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 features are not available in the Open vSwitch kernel datapath
132 that ships as part of the upstream Linux kernel?
134 A: The kernel module in upstream Linux 3.3 and later does not include
135 the following features:
137 - Bridge compatibility, that is, support for the ovs-brcompatd
138 daemon that (if you enable it) lets "brctl" and other Linux
139 bridge tools transparently work with Open vSwitch instead.
141 We do not expect bridge compatibility to ever be available in
142 upstream Linux. If you need bridge compatibility, use the
143 kernel module from the Open vSwitch distribution instead of the
144 upstream Linux kernel module.
146 - Tunnel virtual ports, that is, interfaces with type "gre",
147 "ipsec_gre", "capwap". It is possible to create tunnels in
148 Linux and attach them to Open vSwitch as system devices.
149 However, they cannot be dynamically created through the OVSDB
150 protocol or set the tunnel ids as a flow action.
152 Work is in progress in adding these features to the upstream
153 Linux version of the Open vSwitch kernel module. For now, if
154 you need these features, use the kernel module from the Open
155 vSwitch distribution instead of the upstream Linux kernel
158 - Patch virtual ports, that is, interfaces with type "patch".
159 You can use Linux "veth" devices as a substitute.
161 We don't have any plans to add patch ports upstream.
163 Q: What features are not available when using the userspace datapath?
165 A: Tunnel and patch virtual ports are not supported, as described in the
166 previous answer. It is also not possible to use queue-related
167 actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets
168 may not be transmitted.
174 Q: I thought Open vSwitch was a virtual Ethernet switch, but the
175 documentation keeps talking about bridges. What's a bridge?
177 A: In networking, the terms "bridge" and "switch" are synonyms. Open
178 vSwitch implements an Ethernet switch, which means that it is also
183 A: See the "VLAN" section below.
189 Q: How do I configure a port as an access port?
191 A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
192 the following commands configure br0 with eth0 as a trunk port (the
193 default) and tap0 as an access port for VLAN 9:
196 ovs-vsctl add-port br0 eth0
197 ovs-vsctl add-port br0 tap0 tag=9
199 If you want to configure an already added port as an access port,
200 use "ovs-vsctl set", e.g.:
202 ovs-vsctl set port tap0 tag=9
204 Q: How do I configure a port as a SPAN port, that is, enable mirroring
205 of all traffic to that port?
207 A: The following commands configure br0 with eth0 and tap0 as trunk
208 ports. All traffic coming in or going out on eth0 or tap0 is also
209 mirrored to tap1; any traffic arriving on tap1 is dropped:
212 ovs-vsctl add-port br0 eth0
213 ovs-vsctl add-port br0 tap0
214 ovs-vsctl add-port br0 tap1 \
215 -- --id=@p get port tap1 \
216 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
217 -- set bridge br0 mirrors=@m
219 To later disable mirroring, run:
221 ovs-vsctl clear bridge br0 mirrors
223 Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
224 mirroring of all traffic to that VLAN?
226 A: The following commands configure br0 with eth0 as a trunk port and
227 tap0 as an access port for VLAN 10. All traffic coming in or going
228 out on tap0, as well as traffic coming in or going out on eth0 in
229 VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
230 VLAN 10, in cases where one is present, is dropped as part of
234 ovs-vsctl add-port br0 eth0
235 ovs-vsctl add-port br0 tap0 tag=10
237 -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
239 -- set bridge br0 mirrors=@m
241 To later disable mirroring, run:
243 ovs-vsctl clear bridge br0 mirrors
245 Mirroring to a VLAN can disrupt a network that contains unmanaged
246 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
247 GRE tunnel has fewer caveats than mirroring to a VLAN and should
248 generally be preferred.
250 Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
252 A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
253 of the specified output-vlan. This loss of information may make
254 the mirrored traffic too hard to interpret.
256 To mirror multiple VLANs, use the commands above, but specify a
257 comma-separated list of VLANs as the value for select-vlan. To
258 mirror every VLAN, use the commands above, but omit select-vlan and
261 When a packet arrives on a VLAN that is used as a mirror output
262 VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
263 floods the packet across all the ports for which the mirror output
264 VLAN is configured. (If an OpenFlow controller is in use, then it
265 can override this behavior through the flow table.) If OVS is used
266 as an intermediate switch, rather than an edge switch, this ensures
267 that the RSPAN traffic is distributed through the network.
269 Mirroring to a VLAN can disrupt a network that contains unmanaged
270 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
271 GRE tunnel has fewer caveats than mirroring to a VLAN and should
272 generally be preferred.
274 Q: How do I configure mirroring of all traffic to a GRE tunnel?
276 A: The following commands configure br0 with eth0 and tap0 as trunk
277 ports. All traffic coming in or going out on eth0 or tap0 is also
278 mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
279 traffic arriving on gre0 is dropped:
282 ovs-vsctl add-port br0 eth0
283 ovs-vsctl add-port br0 tap0
284 ovs-vsctl add-port br0 gre0 \
285 -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
286 -- --id=@p get port gre0 \
287 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
288 -- set bridge br0 mirrors=@m
290 To later disable mirroring and destroy the GRE tunnel:
292 ovs-vsctl clear bridge br0 mirrors
293 ovs-vcstl del-port br0 gre0
295 Q: Does Open vSwitch support ERSPAN?
297 A: No. ERSPAN is an undocumented proprietary protocol. As an
298 alternative, Open vSwitch supports mirroring to a GRE tunnel (see
302 Configuration Problems
303 ----------------------
305 Q: I created a bridge and added my Ethernet port to it, using commands
309 ovs-vsctl add-port br0 eth0
311 and as soon as I ran the "add-port" command I lost all connectivity
314 A: A physical Ethernet device that is part of an Open vSwitch bridge
315 should not have an IP address. If one does, then that IP address
316 will not be fully functional.
318 You can restore functionality by moving the IP address to an Open
319 vSwitch "internal" device, such as the network device named after
320 the bridge itself. For example, assuming that eth0's IP address is
321 192.168.128.5, you could run the commands below to fix up the
324 ifconfig eth0 0.0.0.0
325 ifconfig br0 192.168.128.5
327 (If your only connection to the machine running OVS is through the
328 IP address in question, then you would want to run all of these
329 commands on a single command line, or put them into a script.) If
330 there were any additional routes assigned to eth0, then you would
331 also want to use commands to adjust these routes to go through br0.
333 If you use DHCP to obtain an IP address, then you should kill the
334 DHCP client that was listening on the physical Ethernet interface
335 (e.g. eth0) and start one listening on the internal interface
336 (e.g. br0). You might still need to manually clear the IP address
337 from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
339 There is no compelling reason why Open vSwitch must work this way.
340 However, this is the way that the Linux kernel bridge module has
341 always worked, so it's a model that those accustomed to Linux
342 bridging are already used to. Also, the model that most people
343 expect is not implementable without kernel changes on all the
344 versions of Linux that Open vSwitch supports.
346 By the way, this issue is not specific to physical Ethernet
347 devices. It applies to all network devices except Open vswitch
350 Q: I created a bridge and added a couple of Ethernet ports to it,
351 using commands like these:
354 ovs-vsctl add-port br0 eth0
355 ovs-vsctl add-port br0 eth1
357 and now my network seems to have melted: connectivity is unreliable
358 (even connectivity that doesn't go through Open vSwitch), all the
359 LEDs on my physical switches are blinking, wireshark shows
360 duplicated packets, and CPU usage is very high.
362 A: More than likely, you've looped your network. Probably, eth0 and
363 eth1 are connected to the same physical Ethernet switch. This
364 yields a scenario where OVS receives a broadcast packet on eth0 and
365 sends it out on eth1, then the physical switch connected to eth1
366 sends the packet back on eth0, and so on forever. More complicated
367 scenarios, involving a loop through multiple switches, are possible
370 The solution depends on what you are trying to do:
372 - If you added eth0 and eth1 to get higher bandwidth or higher
373 reliability between OVS and your physical Ethernet switch,
374 use a bond. The following commands create br0 and then add
375 eth0 and eth1 as a bond:
378 ovs-vsctl add-bond br0 bond0 eth0 eth1
380 Bonds have tons of configuration options. Please read the
381 documentation on the Port table in ovs-vswitchd.conf.db(5)
384 - Perhaps you don't actually need eth0 and eth1 to be on the
385 same bridge. For example, if you simply want to be able to
386 connect each of them to virtual machines, then you can put
387 each of them on a bridge of its own:
390 ovs-vsctl add-port br0 eth0
393 ovs-vsctl add-port br1 eth1
395 and then connect VMs to br0 and br1. (A potential
396 disadvantage is that traffic cannot directly pass between br0
397 and br1. Instead, it will go out eth0 and come back in eth1,
400 - If you have a redundant or complex network topology and you
401 want to prevent loops, turn on spanning tree protocol (STP).
402 The following commands create br0, enable STP, and add eth0
403 and eth1 to the bridge. The order is important because you
404 don't want have to have a loop in your network even
408 ovs-vsctl set bridge br0 stp_enable=true
409 ovs-vsctl add-port br0 eth0
410 ovs-vsctl add-port br0 eth1
412 The Open vSwitch implementation of STP is not well tested.
413 Please report any bugs you observe, but if you'd rather avoid
414 acting as a beta tester then another option might be your
417 Q: I can't seem to use Open vSwitch in a wireless network.
419 A: Wireless base stations generally only allow packets with the source
420 MAC address of NIC that completed the initial handshake.
421 Therefore, without MAC rewriting, only a single device can
422 communicate over a single wireless link.
424 This isn't specific to Open vSwitch, it's enforced by the access
425 point, so the same problems will show up with the Linux bridge or
426 any other way to do bridging.
428 Q: Is there any documentation on the database tables and fields?
430 A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
432 Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
433 I only see a datapath called "ovs-system". How can I see datapath
434 information about a particular bridge?
436 A: In version 1.9.0, OVS switched to using a single datapath that is
437 shared by all bridges of that type. The "ovs-appctl dpif/*"
438 commands provide similar functionality that is scoped by the bridge.
446 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
447 partition a single switch into multiple switches. Suppose, for
448 example, that you have two groups of machines, group A and group B.
449 You want the machines in group A to be able to talk to each other,
450 and you want the machine in group B to be able to talk to each
451 other, but you don't want the machines in group A to be able to
452 talk to the machines in group B. You can do this with two
453 switches, by plugging the machines in group A into one switch and
454 the machines in group B into the other switch.
456 If you only have one switch, then you can use VLANs to do the same
457 thing, by configuring the ports for machines in group A as VLAN
458 "access ports" for one VLAN and the ports for group B as "access
459 ports" for a different VLAN. The switch will only forward packets
460 between ports that are assigned to the same VLAN, so this
461 effectively subdivides your single switch into two independent
462 switches, one for each group of machines.
464 So far we haven't said anything about VLAN headers. With access
465 ports, like we've described so far, no VLAN header is present in
466 the Ethernet frame. This means that the machines (or switches)
467 connected to access ports need not be aware that VLANs are
468 involved, just like in the case where we use two different physical
471 Now suppose that you have a whole bunch of switches in your
472 network, instead of just one, and that some machines in group A are
473 connected directly to both switches 1 and 2. To allow these
474 machines to talk to each other, you could add an access port for
475 group A's VLAN to switch 1 and another to switch 2, and then
476 connect an Ethernet cable between those ports. That works fine,
477 but it doesn't scale well as the number of switches and the number
478 of VLANs increases, because you use up a lot of valuable switch
479 ports just connecting together your VLANs.
481 This is where VLAN headers come in. Instead of using one cable and
482 two ports per VLAN to connect a pair of switches, we configure a
483 port on each switch as a VLAN "trunk port". Packets sent and
484 received on a trunk port carry a VLAN header that says what VLAN
485 the packet belongs to, so that only two ports total are required to
486 connect the switches, regardless of the number of VLANs in use.
487 Normally, only switches (either physical or virtual) are connected
488 to a trunk port, not individual hosts, because individual hosts
489 don't expect to see a VLAN header in the traffic that they receive.
491 None of the above discussion says anything about particular VLAN
492 numbers. This is because VLAN numbers are completely arbitrary.
493 One must only ensure that a given VLAN is numbered consistently
494 throughout a network and that different VLANs are given different
495 numbers. (That said, VLAN 0 is usually synonymous with a packet
496 that has no VLAN header, and VLAN 4095 is reserved.)
500 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
501 bugs. If you are having problems with VLANs that you suspect to be
502 driver related, then you have several options:
504 - Upgrade to Linux 3.3 or later.
506 - Build and install a fixed version of the particular driver
507 that is causing trouble, if one is available.
509 - Use a NIC whose driver does not have VLAN problems.
511 - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
512 that works around bugs in kernel drivers. To enable VLAN
513 splinters on interface eth0, use the command:
515 ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
517 For VLAN splinters to be effective, Open vSwitch must know
518 which VLANs are in use. See the "VLAN splinters" section in
519 the Interface table in ovs-vswitchd.conf.db(5) for details on
520 how Open vSwitch infers in-use VLANs.
522 VLAN splinters increase memory use and reduce performance, so
523 use them only if needed.
525 - Apply the "vlan workaround" patch from the XenServer kernel
526 patch queue, build Open vSwitch against this patched kernel,
527 and then use ovs-vlan-bug-workaround(8) to enable the VLAN
528 workaround for each interface whose driver is buggy.
530 (This is a nontrivial exercise, so this option is included
531 only for completeness.)
533 It is not always easy to tell whether a Linux kernel driver has
534 buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
535 can help you test. See their manpages for details. Of the two
536 utilities, ovs-test(8) is newer and more thorough, but
537 ovs-vlan-test(8) may be easier to use.
539 Q: VLANs still don't work. I've tested the driver so I know that it's OK.
541 A: Do you have VLANs enabled on the physical switch that OVS is
542 attached to? Make sure that the port is configured to trunk the
543 VLAN or VLANs that you are using with OVS.
545 Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
546 and to its destination host, but OVS seems to drop incoming return
549 A: It's possible that you have the VLAN configured on your physical
550 switch as the "native" VLAN. In this mode, the switch treats
551 incoming packets either tagged with the native VLAN or untagged as
552 part of the native VLAN. It may also send outgoing packets in the
553 native VLAN without a VLAN tag.
555 If this is the case, you have two choices:
557 - Change the physical switch port configuration to tag packets
558 it forwards to OVS with the native VLAN instead of forwarding
561 - Change the OVS configuration for the physical port to a
562 native VLAN mode. For example, the following sets up a
563 bridge with port eth0 in "native-tagged" mode in VLAN 9:
566 ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
568 In this situation, "native-untagged" mode will probably work
569 equally well. Refer to the documentation for the Port table
570 in ovs-vswitchd.conf.db(5) for more information.
572 Q: Can I configure an IP address on a VLAN?
574 A: Yes. Use an "internal port" configured as an access port. For
575 example, the following configures IP address 192.168.0.7 on VLAN 9.
576 That is, OVS will forward packets from eth0 to 192.168.0.7 only if
577 they have an 802.1Q header with VLAN 9. Conversely, traffic
578 forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
582 ovs-vsctl add-port br0 eth0
583 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
584 ifconfig vlan9 192.168.0.7
586 Q: My OpenFlow controller doesn't see the VLANs that I expect.
588 A: The configuration for VLANs in the Open vSwitch database (e.g. via
589 ovs-vsctl) only affects traffic that goes through Open vSwitch's
590 implementation of the OpenFlow "normal switching" action. By
591 default, when Open vSwitch isn't connected to a controller and
592 nothing has been manually configured in the flow table, all traffic
593 goes through the "normal switching" action. But, if you set up
594 OpenFlow flows on your own, through a controller or using ovs-ofctl
595 or through other means, then you have to implement VLAN handling
598 You can use "normal switching" as a component of your OpenFlow
599 actions, e.g. by putting "normal" into the lists of actions on
600 ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
601 controller. This will only be suitable for some situations,
604 Q: I configured ports on a bridge as access ports with different VLAN
608 ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
609 ovs-vsctl add-port br0 eth0
610 ovs-vsctl add-port br0 tap0 tag=9
611 ovs-vsctl add-port br0 tap1 tag=10
613 but the VMs running behind tap0 and tap1 can still communicate,
614 that is, they are not isolated from each other even though they are
617 A: Do you have a controller configured on br0 (as the commands above
618 do)? If so, then this is a variant on the previous question, "My
619 OpenFlow controller doesn't see the VLANs that I expect," and you
620 can refer to the answer there for more information.
626 Q: What versions of OpenFlow does Open vSwitch support?
628 A: Open vSwitch supports OpenFlow 1.0. It also includes a number of
629 extensions that bring many of the features from later versions of
630 OpenFlow. Work is underway to provide support for later versions and
633 http://openvswitch.org/development/openflow-1-x-plan/
635 Q: I'm getting "error type 45250 code 0". What's that?
637 A: This is a Open vSwitch extension to OpenFlow error codes. Open
638 vSwitch uses this extension when it must report an error to an
639 OpenFlow controller but no standard OpenFlow error code is
642 Open vSwitch logs the errors that it sends to controllers, so the
643 easiest thing to do is probably to look at the ovs-vswitchd log to
644 find out what the error was.
646 If you want to dissect the extended error message yourself, the
647 format is documented in include/openflow/nicira-ext.h in the Open
648 vSwitch source distribution. The extended error codes are
649 documented in lib/ofp-errors.h.
651 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
652 doesn't actually appear through the OpenFlow connection, even
653 though I know that it's going through.
654 Q2: Some of the OpenFlow flows that my controller sets up don't seem
655 to apply to certain traffic, especially traffic between OVS and
656 the controller itself.
658 A: By default, Open vSwitch assumes that OpenFlow controllers are
659 connected "in-band", that is, that the controllers are actually
660 part of the network that is being controlled. In in-band mode,
661 Open vSwitch sets up special "hidden" flows to make sure that
662 traffic can make it back and forth between OVS and the controllers.
663 These hidden flows are higher priority than any flows that can be
664 set up through OpenFlow, and they are not visible through normal
665 OpenFlow flow table dumps.
667 Usually, the hidden flows are desirable and helpful, but
668 occasionally they can cause unexpected behavior. You can view the
669 full OpenFlow flow table, including hidden flows, on bridge br0
672 ovs-appctl bridge/dump-flows br0
674 to help you debug. The hidden flows are those with priorities
675 greater than 65535 (the maximum priority that can be set with
678 The DESIGN file at the top level of the Open vSwitch source
679 distribution describes the in-band model in detail.
681 If your controllers are not actually in-band (e.g. they are on
682 localhost via 127.0.0.1, or on a separate network), then you should
683 configure your controllers in "out-of-band" mode. If you have one
684 controller on bridge br0, then you can configure out-of-band mode
687 ovs-vsctl set controller br0 connection-mode=out-of-band
689 Q: I configured all my controllers for out-of-band control mode but
690 "ovs-appctl bridge/dump-flows" still shows some hidden flows.
692 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
693 set-manager"). By default, Open vSwitch assumes that managers need
694 in-band rules set up on every bridge. You can disable these rules
697 ovs-vsctl set bridge br0 other-config:disable-in-band=true
699 This actually disables in-band control entirely for the bridge, as
700 if all the bridge's controllers were configured for out-of-band
703 Q: My OpenFlow controller doesn't see the VLANs that I expect.
705 A: See answer under "VLANs", above.
707 Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
708 but I got a funny message like this:
710 ofp_util|INFO|normalization changed ofp_match, details:
711 ofp_util|INFO| pre: nw_dst=192.168.0.1
714 and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
715 match had disappeared, so that the flow ends up matching every
718 A: The term "normalization" in the log message means that a flow
719 cannot match on an L3 field without saying what L3 protocol is in
720 use. The "ovs-ofctl" command above didn't specify an L3 protocol,
721 so the L3 field match was dropped.
723 In this case, the L3 protocol could be IP or ARP. A correct
724 command for each possibility is, respectively:
726 ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
730 ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
732 Similarly, a flow cannot match on an L4 field without saying what
733 L4 protocol is in use. For example, the flow match "tp_src=1234"
734 is, by itself, meaningless and will be ignored. Instead, to match
735 TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
736 source port 1234, write "udp,tp_src=1234".
738 Q: How can I figure out the OpenFlow port number for a given port?
740 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
741 respond with an OFPT_FEATURES_REPLY that, among other information,
742 includes a mapping between OpenFlow port names and numbers. From a
743 command prompt, "ovs-ofctl show br0" makes such a request and
744 prints the response for switch br0.
746 The Interface table in the Open vSwitch database also maps OpenFlow
747 port names to numbers. To print the OpenFlow port number
748 associated with interface eth0, run:
750 ovs-vsctl get Interface eth0 ofport
752 You can print the entire mapping with:
754 ovs-vsctl -- --columns=name,ofport list Interface
756 but the output mixes together interfaces from all bridges in the
757 database, so it may be confusing if more than one bridge exists.
759 In the Open vSwitch database, ofport value -1 means that the
760 interface could not be created due to an error. (The Open vSwitch
761 log should indicate the reason.) ofport value [] (the empty set)
762 means that the interface hasn't been created yet. The latter is
763 normally an intermittent condition (unless ovs-vswitchd is not
766 Q: I added some flows with my controller or with ovs-ofctl, but when I
767 run "ovs-dpctl dump-flows" I don't see them.
769 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
770 won't display the information that you want. You want to use
771 "ovs-ofctl dump-flows" instead.
773 Q: It looks like each of the interfaces in my bonded port shows up
774 as an individual OpenFlow port. Is that right?
776 A: Yes, Open vSwitch makes individual bond interfaces visible as
777 OpenFlow ports, rather than the bond as a whole. The interfaces
778 are treated together as a bond for only a few purposes:
780 - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
781 controller is not configured, this happens implicitly to
784 - The "autopath" Nicira extension action. However, "autopath"
785 is deprecated and scheduled for removal in February 2013.
787 - Mirrors configured for output to a bonded port.
789 It would make a lot of sense for Open vSwitch to present a bond as
790 a single OpenFlow port. If you want to contribute an
791 implementation of such a feature, please bring it up on the Open
792 vSwitch development mailing list at dev@openvswitch.org.
798 http://openvswitch.org/
projects / openvswitch / blob