1299 - In the "Strong ES Model", where an ES is a host ("End
1300 System"), an IP address is primarily associated with a
1301 particular interface. The host discards packets that arrive
1302 on interface A if they are destined for an IP address that is
1303 configured on interface B. The host never sends packets from
1304 interface A using a source address configured on interface B.
1306 - In the "Weak ES Model", an IP address is primarily associated
1307 with a host. The host accepts packets that arrive on any
1308 interface if they are destined for any of the host's IP
1309 addresses, even if the address is configured on some
1310 interface other than the one on which it arrived. The host
1311 does not restrict itself to sending packets from an IP
1312 address associated with the originating interface.
1314 Linux uses the weak ES model. That means that when packets
1315 destined to the VLAN 9 IP address arrive on eth0 and are bridged to
1316 br0, the kernel IP stack accepts them there for the VLAN 9 IP
1317 address, even though they were not received on vlan9, the network
1320 To simulate the strong ES model on Linux, one may add iptables rule
1321 to filter packets based on source and destination address and
1322 adjust ARP configuration with sysctls.
1324 BSD uses the strong ES model.
1326 ### Q: My OpenFlow controller doesn't see the VLANs that I expect.
1328 A: The configuration for VLANs in the Open vSwitch database (e.g. via
1329 ovs-vsctl) only affects traffic that goes through Open vSwitch's
1330 implementation of the OpenFlow "normal switching" action. By
1331 default, when Open vSwitch isn't connected to a controller and
1332 nothing has been manually configured in the flow table, all traffic
1333 goes through the "normal switching" action. But, if you set up
1334 OpenFlow flows on your own, through a controller or using ovs-ofctl
1335 or through other means, then you have to implement VLAN handling
1338 You can use "normal switching" as a component of your OpenFlow
1339 actions, e.g. by putting "normal" into the lists of actions on
1340 ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
1341 controller. In situations where this is not suitable, you can
1342 implement VLAN handling yourself, e.g.:
1344 - If a packet comes in on an access port, and the flow table
1345 needs to send it out on a trunk port, then the flow can add
1346 the appropriate VLAN tag with the "mod_vlan_vid" action.
1348 - If a packet comes in on a trunk port, and the flow table
1349 needs to send it out on an access port, then the flow can
1350 strip the VLAN tag with the "strip_vlan" action.
1352 ### Q: I configured ports on a bridge as access ports with different VLAN
1355 ovs-vsctl add-br br0
1356 ovs-vsctl set-controller br0 tcp:192.168.0.10:6653
1357 ovs-vsctl add-port br0 eth0
1358 ovs-vsctl add-port br0 tap0 tag=9
1359 ovs-vsctl add-port br0 tap1 tag=10
1361 but the VMs running behind tap0 and tap1 can still communicate,
1362 that is, they are not isolated from each other even though they are
1365 A: Do you have a controller configured on br0 (as the commands above
1366 do)? If so, then this is a variant on the previous question, "My
1367 OpenFlow controller doesn't see the VLANs that I expect," and you
1368 can refer to the answer there for more information.
1370 ### Q: How MAC learning works with VLANs?
1372 A: Open vSwitch implements Independent VLAN Learning (IVL) for
1373 OFPP_NORMAL action. I.e. it logically has separate learning tables
1380 ### Q: What's a VXLAN?
1382 A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means
1383 to solve the scaling challenges of VLAN networks in a multi-tenant
1384 environment. VXLAN is an overlay network which transports an L2 network
1385 over an existing L3 network. For more information on VXLAN, please see
1388 http://tools.ietf.org/html/rfc7348
1390 ### Q: How much of the VXLAN protocol does Open vSwitch currently support?
1392 A: Open vSwitch currently supports the framing format for packets on the
1393 wire. There is currently no support for the multicast aspects of VXLAN.
1394 To get around the lack of multicast support, it is possible to
1395 pre-provision MAC to IP address mappings either manually or from a
1398 ### Q: What destination UDP port does the VXLAN implementation in Open vSwitch
1401 A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which
1402 is 4789. However, it is possible to configure the destination UDP port
1403 manually on a per-VXLAN tunnel basis. An example of this configuration is
1406 ovs-vsctl add-br br0
1407 ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1
1408 type=vxlan options:remote_ip=192.168.1.2 options:key=flow
1409 options:dst_port=8472
1412 Using OpenFlow (Manually or Via Controller)
1413 -------------------------------------------
1415 ### Q: What versions of OpenFlow does Open vSwitch support?
1417 A: The following table lists the versions of OpenFlow supported by
1418 each version of Open vSwitch:
1420 Open vSwitch OF1.0 OF1.1 OF1.2 OF1.3 OF1.4 OF1.5
1421 ###============ ===== ===== ===== ===== ===== =====
1422 1.9 and earlier yes --- --- --- --- ---
1423 1.10 yes --- [*] [*] --- ---
1424 1.11 yes --- [*] [*] --- ---
1425 2.0 yes [*] [*] [*] --- ---
1426 2.1 yes [*] [*] [*] --- ---
1427 2.2 yes [*] [*] [*] [%] [*]
1428 2.3 yes yes yes yes [*] [*]
1430 [*] Supported, with one or more missing features.
1431 [%] Experimental, unsafe implementation.
1433 Open vSwitch 2.3 enables OpenFlow 1.0, 1.1, 1.2, and 1.3 by default
1434 in ovs-vswitchd. In Open vSwitch 1.10 through 2.2, OpenFlow 1.1,
1435 1.2, and 1.3 must be enabled manually in ovs-vswitchd. OpenFlow
1436 1.4 and 1.5 are also supported, with missing features, in Open
1437 vSwitch 2.3 and later, but not enabled by default. In any case,
1438 the user may override the default:
1440 - To enable OpenFlow 1.0, 1.1, 1.2, and 1.3 on bridge br0:
1442 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
1444 - To enable OpenFlow 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5 on bridge br0:
1446 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13,OpenFlow14,OpenFlow15
1448 - To enable only OpenFlow 1.0 on bridge br0:
1450 ovs-vsctl set bridge br0 protocols=OpenFlow10
1452 All current versions of ovs-ofctl enable only OpenFlow 1.0 by
1453 default. Use the -O option to enable support for later versions of
1454 OpenFlow in ovs-ofctl. For example:
1456 ovs-ofctl -O OpenFlow13 dump-flows br0
1458 (Open vSwitch 2.2 had an experimental implementation of OpenFlow
1459 1.4 that could cause crashes. We don't recommend enabling it.)
1461 [OPENFLOW-1.1+.md] in the Open vSwitch source tree tracks support for
1462 OpenFlow 1.1 and later features. When support for OpenFlow 1.4 and
1463 1.5 is solidly implemented, Open vSwitch will enable those version
1466 ### Q: Does Open vSwitch support MPLS?
1468 A: Before version 1.11, Open vSwitch did not support MPLS. That is,
1469 these versions can match on MPLS Ethernet types, but they cannot
1470 match, push, or pop MPLS labels, nor can they look past MPLS labels
1471 into the encapsulated packet.
1473 Open vSwitch versions 1.11, 2.0, and 2.1 have very minimal support
1474 for MPLS. With the userspace datapath only, these versions can
1475 match, push, or pop a single MPLS label, but they still cannot look
1476 past MPLS labels (even after popping them) into the encapsulated
1477 packet. Kernel datapath support is unchanged from earlier
1480 Open vSwitch version 2.3 can match, push, or pop a single MPLS
1481 label and look past the MPLS label into the encapsulated packet.
1482 Both userspace and kernel datapaths will be supported, but MPLS
1483 processing always happens in userspace either way, so kernel
1484 datapath performance will be disappointing.
1486 Open vSwitch version 2.4 can match, push, or pop up to 3 MPLS
1487 labels and look past the MPLS label into the encapsulated packet.
1488 It will have kernel support for MPLS, yielding improved
1491 ### Q: I'm getting "error type 45250 code 0". What's that?
1493 A: This is a Open vSwitch extension to OpenFlow error codes. Open
1494 vSwitch uses this extension when it must report an error to an
1495 OpenFlow controller but no standard OpenFlow error code is
1498 Open vSwitch logs the errors that it sends to controllers, so the
1499 easiest thing to do is probably to look at the ovs-vswitchd log to
1500 find out what the error was.
1502 If you want to dissect the extended error message yourself, the
1503 format is documented in include/openflow/nicira-ext.h in the Open
1504 vSwitch source distribution. The extended error codes are
1505 documented in lib/ofp-errors.h.
1507 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
1508 doesn't actually appear through the OpenFlow connection, even
1509 though I know that it's going through.
1510 Q2: Some of the OpenFlow flows that my controller sets up don't seem
1511 to apply to certain traffic, especially traffic between OVS and
1512 the controller itself.
1514 A: By default, Open vSwitch assumes that OpenFlow controllers are
1515 connected "in-band", that is, that the controllers are actually
1516 part of the network that is being controlled. In in-band mode,
1517 Open vSwitch sets up special "hidden" flows to make sure that
1518 traffic can make it back and forth between OVS and the controllers.
1519 These hidden flows are higher priority than any flows that can be
1520 set up through OpenFlow, and they are not visible through normal
1521 OpenFlow flow table dumps.
1523 Usually, the hidden flows are desirable and helpful, but
1524 occasionally they can cause unexpected behavior. You can view the
1525 full OpenFlow flow table, including hidden flows, on bridge br0
1528 ovs-appctl bridge/dump-flows br0
1530 to help you debug. The hidden flows are those with priorities
1531 greater than 65535 (the maximum priority that can be set with
1534 The DESIGN file at the top level of the Open vSwitch source
1535 distribution describes the in-band model in detail.
1537 If your controllers are not actually in-band (e.g. they are on
1538 localhost via 127.0.0.1, or on a separate network), then you should
1539 configure your controllers in "out-of-band" mode. If you have one
1540 controller on bridge br0, then you can configure out-of-band mode
1543 ovs-vsctl set controller br0 connection-mode=out-of-band
1545 ### Q: I configured all my controllers for out-of-band control mode but
1546 "ovs-appctl bridge/dump-flows" still shows some hidden flows.
1548 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
1549 set-manager"). By default, Open vSwitch assumes that managers need
1550 in-band rules set up on every bridge. You can disable these rules
1553 ovs-vsctl set bridge br0 other-config:disable-in-band=true
1555 This actually disables in-band control entirely for the bridge, as
1556 if all the bridge's controllers were configured for out-of-band
1559 ### Q: My OpenFlow controller doesn't see the VLANs that I expect.
1561 A: See answer under "VLANs", above.
1563 ### Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
1564 but I got a funny message like this:
1566 ofp_util|INFO|normalization changed ofp_match, details:
1567 ofp_util|INFO| pre: nw_dst=192.168.0.1
1570 and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
1571 match had disappeared, so that the flow ends up matching every
1574 A: The term "normalization" in the log message means that a flow
1575 cannot match on an L3 field without saying what L3 protocol is in
1576 use. The "ovs-ofctl" command above didn't specify an L3 protocol,
1577 so the L3 field match was dropped.
1579 In this case, the L3 protocol could be IP or ARP. A correct
1580 command for each possibility is, respectively:
1582 ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
1586 ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
1588 Similarly, a flow cannot match on an L4 field without saying what
1589 L4 protocol is in use. For example, the flow match "tp_src=1234"
1590 is, by itself, meaningless and will be ignored. Instead, to match
1591 TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
1592 source port 1234, write "udp,tp_src=1234".
1594 ### Q: How can I figure out the OpenFlow port number for a given port?
1596 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
1597 respond with an OFPT_FEATURES_REPLY that, among other information,
1598 includes a mapping between OpenFlow port names and numbers. From a
1599 command prompt, "ovs-ofctl show br0" makes such a request and
1600 prints the response for switch br0.
1602 The Interface table in the Open vSwitch database also maps OpenFlow
1603 port names to numbers. To print the OpenFlow port number
1604 associated with interface eth0, run:
1606 ovs-vsctl get Interface eth0 ofport
1608 You can print the entire mapping with:
1610 ovs-vsctl -- --columns=name,ofport list Interface
1612 but the output mixes together interfaces from all bridges in the
1613 database, so it may be confusing if more than one bridge exists.
1615 In the Open vSwitch database, ofport value -1 means that the
1616 interface could not be created due to an error. (The Open vSwitch
1617 log should indicate the reason.) ofport value [] (the empty set)
1618 means that the interface hasn't been created yet. The latter is
1619 normally an intermittent condition (unless ovs-vswitchd is not
1622 ### Q: I added some flows with my controller or with ovs-ofctl, but when I
1623 run "ovs-dpctl dump-flows" I don't see them.
1625 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
1626 won't display the information that you want. You want to use
1627 "ovs-ofctl dump-flows" instead.
1629 ### Q: It looks like each of the interfaces in my bonded port shows up
1630 as an individual OpenFlow port. Is that right?
1632 A: Yes, Open vSwitch makes individual bond interfaces visible as
1633 OpenFlow ports, rather than the bond as a whole. The interfaces
1634 are treated together as a bond for only a few purposes:
1636 - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
1637 controller is not configured, this happens implicitly to
1640 - Mirrors configured for output to a bonded port.
1642 It would make a lot of sense for Open vSwitch to present a bond as
1643 a single OpenFlow port. If you want to contribute an
1644 implementation of such a feature, please bring it up on the Open
1645 vSwitch development mailing list at dev@openvswitch.org.
1647 ### Q: I have a sophisticated network setup involving Open vSwitch, VMs or
1648 multiple hosts, and other components. The behavior isn't what I
1651 A: To debug network behavior problems, trace the path of a packet,
1652 hop-by-hop, from its origin in one host to a remote host. If
1653 that's correct, then trace the path of the response packet back to
1656 The open source tool called "plotnetcfg" can help to understand the
1657 relationship between the networking devices on a single host.
1659 Usually a simple ICMP echo request and reply ("ping") packet is
1660 good enough. Start by initiating an ongoing "ping" from the origin
1661 host to a remote host. If you are tracking down a connectivity
1662 problem, the "ping" will not display any successful output, but
1663 packets are still being sent. (In this case the packets being sent
1664 are likely ARP rather than ICMP.)
1666 Tools available for tracing include the following:
1668 - "tcpdump" and "wireshark" for observing hops across network
1669 devices, such as Open vSwitch internal devices and physical
1672 - "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
1673 later or "ovs-dpctl dump-flows <br>" in earlier versions.
1674 These tools allow one to observe the actions being taken on
1675 packets in ongoing flows.
1677 See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
1678 documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
1679 documentation, and "Why are there so many different ways to
1680 dump flows?" above for some background.
1682 - "ovs-appctl ofproto/trace" to observe the logic behind how
1683 ovs-vswitchd treats packets. See ovs-vswitchd(8) for
1684 documentation. You can out more details about a given flow
1685 that "ovs-dpctl dump-flows" displays, by cutting and pasting
1686 a flow from the output into an "ovs-appctl ofproto/trace"
1689 - SPAN, RSPAN, and ERSPAN features of physical switches, to
1690 observe what goes on at these physical hops.
1692 Starting at the origin of a given packet, observe the packet at
1693 each hop in turn. For example, in one plausible scenario, you
1696 1. "tcpdump" the "eth" interface through which an ARP egresses
1697 a VM, from inside the VM.
1699 2. "tcpdump" the "vif" or "tap" interface through which the ARP
1700 ingresses the host machine.
1702 3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
1703 the host interface through which the ARP egresses the
1704 physical machine. You may need to use "ovs-dpctl show" to
1705 interpret the port numbers. If the output seems surprising,
1706 you can use "ovs-appctl ofproto/trace" to observe details of
1707 how ovs-vswitchd determined the actions in the "ovs-dpctl
1710 4. "tcpdump" the "eth" interface through which the ARP egresses
1711 the physical machine.
1713 5. "tcpdump" the "eth" interface through which the ARP
1714 ingresses the physical machine, at the remote host that
1717 6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
1718 remote host that receives the ARP and observe the VM "vif"
1719 or "tap" interface to which the flow is directed. Again,
1720 "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
1722 7. "tcpdump" the "vif" or "tap" interface to which the ARP is
1725 8. "tcpdump" the "eth" interface through which the ARP
1726 ingresses a VM, from inside the VM.
1728 It is likely that during one of these steps you will figure out the
1729 problem. If not, then follow the ARP reply back to the origin, in
1732 ### Q: How do I make a flow drop packets?
1734 A: To drop a packet is to receive it without forwarding it. OpenFlow
1735 explicitly specifies forwarding actions. Thus, a flow with an
1736 empty set of actions does not forward packets anywhere, causing
1737 them to be dropped. You can specify an empty set of actions with
1738 "actions=" on the ovs-ofctl command line. For example:
1740 ovs-ofctl add-flow br0 priority=65535,actions=
1742 would cause every packet entering switch br0 to be dropped.
1744 You can write "drop" explicitly if you like. The effect is the
1745 same. Thus, the following command also causes every packet
1746 entering switch br0 to be dropped:
1748 ovs-ofctl add-flow br0 priority=65535,actions=drop
1750 "drop" is not an action, either in OpenFlow or Open vSwitch.
1751 Rather, it is only a way to say that there are no actions.
1753 ### Q: I added a flow to send packets out the ingress port, like this:
1755 ovs-ofctl add-flow br0 in_port=2,actions=2
1757 but OVS drops the packets instead.
1759 A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
1760 out its ingress port. The rationale is that dropping these packets
1761 makes it harder to loop the network. Sometimes this behavior can
1762 even be convenient, e.g. it is often the desired behavior in a flow
1763 that forwards a packet to several ports ("floods" the packet).
1765 Sometimes one really needs to send a packet out its ingress port
1766 ("hairpin"). In this case, output to OFPP_IN_PORT, which in
1767 ovs-ofctl syntax is expressed as just "in_port", e.g.:
1769 ovs-ofctl add-flow br0 in_port=2,actions=in_port
1771 This also works in some circumstances where the flow doesn't match
1772 on the input port. For example, if you know that your switch has
1773 five ports numbered 2 through 6, then the following will send every
1774 received packet out every port, even its ingress port:
1776 ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
1780 ovs-ofctl add-flow br0 actions=all,in_port
1782 Sometimes, in complicated flow tables with multiple levels of
1783 "resubmit" actions, a flow needs to output to a particular port
1784 that may or may not be the ingress port. It's difficult to take
1785 advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch
1786 provides, as an OpenFlow extension, the ability to modify the
1787 in_port field. Whatever value is currently in the in_port field is
1788 the port to which outputs will be dropped, as well as the
1789 destination for OFPP_IN_PORT. This means that the following will
1790 reliably output to port 2 or to ports 2 through 6, respectively:
1792 ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
1793 ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
1795 If the input port is important, then one may save and restore it on
1798 ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
1799 load:0->NXM_OF_IN_PORT[],\
1801 pop:NXM_OF_IN_PORT[]
1803 ### Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2
1804 on port 2. I set up flows to forward only traffic destined to the
1805 other host and drop other traffic, like this:
1807 priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2
1808 priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1
1809 priority=0,actions=drop
1811 But it doesn't work--I don't get any connectivity when I do this.
1814 A: These flows drop the ARP packets that IP hosts use to establish IP
1815 connectivity over Ethernet. To solve the problem, add flows to
1816 allow ARP to pass between the hosts:
1818 priority=5,in_port=1,arp,actions=2
1819 priority=5,in_port=2,arp,actions=1
1821 This issue can manifest other ways, too. The following flows that
1822 match on Ethernet addresses instead of IP addresses will also drop
1823 ARP packets, because ARP requests are broadcast instead of being
1824 directed to a specific host:
1826 priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2
1827 priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1
1828 priority=0,actions=drop
1830 The solution already described above will also work in this case.
1831 It may be better to add flows to allow all multicast and broadcast
1834 priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
1835 priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
1837 ### Q: My bridge disconnects from my controller on add-port/del-port.
1839 A: Reconfiguring your bridge can change your bridge's datapath-id because
1840 Open vSwitch generates datapath-id from the MAC address of one of its ports.
1841 In that case, Open vSwitch disconnects from controllers because there's
1842 no graceful way to notify controllers about the change of datapath-id.
1844 To avoid the behaviour, you can configure datapath-id manually.
1846 ovs-vsctl set bridge br0 other-config:datapath-id=0123456789abcdef
1848 ### Q: My controller is getting errors about "buffers". What's going on?
1850 A: When a switch sends a packet to an OpenFlow controller using a
1851 "packet-in" message, it can also keep a copy of that packet in a
1852 "buffer", identified by a 32-bit integer "buffer_id". There are
1853 two advantages to buffering. First, when the controller wants to
1854 tell the switch to do something with the buffered packet (with a
1855 "packet-out" OpenFlow request), it does not need to send another
1856 copy of the packet back across the OpenFlow connection, which
1857 reduces the bandwidth cost of the connection and improves latency.
1858 This enables the second advantage: the switch can optionally send
1859 only the first part of the packet to the controller (assuming that
1860 the switch only needs to look at the first few bytes of the
1861 packet), further reducing bandwidth and improving latency.
1863 However, buffering introduces some issues of its own. First, any
1864 switch has limited resources, so if the controller does not use a
1865 buffered packet, the switch has to decide how long to keep it
1866 buffered. When many packets are sent to a controller and buffered,
1867 Open vSwitch can discard buffered packets that the controller has
1868 not used after as little as 5 seconds. This means that
1869 controllers, if they make use of packet buffering, should use the
1870 buffered packets promptly. (This includes sending a "packet-out"
1871 with no actions if the controller does not want to do anything with
1872 a buffered packet, to clear the packet buffer and effectively
1875 Second, packet buffers are one-time-use, meaning that a controller
1876 cannot use a single packet buffer in two or more "packet-out"
1877 commands. Open vSwitch will respond with an error to the second
1878 and subsequent "packet-out"s in such a case.
1880 Finally, a common error early in controller development is to try
1881 to use buffer_id 0 in a "packet-out" message as if 0 represented
1882 "no buffered packet". This is incorrect usage: the buffer_id with
1883 this meaning is actually 0xffffffff.
1885 ovs-vswitchd(8) describes some details of Open vSwitch packet
1886 buffering that the OpenFlow specification requires implementations
1893 ### Q: How do I implement a new OpenFlow message?
1895 A: Add your new message to "enum ofpraw" and "enum ofptype" in
1896 lib/ofp-msgs.h, following the existing pattern. Then recompile and
1897 fix all of the new warnings, implementing new functionality for the
1898 new message as needed. (If you configure with --enable-Werror, as
1899 described in [INSTALL.md], then it is impossible to miss any warnings.)
1901 If you need to add an OpenFlow vendor extension message for a
1902 vendor that doesn't yet have any extension messages, then you will
1903 also need to edit build-aux/extract-ofp-msgs.
1905 ### Q: How do I add support for a new field or header?
1907 A: Add new members for your field to "struct flow" in lib/flow.h, and
1908 add new enumerations for your new field to "enum mf_field_id" in
1909 lib/meta-flow.h, following the existing pattern. Also, add support
1910 to miniflow_extract() in lib/flow.c for extracting your new field
1911 from a packet into struct miniflow. Then recompile and fix all of
1912 the new warnings, implementing new functionality for the new field
1913 or header as needed. (If you configure with --enable-Werror, as
1914 described in [INSTALL.md], then it is impossible to miss any
1917 If you want kernel datapath support for your new field, you also
1918 need to modify the kernel module for the operating systems you are
1919 interested in. This isn't mandatory, since fields understood only
1920 by userspace work too (with a performance penalty), so it's
1921 reasonable to start development without it. If you implement
1922 kernel module support for Linux, then the Linux kernel "netdev"
1923 mailing list is the place to submit that support first; please read
1924 up on the Linux kernel development process separately. The Windows
1925 datapath kernel module support, on the other hand, is maintained
1926 within the OVS tree, so patches for that can go directly to
1929 ### Q: How do I add support for a new OpenFlow action?
1931 A: Add your new action to "enum ofp_raw_action_type" in
1932 lib/ofp-actions.c, following the existing pattern. Then recompile
1933 and fix all of the new warnings, implementing new functionality for
1934 the new action as needed. (If you configure with --enable-Werror,
1935 as described in [INSTALL.md], then it is impossible to miss any
1938 If you need to add an OpenFlow vendor extension action for a vendor
1939 that doesn't yet have any extension actions, then you will also
1940 need to edit build-aux/extract-ofp-actions.
1946 bugs@openvswitch.org
1947 http://openvswitch.org/
1949 [PORTING.md]:PORTING.md
1950 [WHY-OVS.md]:WHY-OVS.md
1951 [INSTALL.md]:INSTALL.md
1952 [OPENFLOW-1.1+.md]:OPENFLOW-1.1+.md
1953 [INSTALL.DPDK.md]:INSTALL.DPDK.md
projects / cascardo / ovs.git / blob