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
421 Q: Why are there so many different ways to dump flows?
423 A: Open vSwitch uses different kinds of flows for different purposes:
425 - OpenFlow flows are the most important kind of flow. OpenFlow
426 controllers use these flows to define a switch's policy.
427 OpenFlow flows support wildcards, priorities, and multiple
430 When in-band control is in use, Open vSwitch sets up a few
431 "hidden" flows, with priority higher than a controller or the
432 user can configure, that are not visible via OpenFlow. (See
433 the "Controller" section of the FAQ for more information
436 - The Open vSwitch software switch implementation uses a second
437 kind of flow internally. These flows, called "exact-match"
438 or "datapath" or "kernel" flows, do not support wildcards or
439 priorities and comprise only a single table, which makes them
440 suitable for caching. OpenFlow flows and exact-match flows
441 also support different actions and number ports differently.
443 Exact-match flows are an implementation detail that is
444 subject to change in future versions of Open vSwitch. Even
445 with the current version of Open vSwitch, hardware switch
446 implementations do not necessarily use exact-match flows.
448 Each of the commands for dumping flows has a different purpose:
450 - "ovs-ofctl dump-flows <br>" dumps OpenFlow flows, excluding
451 hidden flows. This is the most commonly useful form of flow
452 dump. (Unlike the other commands, this should work with any
453 OpenFlow switch, not just Open vSwitch.)
455 - "ovs-appctl bridge/dump-flows <br>" dumps OpenFlow flows,
456 including hidden flows. This is occasionally useful for
457 troubleshooting suspected issues with in-band control.
459 - "ovs-dpctl dump-flows [dp]" dumps the exact-match flow table
460 entries for a Linux kernel-based datapath. In Open vSwitch
461 1.10 and later, ovs-vswitchd merges multiple switches into a
462 single datapath, so it will show all the flows on all your
463 kernel-based switches. This command can occasionally be
464 useful for debugging.
466 - "ovs-appctl dpif/dump-flows <br>", new in Open vSwitch 1.10,
467 dumps exact-match flows for only the specified bridge,
468 regardless of the type.
474 Q: I just upgraded and I see a performance drop. Why?
476 A: The OVS kernel datapath may have been updated to a newer version than
477 the OVS userspace components. Sometimes new versions of OVS kernel
478 module add functionality that is backwards compatible with older
479 userspace components but may cause a drop in performance with them.
480 Especially, if a kernel module from OVS 2.1 or newer is paired with
481 OVS userspace 1.10 or older, there will be a performance drop for
484 Updating the OVS userspace components to the latest released
485 version should fix the performance degradation.
487 To get the best possible performance and functionality, it is
488 recommended to pair the same versions of the kernel module and OVS
492 Configuration Problems
493 ----------------------
495 Q: I created a bridge and added my Ethernet port to it, using commands
499 ovs-vsctl add-port br0 eth0
501 and as soon as I ran the "add-port" command I lost all connectivity
504 A: A physical Ethernet device that is part of an Open vSwitch bridge
505 should not have an IP address. If one does, then that IP address
506 will not be fully functional.
508 You can restore functionality by moving the IP address to an Open
509 vSwitch "internal" device, such as the network device named after
510 the bridge itself. For example, assuming that eth0's IP address is
511 192.168.128.5, you could run the commands below to fix up the
514 ifconfig eth0 0.0.0.0
515 ifconfig br0 192.168.128.5
517 (If your only connection to the machine running OVS is through the
518 IP address in question, then you would want to run all of these
519 commands on a single command line, or put them into a script.) If
520 there were any additional routes assigned to eth0, then you would
521 also want to use commands to adjust these routes to go through br0.
523 If you use DHCP to obtain an IP address, then you should kill the
524 DHCP client that was listening on the physical Ethernet interface
525 (e.g. eth0) and start one listening on the internal interface
526 (e.g. br0). You might still need to manually clear the IP address
527 from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
529 There is no compelling reason why Open vSwitch must work this way.
530 However, this is the way that the Linux kernel bridge module has
531 always worked, so it's a model that those accustomed to Linux
532 bridging are already used to. Also, the model that most people
533 expect is not implementable without kernel changes on all the
534 versions of Linux that Open vSwitch supports.
536 By the way, this issue is not specific to physical Ethernet
537 devices. It applies to all network devices except Open vswitch
540 Q: I created a bridge and added a couple of Ethernet ports to it,
541 using commands like these:
544 ovs-vsctl add-port br0 eth0
545 ovs-vsctl add-port br0 eth1
547 and now my network seems to have melted: connectivity is unreliable
548 (even connectivity that doesn't go through Open vSwitch), all the
549 LEDs on my physical switches are blinking, wireshark shows
550 duplicated packets, and CPU usage is very high.
552 A: More than likely, you've looped your network. Probably, eth0 and
553 eth1 are connected to the same physical Ethernet switch. This
554 yields a scenario where OVS receives a broadcast packet on eth0 and
555 sends it out on eth1, then the physical switch connected to eth1
556 sends the packet back on eth0, and so on forever. More complicated
557 scenarios, involving a loop through multiple switches, are possible
560 The solution depends on what you are trying to do:
562 - If you added eth0 and eth1 to get higher bandwidth or higher
563 reliability between OVS and your physical Ethernet switch,
564 use a bond. The following commands create br0 and then add
565 eth0 and eth1 as a bond:
568 ovs-vsctl add-bond br0 bond0 eth0 eth1
570 Bonds have tons of configuration options. Please read the
571 documentation on the Port table in ovs-vswitchd.conf.db(5)
574 - Perhaps you don't actually need eth0 and eth1 to be on the
575 same bridge. For example, if you simply want to be able to
576 connect each of them to virtual machines, then you can put
577 each of them on a bridge of its own:
580 ovs-vsctl add-port br0 eth0
583 ovs-vsctl add-port br1 eth1
585 and then connect VMs to br0 and br1. (A potential
586 disadvantage is that traffic cannot directly pass between br0
587 and br1. Instead, it will go out eth0 and come back in eth1,
590 - If you have a redundant or complex network topology and you
591 want to prevent loops, turn on spanning tree protocol (STP).
592 The following commands create br0, enable STP, and add eth0
593 and eth1 to the bridge. The order is important because you
594 don't want have to have a loop in your network even
598 ovs-vsctl set bridge br0 stp_enable=true
599 ovs-vsctl add-port br0 eth0
600 ovs-vsctl add-port br0 eth1
602 The Open vSwitch implementation of STP is not well tested.
603 Please report any bugs you observe, but if you'd rather avoid
604 acting as a beta tester then another option might be your
607 Q: I can't seem to use Open vSwitch in a wireless network.
609 A: Wireless base stations generally only allow packets with the source
610 MAC address of NIC that completed the initial handshake.
611 Therefore, without MAC rewriting, only a single device can
612 communicate over a single wireless link.
614 This isn't specific to Open vSwitch, it's enforced by the access
615 point, so the same problems will show up with the Linux bridge or
616 any other way to do bridging.
618 Q: I can't seem to add my PPP interface to an Open vSwitch bridge.
620 A: PPP most commonly carries IP packets, but Open vSwitch works only
621 with Ethernet frames. The correct way to interface PPP to an
622 Ethernet network is usually to use routing instead of switching.
624 Q: Is there any documentation on the database tables and fields?
626 A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference.
628 Q: When I run ovs-dpctl I no longer see the bridges I created. Instead,
629 I only see a datapath called "ovs-system". How can I see datapath
630 information about a particular bridge?
632 A: In version 1.9.0, OVS switched to using a single datapath that is
633 shared by all bridges of that type. The "ovs-appctl dpif/*"
634 commands provide similar functionality that is scoped by the bridge.
637 Quality of Service (QoS)
638 ------------------------
640 Q: How do I configure Quality of Service (QoS)?
642 A: Suppose that you want to set up bridge br0 connected to physical
643 Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
644 vif1.0 and vif2.0, and that you want to limit traffic from vif1.0
645 to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps. Then, you
646 could configure the bridge this way:
650 add-port br0 eth0 -- \
651 add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \
652 add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \
653 set port eth0 qos=@newqos -- \
654 --id=@newqos create qos type=linux-htb \
655 other-config:max-rate=1000000000 \
656 queues:123=@vif10queue \
657 queues:234=@vif20queue -- \
658 --id=@vif10queue create queue other-config:max-rate=10000000 -- \
659 --id=@vif20queue create queue other-config:max-rate=20000000
661 At this point, bridge br0 is configured with the ports and eth0 is
662 configured with the queues that you need for QoS, but nothing is
663 actually directing packets from vif1.0 or vif2.0 to the queues that
664 we have set up for them. That means that all of the packets to
665 eth0 are going to the "default queue", which is not what we want.
667 We use OpenFlow to direct packets from vif1.0 and vif2.0 to the
668 queues reserved for them:
670 ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal
671 ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal
673 Each of the above flows matches on the input port, sets up the
674 appropriate queue (123 for vif1.0, 234 for vif2.0), and then
675 executes the "normal" action, which performs the same switching
676 that Open vSwitch would have done without any OpenFlow flows being
677 present. (We know that vif1.0 and vif2.0 have OpenFlow port
678 numbers 5 and 6, respectively, because we set their ofport_request
679 columns above. If we had not done that, then we would have needed
680 to find out their port numbers before setting up these flows.)
682 Now traffic going from vif1.0 or vif2.0 to eth0 should be
685 By the way, if you delete the bridge created by the above commands,
690 then that will leave one unreferenced QoS record and two
691 unreferenced Queue records in the Open vSwich database. One way to
692 clear them out, assuming you don't have other QoS or Queue records
693 that you want to keep, is:
695 ovs-vsctl -- --all destroy QoS -- --all destroy Queue
697 If you do want to keep some QoS or Queue records, or the Open
698 vSwitch you are using is older than version 1.8 (which added the
699 --all option), then you will have to destroy QoS and Queue records
702 Q: I configured Quality of Service (QoS) in my OpenFlow network by
703 adding records to the QoS and Queue table, but the results aren't
706 A: Did you install OpenFlow flows that use your queues? This is the
707 primary way to tell Open vSwitch which queues you want to use. If
708 you don't do this, then the default queue will be used, which will
709 probably not have the effect you want.
711 Refer to the previous question for an example.
713 Q: I configured QoS, correctly, but my measurements show that it isn't
714 working as well as I expect.
716 A: With the Linux kernel, the Open vSwitch implementation of QoS has
719 - Open vSwitch configures a subset of Linux kernel QoS
720 features, according to what is in OVSDB. It is possible that
721 this code has bugs. If you believe that this is so, then you
722 can configure the Linux traffic control (QoS) stack directly
723 with the "tc" program. If you get better results that way,
724 you can send a detailed bug report to bugs@openvswitch.org.
726 It is certain that Open vSwitch cannot configure every Linux
727 kernel QoS feature. If you need some feature that OVS cannot
728 configure, then you can also use "tc" directly (or add that
731 - The Open vSwitch implementation of OpenFlow allows flows to
732 be directed to particular queues. This is pretty simple and
733 unlikely to have serious bugs at this point.
735 However, most problems with QoS on Linux are not bugs in Open
736 vSwitch at all. They tend to be either configuration errors
737 (please see the earlier questions in this section) or issues with
738 the traffic control (QoS) stack in Linux. The Open vSwitch
739 developers are not experts on Linux traffic control. We suggest
740 that, if you believe you are encountering a problem with Linux
741 traffic control, that you consult the tc manpages (e.g. tc(8),
742 tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or
743 mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev).
751 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
752 partition a single switch into multiple switches. Suppose, for
753 example, that you have two groups of machines, group A and group B.
754 You want the machines in group A to be able to talk to each other,
755 and you want the machine in group B to be able to talk to each
756 other, but you don't want the machines in group A to be able to
757 talk to the machines in group B. You can do this with two
758 switches, by plugging the machines in group A into one switch and
759 the machines in group B into the other switch.
761 If you only have one switch, then you can use VLANs to do the same
762 thing, by configuring the ports for machines in group A as VLAN
763 "access ports" for one VLAN and the ports for group B as "access
764 ports" for a different VLAN. The switch will only forward packets
765 between ports that are assigned to the same VLAN, so this
766 effectively subdivides your single switch into two independent
767 switches, one for each group of machines.
769 So far we haven't said anything about VLAN headers. With access
770 ports, like we've described so far, no VLAN header is present in
771 the Ethernet frame. This means that the machines (or switches)
772 connected to access ports need not be aware that VLANs are
773 involved, just like in the case where we use two different physical
776 Now suppose that you have a whole bunch of switches in your
777 network, instead of just one, and that some machines in group A are
778 connected directly to both switches 1 and 2. To allow these
779 machines to talk to each other, you could add an access port for
780 group A's VLAN to switch 1 and another to switch 2, and then
781 connect an Ethernet cable between those ports. That works fine,
782 but it doesn't scale well as the number of switches and the number
783 of VLANs increases, because you use up a lot of valuable switch
784 ports just connecting together your VLANs.
786 This is where VLAN headers come in. Instead of using one cable and
787 two ports per VLAN to connect a pair of switches, we configure a
788 port on each switch as a VLAN "trunk port". Packets sent and
789 received on a trunk port carry a VLAN header that says what VLAN
790 the packet belongs to, so that only two ports total are required to
791 connect the switches, regardless of the number of VLANs in use.
792 Normally, only switches (either physical or virtual) are connected
793 to a trunk port, not individual hosts, because individual hosts
794 don't expect to see a VLAN header in the traffic that they receive.
796 None of the above discussion says anything about particular VLAN
797 numbers. This is because VLAN numbers are completely arbitrary.
798 One must only ensure that a given VLAN is numbered consistently
799 throughout a network and that different VLANs are given different
800 numbers. (That said, VLAN 0 is usually synonymous with a packet
801 that has no VLAN header, and VLAN 4095 is reserved.)
805 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
806 bugs. If you are having problems with VLANs that you suspect to be
807 driver related, then you have several options:
809 - Upgrade to Linux 3.3 or later.
811 - Build and install a fixed version of the particular driver
812 that is causing trouble, if one is available.
814 - Use a NIC whose driver does not have VLAN problems.
816 - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
817 that works around bugs in kernel drivers. To enable VLAN
818 splinters on interface eth0, use the command:
820 ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
822 For VLAN splinters to be effective, Open vSwitch must know
823 which VLANs are in use. See the "VLAN splinters" section in
824 the Interface table in ovs-vswitchd.conf.db(5) for details on
825 how Open vSwitch infers in-use VLANs.
827 VLAN splinters increase memory use and reduce performance, so
828 use them only if needed.
830 - Apply the "vlan workaround" patch from the XenServer kernel
831 patch queue, build Open vSwitch against this patched kernel,
832 and then use ovs-vlan-bug-workaround(8) to enable the VLAN
833 workaround for each interface whose driver is buggy.
835 (This is a nontrivial exercise, so this option is included
836 only for completeness.)
838 It is not always easy to tell whether a Linux kernel driver has
839 buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities
840 can help you test. See their manpages for details. Of the two
841 utilities, ovs-test(8) is newer and more thorough, but
842 ovs-vlan-test(8) may be easier to use.
844 Q: VLANs still don't work. I've tested the driver so I know that it's OK.
846 A: Do you have VLANs enabled on the physical switch that OVS is
847 attached to? Make sure that the port is configured to trunk the
848 VLAN or VLANs that you are using with OVS.
850 Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
851 and to its destination host, but OVS seems to drop incoming return
854 A: It's possible that you have the VLAN configured on your physical
855 switch as the "native" VLAN. In this mode, the switch treats
856 incoming packets either tagged with the native VLAN or untagged as
857 part of the native VLAN. It may also send outgoing packets in the
858 native VLAN without a VLAN tag.
860 If this is the case, you have two choices:
862 - Change the physical switch port configuration to tag packets
863 it forwards to OVS with the native VLAN instead of forwarding
866 - Change the OVS configuration for the physical port to a
867 native VLAN mode. For example, the following sets up a
868 bridge with port eth0 in "native-tagged" mode in VLAN 9:
871 ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
873 In this situation, "native-untagged" mode will probably work
874 equally well. Refer to the documentation for the Port table
875 in ovs-vswitchd.conf.db(5) for more information.
877 Q: I added a pair of VMs on different VLANs, like this:
880 ovs-vsctl add-port br0 eth0
881 ovs-vsctl add-port br0 tap0 tag=9
882 ovs-vsctl add-port br0 tap1 tag=10
884 but the VMs can't access each other, the external network, or the
887 A: It is to be expected that the VMs can't access each other. VLANs
888 are a means to partition a network. When you configured tap0 and
889 tap1 as access ports for different VLANs, you indicated that they
890 should be isolated from each other.
892 As for the external network and the Internet, it seems likely that
893 the machines you are trying to access are not on VLAN 9 (or 10) and
894 that the Internet is not available on VLAN 9 (or 10).
896 Q: I added a pair of VMs on the same VLAN, like this:
899 ovs-vsctl add-port br0 eth0
900 ovs-vsctl add-port br0 tap0 tag=9
901 ovs-vsctl add-port br0 tap1 tag=9
903 The VMs can access each other, but not the external network or the
906 A: It seems likely that the machines you are trying to access in the
907 external network are not on VLAN 9 and that the Internet is not
908 available on VLAN 9. Also, ensure VLAN 9 is set up as an allowed
909 trunk VLAN on the upstream switch port to which eth0 is connected.
911 Q: Can I configure an IP address on a VLAN?
913 A: Yes. Use an "internal port" configured as an access port. For
914 example, the following configures IP address 192.168.0.7 on VLAN 9.
915 That is, OVS will forward packets from eth0 to 192.168.0.7 only if
916 they have an 802.1Q header with VLAN 9. Conversely, traffic
917 forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
921 ovs-vsctl add-port br0 eth0
922 ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
923 ifconfig vlan9 192.168.0.7
925 Q: My OpenFlow controller doesn't see the VLANs that I expect.
927 A: The configuration for VLANs in the Open vSwitch database (e.g. via
928 ovs-vsctl) only affects traffic that goes through Open vSwitch's
929 implementation of the OpenFlow "normal switching" action. By
930 default, when Open vSwitch isn't connected to a controller and
931 nothing has been manually configured in the flow table, all traffic
932 goes through the "normal switching" action. But, if you set up
933 OpenFlow flows on your own, through a controller or using ovs-ofctl
934 or through other means, then you have to implement VLAN handling
937 You can use "normal switching" as a component of your OpenFlow
938 actions, e.g. by putting "normal" into the lists of actions on
939 ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
940 controller. In situations where this is not suitable, you can
941 implement VLAN handling yourself, e.g.:
943 - If a packet comes in on an access port, and the flow table
944 needs to send it out on a trunk port, then the flow can add
945 the appropriate VLAN tag with the "mod_vlan_vid" action.
947 - If a packet comes in on a trunk port, and the flow table
948 needs to send it out on an access port, then the flow can
949 strip the VLAN tag with the "strip_vlan" action.
951 Q: I configured ports on a bridge as access ports with different VLAN
955 ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
956 ovs-vsctl add-port br0 eth0
957 ovs-vsctl add-port br0 tap0 tag=9
958 ovs-vsctl add-port br0 tap1 tag=10
960 but the VMs running behind tap0 and tap1 can still communicate,
961 that is, they are not isolated from each other even though they are
964 A: Do you have a controller configured on br0 (as the commands above
965 do)? If so, then this is a variant on the previous question, "My
966 OpenFlow controller doesn't see the VLANs that I expect," and you
967 can refer to the answer there for more information.
975 A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means
976 to solve the scaling challenges of VLAN networks in a multi-tenant
977 environment. VXLAN is an overlay network which transports an L2 network
978 over an existing L3 network. For more information on VXLAN, please see
979 the IETF draft available here:
981 http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-03
983 Q: How much of the VXLAN protocol does Open vSwitch currently support?
985 A: Open vSwitch currently supports the framing format for packets on the
986 wire. There is currently no support for the multicast aspects of VXLAN.
987 To get around the lack of multicast support, it is possible to
988 pre-provision MAC to IP address mappings either manually or from a
991 Q: What destination UDP port does the VXLAN implementation in Open vSwitch
994 A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which
995 is 4789. However, it is possible to configure the destination UDP port
996 manually on a per-VXLAN tunnel basis. An example of this configuration is
1000 ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1
1001 type=vxlan options:remote_ip=192.168.1.2 options:key=flow
1002 options:dst_port=8472
1005 Using OpenFlow (Manually or Via Controller)
1006 -------------------------------------------
1008 Q: What versions of OpenFlow does Open vSwitch support?
1010 A: Open vSwitch 1.9 and earlier support only OpenFlow 1.0 (plus
1011 extensions that bring in many of the features from later versions
1014 Open vSwitch 1.10 and later have experimental support for OpenFlow
1015 1.2 and 1.3. On these versions of Open vSwitch, the following
1016 command enables OpenFlow 1.0, 1.2, and 1.3 on bridge br0:
1018 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow12,OpenFlow13
1020 Open vSwitch version 1.12 and later will have experimental support
1021 for OpenFlow 1.1, 1.2, and 1.3. On these versions of Open vSwitch,
1022 the following command enables OpenFlow 1.0, 1.1, 1.2, and 1.3 on
1025 ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
1027 Use the -O option to enable support for later versions of OpenFlow
1028 in ovs-ofctl. For example:
1030 ovs-ofctl -O OpenFlow13 dump-flows br0
1032 Support for OpenFlow 1.1, 1.2, and 1.3 is still incomplete. Work
1033 to be done is tracked in OPENFLOW-1.1+ in the Open vSwitch sources
1034 (also via http://openvswitch.org/development/openflow-1-x-plan/).
1035 When support for a given OpenFlow version is solidly implemented,
1036 Open vSwitch will enable that version by default.
1038 Q: I'm getting "error type 45250 code 0". What's that?
1040 A: This is a Open vSwitch extension to OpenFlow error codes. Open
1041 vSwitch uses this extension when it must report an error to an
1042 OpenFlow controller but no standard OpenFlow error code is
1045 Open vSwitch logs the errors that it sends to controllers, so the
1046 easiest thing to do is probably to look at the ovs-vswitchd log to
1047 find out what the error was.
1049 If you want to dissect the extended error message yourself, the
1050 format is documented in include/openflow/nicira-ext.h in the Open
1051 vSwitch source distribution. The extended error codes are
1052 documented in lib/ofp-errors.h.
1054 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
1055 doesn't actually appear through the OpenFlow connection, even
1056 though I know that it's going through.
1057 Q2: Some of the OpenFlow flows that my controller sets up don't seem
1058 to apply to certain traffic, especially traffic between OVS and
1059 the controller itself.
1061 A: By default, Open vSwitch assumes that OpenFlow controllers are
1062 connected "in-band", that is, that the controllers are actually
1063 part of the network that is being controlled. In in-band mode,
1064 Open vSwitch sets up special "hidden" flows to make sure that
1065 traffic can make it back and forth between OVS and the controllers.
1066 These hidden flows are higher priority than any flows that can be
1067 set up through OpenFlow, and they are not visible through normal
1068 OpenFlow flow table dumps.
1070 Usually, the hidden flows are desirable and helpful, but
1071 occasionally they can cause unexpected behavior. You can view the
1072 full OpenFlow flow table, including hidden flows, on bridge br0
1075 ovs-appctl bridge/dump-flows br0
1077 to help you debug. The hidden flows are those with priorities
1078 greater than 65535 (the maximum priority that can be set with
1081 The DESIGN file at the top level of the Open vSwitch source
1082 distribution describes the in-band model in detail.
1084 If your controllers are not actually in-band (e.g. they are on
1085 localhost via 127.0.0.1, or on a separate network), then you should
1086 configure your controllers in "out-of-band" mode. If you have one
1087 controller on bridge br0, then you can configure out-of-band mode
1090 ovs-vsctl set controller br0 connection-mode=out-of-band
1092 Q: I configured all my controllers for out-of-band control mode but
1093 "ovs-appctl bridge/dump-flows" still shows some hidden flows.
1095 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
1096 set-manager"). By default, Open vSwitch assumes that managers need
1097 in-band rules set up on every bridge. You can disable these rules
1100 ovs-vsctl set bridge br0 other-config:disable-in-band=true
1102 This actually disables in-band control entirely for the bridge, as
1103 if all the bridge's controllers were configured for out-of-band
1106 Q: My OpenFlow controller doesn't see the VLANs that I expect.
1108 A: See answer under "VLANs", above.
1110 Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
1111 but I got a funny message like this:
1113 ofp_util|INFO|normalization changed ofp_match, details:
1114 ofp_util|INFO| pre: nw_dst=192.168.0.1
1117 and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
1118 match had disappeared, so that the flow ends up matching every
1121 A: The term "normalization" in the log message means that a flow
1122 cannot match on an L3 field without saying what L3 protocol is in
1123 use. The "ovs-ofctl" command above didn't specify an L3 protocol,
1124 so the L3 field match was dropped.
1126 In this case, the L3 protocol could be IP or ARP. A correct
1127 command for each possibility is, respectively:
1129 ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
1133 ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
1135 Similarly, a flow cannot match on an L4 field without saying what
1136 L4 protocol is in use. For example, the flow match "tp_src=1234"
1137 is, by itself, meaningless and will be ignored. Instead, to match
1138 TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
1139 source port 1234, write "udp,tp_src=1234".
1141 Q: How can I figure out the OpenFlow port number for a given port?
1143 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
1144 respond with an OFPT_FEATURES_REPLY that, among other information,
1145 includes a mapping between OpenFlow port names and numbers. From a
1146 command prompt, "ovs-ofctl show br0" makes such a request and
1147 prints the response for switch br0.
1149 The Interface table in the Open vSwitch database also maps OpenFlow
1150 port names to numbers. To print the OpenFlow port number
1151 associated with interface eth0, run:
1153 ovs-vsctl get Interface eth0 ofport
1155 You can print the entire mapping with:
1157 ovs-vsctl -- --columns=name,ofport list Interface
1159 but the output mixes together interfaces from all bridges in the
1160 database, so it may be confusing if more than one bridge exists.
1162 In the Open vSwitch database, ofport value -1 means that the
1163 interface could not be created due to an error. (The Open vSwitch
1164 log should indicate the reason.) ofport value [] (the empty set)
1165 means that the interface hasn't been created yet. The latter is
1166 normally an intermittent condition (unless ovs-vswitchd is not
1169 Q: I added some flows with my controller or with ovs-ofctl, but when I
1170 run "ovs-dpctl dump-flows" I don't see them.
1172 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch. It
1173 won't display the information that you want. You want to use
1174 "ovs-ofctl dump-flows" instead.
1176 Q: It looks like each of the interfaces in my bonded port shows up
1177 as an individual OpenFlow port. Is that right?
1179 A: Yes, Open vSwitch makes individual bond interfaces visible as
1180 OpenFlow ports, rather than the bond as a whole. The interfaces
1181 are treated together as a bond for only a few purposes:
1183 - Sending a packet to the OFPP_NORMAL port. (When an OpenFlow
1184 controller is not configured, this happens implicitly to
1187 - Mirrors configured for output to a bonded port.
1189 It would make a lot of sense for Open vSwitch to present a bond as
1190 a single OpenFlow port. If you want to contribute an
1191 implementation of such a feature, please bring it up on the Open
1192 vSwitch development mailing list at dev@openvswitch.org.
1194 Q: I have a sophisticated network setup involving Open vSwitch, VMs or
1195 multiple hosts, and other components. The behavior isn't what I
1198 A: To debug network behavior problems, trace the path of a packet,
1199 hop-by-hop, from its origin in one host to a remote host. If
1200 that's correct, then trace the path of the response packet back to
1203 Usually a simple ICMP echo request and reply ("ping") packet is
1204 good enough. Start by initiating an ongoing "ping" from the origin
1205 host to a remote host. If you are tracking down a connectivity
1206 problem, the "ping" will not display any successful output, but
1207 packets are still being sent. (In this case the packets being sent
1208 are likely ARP rather than ICMP.)
1210 Tools available for tracing include the following:
1212 - "tcpdump" and "wireshark" for observing hops across network
1213 devices, such as Open vSwitch internal devices and physical
1216 - "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
1217 later or "ovs-dpctl dump-flows <br>" in earlier versions.
1218 These tools allow one to observe the actions being taken on
1219 packets in ongoing flows.
1221 See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
1222 documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
1223 documentation, and "Why are there so many different ways to
1224 dump flows?" above for some background.
1226 - "ovs-appctl ofproto/trace" to observe the logic behind how
1227 ovs-vswitchd treats packets. See ovs-vswitchd(8) for
1228 documentation. You can out more details about a given flow
1229 that "ovs-dpctl dump-flows" displays, by cutting and pasting
1230 a flow from the output into an "ovs-appctl ofproto/trace"
1233 - SPAN, RSPAN, and ERSPAN features of physical switches, to
1234 observe what goes on at these physical hops.
1236 Starting at the origin of a given packet, observe the packet at
1237 each hop in turn. For example, in one plausible scenario, you
1240 1. "tcpdump" the "eth" interface through which an ARP egresses
1241 a VM, from inside the VM.
1243 2. "tcpdump" the "vif" or "tap" interface through which the ARP
1244 ingresses the host machine.
1246 3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
1247 the host interface through which the ARP egresses the
1248 physical machine. You may need to use "ovs-dpctl show" to
1249 interpret the port numbers. If the output seems surprising,
1250 you can use "ovs-appctl ofproto/trace" to observe details of
1251 how ovs-vswitchd determined the actions in the "ovs-dpctl
1254 4. "tcpdump" the "eth" interface through which the ARP egresses
1255 the physical machine.
1257 5. "tcpdump" the "eth" interface through which the ARP
1258 ingresses the physical machine, at the remote host that
1261 6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
1262 remote host that receives the ARP and observe the VM "vif"
1263 or "tap" interface to which the flow is directed. Again,
1264 "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
1266 7. "tcpdump" the "vif" or "tap" interface to which the ARP is
1269 8. "tcpdump" the "eth" interface through which the ARP
1270 ingresses a VM, from inside the VM.
1272 It is likely that during one of these steps you will figure out the
1273 problem. If not, then follow the ARP reply back to the origin, in
1276 Q: How do I make a flow drop packets?
1278 A: To drop a packet is to receive it without forwarding it. OpenFlow
1279 explicitly specifies forwarding actions. Thus, a flow with an
1280 empty set of actions does not forward packets anywhere, causing
1281 them to be dropped. You can specify an empty set of actions with
1282 "actions=" on the ovs-ofctl command line. For example:
1284 ovs-ofctl add-flow br0 priority=65535,actions=
1286 would cause every packet entering switch br0 to be dropped.
1288 You can write "drop" explicitly if you like. The effect is the
1289 same. Thus, the following command also causes every packet
1290 entering switch br0 to be dropped:
1292 ovs-ofctl add-flow br0 priority=65535,actions=drop
1294 "drop" is not an action, either in OpenFlow or Open vSwitch.
1295 Rather, it is only a way to say that there are no actions.
1297 Q: I added a flow to send packets out the ingress port, like this:
1299 ovs-ofctl add-flow br0 in_port=2,actions=2
1301 but OVS drops the packets instead.
1303 A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
1304 out its ingress port. The rationale is that dropping these packets
1305 makes it harder to loop the network. Sometimes this behavior can
1306 even be convenient, e.g. it is often the desired behavior in a flow
1307 that forwards a packet to several ports ("floods" the packet).
1309 Sometimes one really needs to send a packet out its ingress port.
1310 In this case, output to OFPP_IN_PORT, which in ovs-ofctl syntax is
1311 expressed as just "in_port", e.g.:
1313 ovs-ofctl add-flow br0 in_port=2,actions=in_port
1315 This also works in some circumstances where the flow doesn't match
1316 on the input port. For example, if you know that your switch has
1317 five ports numbered 2 through 6, then the following will send every
1318 received packet out every port, even its ingress port:
1320 ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
1324 ovs-ofctl add-flow br0 actions=all,in_port
1326 Sometimes, in complicated flow tables with multiple levels of
1327 "resubmit" actions, a flow needs to output to a particular port
1328 that may or may not be the ingress port. It's difficult to take
1329 advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch
1330 provides, as an OpenFlow extension, the ability to modify the
1331 in_port field. Whatever value is currently in the in_port field is
1332 the port to which outputs will be dropped, as well as the
1333 destination for OFPP_IN_PORT. This means that the following will
1334 reliably output to port 2 or to ports 2 through 6, respectively:
1336 ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
1337 ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
1339 If the input port is important, then one may save and restore it on
1342 ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
1343 load:0->NXM_OF_IN_PORT[],\
1345 pop:NXM_OF_IN_PORT[]
1347 Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2
1348 on port 2. I set up flows to forward only traffic destined to the
1349 other host and drop other traffic, like this:
1351 priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2
1352 priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1
1353 priority=0,actions=drop
1355 But it doesn't work--I don't get any connectivity when I do this.
1358 A: These flows drop the ARP packets that IP hosts use to establish IP
1359 connectivity over Ethernet. To solve the problem, add flows to
1360 allow ARP to pass between the hosts:
1362 priority=5,in_port=1,arp,actions=2
1363 priority=5,in_port=2,arp,actions=1
1365 This issue can manifest other ways, too. The following flows that
1366 match on Ethernet addresses instead of IP addresses will also drop
1367 ARP packets, because ARP requests are broadcast instead of being
1368 directed to a specific host:
1370 priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2
1371 priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1
1372 priority=0,actions=drop
1374 The solution already described above will also work in this case.
1375 It may be better to add flows to allow all multicast and broadcast
1378 priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
1379 priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
1384 bugs@openvswitch.org
1385 http://openvswitch.org/
git://git.onelab.eu / sliver-openvswitch.git / blob