1 Open vSwitch <http://openvswitch.org>
3 Frequently Asked Questions
4 ==========================
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 environments. A
13 vswitch forwards traffic between different VMs on the same physical host
14 and also forwards traffic between VMs and the physical network. Open
15 vSwitch supports standard management interfaces (e.g. sFlow, NetFlow,
16 RSPAN, CLI), and is open to programmatic extension and control using
17 OpenFlow and the OVSDB management protocol.
19 Open vSwitch as designed to be compatible with modern switching
20 chipsets. This means that it can be ported to existing high-fanout
21 switches allowing the same flexible control of the physical
22 infrastructure as the virtual infrastructure. It also means that
23 Open vSwitch will be able to take advantage of on-NIC switching
24 chipsets as their functionality matures.
26 Q: What virtualization platforms can use Open vSwitch?
28 A: Open vSwitch can currently run on any Linux-based virtualization
29 platform (kernel 2.6.18 and newer), including: KVM, VirtualBox, Xen,
30 Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the
31 mainline kernel. The bulk of the code is written in platform-
32 independent C and is easily ported to other environments. We welcome
33 inquires about integrating Open vSwitch with other virtualization
36 Q: How can I try Open vSwitch?
38 A: The Open vSwitch source code can be built on a Linux system. You can
39 build and experiment with Open vSwitch on any Linux machine.
40 Packages for various Linux distributions are available on many
41 platforms, including: Debian, Ubuntu, Fedora.
43 You may also download and run a virtualization platform that already
44 has Open vSwitch integrated. For example, download a recent ISO for
45 XenServer or Xen Cloud Platform. Be aware that the version
46 integrated with a particular platform may not be the most recent Open
49 Q: Does Open vSwitch only work on Linux?
51 A: No, Open vSwitch has been ported to a number of different operating
52 systems and hardware platforms. Most of the development work occurs
53 on Linux, but the code should be portable to any POSIX system. We've
54 seen Open vSwitch ported to a number of different platforms,
55 including FreeBSD, Windows, and even non-POSIX embedded systems.
57 By definition, the Open vSwitch Linux kernel module only works on
58 Linux and will provide the highest performance. However, a userspace
59 datapath is available that should be very portable.
61 Q: What's involved with porting Open vSwitch to a new platform or
64 A: The PORTING document describes how one would go about porting Open
65 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 WHY-OVS for a
72 more detailed description of how Open vSwitch relates to the Linux
75 Q: How is Open vSwitch related to distributed virtual switches like the
76 VMware vNetwork distributed switch or the Cisco Nexus 1000V?
78 A: Distributed vswitch applications (e.g., VMware vNetwork distributed
79 switch, Cisco Nexus 1000V) provide a centralized way to configure and
80 monitor the network state of VMs that are spread across many physical
81 hosts. Open vSwitch is not a distributed vswitch itself, rather it
82 runs on each physical host and supports remote management in a way
83 that makes it easier for developers of virtualization/cloud
84 management platforms to offer distributed vswitch capabilities.
86 To aid in distribution, Open vSwitch provides two open protocols that
87 are specially designed for remote management in virtualized network
88 environments: OpenFlow, which exposes flow-based forwarding state,
89 and the OVSDB management protocol, which exposes switch port state.
90 In addition to the switch implementation itself, Open vSwitch
91 includes tools (ovs-controller, ovs-ofctl, ovs-vsctl) that developers
92 can script and extend to provide distributed vswitch capabilities
93 that are closely integrated with their virtualization management
96 Q: Why doesn't Open vSwitch support distribution?
98 A: Open vSwitch is intended to be a useful component for building
99 flexible network infrastructure. There are many different approaches
100 to distribution which balance trade-offs between simplicity,
101 scalability, hardware compatibility, convergence times, logical
102 forwarding model, etc. The goal of Open vSwitch is to be able to
103 support all as a primitive building block rather than choose a
104 particular point in the distributed design space.
106 Q: How can I contribute to the Open vSwitch Community?
108 A: You can start by joining the mailing lists and helping to answer
109 questions. You can also suggest improvements to documentation. If
110 you have a feature or bug you would like to work on, send a mail to
111 one of the mailing lists:
113 http://openvswitch.org/mlists/
120 Q: What does it mean for an Open vSwitch release to be LTS (long-term
123 A: All official releases have been through a comprehensive testing
124 process and are suitable for production use. Planned releases will
125 occur several times a year. If a significant bug is identified in an
126 LTS release, we will provide an updated release that includes the
127 fix. Releases that are not LTS may not be fixed and may just be
128 supplanted by the next major release. The current LTS release is
131 Q: What Linux kernel versions does each Open vSwitch release work with?
133 A: The following table lists the Linux kernel versions against which the
134 given versions of the Open vSwitch kernel module will successfully
135 build. The Linux kernel versions are upstream kernel versions, so
136 modified Linux kernels modified from the upstream sources may not
137 build in some cases even if they are based on a supported version.
138 This is most notably true of Red Hat Enterprise Linux (RHEL) kernels,
139 which are extensively modified from upstream.
141 Open vSwitch Linux kernel
142 ------------ -------------
150 Open vSwitch userspace should also work with the Linux kernel module
151 built into Linux 3.3 and later.
153 Open vSwitch userspace is not sensitive to the Linux kernel version.
154 It should build against almost any kernel, certainly against 2.6.18
157 Q: What features are not available in the Open vSwitch kernel datapath
158 that ships as part of the upstream Linux kernel?
160 A: The kernel module in upstream Linux 3.3 and later does not include
161 the following features:
163 - Bridge compatibility, that is, support for the ovs-brcompatd
164 daemon that (if you enable it) lets "brctl" and other Linux
165 bridge tools transparently work with Open vSwitch instead.
167 We do not expect bridge compatibility to ever be available in
168 upstream Linux. If you need bridge compatibility, use the
169 kernel module from the Open vSwitch distribution instead of the
170 upstream Linux kernel module.
172 - Tunnel virtual ports, that is, interfaces with type "gre",
173 "ipsec_gre", "capwap". It is possible to create tunnels in
174 Linux and attach them to Open vSwitch as system devices.
175 However, they cannot be dynamically created through the OVSDB
176 protocol or set the tunnel ids as a flow action.
178 Work is in progress in adding these features to the upstream
179 Linux version of the Open vSwitch kernel module. For now, if
180 you need these features, use the kernel module from the Open
181 vSwitch distribution instead of the upstream Linux kernel
184 - Patch virtual ports, that is, interfaces with type "patch".
185 You can use Linux "veth" devices as a substitute.
187 We don't have any plans to add patch ports upstream.
189 Q: What features are not available when using the userspace datapath?
191 A: Tunnel and patch virtual ports are not supported, as described in the
192 previous answer. It is also not possible to use queue-related
193 actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets
194 may not be transmitted.
200 Q: I thought Open vSwitch was a virtual Ethernet switch, but the
201 documentation keeps talking about bridges. What's a bridge?
203 A: In networking, the terms "bridge" and "switch" are synonyms. Open
204 vSwitch implements an Ethernet switch, which means that it is also
209 A: See the "VLAN" section below.
215 Q: How do I configure a port as an access port?
217 A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
218 the following commands configure br0 with eth0 as a trunk port (the
219 default) and tap0 as an access port for VLAN 9:
222 ovs-vsctl add-port br0 eth0
223 ovs-vsctl add-port br0 tap0 tag=9
225 If you want to configure an already added port as an access port,
226 use "ovs-vsctl set", e.g.:
228 ovs-vsctl set port tap0 tag=9
230 Q: How do I configure a port as a SPAN port, that is, enable mirroring
231 of all traffic to that port?
233 A: The following commands configure br0 with eth0 and tap0 as trunk
234 ports. All traffic coming in or going out on eth0 or tap0 is also
235 mirrored to tap1; any traffic arriving on tap1 is dropped:
238 ovs-vsctl add-port br0 eth0
239 ovs-vsctl add-port br0 tap0
240 ovs-vsctl add-port br0 tap1 \
241 -- --id=@p get port tap1 \
242 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
243 -- set bridge br0 mirrors=@m
245 To later disable mirroring, run:
247 ovs-vsctl clear bridge br0 mirrors
249 Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
250 mirroring of all traffic to that VLAN?
252 A: The following commands configure br0 with eth0 as a trunk port and
253 tap0 as an access port for VLAN 10. All traffic coming in or going
254 out on tap0, as well as traffic coming in or going out on eth0 in
255 VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
256 VLAN 10, in cases where one is present, is dropped as part of
260 ovs-vsctl add-port br0 eth0
261 ovs-vsctl add-port br0 tap0 tag=10
263 -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
265 -- set bridge br0 mirrors=@m
267 To later disable mirroring, run:
269 ovs-vsctl clear bridge br0 mirrors
271 Mirroring to a VLAN can disrupt a network that contains unmanaged
272 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
273 GRE tunnel has fewer caveats than mirroring to a VLAN and should
274 generally be preferred.
276 Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
278 A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
279 of the specified output-vlan. This loss of information may make
280 the mirrored traffic too hard to interpret.
282 To mirror multiple VLANs, use the commands above, but specify a
283 comma-separated list of VLANs as the value for select-vlan. To
284 mirror every VLAN, use the commands above, but omit select-vlan and
287 When a packet arrives on a VLAN that is used as a mirror output
288 VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
289 floods the packet across all the ports for which the mirror output
290 VLAN is configured. (If an OpenFlow controller is in use, then it
291 can override this behavior through the flow table.) If OVS is used
292 as an intermediate switch, rather than an edge switch, this ensures
293 that the RSPAN traffic is distributed through the network.
295 Mirroring to a VLAN can disrupt a network that contains unmanaged
296 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
297 GRE tunnel has fewer caveats than mirroring to a VLAN and should
298 generally be preferred.
300 Q: How do I configure mirroring of all traffic to a GRE tunnel?
302 A: The following commands configure br0 with eth0 and tap0 as trunk
303 ports. All traffic coming in or going out on eth0 or tap0 is also
304 mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
305 traffic arriving on gre0 is dropped:
308 ovs-vsctl add-port br0 eth0
309 ovs-vsctl add-port br0 tap0
310 ovs-vsctl add-port br0 gre0 \
311 -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
312 -- --id=@p get port gre0 \
313 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
314 -- set bridge br0 mirrors=@m
316 To later disable mirroring and destroy the GRE tunnel:
318 ovs-vsctl clear bridge br0 mirrors
319 ovs-vcstl del-port br0 gre0
321 Q: Does Open vSwitch support ERSPAN?
323 A: No. ERSPAN is an undocumented proprietary protocol. As an
324 alternative, Open vSwitch supports mirroring to a GRE tunnel (see
328 Configuration Problems
329 ----------------------
331 Q: I created a bridge and added my Ethernet port to it, using commands
335 ovs-vsctl add-port br0 eth0
337 and as soon as I ran the "add-port" command I lost all connectivity
340 A: A physical Ethernet device that is part of an Open vSwitch bridge
341 should not have an IP address. If one does, then that IP address
342 will not be fully functional.
344 You can restore functionality by moving the IP address to an Open
345 vSwitch "internal" device, such as the network device named after
346 the bridge itself. For example, assuming that eth0's IP address is
347 192.168.128.5, you could run the commands below to fix up the
350 ifconfig eth0 0.0.0.0
351 ifconfig br0 192.168.128.5
353 (If your only connection to the machine running OVS is through the
354 IP address in question, then you would want to run all of these
355 commands on a single command line, or put them into a script.) If
356 there were any additional routes assigned to eth0, then you would
357 also want to use commands to adjust these routes to go through br0.
359 If you use DHCP to obtain an IP address, then you should kill the
360 DHCP client that was listening on the physical Ethernet interface
361 (e.g. eth0) and start one listening on the internal interface
362 (e.g. br0). You might still need to manually clear the IP address
363 from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
365 There is no compelling reason why Open vSwitch must work this way.
366 However, this is the way that the Linux kernel bridge module has
367 always worked, so it's a model that those accustomed to Linux
368 bridging are already used to. Also, the model that most people
369 expect is not implementable without kernel changes on all the
370 versions of Linux that Open vSwitch supports.
372 By the way, this issue is not specific to physical Ethernet
373 devices. It applies to all network devices except Open vswitch
376 Q: I created a bridge and added a couple of Ethernet ports to it,
377 using commands like these:
380 ovs-vsctl add-port br0 eth0
381 ovs-vsctl add-port br0 eth1
383 and now my network seems to have melted: connectivity is unreliable
384 (even connectivity that doesn't go through Open vSwitch), all the
385 LEDs on my physical switches are blinking, wireshark shows
386 duplicated packets, and CPU usage is very high.
388 A: More than likely, you've looped your network. Probably, eth0 and
389 eth1 are connected to the same physical Ethernet switch. This
390 yields a scenario where OVS receives a broadcast packet on eth0 and
391 sends it out on eth1, then the physical switch connected to eth1
392 sends the packet back on eth0, and so on forever. More complicated
393 scenarios, involving a loop through multiple switches, are possible
396 The solution depends on what you are trying to do:
398 - If you added eth0 and eth1 to get higher bandwidth or higher
399 reliability between OVS and your physical Ethernet switch,
400 use a bond. The following commands create br0 and then add
401 eth0 and eth1 as a bond:
404 ovs-vsctl add-bond br0 bond0 eth0 eth1
406 Bonds have tons of configuration options. Please read the
407 documentation on the Port table in ovs-vswitchd.conf.db(5)
410 - Perhaps you don't actually need eth0 and eth1 to be on the
411 same bridge. For example, if you simply want to be able to
412 connect each of them to virtual machines, then you can put
413 each of them on a bridge of its own:
416 ovs-vsctl add-port br0 eth0
419 ovs-vsctl add-port br1 eth1
421 and then connect VMs to br0 and br1. (A potential
422 disadvantage is that traffic cannot directly pass between br0
423 and br1. Instead, it will go out eth0 and come back in eth1,
426 - If you have a redundant or complex network topology and you
427 want to prevent loops, turn on spanning tree protocol (STP).
428 The following commands create br0, enable STP, and add eth0
429 and eth1 to the bridge. The order is important because you
430 don't want have to have a loop in your network even
434 ovs-vsctl set bridge br0 stp_enable=true
435 ovs-vsctl add-port br0 eth0
436 ovs-vsctl add-port br0 eth1
438 The Open vSwitch implementation of STP is not well tested.
439 Please report any bugs you observe, but if you'd rather avoid
440 acting as a beta tester then another option might be your
443 Q: I can't seem to use Open vSwitch in a wireless network.
445 A: Wireless base stations generally only allow packets with the source
446 MAC address of NIC that completed the initial handshake.
447 Therefore, without MAC rewriting, only a single device can
448 communicate over a single wireless link.
450 This isn't specific to Open vSwitch, it's enforced by the access
451 point, so the same problems will show up with the Linux bridge or
452 any other way to do bridging.
454 Q: Is there any documentation on the database tables and fields?
456 A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
458 Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
459 I only see a datapath called "ovs-system". How can I see datapath
460 information about a particular bridge?
462 A: In version 1.9.0, OVS switched to using a single datapath that is
463 shared by all bridges of that type. The "ovs-appctl dpif/*"
464 commands provide similar functionality that is scoped by the bridge.
472 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
473 partition a single switch into multiple switches. Suppose, for
474 example, that you have two groups of machines, group A and group B.
475 You want the machines in group A to be able to talk to each other,
476 and you want the machine in group B to be able to talk to each
477 other, but you don't want the machines in group A to be able to
478 talk to the machines in group B. You can do this with two
479 switches, by plugging the machines in group A into one switch and
480 the machines in group B into the other switch.
482 If you only have one switch, then you can use VLANs to do the same
483 thing, by configuring the ports for machines in group A as VLAN
484 "access ports" for one VLAN and the ports for group B as "access
485 ports" for a different VLAN. The switch will only forward packets
486 between ports that are assigned to the same VLAN, so this
487 effectively subdivides your single switch into two independent
488 switches, one for each group of machines.
490 So far we haven't said anything about VLAN headers. With access
491 ports, like we've described so far, no VLAN header is present in
492 the Ethernet frame. This means that the machines (or switches)
493 connected to access ports need not be aware that VLANs are
494 involved, just like in the case where we use two different physical
497 Now suppose that you have a whole bunch of switches in your
498 network, instead of just one, and that some machines in group A are
499 connected directly to both switches 1 and 2. To allow these
500 machines to talk to each other, you could add an access port for
501 group A's VLAN to switch 1 and another to switch 2, and then
502 connect an Ethernet cable between those ports. That works fine,
503 but it doesn't scale well as the number of switches and the number
504 of VLANs increases, because you use up a lot of valuable switch
505 ports just connecting together your VLANs.
507 This is where VLAN headers come in. Instead of using one cable and
508 two ports per VLAN to connect a pair of switches, we configure a
509 port on each switch as a VLAN "trunk port". Packets sent and
510 received on a trunk port carry a VLAN header that says what VLAN
511 the packet belongs to, so that only two ports total are required to
512 connect the switches, regardless of the number of VLANs in use.
513 Normally, only switches (either physical or virtual) are connected
514 to a trunk port, not individual hosts, because individual hosts
515 don't expect to see a VLAN header in the traffic that they receive.
517 None of the above discussion says anything about particular VLAN
518 numbers. This is because VLAN numbers are completely arbitrary.
519 One must only ensure that a given VLAN is numbered consistently
520 throughout a network and that different VLANs are given different
521 numbers. (That said, VLAN 0 is usually synonymous with a packet
522 that has no VLAN header, and VLAN 4095 is reserved.)
526 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
527 bugs. If you are having problems with VLANs that you suspect to be
528 driver related, then you have several options:
530 - Upgrade to Linux 3.3 or later.
532 - Build and install a fixed version of the particular driver
533 that is causing trouble, if one is available.
535 - Use a NIC whose driver does not have VLAN problems.
537 - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
538 that works around bugs in kernel drivers. To enable VLAN
539 splinters on interface eth0, use the command:
541 ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
543 For VLAN splinters to be effective, Open vSwitch must know
544 which VLANs are in use. See the "VLAN splinters" section in
545 the Interface table in ovs-vswitchd.conf.db(5) for details on
546 how Open vSwitch infers in-use VLANs.
548 VLAN splinters increase memory use and reduce performance, so
549 use them only if needed.
551 - Apply the "vlan workaround" patch from the XenServer kernel
552 patch queue, build Open vSwitch against this patched kernel,
553 and then use ovs-vlan-bug-workaround(8) to enable the VLAN
554 workaround for each interface whose driver is buggy.
556 (This is a nontrivial exercise, so this option is included
557 only for completeness.)
559 It is not always easy to tell whether a Linux kernel driver has
560 buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
561 can help you test. See their manpages for details. Of the two
562 utilities, ovs-test(8) is newer and more thorough, but
563 ovs-vlan-test(8) may be easier to use.
565 Q: VLANs still don't work. I've tested the driver so I know that it's OK.
567 A: Do you have VLANs enabled on the physical switch that OVS is
568 attached to? Make sure that the port is configured to trunk the
569 VLAN or VLANs that you are using with OVS.
571 Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
572 and to its destination host, but OVS seems to drop incoming return
575 A: It's possible that you have the VLAN configured on your physical
576 switch as the "native" VLAN. In this mode, the switch treats
577 incoming packets either tagged with the native VLAN or untagged as
578 part of the native VLAN. It may also send outgoing packets in the
579 native VLAN without a VLAN tag.
581 If this is the case, you have two choices:
583 - Change the physical switch port configuration to tag packets
584 it forwards to OVS with the native VLAN instead of forwarding
587 - Change the OVS configuration for the physical port to a
588 native VLAN mode. For example, the following sets up a
589 bridge with port eth0 in "native-tagged" mode in VLAN 9:
592 ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
594 In this situation, "native-untagged" mode will probably work
595 equally well. Refer to the documentation for the Port table
596 in ovs-vswitchd.conf.db(5) for more information.
598 Q: I added a pair of VMs on different VLANs, like this:
601 ovs-vsctl add-port br0 eth0
602 ovs-vsctl add-port br0 tap0 tag=9
603 ovs-vsctl add-port br0 tap1 tag=10
605 but the VMs can't access each other, the external network, or the
608 A: It is to be expected that the VMs can't access each other. VLANs
609 are a means to partition a network. When you configured tap0 and
610 tap1 as access ports for different VLANs, you indicated that they
611 should be isolated from each other.
613 As for the external network and the Internet, it seems likely that
614 the machines you are trying to access are not on VLAN 9 (or 10) and
615 that the Internet is not available on VLAN 9 (or 10).
617 Q: Can I configure an IP address on a VLAN?
619 A: Yes. Use an "internal port" configured as an access port. For
620 example, the following configures IP address 192.168.0.7 on VLAN 9.
621 That is, OVS will forward packets from eth0 to 192.168.0.7 only if
622 they have an 802.1Q header with VLAN 9. Conversely, traffic
623 forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
627 ovs-vsctl add-port br0 eth0
628 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
629 ifconfig vlan9 192.168.0.7
631 Q: My OpenFlow controller doesn't see the VLANs that I expect.
633 A: The configuration for VLANs in the Open vSwitch database (e.g. via
634 ovs-vsctl) only affects traffic that goes through Open vSwitch's
635 implementation of the OpenFlow "normal switching" action. By
636 default, when Open vSwitch isn't connected to a controller and
637 nothing has been manually configured in the flow table, all traffic
638 goes through the "normal switching" action. But, if you set up
639 OpenFlow flows on your own, through a controller or using ovs-ofctl
640 or through other means, then you have to implement VLAN handling
643 You can use "normal switching" as a component of your OpenFlow
644 actions, e.g. by putting "normal" into the lists of actions on
645 ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
646 controller. This will only be suitable for some situations,
649 Q: I configured ports on a bridge as access ports with different VLAN
653 ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
654 ovs-vsctl add-port br0 eth0
655 ovs-vsctl add-port br0 tap0 tag=9
656 ovs-vsctl add-port br0 tap1 tag=10
658 but the VMs running behind tap0 and tap1 can still communicate,
659 that is, they are not isolated from each other even though they are
662 A: Do you have a controller configured on br0 (as the commands above
663 do)? If so, then this is a variant on the previous question, "My
664 OpenFlow controller doesn't see the VLANs that I expect," and you
665 can refer to the answer there for more information.
671 Q: What versions of OpenFlow does Open vSwitch support?
673 A: Open vSwitch supports OpenFlow 1.0. It also includes a number of
674 extensions that bring many of the features from later versions of
675 OpenFlow. Work is underway to provide support for later versions and
678 http://openvswitch.org/development/openflow-1-x-plan/
680 Q: I'm getting "error type 45250 code 0". What's that?
682 A: This is a Open vSwitch extension to OpenFlow error codes. Open
683 vSwitch uses this extension when it must report an error to an
684 OpenFlow controller but no standard OpenFlow error code is
687 Open vSwitch logs the errors that it sends to controllers, so the
688 easiest thing to do is probably to look at the ovs-vswitchd log to
689 find out what the error was.
691 If you want to dissect the extended error message yourself, the
692 format is documented in include/openflow/nicira-ext.h in the Open
693 vSwitch source distribution. The extended error codes are
694 documented in lib/ofp-errors.h.
696 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
697 doesn't actually appear through the OpenFlow connection, even
698 though I know that it's going through.
699 Q2: Some of the OpenFlow flows that my controller sets up don't seem
700 to apply to certain traffic, especially traffic between OVS and
701 the controller itself.
703 A: By default, Open vSwitch assumes that OpenFlow controllers are
704 connected "in-band", that is, that the controllers are actually
705 part of the network that is being controlled. In in-band mode,
706 Open vSwitch sets up special "hidden" flows to make sure that
707 traffic can make it back and forth between OVS and the controllers.
708 These hidden flows are higher priority than any flows that can be
709 set up through OpenFlow, and they are not visible through normal
710 OpenFlow flow table dumps.
712 Usually, the hidden flows are desirable and helpful, but
713 occasionally they can cause unexpected behavior. You can view the
714 full OpenFlow flow table, including hidden flows, on bridge br0
717 ovs-appctl bridge/dump-flows br0
719 to help you debug. The hidden flows are those with priorities
720 greater than 65535 (the maximum priority that can be set with
723 The DESIGN file at the top level of the Open vSwitch source
724 distribution describes the in-band model in detail.
726 If your controllers are not actually in-band (e.g. they are on
727 localhost via 127.0.0.1, or on a separate network), then you should
728 configure your controllers in "out-of-band" mode. If you have one
729 controller on bridge br0, then you can configure out-of-band mode
732 ovs-vsctl set controller br0 connection-mode=out-of-band
734 Q: I configured all my controllers for out-of-band control mode but
735 "ovs-appctl bridge/dump-flows" still shows some hidden flows.
737 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
738 set-manager"). By default, Open vSwitch assumes that managers need
739 in-band rules set up on every bridge. You can disable these rules
742 ovs-vsctl set bridge br0 other-config:disable-in-band=true
744 This actually disables in-band control entirely for the bridge, as
745 if all the bridge's controllers were configured for out-of-band
748 Q: My OpenFlow controller doesn't see the VLANs that I expect.
750 A: See answer under "VLANs", above.
752 Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
753 but I got a funny message like this:
755 ofp_util|INFO|normalization changed ofp_match, details:
756 ofp_util|INFO| pre: nw_dst=192.168.0.1
759 and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
760 match had disappeared, so that the flow ends up matching every
763 A: The term "normalization" in the log message means that a flow
764 cannot match on an L3 field without saying what L3 protocol is in
765 use. The "ovs-ofctl" command above didn't specify an L3 protocol,
766 so the L3 field match was dropped.
768 In this case, the L3 protocol could be IP or ARP. A correct
769 command for each possibility is, respectively:
771 ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
775 ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
777 Similarly, a flow cannot match on an L4 field without saying what
778 L4 protocol is in use. For example, the flow match "tp_src=1234"
779 is, by itself, meaningless and will be ignored. Instead, to match
780 TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
781 source port 1234, write "udp,tp_src=1234".
783 Q: How can I figure out the OpenFlow port number for a given port?
785 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
786 respond with an OFPT_FEATURES_REPLY that, among other information,
787 includes a mapping between OpenFlow port names and numbers. From a
788 command prompt, "ovs-ofctl show br0" makes such a request and
789 prints the response for switch br0.
791 The Interface table in the Open vSwitch database also maps OpenFlow
792 port names to numbers. To print the OpenFlow port number
793 associated with interface eth0, run:
795 ovs-vsctl get Interface eth0 ofport
797 You can print the entire mapping with:
799 ovs-vsctl -- --columns=name,ofport list Interface
801 but the output mixes together interfaces from all bridges in the
802 database, so it may be confusing if more than one bridge exists.
804 In the Open vSwitch database, ofport value -1 means that the
805 interface could not be created due to an error. (The Open vSwitch
806 log should indicate the reason.) ofport value [] (the empty set)
807 means that the interface hasn't been created yet. The latter is
808 normally an intermittent condition (unless ovs-vswitchd is not
811 Q: I added some flows with my controller or with ovs-ofctl, but when I
812 run "ovs-dpctl dump-flows" I don't see them.
814 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
815 won't display the information that you want. You want to use
816 "ovs-ofctl dump-flows" instead.
818 Q: It looks like each of the interfaces in my bonded port shows up
819 as an individual OpenFlow port. Is that right?
821 A: Yes, Open vSwitch makes individual bond interfaces visible as
822 OpenFlow ports, rather than the bond as a whole. The interfaces
823 are treated together as a bond for only a few purposes:
825 - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
826 controller is not configured, this happens implicitly to
829 - The "autopath" Nicira extension action. However, "autopath"
830 is deprecated and scheduled for removal in February 2013.
832 - Mirrors configured for output to a bonded port.
834 It would make a lot of sense for Open vSwitch to present a bond as
835 a single OpenFlow port. If you want to contribute an
836 implementation of such a feature, please bring it up on the Open
837 vSwitch development mailing list at dev@openvswitch.org.
843 http://openvswitch.org/
git://git.onelab.eu / sliver-openvswitch.git / blob