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
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
65 A: The PORTING document describes how one would go about porting Open
66 vSwitch to a new operating system or hardware platform.
68 Q: Why would I use Open vSwitch instead of the Linux bridge?
70 A: Open vSwitch is specially designed to make it easier to manage VM
71 network configuration and monitor state spread across many physical
72 hosts in dynamic virtualized environments. Please see WHY-OVS for a
73 more detailed description of how Open vSwitch relates to the Linux
76 Q: How is Open vSwitch related to distributed virtual switches like the
77 VMware vNetwork distributed switch or the Cisco Nexus 1000V?
79 A: Distributed vswitch applications (e.g., VMware vNetwork distributed
80 switch, Cisco Nexus 1000V) provide a centralized way to configure and
81 monitor the network state of VMs that are spread across many physical
82 hosts. Open vSwitch is not a distributed vswitch itself, rather it
83 runs on each physical host and supports remote management in a way
84 that makes it easier for developers of virtualization/cloud
85 management platforms to offer distributed vswitch capabilities.
87 To aid in distribution, Open vSwitch provides two open protocols that
88 are specially designed for remote management in virtualized network
89 environments: OpenFlow, which exposes flow-based forwarding state,
90 and the OVSDB management protocol, which exposes switch port state.
91 In addition to the switch implementation itself, Open vSwitch
92 includes tools (ovs-ofctl, ovs-vsctl) that developers can script and
93 extend to provide distributed vswitch capabilities that are closely
94 integrated with their virtualization management platform.
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/
119 Q: What does it mean for an Open vSwitch release to be LTS (long-term
122 A: All official releases have been through a comprehensive testing
123 process and are suitable for production use. Planned releases will
124 occur several times a year. If a significant bug is identified in an
125 LTS release, we will provide an updated release that includes the
126 fix. Releases that are not LTS may not be fixed and may just be
127 supplanted by the next major release. The current LTS release is
130 Q: What Linux kernel versions does each Open vSwitch release work with?
132 A: The following table lists the Linux kernel versions against which the
133 given versions of the Open vSwitch kernel module will successfully
134 build. The Linux kernel versions are upstream kernel versions, so
135 Linux kernels modified from the upstream sources may not build in
136 some cases even if they are based on a supported version. This is
137 most notably true of Red Hat Enterprise Linux (RHEL) kernels, which
138 are extensively modified from upstream.
140 Open vSwitch Linux kernel
141 ------------ -------------
154 Open vSwitch userspace should also work with the Linux kernel module
155 built into Linux 3.3 and later.
157 Open vSwitch userspace is not sensitive to the Linux kernel version.
158 It should build against almost any kernel, certainly against 2.6.32
161 Q: I get an error like this when I configure Open vSwitch:
163 configure: error: Linux kernel in <dir> is version <x>, but
164 version newer than <y> is not supported (please refer to the
169 A: If there is a newer version of Open vSwitch, consider building that
170 one, because it may support the kernel that you are building
171 against. (To find out, consult the table in the previous answer.)
173 Otherwise, use the Linux kernel module supplied with the kernel
174 that you are using. All versions of Open vSwitch userspace are
175 compatible with all versions of the Open vSwitch kernel module, so
176 this will also work. See also the following question.
178 Q: What features are not available in the Open vSwitch kernel datapath
179 that ships as part of the upstream Linux kernel?
181 A: The kernel module in upstream Linux does not include support for
182 LISP. Work is in progress to add support for LISP to the upstream
183 Linux version of the Open vSwitch kernel module. For now, if you
184 need this feature, use the kernel module from the Open vSwitch
185 distribution instead of the upstream Linux kernel module.
187 Certain features require kernel support to function or to have
188 reasonable performance. If the ovs-vswitchd log file indicates that
189 a feature is not supported, consider upgrading to a newer upstream
190 Linux release or using the kernel module paired with the userspace
193 Q: What features are not available when using the userspace datapath?
195 A: Tunnel virtual ports are not supported, as described in the
196 previous answer. It is also not possible to use queue-related
197 actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets
198 may not be transmitted.
200 Q: What Linux kernel versions does IPFIX flow monitoring work with?
202 A: IPFIX flow monitoring requires the Linux kernel module from Open
203 vSwitch version 1.10.90 or later.
205 Q: Should userspace or kernel be upgraded first to minimize downtime?
207 In general, the Open vSwitch userspace should be used with the
208 kernel version included in the same release or with the version
209 from upstream Linux. However, when upgrading between two releases
210 of Open vSwitch it is best to migrate userspace first to reduce
211 the possibility of incompatibilities.
213 Q: What happened to the bridge compatibility feature?
215 A: Bridge compatibility was a feature of Open vSwitch 1.9 and earlier.
216 When it was enabled, Open vSwitch imitated the interface of the
217 Linux kernel "bridge" module. This allowed users to drop Open
218 vSwitch into environments designed to use the Linux kernel bridge
219 module without adapting the environment to use Open vSwitch.
221 Open vSwitch 1.10 and later do not support bridge compatibility.
222 The feature was dropped because version 1.10 adopted a new internal
223 architecture that made bridge compatibility difficult to maintain.
224 Now that many environments use OVS directly, it would be rarely
227 To use bridge compatibility, install OVS 1.9 or earlier, including
228 the accompanying kernel modules (both the main and bridge
229 compatibility modules), following the instructions that come with
230 the release. Be sure to start the ovs-brcompatd daemon.
236 Q: I thought Open vSwitch was a virtual Ethernet switch, but the
237 documentation keeps talking about bridges. What's a bridge?
239 A: In networking, the terms "bridge" and "switch" are synonyms. Open
240 vSwitch implements an Ethernet switch, which means that it is also
245 A: See the "VLAN" section below.
251 Q: How do I configure a port as an access port?
253 A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
254 the following commands configure br0 with eth0 as a trunk port (the
255 default) and tap0 as an access port for VLAN 9:
258 ovs-vsctl add-port br0 eth0
259 ovs-vsctl add-port br0 tap0 tag=9
261 If you want to configure an already added port as an access port,
262 use "ovs-vsctl set", e.g.:
264 ovs-vsctl set port tap0 tag=9
266 Q: How do I configure a port as a SPAN port, that is, enable mirroring
267 of all traffic to that port?
269 A: The following commands configure br0 with eth0 and tap0 as trunk
270 ports. All traffic coming in or going out on eth0 or tap0 is also
271 mirrored to tap1; any traffic arriving on tap1 is dropped:
274 ovs-vsctl add-port br0 eth0
275 ovs-vsctl add-port br0 tap0
276 ovs-vsctl add-port br0 tap1 \
277 -- --id=@p get port tap1 \
278 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
279 -- set bridge br0 mirrors=@m
281 To later disable mirroring, run:
283 ovs-vsctl clear bridge br0 mirrors
285 Q: Does Open vSwitch support configuring a port in promiscuous mode?
287 A: Yes. How you configure it depends on what you mean by "promiscuous
290 - Conventionally, "promiscuous mode" is a feature of a network
291 interface card. Ordinarily, a NIC passes to the CPU only the
292 packets actually destined to its host machine. It discards
293 the rest to avoid wasting memory and CPU cycles. When
294 promiscuous mode is enabled, however, it passes every packet
295 to the CPU. On an old-style shared-media or hub-based
296 network, this allows the host to spy on all packets on the
297 network. But in the switched networks that are almost
298 everywhere these days, promiscuous mode doesn't have much
299 effect, because few packets not destined to a host are
300 delivered to the host's NIC.
302 This form of promiscuous mode is configured in the guest OS of
303 the VMs on your bridge, e.g. with "ifconfig".
305 - The VMware vSwitch uses a different definition of "promiscuous
306 mode". When you configure promiscuous mode on a VMware vNIC,
307 the vSwitch sends a copy of every packet received by the
308 vSwitch to that vNIC. That has a much bigger effect than just
309 enabling promiscuous mode in a guest OS. Rather than getting
310 a few stray packets for which the switch does not yet know the
311 correct destination, the vNIC gets every packet. The effect
312 is similar to replacing the vSwitch by a virtual hub.
314 This "promiscuous mode" is what switches normally call "port
315 mirroring" or "SPAN". For information on how to configure
316 SPAN, see "How do I configure a port as a SPAN port, that is,
317 enable mirroring of all traffic to that port?"
319 Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
320 mirroring of all traffic to that VLAN?
322 A: The following commands configure br0 with eth0 as a trunk port and
323 tap0 as an access port for VLAN 10. All traffic coming in or going
324 out on tap0, as well as traffic coming in or going out on eth0 in
325 VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
326 VLAN 10, in cases where one is present, is dropped as part of
330 ovs-vsctl add-port br0 eth0
331 ovs-vsctl add-port br0 tap0 tag=10
333 -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
335 -- set bridge br0 mirrors=@m
337 To later disable mirroring, run:
339 ovs-vsctl clear bridge br0 mirrors
341 Mirroring to a VLAN can disrupt a network that contains unmanaged
342 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
343 GRE tunnel has fewer caveats than mirroring to a VLAN and should
344 generally be preferred.
346 Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
348 A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
349 of the specified output-vlan. This loss of information may make
350 the mirrored traffic too hard to interpret.
352 To mirror multiple VLANs, use the commands above, but specify a
353 comma-separated list of VLANs as the value for select-vlan. To
354 mirror every VLAN, use the commands above, but omit select-vlan and
357 When a packet arrives on a VLAN that is used as a mirror output
358 VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
359 floods the packet across all the ports for which the mirror output
360 VLAN is configured. (If an OpenFlow controller is in use, then it
361 can override this behavior through the flow table.) If OVS is used
362 as an intermediate switch, rather than an edge switch, this ensures
363 that the RSPAN traffic is distributed through the network.
365 Mirroring to a VLAN can disrupt a network that contains unmanaged
366 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
367 GRE tunnel has fewer caveats than mirroring to a VLAN and should
368 generally be preferred.
370 Q: How do I configure mirroring of all traffic to a GRE tunnel?
372 A: The following commands configure br0 with eth0 and tap0 as trunk
373 ports. All traffic coming in or going out on eth0 or tap0 is also
374 mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
375 traffic arriving on gre0 is dropped:
378 ovs-vsctl add-port br0 eth0
379 ovs-vsctl add-port br0 tap0
380 ovs-vsctl add-port br0 gre0 \
381 -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
382 -- --id=@p get port gre0 \
383 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
384 -- set bridge br0 mirrors=@m
386 To later disable mirroring and destroy the GRE tunnel:
388 ovs-vsctl clear bridge br0 mirrors
389 ovs-vcstl del-port br0 gre0
391 Q: Does Open vSwitch support ERSPAN?
393 A: No. ERSPAN is an undocumented proprietary protocol. As an
394 alternative, Open vSwitch supports mirroring to a GRE tunnel (see
397 Q: How do I connect two bridges?
399 A: First, why do you want to do this? Two connected bridges are not
400 much different from a single bridge, so you might as well just have
401 a single bridge with all your ports on it.
403 If you still want to connect two bridges, you can use a pair of
404 patch ports. The following example creates bridges br0 and br1,
405 adds eth0 and tap0 to br0, adds tap1 to br1, and then connects br0
406 and br1 with a pair of patch ports.
409 ovs-vsctl add-port br0 eth0
410 ovs-vsctl add-port br0 tap0
412 ovs-vsctl add-port br1 tap1
414 -- add-port br0 patch0 \
415 -- set interface patch0 type=patch options:peer=patch1 \
416 -- add-port br1 patch1 \
417 -- set interface patch1 type=patch options:peer=patch0
419 Bridges connected with patch ports are much like a single bridge.
420 For instance, if the example above also added eth1 to br1, and both
421 eth0 and eth1 happened to be connected to the same next-hop switch,
422 then you could loop your network just as you would if you added
423 eth0 and eth1 to the same bridge (see the "Configuration Problems"
424 section below for more information).
426 If you are using Open vSwitch 1.9 or an earlier version, then you
427 need to be using the kernel module bundled with Open vSwitch rather
428 than the one that is integrated into Linux 3.3 and later, because
429 Open vSwitch 1.9 and earlier versions need kernel support for patch
430 ports. This also means that in Open vSwitch 1.9 and earlier, patch
431 ports will not work with the userspace datapath, only with the
435 Implementation Details
436 ----------------------
438 Q: I hear OVS has a couple of kinds of flows. Can you tell me about them?
440 A: Open vSwitch uses different kinds of flows for different purposes:
442 - OpenFlow flows are the most important kind of flow. OpenFlow
443 controllers use these flows to define a switch's policy.
444 OpenFlow flows support wildcards, priorities, and multiple
447 When in-band control is in use, Open vSwitch sets up a few
448 "hidden" flows, with priority higher than a controller or the
449 user can configure, that are not visible via OpenFlow. (See
450 the "Controller" section of the FAQ for more information
453 - The Open vSwitch software switch implementation uses a second
454 kind of flow internally. These flows, called "datapath" or
455 "kernel" flows, do not support priorities and comprise only a
456 single table, which makes them suitable for caching. (Like
457 OpenFlow flows, datapath flows do support wildcarding, in Open
458 vSwitch 1.11 and later.) OpenFlow flows and datapath flows
459 also support different actions and number ports differently.
461 Datapath flows are an implementation detail that is subject to
462 change in future versions of Open vSwitch. Even with the
463 current version of Open vSwitch, hardware switch
464 implementations do not necessarily use this architecture.
466 Users and controllers directly control only the OpenFlow flow
467 table. Open vSwitch manages the datapath flow table itself, so
468 users should not normally be concerned with it.
470 Q: Why are there so many different ways to dump flows?
472 A: Open vSwitch has two kinds of flows (see the previous question), so
473 it has commands with different purposes for dumping each kind of
476 - "ovs-ofctl dump-flows <br>" dumps OpenFlow flows, excluding
477 hidden flows. This is the most commonly useful form of flow
478 dump. (Unlike the other commands, this should work with any
479 OpenFlow switch, not just Open vSwitch.)
481 - "ovs-appctl bridge/dump-flows <br>" dumps OpenFlow flows,
482 including hidden flows. This is occasionally useful for
483 troubleshooting suspected issues with in-band control.
485 - "ovs-dpctl dump-flows [dp]" dumps the datapath flow table
486 entries for a Linux kernel-based datapath. In Open vSwitch
487 1.10 and later, ovs-vswitchd merges multiple switches into a
488 single datapath, so it will show all the flows on all your
489 kernel-based switches. This command can occasionally be
490 useful for debugging.
492 - "ovs-appctl dpif/dump-flows <br>", new in Open vSwitch 1.10,
493 dumps datapath flows for only the specified bridge, regardless
500 Q: I just upgraded and I see a performance drop. Why?
502 A: The OVS kernel datapath may have been updated to a newer version than
503 the OVS userspace components. Sometimes new versions of OVS kernel
504 module add functionality that is backwards compatible with older
505 userspace components but may cause a drop in performance with them.
506 Especially, if a kernel module from OVS 2.1 or newer is paired with
507 OVS userspace 1.10 or older, there will be a performance drop for
510 Updating the OVS userspace components to the latest released
511 version should fix the performance degradation.
513 To get the best possible performance and functionality, it is
514 recommended to pair the same versions of the kernel module and OVS
518 Configuration Problems
519 ----------------------
521 Q: I created a bridge and added my Ethernet port to it, using commands
525 ovs-vsctl add-port br0 eth0
527 and as soon as I ran the "add-port" command I lost all connectivity
530 A: A physical Ethernet device that is part of an Open vSwitch bridge
531 should not have an IP address. If one does, then that IP address
532 will not be fully functional.
534 You can restore functionality by moving the IP address to an Open
535 vSwitch "internal" device, such as the network device named after
536 the bridge itself. For example, assuming that eth0's IP address is
537 192.168.128.5, you could run the commands below to fix up the
540 ifconfig eth0 0.0.0.0
541 ifconfig br0 192.168.128.5
543 (If your only connection to the machine running OVS is through the
544 IP address in question, then you would want to run all of these
545 commands on a single command line, or put them into a script.) If
546 there were any additional routes assigned to eth0, then you would
547 also want to use commands to adjust these routes to go through br0.
549 If you use DHCP to obtain an IP address, then you should kill the
550 DHCP client that was listening on the physical Ethernet interface
551 (e.g. eth0) and start one listening on the internal interface
552 (e.g. br0). You might still need to manually clear the IP address
553 from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
555 There is no compelling reason why Open vSwitch must work this way.
556 However, this is the way that the Linux kernel bridge module has
557 always worked, so it's a model that those accustomed to Linux
558 bridging are already used to. Also, the model that most people
559 expect is not implementable without kernel changes on all the
560 versions of Linux that Open vSwitch supports.
562 By the way, this issue is not specific to physical Ethernet
563 devices. It applies to all network devices except Open vswitch
566 Q: I created a bridge and added a couple of Ethernet ports to it,
567 using commands like these:
570 ovs-vsctl add-port br0 eth0
571 ovs-vsctl add-port br0 eth1
573 and now my network seems to have melted: connectivity is unreliable
574 (even connectivity that doesn't go through Open vSwitch), all the
575 LEDs on my physical switches are blinking, wireshark shows
576 duplicated packets, and CPU usage is very high.
578 A: More than likely, you've looped your network. Probably, eth0 and
579 eth1 are connected to the same physical Ethernet switch. This
580 yields a scenario where OVS receives a broadcast packet on eth0 and
581 sends it out on eth1, then the physical switch connected to eth1
582 sends the packet back on eth0, and so on forever. More complicated
583 scenarios, involving a loop through multiple switches, are possible
586 The solution depends on what you are trying to do:
588 - If you added eth0 and eth1 to get higher bandwidth or higher
589 reliability between OVS and your physical Ethernet switch,
590 use a bond. The following commands create br0 and then add
591 eth0 and eth1 as a bond:
594 ovs-vsctl add-bond br0 bond0 eth0 eth1
596 Bonds have tons of configuration options. Please read the
597 documentation on the Port table in ovs-vswitchd.conf.db(5)
600 - Perhaps you don't actually need eth0 and eth1 to be on the
601 same bridge. For example, if you simply want to be able to
602 connect each of them to virtual machines, then you can put
603 each of them on a bridge of its own:
606 ovs-vsctl add-port br0 eth0
609 ovs-vsctl add-port br1 eth1
611 and then connect VMs to br0 and br1. (A potential
612 disadvantage is that traffic cannot directly pass between br0
613 and br1. Instead, it will go out eth0 and come back in eth1,
616 - If you have a redundant or complex network topology and you
617 want to prevent loops, turn on spanning tree protocol (STP).
618 The following commands create br0, enable STP, and add eth0
619 and eth1 to the bridge. The order is important because you
620 don't want have to have a loop in your network even
624 ovs-vsctl set bridge br0 stp_enable=true
625 ovs-vsctl add-port br0 eth0
626 ovs-vsctl add-port br0 eth1
628 The Open vSwitch implementation of STP is not well tested.
629 Please report any bugs you observe, but if you'd rather avoid
630 acting as a beta tester then another option might be your
633 Q: I can't seem to use Open vSwitch in a wireless network.
635 A: Wireless base stations generally only allow packets with the source
636 MAC address of NIC that completed the initial handshake.
637 Therefore, without MAC rewriting, only a single device can
638 communicate over a single wireless link.
640 This isn't specific to Open vSwitch, it's enforced by the access
641 point, so the same problems will show up with the Linux bridge or
642 any other way to do bridging.
644 Q: I can't seem to add my PPP interface to an Open vSwitch bridge.
646 A: PPP most commonly carries IP packets, but Open vSwitch works only
647 with Ethernet frames. The correct way to interface PPP to an
648 Ethernet network is usually to use routing instead of switching.
650 Q: Is there any documentation on the database tables and fields?
652 A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
654 Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
655 I only see a datapath called "ovs-system". How can I see datapath
656 information about a particular bridge?
658 A: In version 1.9.0, OVS switched to using a single datapath that is
659 shared by all bridges of that type. The "ovs-appctl dpif/*"
660 commands provide similar functionality that is scoped by the bridge.
662 Q: I created a GRE port using ovs-vsctl so why can't I send traffic or
663 see the port in the datapath?
665 A: On Linux kernels before 3.11, the OVS GRE module and Linux GRE module
666 cannot be loaded at the same time. It is likely that on your system the
667 Linux GRE module is already loaded and blocking OVS (to confirm, check
668 dmesg for errors regarding GRE registration). To fix this, unload all
669 GRE modules that appear in lsmod as well as the OVS kernel module. You
670 can then reload the OVS module following the directions in INSTALL,
671 which will ensure that dependencies are satisfied.
674 Quality of Service (QoS)
675 ------------------------
677 Q: How do I configure Quality of Service (QoS)?
679 A: Suppose that you want to set up bridge br0 connected to physical
680 Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
681 vif1.0 and vif2.0, and that you want to limit traffic from vif1.0
682 to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps. Then, you
683 could configure the bridge this way:
687 add-port br0 eth0 -- \
688 add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \
689 add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \
690 set port eth0 qos=@newqos -- \
691 --id=@newqos create qos type=linux-htb \
692 other-config:max-rate=1000000000 \
693 queues:123=@vif10queue \
694 queues:234=@vif20queue -- \
695 --id=@vif10queue create queue other-config:max-rate=10000000 -- \
696 --id=@vif20queue create queue other-config:max-rate=20000000
698 At this point, bridge br0 is configured with the ports and eth0 is
699 configured with the queues that you need for QoS, but nothing is
700 actually directing packets from vif1.0 or vif2.0 to the queues that
701 we have set up for them. That means that all of the packets to
702 eth0 are going to the "default queue", which is not what we want.
704 We use OpenFlow to direct packets from vif1.0 and vif2.0 to the
705 queues reserved for them:
707 ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal
708 ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal
710 Each of the above flows matches on the input port, sets up the
711 appropriate queue (123 for vif1.0, 234 for vif2.0), and then
712 executes the "normal" action, which performs the same switching
713 that Open vSwitch would have done without any OpenFlow flows being
714 present. (We know that vif1.0 and vif2.0 have OpenFlow port
715 numbers 5 and 6, respectively, because we set their ofport_request
716 columns above. If we had not done that, then we would have needed
717 to find out their port numbers before setting up these flows.)
719 Now traffic going from vif1.0 or vif2.0 to eth0 should be
722 By the way, if you delete the bridge created by the above commands,
727 then that will leave one unreferenced QoS record and two
728 unreferenced Queue records in the Open vSwich database. One way to
729 clear them out, assuming you don't have other QoS or Queue records
730 that you want to keep, is:
732 ovs-vsctl -- --all destroy QoS -- --all destroy Queue
734 If you do want to keep some QoS or Queue records, or the Open
735 vSwitch you are using is older than version 1.8 (which added the
736 --all option), then you will have to destroy QoS and Queue records
739 Q: I configured Quality of Service (QoS) in my OpenFlow network by
740 adding records to the QoS and Queue table, but the results aren't
743 A: Did you install OpenFlow flows that use your queues? This is the
744 primary way to tell Open vSwitch which queues you want to use. If
745 you don't do this, then the default queue will be used, which will
746 probably not have the effect you want.
748 Refer to the previous question for an example.
750 Q: I'd like to take advantage of some QoS feature that Open vSwitch
751 doesn't yet support. How do I do that?
753 A: Open vSwitch does not implement QoS itself. Instead, it can
754 configure some, but not all, of the QoS features built into the
755 Linux kernel. If you need some QoS feature that OVS cannot
756 configure itself, then the first step is to figure out whether
757 Linux QoS supports that feature. If it does, then you can submit a
758 patch to support Open vSwitch configuration for that feature, or
759 you can use "tc" directly to configure the feature in Linux. (If
760 Linux QoS doesn't support the feature you want, then first you have
761 to add that support to Linux.)
763 Q: I configured QoS, correctly, but my measurements show that it isn't
764 working as well as I expect.
766 A: With the Linux kernel, the Open vSwitch implementation of QoS has
769 - Open vSwitch configures a subset of Linux kernel QoS
770 features, according to what is in OVSDB. It is possible that
771 this code has bugs. If you believe that this is so, then you
772 can configure the Linux traffic control (QoS) stack directly
773 with the "tc" program. If you get better results that way,
774 you can send a detailed bug report to bugs@openvswitch.org.
776 It is certain that Open vSwitch cannot configure every Linux
777 kernel QoS feature. If you need some feature that OVS cannot
778 configure, then you can also use "tc" directly (or add that
781 - The Open vSwitch implementation of OpenFlow allows flows to
782 be directed to particular queues. This is pretty simple and
783 unlikely to have serious bugs at this point.
785 However, most problems with QoS on Linux are not bugs in Open
786 vSwitch at all. They tend to be either configuration errors
787 (please see the earlier questions in this section) or issues with
788 the traffic control (QoS) stack in Linux. The Open vSwitch
789 developers are not experts on Linux traffic control. We suggest
790 that, if you believe you are encountering a problem with Linux
791 traffic control, that you consult the tc manpages (e.g. tc(8),
792 tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or
793 mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev).
795 Q: Does Open vSwitch support OpenFlow meters?
797 A: Since version 2.0, Open vSwitch has OpenFlow protocol support for
798 OpenFlow meters. There is no implementation of meters in the Open
799 vSwitch software switch (neither the kernel-based nor userspace
808 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
809 partition a single switch into multiple switches. Suppose, for
810 example, that you have two groups of machines, group A and group B.
811 You want the machines in group A to be able to talk to each other,
812 and you want the machine in group B to be able to talk to each
813 other, but you don't want the machines in group A to be able to
814 talk to the machines in group B. You can do this with two
815 switches, by plugging the machines in group A into one switch and
816 the machines in group B into the other switch.
818 If you only have one switch, then you can use VLANs to do the same
819 thing, by configuring the ports for machines in group A as VLAN
820 "access ports" for one VLAN and the ports for group B as "access
821 ports" for a different VLAN. The switch will only forward packets
822 between ports that are assigned to the same VLAN, so this
823 effectively subdivides your single switch into two independent
824 switches, one for each group of machines.
826 So far we haven't said anything about VLAN headers. With access
827 ports, like we've described so far, no VLAN header is present in
828 the Ethernet frame. This means that the machines (or switches)
829 connected to access ports need not be aware that VLANs are
830 involved, just like in the case where we use two different physical
833 Now suppose that you have a whole bunch of switches in your
834 network, instead of just one, and that some machines in group A are
835 connected directly to both switches 1 and 2. To allow these
836 machines to talk to each other, you could add an access port for
837 group A's VLAN to switch 1 and another to switch 2, and then
838 connect an Ethernet cable between those ports. That works fine,
839 but it doesn't scale well as the number of switches and the number
840 of VLANs increases, because you use up a lot of valuable switch
841 ports just connecting together your VLANs.
843 This is where VLAN headers come in. Instead of using one cable and
844 two ports per VLAN to connect a pair of switches, we configure a
845 port on each switch as a VLAN "trunk port". Packets sent and
846 received on a trunk port carry a VLAN header that says what VLAN
847 the packet belongs to, so that only two ports total are required to
848 connect the switches, regardless of the number of VLANs in use.
849 Normally, only switches (either physical or virtual) are connected
850 to a trunk port, not individual hosts, because individual hosts
851 don't expect to see a VLAN header in the traffic that they receive.
853 None of the above discussion says anything about particular VLAN
854 numbers. This is because VLAN numbers are completely arbitrary.
855 One must only ensure that a given VLAN is numbered consistently
856 throughout a network and that different VLANs are given different
857 numbers. (That said, VLAN 0 is usually synonymous with a packet
858 that has no VLAN header, and VLAN 4095 is reserved.)
862 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
863 bugs. If you are having problems with VLANs that you suspect to be
864 driver related, then you have several options:
866 - Upgrade to Linux 3.3 or later.
868 - Build and install a fixed version of the particular driver
869 that is causing trouble, if one is available.
871 - Use a NIC whose driver does not have VLAN problems.
873 - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
874 that works around bugs in kernel drivers. To enable VLAN
875 splinters on interface eth0, use the command:
877 ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
879 For VLAN splinters to be effective, Open vSwitch must know
880 which VLANs are in use. See the "VLAN splinters" section in
881 the Interface table in ovs-vswitchd.conf.db(5) for details on
882 how Open vSwitch infers in-use VLANs.
884 VLAN splinters increase memory use and reduce performance, so
885 use them only if needed.
887 - Apply the "vlan workaround" patch from the XenServer kernel
888 patch queue, build Open vSwitch against this patched kernel,
889 and then use ovs-vlan-bug-workaround(8) to enable the VLAN
890 workaround for each interface whose driver is buggy.
892 (This is a nontrivial exercise, so this option is included
893 only for completeness.)
895 It is not always easy to tell whether a Linux kernel driver has
896 buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
897 can help you test. See their manpages for details. Of the two
898 utilities, ovs-test(8) is newer and more thorough, but
899 ovs-vlan-test(8) may be easier to use.
901 Q: VLANs still don't work. I've tested the driver so I know that it's OK.
903 A: Do you have VLANs enabled on the physical switch that OVS is
904 attached to? Make sure that the port is configured to trunk the
905 VLAN or VLANs that you are using with OVS.
907 Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
908 and to its destination host, but OVS seems to drop incoming return
911 A: It's possible that you have the VLAN configured on your physical
912 switch as the "native" VLAN. In this mode, the switch treats
913 incoming packets either tagged with the native VLAN or untagged as
914 part of the native VLAN. It may also send outgoing packets in the
915 native VLAN without a VLAN tag.
917 If this is the case, you have two choices:
919 - Change the physical switch port configuration to tag packets
920 it forwards to OVS with the native VLAN instead of forwarding
923 - Change the OVS configuration for the physical port to a
924 native VLAN mode. For example, the following sets up a
925 bridge with port eth0 in "native-tagged" mode in VLAN 9:
928 ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
930 In this situation, "native-untagged" mode will probably work
931 equally well. Refer to the documentation for the Port table
932 in ovs-vswitchd.conf.db(5) for more information.
934 Q: I added a pair of VMs on different VLANs, like this:
937 ovs-vsctl add-port br0 eth0
938 ovs-vsctl add-port br0 tap0 tag=9
939 ovs-vsctl add-port br0 tap1 tag=10
941 but the VMs can't access each other, the external network, or the
944 A: It is to be expected that the VMs can't access each other. VLANs
945 are a means to partition a network. When you configured tap0 and
946 tap1 as access ports for different VLANs, you indicated that they
947 should be isolated from each other.
949 As for the external network and the Internet, it seems likely that
950 the machines you are trying to access are not on VLAN 9 (or 10) and
951 that the Internet is not available on VLAN 9 (or 10).
953 Q: I added a pair of VMs on the same VLAN, like this:
956 ovs-vsctl add-port br0 eth0
957 ovs-vsctl add-port br0 tap0 tag=9
958 ovs-vsctl add-port br0 tap1 tag=9
960 The VMs can access each other, but not the external network or the
963 A: It seems likely that the machines you are trying to access in the
964 external network are not on VLAN 9 and that the Internet is not
965 available on VLAN 9. Also, ensure VLAN 9 is set up as an allowed
966 trunk VLAN on the upstream switch port to which eth0 is connected.
968 Q: Can I configure an IP address on a VLAN?
970 A: Yes. Use an "internal port" configured as an access port. For
971 example, the following configures IP address 192.168.0.7 on VLAN 9.
972 That is, OVS will forward packets from eth0 to 192.168.0.7 only if
973 they have an 802.1Q header with VLAN 9. Conversely, traffic
974 forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
978 ovs-vsctl add-port br0 eth0
979 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
980 ifconfig vlan9 192.168.0.7
982 See also the following question.
984 Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
988 ovs-vsctl add-port br0 eth0
989 ifconfig br0 192.168.0.5
990 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
991 ifconfig vlan9 192.168.0.9
993 but other hosts that are only on VLAN 0 can reach the IP address
994 configured on VLAN 9. What's going on?
996 A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
997 approaches to IP address handling in Internet hosts:
999 - In the "Strong ES Model", where an ES is a host ("End
1000 System"), an IP address is primarily associated with a
1001 particular interface. The host discards packets that arrive
1002 on interface A if they are destined for an IP address that is
1003 configured on interface B. The host never sends packets from
1004 interface A using a source address configured on interface B.
1006 - In the "Weak ES Model", an IP address is primarily associated
1007 with a host. The host accepts packets that arrive on any
1008 interface if they are destined for any of the host's IP
1009 addresses, even if the address is configured on some
1010 interface other than the one on which it arrived. The host
1011 does not restrict itself to sending packets from an IP
1012 address associated with the originating interface.
1014 Linux uses the weak ES model. That means that when packets
1015 destined to the VLAN 9 IP address arrive on eth0 and are bridged to
1016 br0, the kernel IP stack accepts them there for the VLAN 9 IP
1017 address, even though they were not received on vlan9, the network
1020 To simulate the strong ES model on Linux, one may add iptables rule
1021 to filter packets based on source and destination address and
1022 adjust ARP configuration with sysctls.
1024 BSD uses the strong ES model.
1026 Q: My OpenFlow controller doesn't see the VLANs that I expect.
1028 A: The configuration for VLANs in the Open vSwitch database (e.g. via
1029 ovs-vsctl) only affects traffic that goes through Open vSwitch's
1030 implementation of the OpenFlow "normal switching" action. By
1031 default, when Open vSwitch isn't connected to a controller and
1032 nothing has been manually configured in the flow table, all traffic
1033 goes through the "normal switching" action. But, if you set up
1034 OpenFlow flows on your own, through a controller or using ovs-ofctl
1035 or through other means, then you have to implement VLAN handling
1038 You can use "normal switching" as a component of your OpenFlow
1039 actions, e.g. by putting "normal" into the lists of actions on
1040 ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
1041 controller. In situations where this is not suitable, you can
1042 implement VLAN handling yourself, e.g.:
1044 - If a packet comes in on an access port, and the flow table
1045 needs to send it out on a trunk port, then the flow can add
1046 the appropriate VLAN tag with the "mod_vlan_vid" action.
1048 - If a packet comes in on a trunk port, and the flow table
1049 needs to send it out on an access port, then the flow can
1050 strip the VLAN tag with the "strip_vlan" action.
1052 Q: I configured ports on a bridge as access ports with different VLAN
1055 ovs-vsctl add-br br0
1056 ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
1057 ovs-vsctl add-port br0 eth0
1058 ovs-vsctl add-port br0 tap0 tag=9
1059 ovs-vsctl add-port br0 tap1 tag=10
1061 but the VMs running behind tap0 and tap1 can still communicate,
1062 that is, they are not isolated from each other even though they are
1065 A: Do you have a controller configured on br0 (as the commands above
1066 do)? If so, then this is a variant on the previous question, "My
1067 OpenFlow controller doesn't see the VLANs that I expect," and you
1068 can refer to the answer there for more information.
1076 A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means
1077 to solve the scaling challenges of VLAN networks in a multi-tenant
1078 environment. VXLAN is an overlay network which transports an L2 network
1079 over an existing L3 network. For more information on VXLAN, please see
1080 the IETF draft available here:
1082 http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-03
1084 Q: How much of the VXLAN protocol does Open vSwitch currently support?
1086 A: Open vSwitch currently supports the framing format for packets on the
1087 wire. There is currently no support for the multicast aspects of VXLAN.
1088 To get around the lack of multicast support, it is possible to
1089 pre-provision MAC to IP address mappings either manually or from a
1092 Q: What destination UDP port does the VXLAN implementation in Open vSwitch
1095 A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which
1096 is 4789. However, it is possible to configure the destination UDP port
1097 manually on a per-VXLAN tunnel basis. An example of this configuration is
1100 ovs-vsctl add-br br0
1101 ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1
1102 type=vxlan options:remote_ip=192.168.1.2 options:key=flow
1103 options:dst_port=8472
1106 Using OpenFlow (Manually or Via Controller)
1107 -------------------------------------------
1109 Q: What versions of OpenFlow does Open vSwitch support?
1111 A: The following table lists the versions of OpenFlow supported by
1112 each version of Open vSwitch:
1114 Open vSwitch OF1.0 OF1.1 OF1.2 OF1.3 OF1.4
1115 =============== ===== ===== ===== ===== =====
1116 1.9 and earlier yes --- --- --- ---
1117 1.10 yes --- [*] [*] ---
1118 1.11 yes --- [*] [*] ---
1119 2.0 yes [*] [*] [*] ---
1120 2.1 yes [*] [*] [*] ---
1121 2.2 yes [*] [*] [*] [%]
1122 2.3 yes yes yes yes [%]
1124 [*] Supported, with one or more missing features.
1125 [%] Support is unsafe: ovs-vswitchd will abort when certain
1126 unimplemented features are tested.
1128 Open vSwitch 2.3 enables OpenFlow 1.0, 1.1, 1.2, and 1.3 by default
1129 in ovs-vswitchd. In Open vSwitch 1.10 through 2.2, OpenFlow 1.1,
1130 1.2, and 1.3 must be enabled manually in ovs-vswitchd. Either way,
1131 the user may override the default:
1133 - To enable OpenFlow 1.0, 1.1, 1.2, and 1.3 on bridge br0:
1135 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
1137 - To enable only OpenFlow 1.0 on bridge br0:
1139 ovs-vsctl set bridge br0 protocols=OpenFlow10
1141 All current versions of ovs-ofctl enable only OpenFlow 1.0 by
1142 default. Use the -O option to enable support for later versions of
1143 OpenFlow in ovs-ofctl. For example:
1145 ovs-ofctl -O OpenFlow13 dump-flows br0
1147 OpenFlow 1.4 is a special case, because it is not implemented
1148 safely: ovs-vswitchd will abort when certain unimplemented features
1149 are tested. Thus, for now it is suitable only for experimental
1150 use. ovs-vswitchd will only allow OpenFlow 1.4 to be enabled
1151 (which must be done in the same way described above) when it is
1152 invoked with a special --enable-of14 command line option.
1154 OPENFLOW-1.1+ in the Open vSwitch source tree tracks support for
1155 OpenFlow 1.1 and later features. When support for OpenFlow 1.4 is
1156 solidly implemented, Open vSwitch will enable that version by
1159 Q: Does Open vSwitch support MPLS?
1161 A: Before version 1.11, Open vSwitch did not support MPLS. That is,
1162 these versions can match on MPLS Ethernet types, but they cannot
1163 match, push, or pop MPLS labels, nor can they look past MPLS labels
1164 into the encapsulated packet.
1166 Open vSwitch versions 1.11, 2.0, and 2.1 have very minimal support
1167 for MPLS. With the userspace datapath only, these versions can
1168 match, push, or pop a single MPLS label, but they still cannot look
1169 past MPLS labels (even after popping them) into the encapsulated
1170 packet. Kernel datapath support is unchanged from earlier
1173 Open vSwitch version 2.2 will be able to match, push, or pop up to
1174 3 MPLS labels. Looking past MPLS labels into the encapsulated
1175 packet will still be unsupported. Both userspace and kernel
1176 datapaths will be supported, but MPLS processing always happens in
1177 userspace either way, so kernel datapath performance will be
1180 Q: I'm getting "error type 45250 code 0". What's that?
1182 A: This is a Open vSwitch extension to OpenFlow error codes. Open
1183 vSwitch uses this extension when it must report an error to an
1184 OpenFlow controller but no standard OpenFlow error code is
1187 Open vSwitch logs the errors that it sends to controllers, so the
1188 easiest thing to do is probably to look at the ovs-vswitchd log to
1189 find out what the error was.
1191 If you want to dissect the extended error message yourself, the
1192 format is documented in include/openflow/nicira-ext.h in the Open
1193 vSwitch source distribution. The extended error codes are
1194 documented in lib/ofp-errors.h.
1196 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
1197 doesn't actually appear through the OpenFlow connection, even
1198 though I know that it's going through.
1199 Q2: Some of the OpenFlow flows that my controller sets up don't seem
1200 to apply to certain traffic, especially traffic between OVS and
1201 the controller itself.
1203 A: By default, Open vSwitch assumes that OpenFlow controllers are
1204 connected "in-band", that is, that the controllers are actually
1205 part of the network that is being controlled. In in-band mode,
1206 Open vSwitch sets up special "hidden" flows to make sure that
1207 traffic can make it back and forth between OVS and the controllers.
1208 These hidden flows are higher priority than any flows that can be
1209 set up through OpenFlow, and they are not visible through normal
1210 OpenFlow flow table dumps.
1212 Usually, the hidden flows are desirable and helpful, but
1213 occasionally they can cause unexpected behavior. You can view the
1214 full OpenFlow flow table, including hidden flows, on bridge br0
1217 ovs-appctl bridge/dump-flows br0
1219 to help you debug. The hidden flows are those with priorities
1220 greater than 65535 (the maximum priority that can be set with
1223 The DESIGN file at the top level of the Open vSwitch source
1224 distribution describes the in-band model in detail.
1226 If your controllers are not actually in-band (e.g. they are on
1227 localhost via 127.0.0.1, or on a separate network), then you should
1228 configure your controllers in "out-of-band" mode. If you have one
1229 controller on bridge br0, then you can configure out-of-band mode
1232 ovs-vsctl set controller br0 connection-mode=out-of-band
1234 Q: I configured all my controllers for out-of-band control mode but
1235 "ovs-appctl bridge/dump-flows" still shows some hidden flows.
1237 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
1238 set-manager"). By default, Open vSwitch assumes that managers need
1239 in-band rules set up on every bridge. You can disable these rules
1242 ovs-vsctl set bridge br0 other-config:disable-in-band=true
1244 This actually disables in-band control entirely for the bridge, as
1245 if all the bridge's controllers were configured for out-of-band
1248 Q: My OpenFlow controller doesn't see the VLANs that I expect.
1250 A: See answer under "VLANs", above.
1252 Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
1253 but I got a funny message like this:
1255 ofp_util|INFO|normalization changed ofp_match, details:
1256 ofp_util|INFO| pre: nw_dst=192.168.0.1
1259 and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
1260 match had disappeared, so that the flow ends up matching every
1263 A: The term "normalization" in the log message means that a flow
1264 cannot match on an L3 field without saying what L3 protocol is in
1265 use. The "ovs-ofctl" command above didn't specify an L3 protocol,
1266 so the L3 field match was dropped.
1268 In this case, the L3 protocol could be IP or ARP. A correct
1269 command for each possibility is, respectively:
1271 ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
1275 ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
1277 Similarly, a flow cannot match on an L4 field without saying what
1278 L4 protocol is in use. For example, the flow match "tp_src=1234"
1279 is, by itself, meaningless and will be ignored. Instead, to match
1280 TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
1281 source port 1234, write "udp,tp_src=1234".
1283 Q: How can I figure out the OpenFlow port number for a given port?
1285 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
1286 respond with an OFPT_FEATURES_REPLY that, among other information,
1287 includes a mapping between OpenFlow port names and numbers. From a
1288 command prompt, "ovs-ofctl show br0" makes such a request and
1289 prints the response for switch br0.
1291 The Interface table in the Open vSwitch database also maps OpenFlow
1292 port names to numbers. To print the OpenFlow port number
1293 associated with interface eth0, run:
1295 ovs-vsctl get Interface eth0 ofport
1297 You can print the entire mapping with:
1299 ovs-vsctl -- --columns=name,ofport list Interface
1301 but the output mixes together interfaces from all bridges in the
1302 database, so it may be confusing if more than one bridge exists.
1304 In the Open vSwitch database, ofport value -1 means that the
1305 interface could not be created due to an error. (The Open vSwitch
1306 log should indicate the reason.) ofport value [] (the empty set)
1307 means that the interface hasn't been created yet. The latter is
1308 normally an intermittent condition (unless ovs-vswitchd is not
1311 Q: I added some flows with my controller or with ovs-ofctl, but when I
1312 run "ovs-dpctl dump-flows" I don't see them.
1314 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
1315 won't display the information that you want. You want to use
1316 "ovs-ofctl dump-flows" instead.
1318 Q: It looks like each of the interfaces in my bonded port shows up
1319 as an individual OpenFlow port. Is that right?
1321 A: Yes, Open vSwitch makes individual bond interfaces visible as
1322 OpenFlow ports, rather than the bond as a whole. The interfaces
1323 are treated together as a bond for only a few purposes:
1325 - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
1326 controller is not configured, this happens implicitly to
1329 - Mirrors configured for output to a bonded port.
1331 It would make a lot of sense for Open vSwitch to present a bond as
1332 a single OpenFlow port. If you want to contribute an
1333 implementation of such a feature, please bring it up on the Open
1334 vSwitch development mailing list at dev@openvswitch.org.
1336 Q: I have a sophisticated network setup involving Open vSwitch, VMs or
1337 multiple hosts, and other components. The behavior isn't what I
1340 A: To debug network behavior problems, trace the path of a packet,
1341 hop-by-hop, from its origin in one host to a remote host. If
1342 that's correct, then trace the path of the response packet back to
1345 Usually a simple ICMP echo request and reply ("ping") packet is
1346 good enough. Start by initiating an ongoing "ping" from the origin
1347 host to a remote host. If you are tracking down a connectivity
1348 problem, the "ping" will not display any successful output, but
1349 packets are still being sent. (In this case the packets being sent
1350 are likely ARP rather than ICMP.)
1352 Tools available for tracing include the following:
1354 - "tcpdump" and "wireshark" for observing hops across network
1355 devices, such as Open vSwitch internal devices and physical
1358 - "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
1359 later or "ovs-dpctl dump-flows <br>" in earlier versions.
1360 These tools allow one to observe the actions being taken on
1361 packets in ongoing flows.
1363 See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
1364 documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
1365 documentation, and "Why are there so many different ways to
1366 dump flows?" above for some background.
1368 - "ovs-appctl ofproto/trace" to observe the logic behind how
1369 ovs-vswitchd treats packets. See ovs-vswitchd(8) for
1370 documentation. You can out more details about a given flow
1371 that "ovs-dpctl dump-flows" displays, by cutting and pasting
1372 a flow from the output into an "ovs-appctl ofproto/trace"
1375 - SPAN, RSPAN, and ERSPAN features of physical switches, to
1376 observe what goes on at these physical hops.
1378 Starting at the origin of a given packet, observe the packet at
1379 each hop in turn. For example, in one plausible scenario, you
1382 1. "tcpdump" the "eth" interface through which an ARP egresses
1383 a VM, from inside the VM.
1385 2. "tcpdump" the "vif" or "tap" interface through which the ARP
1386 ingresses the host machine.
1388 3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
1389 the host interface through which the ARP egresses the
1390 physical machine. You may need to use "ovs-dpctl show" to
1391 interpret the port numbers. If the output seems surprising,
1392 you can use "ovs-appctl ofproto/trace" to observe details of
1393 how ovs-vswitchd determined the actions in the "ovs-dpctl
1396 4. "tcpdump" the "eth" interface through which the ARP egresses
1397 the physical machine.
1399 5. "tcpdump" the "eth" interface through which the ARP
1400 ingresses the physical machine, at the remote host that
1403 6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
1404 remote host that receives the ARP and observe the VM "vif"
1405 or "tap" interface to which the flow is directed. Again,
1406 "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
1408 7. "tcpdump" the "vif" or "tap" interface to which the ARP is
1411 8. "tcpdump" the "eth" interface through which the ARP
1412 ingresses a VM, from inside the VM.
1414 It is likely that during one of these steps you will figure out the
1415 problem. If not, then follow the ARP reply back to the origin, in
1418 Q: How do I make a flow drop packets?
1420 A: To drop a packet is to receive it without forwarding it. OpenFlow
1421 explicitly specifies forwarding actions. Thus, a flow with an
1422 empty set of actions does not forward packets anywhere, causing
1423 them to be dropped. You can specify an empty set of actions with
1424 "actions=" on the ovs-ofctl command line. For example:
1426 ovs-ofctl add-flow br0 priority=65535,actions=
1428 would cause every packet entering switch br0 to be dropped.
1430 You can write "drop" explicitly if you like. The effect is the
1431 same. Thus, the following command also causes every packet
1432 entering switch br0 to be dropped:
1434 ovs-ofctl add-flow br0 priority=65535,actions=drop
1436 "drop" is not an action, either in OpenFlow or Open vSwitch.
1437 Rather, it is only a way to say that there are no actions.
1439 Q: I added a flow to send packets out the ingress port, like this:
1441 ovs-ofctl add-flow br0 in_port=2,actions=2
1443 but OVS drops the packets instead.
1445 A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
1446 out its ingress port. The rationale is that dropping these packets
1447 makes it harder to loop the network. Sometimes this behavior can
1448 even be convenient, e.g. it is often the desired behavior in a flow
1449 that forwards a packet to several ports ("floods" the packet).
1451 Sometimes one really needs to send a packet out its ingress port
1452 ("hairpin"). In this case, output to OFPP_IN_PORT, which in
1453 ovs-ofctl syntax is expressed as just "in_port", e.g.:
1455 ovs-ofctl add-flow br0 in_port=2,actions=in_port
1457 This also works in some circumstances where the flow doesn't match
1458 on the input port. For example, if you know that your switch has
1459 five ports numbered 2 through 6, then the following will send every
1460 received packet out every port, even its ingress port:
1462 ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
1466 ovs-ofctl add-flow br0 actions=all,in_port
1468 Sometimes, in complicated flow tables with multiple levels of
1469 "resubmit" actions, a flow needs to output to a particular port
1470 that may or may not be the ingress port. It's difficult to take
1471 advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch
1472 provides, as an OpenFlow extension, the ability to modify the
1473 in_port field. Whatever value is currently in the in_port field is
1474 the port to which outputs will be dropped, as well as the
1475 destination for OFPP_IN_PORT. This means that the following will
1476 reliably output to port 2 or to ports 2 through 6, respectively:
1478 ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
1479 ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
1481 If the input port is important, then one may save and restore it on
1484 ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
1485 load:0->NXM_OF_IN_PORT[],\
1487 pop:NXM_OF_IN_PORT[]
1489 Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2
1490 on port 2. I set up flows to forward only traffic destined to the
1491 other host and drop other traffic, like this:
1493 priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2
1494 priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1
1495 priority=0,actions=drop
1497 But it doesn't work--I don't get any connectivity when I do this.
1500 A: These flows drop the ARP packets that IP hosts use to establish IP
1501 connectivity over Ethernet. To solve the problem, add flows to
1502 allow ARP to pass between the hosts:
1504 priority=5,in_port=1,arp,actions=2
1505 priority=5,in_port=2,arp,actions=1
1507 This issue can manifest other ways, too. The following flows that
1508 match on Ethernet addresses instead of IP addresses will also drop
1509 ARP packets, because ARP requests are broadcast instead of being
1510 directed to a specific host:
1512 priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2
1513 priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1
1514 priority=0,actions=drop
1516 The solution already described above will also work in this case.
1517 It may be better to add flows to allow all multicast and broadcast
1520 priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
1521 priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
1527 Q: How do I implement a new OpenFlow message?
1529 A: Add your new message to "enum ofpraw" and "enum ofptype" in
1530 lib/ofp-msgs.h, following the existing pattern. Then recompile and
1531 fix all of the new warnings, implementing new functionality for the
1532 new message as needed. (If you configure with --enable-Werror, as
1533 described in INSTALL, then it is impossible to miss any warnings.)
1535 If you need to add an OpenFlow vendor extension message for a
1536 vendor that doesn't yet have any extension messages, then you will
1537 also need to edit build-aux/extract-ofp-msgs.
1543 bugs@openvswitch.org
1544 http://openvswitch.org/
projects / mirror_ovs.git / blob