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 ------------ -------------
153 Open vSwitch userspace should also work with the Linux kernel module
154 built into Linux 3.3 and later.
156 Open vSwitch userspace is not sensitive to the Linux kernel version.
157 It should build against almost any kernel, certainly against 2.6.32
160 Q: What Linux kernel versions does IPFIX flow monitoring work with?
162 A: IPFIX flow monitoring requires the Linux kernel module from Open
163 vSwitch version 1.10.90 or later.
165 Q: Should userspace or kernel be upgraded first to minimize downtime?
167 In general, the Open vSwitch userspace should be used with the
168 kernel version included in the same release or with the version
169 from upstream Linux. However, when upgrading between two releases
170 of Open vSwitch it is best to migrate userspace first to reduce
171 the possibility of incompatibilities.
173 Q: What features are not available in the Open vSwitch kernel datapath
174 that ships as part of the upstream Linux kernel?
176 A: The kernel module in upstream Linux 3.3 and later does not include
177 tunnel virtual ports, that is, interfaces with type "gre",
178 "ipsec_gre", "gre64", "ipsec_gre64", "vxlan", or "lisp". It is
179 possible to create tunnels in Linux and attach them to Open vSwitch
180 as system devices. However, they cannot be dynamically created
181 through the OVSDB protocol or set the tunnel ids as a flow action.
183 Work is in progress in adding tunnel virtual ports to the upstream
184 Linux version of the Open vSwitch kernel module. For now, if you
185 need these features, use the kernel module from the Open vSwitch
186 distribution instead of the upstream Linux kernel module.
188 The upstream kernel module does not include patch ports, but this
189 only matters for Open vSwitch 1.9 and earlier, because Open vSwitch
190 1.10 and later implement patch ports without using this kernel
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 happened to the bridge compatibility feature?
202 A: Bridge compatibility was a feature of Open vSwitch 1.9 and earlier.
203 When it was enabled, Open vSwitch imitated the interface of the
204 Linux kernel "bridge" module. This allowed users to drop Open
205 vSwitch into environments designed to use the Linux kernel bridge
206 module without adapting the environment to use Open vSwitch.
208 Open vSwitch 1.10 and later do not support bridge compatibility.
209 The feature was dropped because version 1.10 adopted a new internal
210 architecture that made bridge compatibility difficult to maintain.
211 Now that many environments use OVS directly, it would be rarely
214 To use bridge compatibility, install OVS 1.9 or earlier, including
215 the accompanying kernel modules (both the main and bridge
216 compatibility modules), following the instructions that come with
217 the release. Be sure to start the ovs-brcompatd daemon.
223 Q: I thought Open vSwitch was a virtual Ethernet switch, but the
224 documentation keeps talking about bridges. What's a bridge?
226 A: In networking, the terms "bridge" and "switch" are synonyms. Open
227 vSwitch implements an Ethernet switch, which means that it is also
232 A: See the "VLAN" section below.
238 Q: How do I configure a port as an access port?
240 A: Add "tag=VLAN" to your "ovs-vsctl add-port" command. For example,
241 the following commands configure br0 with eth0 as a trunk port (the
242 default) and tap0 as an access port for VLAN 9:
245 ovs-vsctl add-port br0 eth0
246 ovs-vsctl add-port br0 tap0 tag=9
248 If you want to configure an already added port as an access port,
249 use "ovs-vsctl set", e.g.:
251 ovs-vsctl set port tap0 tag=9
253 Q: How do I configure a port as a SPAN port, that is, enable mirroring
254 of all traffic to that port?
256 A: The following commands configure br0 with eth0 and tap0 as trunk
257 ports. All traffic coming in or going out on eth0 or tap0 is also
258 mirrored to tap1; any traffic arriving on tap1 is dropped:
261 ovs-vsctl add-port br0 eth0
262 ovs-vsctl add-port br0 tap0
263 ovs-vsctl add-port br0 tap1 \
264 -- --id=@p get port tap1 \
265 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
266 -- set bridge br0 mirrors=@m
268 To later disable mirroring, run:
270 ovs-vsctl clear bridge br0 mirrors
272 Q: Does Open vSwitch support configuring a port in promiscuous mode?
274 A: Yes. How you configure it depends on what you mean by "promiscuous
277 - Conventionally, "promiscuous mode" is a feature of a network
278 interface card. Ordinarily, a NIC passes to the CPU only the
279 packets actually destined to its host machine. It discards
280 the rest to avoid wasting memory and CPU cycles. When
281 promiscuous mode is enabled, however, it passes every packet
282 to the CPU. On an old-style shared-media or hub-based
283 network, this allows the host to spy on all packets on the
284 network. But in the switched networks that are almost
285 everywhere these days, promiscuous mode doesn't have much
286 effect, because few packets not destined to a host are
287 delivered to the host's NIC.
289 This form of promiscuous mode is configured in the guest OS of
290 the VMs on your bridge, e.g. with "ifconfig".
292 - The VMware vSwitch uses a different definition of "promiscuous
293 mode". When you configure promiscuous mode on a VMware vNIC,
294 the vSwitch sends a copy of every packet received by the
295 vSwitch to that vNIC. That has a much bigger effect than just
296 enabling promiscuous mode in a guest OS. Rather than getting
297 a few stray packets for which the switch does not yet know the
298 correct destination, the vNIC gets every packet. The effect
299 is similar to replacing the vSwitch by a virtual hub.
301 This "promiscuous mode" is what switches normally call "port
302 mirroring" or "SPAN". For information on how to configure
303 SPAN, see "How do I configure a port as a SPAN port, that is,
304 enable mirroring of all traffic to that port?"
306 Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
307 mirroring of all traffic to that VLAN?
309 A: The following commands configure br0 with eth0 as a trunk port and
310 tap0 as an access port for VLAN 10. All traffic coming in or going
311 out on tap0, as well as traffic coming in or going out on eth0 in
312 VLAN 10, is also mirrored to VLAN 15 on eth0. The original tag for
313 VLAN 10, in cases where one is present, is dropped as part of
317 ovs-vsctl add-port br0 eth0
318 ovs-vsctl add-port br0 tap0 tag=10
320 -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
322 -- set bridge br0 mirrors=@m
324 To later disable mirroring, run:
326 ovs-vsctl clear bridge br0 mirrors
328 Mirroring to a VLAN can disrupt a network that contains unmanaged
329 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
330 GRE tunnel has fewer caveats than mirroring to a VLAN and should
331 generally be preferred.
333 Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
335 A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
336 of the specified output-vlan. This loss of information may make
337 the mirrored traffic too hard to interpret.
339 To mirror multiple VLANs, use the commands above, but specify a
340 comma-separated list of VLANs as the value for select-vlan. To
341 mirror every VLAN, use the commands above, but omit select-vlan and
344 When a packet arrives on a VLAN that is used as a mirror output
345 VLAN, the mirror is disregarded. Instead, in standalone mode, OVS
346 floods the packet across all the ports for which the mirror output
347 VLAN is configured. (If an OpenFlow controller is in use, then it
348 can override this behavior through the flow table.) If OVS is used
349 as an intermediate switch, rather than an edge switch, this ensures
350 that the RSPAN traffic is distributed through the network.
352 Mirroring to a VLAN can disrupt a network that contains unmanaged
353 switches. See ovs-vswitchd.conf.db(5) for details. Mirroring to a
354 GRE tunnel has fewer caveats than mirroring to a VLAN and should
355 generally be preferred.
357 Q: How do I configure mirroring of all traffic to a GRE tunnel?
359 A: The following commands configure br0 with eth0 and tap0 as trunk
360 ports. All traffic coming in or going out on eth0 or tap0 is also
361 mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
362 traffic arriving on gre0 is dropped:
365 ovs-vsctl add-port br0 eth0
366 ovs-vsctl add-port br0 tap0
367 ovs-vsctl add-port br0 gre0 \
368 -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
369 -- --id=@p get port gre0 \
370 -- --id=@m create mirror name=m0 select-all=true output-port=@p \
371 -- set bridge br0 mirrors=@m
373 To later disable mirroring and destroy the GRE tunnel:
375 ovs-vsctl clear bridge br0 mirrors
376 ovs-vcstl del-port br0 gre0
378 Q: Does Open vSwitch support ERSPAN?
380 A: No. ERSPAN is an undocumented proprietary protocol. As an
381 alternative, Open vSwitch supports mirroring to a GRE tunnel (see
384 Q: How do I connect two bridges?
386 A: First, why do you want to do this? Two connected bridges are not
387 much different from a single bridge, so you might as well just have
388 a single bridge with all your ports on it.
390 If you still want to connect two bridges, you can use a pair of
391 patch ports. The following example creates bridges br0 and br1,
392 adds eth0 and tap0 to br0, adds tap1 to br1, and then connects br0
393 and br1 with a pair of patch ports.
396 ovs-vsctl add-port br0 eth0
397 ovs-vsctl add-port br0 tap0
399 ovs-vsctl add-port br1 tap1
401 -- add-port br0 patch0 \
402 -- set interface patch0 type=patch options:peer=patch1 \
403 -- add-port br1 patch1 \
404 -- set interface patch1 type=patch options:peer=patch0
406 Bridges connected with patch ports are much like a single bridge.
407 For instance, if the example above also added eth1 to br1, and both
408 eth0 and eth1 happened to be connected to the same next-hop switch,
409 then you could loop your network just as you would if you added
410 eth0 and eth1 to the same bridge (see the "Configuration Problems"
411 section below for more information).
413 If you are using Open vSwitch 1.9 or an earlier version, then you
414 need to be using the kernel module bundled with Open vSwitch rather
415 than the one that is integrated into Linux 3.3 and later, because
416 Open vSwitch 1.9 and earlier versions need kernel support for patch
417 ports. This also means that in Open vSwitch 1.9 and earlier, patch
418 ports will not work with the userspace datapath, only with the
422 Implementation Details
423 ----------------------
425 Q: I hear OVS has a couple of kinds of flows. Can you tell me about them?
427 A: Open vSwitch uses different kinds of flows for different purposes:
429 - OpenFlow flows are the most important kind of flow. OpenFlow
430 controllers use these flows to define a switch's policy.
431 OpenFlow flows support wildcards, priorities, and multiple
434 When in-band control is in use, Open vSwitch sets up a few
435 "hidden" flows, with priority higher than a controller or the
436 user can configure, that are not visible via OpenFlow. (See
437 the "Controller" section of the FAQ for more information
440 - The Open vSwitch software switch implementation uses a second
441 kind of flow internally. These flows, called "datapath" or
442 "kernel" flows, do not support priorities and comprise only a
443 single table, which makes them suitable for caching. (Like
444 OpenFlow flows, datapath flows do support wildcarding, in Open
445 vSwitch 1.11 and later.) OpenFlow flows and datapath flows
446 also support different actions and number ports differently.
448 Datapath flows are an implementation detail that is subject to
449 change in future versions of Open vSwitch. Even with the
450 current version of Open vSwitch, hardware switch
451 implementations do not necessarily use this architecture.
453 Users and controllers directly control only the OpenFlow flow
454 table. Open vSwitch manages the datapath flow table itself, so
455 users should not normally be concerned with it.
457 Q: Why are there so many different ways to dump flows?
459 A: Open vSwitch has two kinds of flows (see the previous question), so
460 it has commands with different purposes for dumping each kind of
463 - "ovs-ofctl dump-flows <br>" dumps OpenFlow flows, excluding
464 hidden flows. This is the most commonly useful form of flow
465 dump. (Unlike the other commands, this should work with any
466 OpenFlow switch, not just Open vSwitch.)
468 - "ovs-appctl bridge/dump-flows <br>" dumps OpenFlow flows,
469 including hidden flows. This is occasionally useful for
470 troubleshooting suspected issues with in-band control.
472 - "ovs-dpctl dump-flows [dp]" dumps the datapath flow table
473 entries for a Linux kernel-based datapath. In Open vSwitch
474 1.10 and later, ovs-vswitchd merges multiple switches into a
475 single datapath, so it will show all the flows on all your
476 kernel-based switches. This command can occasionally be
477 useful for debugging.
479 - "ovs-appctl dpif/dump-flows <br>", new in Open vSwitch 1.10,
480 dumps datapath flows for only the specified bridge, regardless
487 Q: I just upgraded and I see a performance drop. Why?
489 A: The OVS kernel datapath may have been updated to a newer version than
490 the OVS userspace components. Sometimes new versions of OVS kernel
491 module add functionality that is backwards compatible with older
492 userspace components but may cause a drop in performance with them.
493 Especially, if a kernel module from OVS 2.1 or newer is paired with
494 OVS userspace 1.10 or older, there will be a performance drop for
497 Updating the OVS userspace components to the latest released
498 version should fix the performance degradation.
500 To get the best possible performance and functionality, it is
501 recommended to pair the same versions of the kernel module and OVS
505 Configuration Problems
506 ----------------------
508 Q: I created a bridge and added my Ethernet port to it, using commands
512 ovs-vsctl add-port br0 eth0
514 and as soon as I ran the "add-port" command I lost all connectivity
517 A: A physical Ethernet device that is part of an Open vSwitch bridge
518 should not have an IP address. If one does, then that IP address
519 will not be fully functional.
521 You can restore functionality by moving the IP address to an Open
522 vSwitch "internal" device, such as the network device named after
523 the bridge itself. For example, assuming that eth0's IP address is
524 192.168.128.5, you could run the commands below to fix up the
527 ifconfig eth0 0.0.0.0
528 ifconfig br0 192.168.128.5
530 (If your only connection to the machine running OVS is through the
531 IP address in question, then you would want to run all of these
532 commands on a single command line, or put them into a script.) If
533 there were any additional routes assigned to eth0, then you would
534 also want to use commands to adjust these routes to go through br0.
536 If you use DHCP to obtain an IP address, then you should kill the
537 DHCP client that was listening on the physical Ethernet interface
538 (e.g. eth0) and start one listening on the internal interface
539 (e.g. br0). You might still need to manually clear the IP address
540 from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
542 There is no compelling reason why Open vSwitch must work this way.
543 However, this is the way that the Linux kernel bridge module has
544 always worked, so it's a model that those accustomed to Linux
545 bridging are already used to. Also, the model that most people
546 expect is not implementable without kernel changes on all the
547 versions of Linux that Open vSwitch supports.
549 By the way, this issue is not specific to physical Ethernet
550 devices. It applies to all network devices except Open vswitch
553 Q: I created a bridge and added a couple of Ethernet ports to it,
554 using commands like these:
557 ovs-vsctl add-port br0 eth0
558 ovs-vsctl add-port br0 eth1
560 and now my network seems to have melted: connectivity is unreliable
561 (even connectivity that doesn't go through Open vSwitch), all the
562 LEDs on my physical switches are blinking, wireshark shows
563 duplicated packets, and CPU usage is very high.
565 A: More than likely, you've looped your network. Probably, eth0 and
566 eth1 are connected to the same physical Ethernet switch. This
567 yields a scenario where OVS receives a broadcast packet on eth0 and
568 sends it out on eth1, then the physical switch connected to eth1
569 sends the packet back on eth0, and so on forever. More complicated
570 scenarios, involving a loop through multiple switches, are possible
573 The solution depends on what you are trying to do:
575 - If you added eth0 and eth1 to get higher bandwidth or higher
576 reliability between OVS and your physical Ethernet switch,
577 use a bond. The following commands create br0 and then add
578 eth0 and eth1 as a bond:
581 ovs-vsctl add-bond br0 bond0 eth0 eth1
583 Bonds have tons of configuration options. Please read the
584 documentation on the Port table in ovs-vswitchd.conf.db(5)
587 - Perhaps you don't actually need eth0 and eth1 to be on the
588 same bridge. For example, if you simply want to be able to
589 connect each of them to virtual machines, then you can put
590 each of them on a bridge of its own:
593 ovs-vsctl add-port br0 eth0
596 ovs-vsctl add-port br1 eth1
598 and then connect VMs to br0 and br1. (A potential
599 disadvantage is that traffic cannot directly pass between br0
600 and br1. Instead, it will go out eth0 and come back in eth1,
603 - If you have a redundant or complex network topology and you
604 want to prevent loops, turn on spanning tree protocol (STP).
605 The following commands create br0, enable STP, and add eth0
606 and eth1 to the bridge. The order is important because you
607 don't want have to have a loop in your network even
611 ovs-vsctl set bridge br0 stp_enable=true
612 ovs-vsctl add-port br0 eth0
613 ovs-vsctl add-port br0 eth1
615 The Open vSwitch implementation of STP is not well tested.
616 Please report any bugs you observe, but if you'd rather avoid
617 acting as a beta tester then another option might be your
620 Q: I can't seem to use Open vSwitch in a wireless network.
622 A: Wireless base stations generally only allow packets with the source
623 MAC address of NIC that completed the initial handshake.
624 Therefore, without MAC rewriting, only a single device can
625 communicate over a single wireless link.
627 This isn't specific to Open vSwitch, it's enforced by the access
628 point, so the same problems will show up with the Linux bridge or
629 any other way to do bridging.
631 Q: I can't seem to add my PPP interface to an Open vSwitch bridge.
633 A: PPP most commonly carries IP packets, but Open vSwitch works only
634 with Ethernet frames. The correct way to interface PPP to an
635 Ethernet network is usually to use routing instead of switching.
637 Q: Is there any documentation on the database tables and fields?
639 A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
641 Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
642 I only see a datapath called "ovs-system". How can I see datapath
643 information about a particular bridge?
645 A: In version 1.9.0, OVS switched to using a single datapath that is
646 shared by all bridges of that type. The "ovs-appctl dpif/*"
647 commands provide similar functionality that is scoped by the bridge.
650 Quality of Service (QoS)
651 ------------------------
653 Q: How do I configure Quality of Service (QoS)?
655 A: Suppose that you want to set up bridge br0 connected to physical
656 Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
657 vif1.0 and vif2.0, and that you want to limit traffic from vif1.0
658 to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps. Then, you
659 could configure the bridge this way:
663 add-port br0 eth0 -- \
664 add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \
665 add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \
666 set port eth0 qos=@newqos -- \
667 --id=@newqos create qos type=linux-htb \
668 other-config:max-rate=1000000000 \
669 queues:123=@vif10queue \
670 queues:234=@vif20queue -- \
671 --id=@vif10queue create queue other-config:max-rate=10000000 -- \
672 --id=@vif20queue create queue other-config:max-rate=20000000
674 At this point, bridge br0 is configured with the ports and eth0 is
675 configured with the queues that you need for QoS, but nothing is
676 actually directing packets from vif1.0 or vif2.0 to the queues that
677 we have set up for them. That means that all of the packets to
678 eth0 are going to the "default queue", which is not what we want.
680 We use OpenFlow to direct packets from vif1.0 and vif2.0 to the
681 queues reserved for them:
683 ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal
684 ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal
686 Each of the above flows matches on the input port, sets up the
687 appropriate queue (123 for vif1.0, 234 for vif2.0), and then
688 executes the "normal" action, which performs the same switching
689 that Open vSwitch would have done without any OpenFlow flows being
690 present. (We know that vif1.0 and vif2.0 have OpenFlow port
691 numbers 5 and 6, respectively, because we set their ofport_request
692 columns above. If we had not done that, then we would have needed
693 to find out their port numbers before setting up these flows.)
695 Now traffic going from vif1.0 or vif2.0 to eth0 should be
698 By the way, if you delete the bridge created by the above commands,
703 then that will leave one unreferenced QoS record and two
704 unreferenced Queue records in the Open vSwich database. One way to
705 clear them out, assuming you don't have other QoS or Queue records
706 that you want to keep, is:
708 ovs-vsctl -- --all destroy QoS -- --all destroy Queue
710 If you do want to keep some QoS or Queue records, or the Open
711 vSwitch you are using is older than version 1.8 (which added the
712 --all option), then you will have to destroy QoS and Queue records
715 Q: I configured Quality of Service (QoS) in my OpenFlow network by
716 adding records to the QoS and Queue table, but the results aren't
719 A: Did you install OpenFlow flows that use your queues? This is the
720 primary way to tell Open vSwitch which queues you want to use. If
721 you don't do this, then the default queue will be used, which will
722 probably not have the effect you want.
724 Refer to the previous question for an example.
726 Q: I'd like to take advantage of some QoS feature that Open vSwitch
727 doesn't yet support. How do I do that?
729 A: Open vSwitch does not implement QoS itself. Instead, it can
730 configure some, but not all, of the QoS features built into the
731 Linux kernel. If you need some QoS feature that OVS cannot
732 configure itself, then the first step is to figure out whether
733 Linux QoS supports that feature. If it does, then you can submit a
734 patch to support Open vSwitch configuration for that feature, or
735 you can use "tc" directly to configure the feature in Linux. (If
736 Linux QoS doesn't support the feature you want, then first you have
737 to add that support to Linux.)
739 Q: I configured QoS, correctly, but my measurements show that it isn't
740 working as well as I expect.
742 A: With the Linux kernel, the Open vSwitch implementation of QoS has
745 - Open vSwitch configures a subset of Linux kernel QoS
746 features, according to what is in OVSDB. It is possible that
747 this code has bugs. If you believe that this is so, then you
748 can configure the Linux traffic control (QoS) stack directly
749 with the "tc" program. If you get better results that way,
750 you can send a detailed bug report to bugs@openvswitch.org.
752 It is certain that Open vSwitch cannot configure every Linux
753 kernel QoS feature. If you need some feature that OVS cannot
754 configure, then you can also use "tc" directly (or add that
757 - The Open vSwitch implementation of OpenFlow allows flows to
758 be directed to particular queues. This is pretty simple and
759 unlikely to have serious bugs at this point.
761 However, most problems with QoS on Linux are not bugs in Open
762 vSwitch at all. They tend to be either configuration errors
763 (please see the earlier questions in this section) or issues with
764 the traffic control (QoS) stack in Linux. The Open vSwitch
765 developers are not experts on Linux traffic control. We suggest
766 that, if you believe you are encountering a problem with Linux
767 traffic control, that you consult the tc manpages (e.g. tc(8),
768 tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or
769 mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev).
777 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
778 partition a single switch into multiple switches. Suppose, for
779 example, that you have two groups of machines, group A and group B.
780 You want the machines in group A to be able to talk to each other,
781 and you want the machine in group B to be able to talk to each
782 other, but you don't want the machines in group A to be able to
783 talk to the machines in group B. You can do this with two
784 switches, by plugging the machines in group A into one switch and
785 the machines in group B into the other switch.
787 If you only have one switch, then you can use VLANs to do the same
788 thing, by configuring the ports for machines in group A as VLAN
789 "access ports" for one VLAN and the ports for group B as "access
790 ports" for a different VLAN. The switch will only forward packets
791 between ports that are assigned to the same VLAN, so this
792 effectively subdivides your single switch into two independent
793 switches, one for each group of machines.
795 So far we haven't said anything about VLAN headers. With access
796 ports, like we've described so far, no VLAN header is present in
797 the Ethernet frame. This means that the machines (or switches)
798 connected to access ports need not be aware that VLANs are
799 involved, just like in the case where we use two different physical
802 Now suppose that you have a whole bunch of switches in your
803 network, instead of just one, and that some machines in group A are
804 connected directly to both switches 1 and 2. To allow these
805 machines to talk to each other, you could add an access port for
806 group A's VLAN to switch 1 and another to switch 2, and then
807 connect an Ethernet cable between those ports. That works fine,
808 but it doesn't scale well as the number of switches and the number
809 of VLANs increases, because you use up a lot of valuable switch
810 ports just connecting together your VLANs.
812 This is where VLAN headers come in. Instead of using one cable and
813 two ports per VLAN to connect a pair of switches, we configure a
814 port on each switch as a VLAN "trunk port". Packets sent and
815 received on a trunk port carry a VLAN header that says what VLAN
816 the packet belongs to, so that only two ports total are required to
817 connect the switches, regardless of the number of VLANs in use.
818 Normally, only switches (either physical or virtual) are connected
819 to a trunk port, not individual hosts, because individual hosts
820 don't expect to see a VLAN header in the traffic that they receive.
822 None of the above discussion says anything about particular VLAN
823 numbers. This is because VLAN numbers are completely arbitrary.
824 One must only ensure that a given VLAN is numbered consistently
825 throughout a network and that different VLANs are given different
826 numbers. (That said, VLAN 0 is usually synonymous with a packet
827 that has no VLAN header, and VLAN 4095 is reserved.)
831 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
832 bugs. If you are having problems with VLANs that you suspect to be
833 driver related, then you have several options:
835 - Upgrade to Linux 3.3 or later.
837 - Build and install a fixed version of the particular driver
838 that is causing trouble, if one is available.
840 - Use a NIC whose driver does not have VLAN problems.
842 - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
843 that works around bugs in kernel drivers. To enable VLAN
844 splinters on interface eth0, use the command:
846 ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
848 For VLAN splinters to be effective, Open vSwitch must know
849 which VLANs are in use. See the "VLAN splinters" section in
850 the Interface table in ovs-vswitchd.conf.db(5) for details on
851 how Open vSwitch infers in-use VLANs.
853 VLAN splinters increase memory use and reduce performance, so
854 use them only if needed.
856 - Apply the "vlan workaround" patch from the XenServer kernel
857 patch queue, build Open vSwitch against this patched kernel,
858 and then use ovs-vlan-bug-workaround(8) to enable the VLAN
859 workaround for each interface whose driver is buggy.
861 (This is a nontrivial exercise, so this option is included
862 only for completeness.)
864 It is not always easy to tell whether a Linux kernel driver has
865 buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
866 can help you test. See their manpages for details. Of the two
867 utilities, ovs-test(8) is newer and more thorough, but
868 ovs-vlan-test(8) may be easier to use.
870 Q: VLANs still don't work. I've tested the driver so I know that it's OK.
872 A: Do you have VLANs enabled on the physical switch that OVS is
873 attached to? Make sure that the port is configured to trunk the
874 VLAN or VLANs that you are using with OVS.
876 Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
877 and to its destination host, but OVS seems to drop incoming return
880 A: It's possible that you have the VLAN configured on your physical
881 switch as the "native" VLAN. In this mode, the switch treats
882 incoming packets either tagged with the native VLAN or untagged as
883 part of the native VLAN. It may also send outgoing packets in the
884 native VLAN without a VLAN tag.
886 If this is the case, you have two choices:
888 - Change the physical switch port configuration to tag packets
889 it forwards to OVS with the native VLAN instead of forwarding
892 - Change the OVS configuration for the physical port to a
893 native VLAN mode. For example, the following sets up a
894 bridge with port eth0 in "native-tagged" mode in VLAN 9:
897 ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
899 In this situation, "native-untagged" mode will probably work
900 equally well. Refer to the documentation for the Port table
901 in ovs-vswitchd.conf.db(5) for more information.
903 Q: I added a pair of VMs on different VLANs, like this:
906 ovs-vsctl add-port br0 eth0
907 ovs-vsctl add-port br0 tap0 tag=9
908 ovs-vsctl add-port br0 tap1 tag=10
910 but the VMs can't access each other, the external network, or the
913 A: It is to be expected that the VMs can't access each other. VLANs
914 are a means to partition a network. When you configured tap0 and
915 tap1 as access ports for different VLANs, you indicated that they
916 should be isolated from each other.
918 As for the external network and the Internet, it seems likely that
919 the machines you are trying to access are not on VLAN 9 (or 10) and
920 that the Internet is not available on VLAN 9 (or 10).
922 Q: I added a pair of VMs on the same VLAN, like this:
925 ovs-vsctl add-port br0 eth0
926 ovs-vsctl add-port br0 tap0 tag=9
927 ovs-vsctl add-port br0 tap1 tag=9
929 The VMs can access each other, but not the external network or the
932 A: It seems likely that the machines you are trying to access in the
933 external network are not on VLAN 9 and that the Internet is not
934 available on VLAN 9. Also, ensure VLAN 9 is set up as an allowed
935 trunk VLAN on the upstream switch port to which eth0 is connected.
937 Q: Can I configure an IP address on a VLAN?
939 A: Yes. Use an "internal port" configured as an access port. For
940 example, the following configures IP address 192.168.0.7 on VLAN 9.
941 That is, OVS will forward packets from eth0 to 192.168.0.7 only if
942 they have an 802.1Q header with VLAN 9. Conversely, traffic
943 forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
947 ovs-vsctl add-port br0 eth0
948 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
949 ifconfig vlan9 192.168.0.7
951 See also the following question.
953 Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
957 ovs-vsctl add-port br0 eth0
958 ifconfig br0 192.168.0.5
959 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
960 ifconfig vlan9 192.168.0.9
962 but other hosts that are only on VLAN 0 can reach the IP address
963 configured on VLAN 9. What's going on?
965 A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
966 approaches to IP address handling in Internet hosts:
968 - In the "Strong ES Model", where an ES is a host ("End
969 System"), an IP address is primarily associated with a
970 particular interface. The host discards packets that arrive
971 on interface A if they are destined for an IP address that is
972 configured on interface B. The host never sends packets from
973 interface A using a source address configured on interface B.
975 - In the "Weak ES Model", an IP address is primarily associated
976 with a host. The host accepts packets that arrive on any
977 interface if they are destined for any of the host's IP
978 addresses, even if the address is configured on some
979 interface other than the one on which it arrived. The host
980 does not restrict itself to sending packets from an IP
981 address associated with the originating interface.
983 Linux uses the weak ES model. That means that when packets
984 destined to the VLAN 9 IP address arrive on eth0 and are bridged to
985 br0, the kernel IP stack accepts them there for the VLAN 9 IP
986 address, even though they were not received on vlan9, the network
989 To simulate the strong ES model on Linux, one may add iptables rule
990 to filter packets based on source and destination address and
991 adjust ARP configuration with sysctls.
993 BSD uses the strong ES model.
995 Q: My OpenFlow controller doesn't see the VLANs that I expect.
997 A: The configuration for VLANs in the Open vSwitch database (e.g. via
998 ovs-vsctl) only affects traffic that goes through Open vSwitch's
999 implementation of the OpenFlow "normal switching" action. By
1000 default, when Open vSwitch isn't connected to a controller and
1001 nothing has been manually configured in the flow table, all traffic
1002 goes through the "normal switching" action. But, if you set up
1003 OpenFlow flows on your own, through a controller or using ovs-ofctl
1004 or through other means, then you have to implement VLAN handling
1007 You can use "normal switching" as a component of your OpenFlow
1008 actions, e.g. by putting "normal" into the lists of actions on
1009 ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
1010 controller. In situations where this is not suitable, you can
1011 implement VLAN handling yourself, e.g.:
1013 - If a packet comes in on an access port, and the flow table
1014 needs to send it out on a trunk port, then the flow can add
1015 the appropriate VLAN tag with the "mod_vlan_vid" action.
1017 - If a packet comes in on a trunk port, and the flow table
1018 needs to send it out on an access port, then the flow can
1019 strip the VLAN tag with the "strip_vlan" action.
1021 Q: I configured ports on a bridge as access ports with different VLAN
1024 ovs-vsctl add-br br0
1025 ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
1026 ovs-vsctl add-port br0 eth0
1027 ovs-vsctl add-port br0 tap0 tag=9
1028 ovs-vsctl add-port br0 tap1 tag=10
1030 but the VMs running behind tap0 and tap1 can still communicate,
1031 that is, they are not isolated from each other even though they are
1034 A: Do you have a controller configured on br0 (as the commands above
1035 do)? If so, then this is a variant on the previous question, "My
1036 OpenFlow controller doesn't see the VLANs that I expect," and you
1037 can refer to the answer there for more information.
1045 A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means
1046 to solve the scaling challenges of VLAN networks in a multi-tenant
1047 environment. VXLAN is an overlay network which transports an L2 network
1048 over an existing L3 network. For more information on VXLAN, please see
1049 the IETF draft available here:
1051 http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-03
1053 Q: How much of the VXLAN protocol does Open vSwitch currently support?
1055 A: Open vSwitch currently supports the framing format for packets on the
1056 wire. There is currently no support for the multicast aspects of VXLAN.
1057 To get around the lack of multicast support, it is possible to
1058 pre-provision MAC to IP address mappings either manually or from a
1061 Q: What destination UDP port does the VXLAN implementation in Open vSwitch
1064 A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which
1065 is 4789. However, it is possible to configure the destination UDP port
1066 manually on a per-VXLAN tunnel basis. An example of this configuration is
1069 ovs-vsctl add-br br0
1070 ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1
1071 type=vxlan options:remote_ip=192.168.1.2 options:key=flow
1072 options:dst_port=8472
1075 Using OpenFlow (Manually or Via Controller)
1076 -------------------------------------------
1078 Q: What versions of OpenFlow does Open vSwitch support?
1080 A: Open vSwitch 1.9 and earlier support only OpenFlow 1.0 (plus
1081 extensions that bring in many of the features from later versions
1084 Open vSwitch 1.10 and later have experimental support for OpenFlow
1085 1.2 and 1.3. On these versions of Open vSwitch, the following
1086 command enables OpenFlow 1.0, 1.2, and 1.3 on bridge br0:
1088 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow12,OpenFlow13
1090 Open vSwitch version 1.12 and later will have experimental support
1091 for OpenFlow 1.1, 1.2, and 1.3. On these versions of Open vSwitch,
1092 the following command enables OpenFlow 1.0, 1.1, 1.2, and 1.3 on
1095 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
1097 Use the -O option to enable support for later versions of OpenFlow
1098 in ovs-ofctl. For example:
1100 ovs-ofctl -O OpenFlow13 dump-flows br0
1102 Support for OpenFlow 1.1, 1.2, and 1.3 is still incomplete. Work
1103 to be done is tracked in OPENFLOW-1.1+ in the Open vSwitch sources
1104 (also via http://openvswitch.org/development/openflow-1-x-plan/).
1105 When support for a given OpenFlow version is solidly implemented,
1106 Open vSwitch will enable that version by default.
1108 Q: I'm getting "error type 45250 code 0". What's that?
1110 A: This is a Open vSwitch extension to OpenFlow error codes. Open
1111 vSwitch uses this extension when it must report an error to an
1112 OpenFlow controller but no standard OpenFlow error code is
1115 Open vSwitch logs the errors that it sends to controllers, so the
1116 easiest thing to do is probably to look at the ovs-vswitchd log to
1117 find out what the error was.
1119 If you want to dissect the extended error message yourself, the
1120 format is documented in include/openflow/nicira-ext.h in the Open
1121 vSwitch source distribution. The extended error codes are
1122 documented in lib/ofp-errors.h.
1124 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
1125 doesn't actually appear through the OpenFlow connection, even
1126 though I know that it's going through.
1127 Q2: Some of the OpenFlow flows that my controller sets up don't seem
1128 to apply to certain traffic, especially traffic between OVS and
1129 the controller itself.
1131 A: By default, Open vSwitch assumes that OpenFlow controllers are
1132 connected "in-band", that is, that the controllers are actually
1133 part of the network that is being controlled. In in-band mode,
1134 Open vSwitch sets up special "hidden" flows to make sure that
1135 traffic can make it back and forth between OVS and the controllers.
1136 These hidden flows are higher priority than any flows that can be
1137 set up through OpenFlow, and they are not visible through normal
1138 OpenFlow flow table dumps.
1140 Usually, the hidden flows are desirable and helpful, but
1141 occasionally they can cause unexpected behavior. You can view the
1142 full OpenFlow flow table, including hidden flows, on bridge br0
1145 ovs-appctl bridge/dump-flows br0
1147 to help you debug. The hidden flows are those with priorities
1148 greater than 65535 (the maximum priority that can be set with
1151 The DESIGN file at the top level of the Open vSwitch source
1152 distribution describes the in-band model in detail.
1154 If your controllers are not actually in-band (e.g. they are on
1155 localhost via 127.0.0.1, or on a separate network), then you should
1156 configure your controllers in "out-of-band" mode. If you have one
1157 controller on bridge br0, then you can configure out-of-band mode
1160 ovs-vsctl set controller br0 connection-mode=out-of-band
1162 Q: I configured all my controllers for out-of-band control mode but
1163 "ovs-appctl bridge/dump-flows" still shows some hidden flows.
1165 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
1166 set-manager"). By default, Open vSwitch assumes that managers need
1167 in-band rules set up on every bridge. You can disable these rules
1170 ovs-vsctl set bridge br0 other-config:disable-in-band=true
1172 This actually disables in-band control entirely for the bridge, as
1173 if all the bridge's controllers were configured for out-of-band
1176 Q: My OpenFlow controller doesn't see the VLANs that I expect.
1178 A: See answer under "VLANs", above.
1180 Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
1181 but I got a funny message like this:
1183 ofp_util|INFO|normalization changed ofp_match, details:
1184 ofp_util|INFO| pre: nw_dst=192.168.0.1
1187 and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
1188 match had disappeared, so that the flow ends up matching every
1191 A: The term "normalization" in the log message means that a flow
1192 cannot match on an L3 field without saying what L3 protocol is in
1193 use. The "ovs-ofctl" command above didn't specify an L3 protocol,
1194 so the L3 field match was dropped.
1196 In this case, the L3 protocol could be IP or ARP. A correct
1197 command for each possibility is, respectively:
1199 ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
1203 ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
1205 Similarly, a flow cannot match on an L4 field without saying what
1206 L4 protocol is in use. For example, the flow match "tp_src=1234"
1207 is, by itself, meaningless and will be ignored. Instead, to match
1208 TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
1209 source port 1234, write "udp,tp_src=1234".
1211 Q: How can I figure out the OpenFlow port number for a given port?
1213 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
1214 respond with an OFPT_FEATURES_REPLY that, among other information,
1215 includes a mapping between OpenFlow port names and numbers. From a
1216 command prompt, "ovs-ofctl show br0" makes such a request and
1217 prints the response for switch br0.
1219 The Interface table in the Open vSwitch database also maps OpenFlow
1220 port names to numbers. To print the OpenFlow port number
1221 associated with interface eth0, run:
1223 ovs-vsctl get Interface eth0 ofport
1225 You can print the entire mapping with:
1227 ovs-vsctl -- --columns=name,ofport list Interface
1229 but the output mixes together interfaces from all bridges in the
1230 database, so it may be confusing if more than one bridge exists.
1232 In the Open vSwitch database, ofport value -1 means that the
1233 interface could not be created due to an error. (The Open vSwitch
1234 log should indicate the reason.) ofport value [] (the empty set)
1235 means that the interface hasn't been created yet. The latter is
1236 normally an intermittent condition (unless ovs-vswitchd is not
1239 Q: I added some flows with my controller or with ovs-ofctl, but when I
1240 run "ovs-dpctl dump-flows" I don't see them.
1242 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
1243 won't display the information that you want. You want to use
1244 "ovs-ofctl dump-flows" instead.
1246 Q: It looks like each of the interfaces in my bonded port shows up
1247 as an individual OpenFlow port. Is that right?
1249 A: Yes, Open vSwitch makes individual bond interfaces visible as
1250 OpenFlow ports, rather than the bond as a whole. The interfaces
1251 are treated together as a bond for only a few purposes:
1253 - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
1254 controller is not configured, this happens implicitly to
1257 - Mirrors configured for output to a bonded port.
1259 It would make a lot of sense for Open vSwitch to present a bond as
1260 a single OpenFlow port. If you want to contribute an
1261 implementation of such a feature, please bring it up on the Open
1262 vSwitch development mailing list at dev@openvswitch.org.
1264 Q: I have a sophisticated network setup involving Open vSwitch, VMs or
1265 multiple hosts, and other components. The behavior isn't what I
1268 A: To debug network behavior problems, trace the path of a packet,
1269 hop-by-hop, from its origin in one host to a remote host. If
1270 that's correct, then trace the path of the response packet back to
1273 Usually a simple ICMP echo request and reply ("ping") packet is
1274 good enough. Start by initiating an ongoing "ping" from the origin
1275 host to a remote host. If you are tracking down a connectivity
1276 problem, the "ping" will not display any successful output, but
1277 packets are still being sent. (In this case the packets being sent
1278 are likely ARP rather than ICMP.)
1280 Tools available for tracing include the following:
1282 - "tcpdump" and "wireshark" for observing hops across network
1283 devices, such as Open vSwitch internal devices and physical
1286 - "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
1287 later or "ovs-dpctl dump-flows <br>" in earlier versions.
1288 These tools allow one to observe the actions being taken on
1289 packets in ongoing flows.
1291 See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
1292 documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
1293 documentation, and "Why are there so many different ways to
1294 dump flows?" above for some background.
1296 - "ovs-appctl ofproto/trace" to observe the logic behind how
1297 ovs-vswitchd treats packets. See ovs-vswitchd(8) for
1298 documentation. You can out more details about a given flow
1299 that "ovs-dpctl dump-flows" displays, by cutting and pasting
1300 a flow from the output into an "ovs-appctl ofproto/trace"
1303 - SPAN, RSPAN, and ERSPAN features of physical switches, to
1304 observe what goes on at these physical hops.
1306 Starting at the origin of a given packet, observe the packet at
1307 each hop in turn. For example, in one plausible scenario, you
1310 1. "tcpdump" the "eth" interface through which an ARP egresses
1311 a VM, from inside the VM.
1313 2. "tcpdump" the "vif" or "tap" interface through which the ARP
1314 ingresses the host machine.
1316 3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
1317 the host interface through which the ARP egresses the
1318 physical machine. You may need to use "ovs-dpctl show" to
1319 interpret the port numbers. If the output seems surprising,
1320 you can use "ovs-appctl ofproto/trace" to observe details of
1321 how ovs-vswitchd determined the actions in the "ovs-dpctl
1324 4. "tcpdump" the "eth" interface through which the ARP egresses
1325 the physical machine.
1327 5. "tcpdump" the "eth" interface through which the ARP
1328 ingresses the physical machine, at the remote host that
1331 6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
1332 remote host that receives the ARP and observe the VM "vif"
1333 or "tap" interface to which the flow is directed. Again,
1334 "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
1336 7. "tcpdump" the "vif" or "tap" interface to which the ARP is
1339 8. "tcpdump" the "eth" interface through which the ARP
1340 ingresses a VM, from inside the VM.
1342 It is likely that during one of these steps you will figure out the
1343 problem. If not, then follow the ARP reply back to the origin, in
1346 Q: How do I make a flow drop packets?
1348 A: To drop a packet is to receive it without forwarding it. OpenFlow
1349 explicitly specifies forwarding actions. Thus, a flow with an
1350 empty set of actions does not forward packets anywhere, causing
1351 them to be dropped. You can specify an empty set of actions with
1352 "actions=" on the ovs-ofctl command line. For example:
1354 ovs-ofctl add-flow br0 priority=65535,actions=
1356 would cause every packet entering switch br0 to be dropped.
1358 You can write "drop" explicitly if you like. The effect is the
1359 same. Thus, the following command also causes every packet
1360 entering switch br0 to be dropped:
1362 ovs-ofctl add-flow br0 priority=65535,actions=drop
1364 "drop" is not an action, either in OpenFlow or Open vSwitch.
1365 Rather, it is only a way to say that there are no actions.
1367 Q: I added a flow to send packets out the ingress port, like this:
1369 ovs-ofctl add-flow br0 in_port=2,actions=2
1371 but OVS drops the packets instead.
1373 A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
1374 out its ingress port. The rationale is that dropping these packets
1375 makes it harder to loop the network. Sometimes this behavior can
1376 even be convenient, e.g. it is often the desired behavior in a flow
1377 that forwards a packet to several ports ("floods" the packet).
1379 Sometimes one really needs to send a packet out its ingress port.
1380 In this case, output to OFPP_IN_PORT, which in ovs-ofctl syntax is
1381 expressed as just "in_port", e.g.:
1383 ovs-ofctl add-flow br0 in_port=2,actions=in_port
1385 This also works in some circumstances where the flow doesn't match
1386 on the input port. For example, if you know that your switch has
1387 five ports numbered 2 through 6, then the following will send every
1388 received packet out every port, even its ingress port:
1390 ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
1394 ovs-ofctl add-flow br0 actions=all,in_port
1396 Sometimes, in complicated flow tables with multiple levels of
1397 "resubmit" actions, a flow needs to output to a particular port
1398 that may or may not be the ingress port. It's difficult to take
1399 advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch
1400 provides, as an OpenFlow extension, the ability to modify the
1401 in_port field. Whatever value is currently in the in_port field is
1402 the port to which outputs will be dropped, as well as the
1403 destination for OFPP_IN_PORT. This means that the following will
1404 reliably output to port 2 or to ports 2 through 6, respectively:
1406 ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
1407 ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
1409 If the input port is important, then one may save and restore it on
1412 ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
1413 load:0->NXM_OF_IN_PORT[],\
1415 pop:NXM_OF_IN_PORT[]
1417 Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2
1418 on port 2. I set up flows to forward only traffic destined to the
1419 other host and drop other traffic, like this:
1421 priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2
1422 priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1
1423 priority=0,actions=drop
1425 But it doesn't work--I don't get any connectivity when I do this.
1428 A: These flows drop the ARP packets that IP hosts use to establish IP
1429 connectivity over Ethernet. To solve the problem, add flows to
1430 allow ARP to pass between the hosts:
1432 priority=5,in_port=1,arp,actions=2
1433 priority=5,in_port=2,arp,actions=1
1435 This issue can manifest other ways, too. The following flows that
1436 match on Ethernet addresses instead of IP addresses will also drop
1437 ARP packets, because ARP requests are broadcast instead of being
1438 directed to a specific host:
1440 priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2
1441 priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1
1442 priority=0,actions=drop
1444 The solution already described above will also work in this case.
1445 It may be better to add flows to allow all multicast and broadcast
1448 priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
1449 priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
1454 bugs@openvswitch.org
1455 http://openvswitch.org/
git://git.onelab.eu / sliver-openvswitch.git / blob