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1 | Open vSwitch <http://openvswitch.org> |
2 | ||
3 | Frequently Asked Questions | |
4 | ========================== | |
5 | ||
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6 | General |
7 | ------- | |
8 | ||
9 | Q: What is Open vSwitch? | |
10 | ||
11 | A: Open vSwitch is a production quality open source software switch | |
12 | designed to be used as a vswitch in virtualized server environments. A | |
13 | vswitch forwards traffic between different VMs on the same physical host | |
14 | and also forwards traffic between VMs and the physical network. Open | |
15 | vSwitch supports standard management interfaces (e.g. sFlow, NetFlow, | |
16 | RSPAN, CLI), and is open to programmatic extension and control using | |
17 | OpenFlow and the OVSDB management protocol. | |
18 | ||
19 | Open vSwitch as designed to be compatible with modern switching | |
20 | chipsets. This means that it can be ported to existing high-fanout | |
21 | switches allowing the same flexible control of the physical | |
22 | infrastructure as the virtual infrastructure. It also means that | |
23 | Open vSwitch will be able to take advantage of on-NIC switching | |
24 | chipsets as their functionality matures. | |
25 | ||
26 | Q: What virtualization platforms can use Open vSwitch? | |
27 | ||
28 | A: Open vSwitch can currently run on any Linux-based virtualization | |
29 | platform (kernel 2.6.18 and newer), including: KVM, VirtualBox, Xen, | |
30 | Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the | |
31 | mainline kernel. The bulk of the code is written in platform- | |
32 | independent C and is easily ported to other environments. We welcome | |
33 | inquires about integrating Open vSwitch with other virtualization | |
34 | platforms. | |
35 | ||
36 | Q: How can I try Open vSwitch? | |
37 | ||
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38 | A: The Open vSwitch source code can be built on a Linux system. You can |
39 | build and experiment with Open vSwitch on any Linux machine. | |
40 | Packages for various Linux distributions are available on many | |
41 | platforms, including: Debian, Ubuntu, Fedora. | |
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42 | |
43 | You may also download and run a virtualization platform that already | |
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44 | has Open vSwitch integrated. For example, download a recent ISO for |
45 | XenServer or Xen Cloud Platform. Be aware that the version | |
46 | integrated with a particular platform may not be the most recent Open | |
47 | vSwitch release. | |
48 | ||
49 | Q: Does Open vSwitch only work on Linux? | |
50 | ||
51 | A: No, Open vSwitch has been ported to a number of different operating | |
52 | systems and hardware platforms. Most of the development work occurs | |
53 | on Linux, but the code should be portable to any POSIX system. We've | |
54 | seen Open vSwitch ported to a number of different platforms, | |
55 | including FreeBSD, Windows, and even non-POSIX embedded systems. | |
56 | ||
57 | By definition, the Open vSwitch Linux kernel module only works on | |
58 | Linux and will provide the highest performance. However, a userspace | |
59 | datapath is available that should be very portable. | |
60 | ||
61 | Q: What's involved with porting Open vSwitch to a new platform or | |
62 | switching ASIC? | |
63 | ||
64 | A: The PORTING document describes how one would go about porting Open | |
65 | vSwitch to a new operating system or hardware platform. | |
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66 | |
67 | Q: Why would I use Open vSwitch instead of the Linux bridge? | |
68 | ||
69 | A: Open vSwitch is specially designed to make it easier to manage VM | |
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70 | network configuration and monitor state spread across many physical |
71 | hosts in dynamic virtualized environments. Please see WHY-OVS for a | |
72 | more detailed description of how Open vSwitch relates to the Linux | |
73 | Bridge. | |
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74 | |
75 | Q: How is Open vSwitch related to distributed virtual switches like the | |
76 | VMware vNetwork distributed switch or the Cisco Nexus 1000V? | |
77 | ||
78 | A: Distributed vswitch applications (e.g., VMware vNetwork distributed | |
79 | switch, Cisco Nexus 1000V) provide a centralized way to configure and | |
80 | monitor the network state of VMs that are spread across many physical | |
81 | hosts. Open vSwitch is not a distributed vswitch itself, rather it | |
82 | runs on each physical host and supports remote management in a way | |
83 | that makes it easier for developers of virtualization/cloud | |
84 | management platforms to offer distributed vswitch capabilities. | |
85 | ||
86 | To aid in distribution, Open vSwitch provides two open protocols that | |
87 | are specially designed for remote management in virtualized network | |
88 | environments: OpenFlow, which exposes flow-based forwarding state, | |
89 | and the OVSDB management protocol, which exposes switch port state. | |
90 | In addition to the switch implementation itself, Open vSwitch | |
91 | includes tools (ovs-controller, ovs-ofctl, ovs-vsctl) that developers | |
92 | can script and extend to provide distributed vswitch capabilities | |
93 | that are closely integrated with their virtualization management | |
94 | platform. | |
95 | ||
96 | Q: Why doesn't Open vSwitch support distribution? | |
97 | ||
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. | |
105 | ||
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106 | Q: How can I contribute to the Open vSwitch Community? |
107 | ||
108 | A: You can start by joining the mailing lists and helping to answer | |
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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: | |
112 | ||
113 | http://openvswitch.org/mlists/ | |
114 | ||
115 | ||
116 | ||
117 | Releases | |
118 | -------- | |
119 | ||
120 | Q: What does it mean for an Open vSwitch release to be LTS (long-term | |
121 | support)? | |
3fc7dc18 | 122 | |
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123 | A: All official releases have been through a comprehensive testing |
124 | process and are suitable for production use. Planned releases will | |
125 | occur several times a year. If a significant bug is identified in an | |
126 | LTS release, we will provide an updated release that includes the | |
127 | fix. Releases that are not LTS may not be fixed and may just be | |
128 | supplanted by the next major release. The current LTS release is | |
129 | 1.4.x. | |
130 | ||
131 | Q: What features are not available in the Open vSwitch kernel datapath | |
132 | that ships as part of the upstream Linux kernel? | |
133 | ||
134 | A: The kernel module in upstream Linux 3.3 and later does not include | |
135 | the following features: | |
136 | ||
137 | - Bridge compatibility, that is, support for the ovs-brcompatd | |
138 | daemon that (if you enable it) lets "brctl" and other Linux | |
139 | bridge tools transparently work with Open vSwitch instead. | |
140 | ||
141 | We do not expect bridge compatibility to ever be available in | |
142 | upstream Linux. If you need bridge compatibility, use the | |
143 | kernel module from the Open vSwitch distribution instead of the | |
144 | upstream Linux kernel module. | |
145 | ||
146 | - Tunnel and patch virtual ports, that is, interfaces with type | |
147 | "gre", "ipsec_gre", "capwap", or "patch". It is possible to | |
148 | create tunnels in Linux and attach them to Open vSwitch as | |
149 | system devices. However, they cannot be dynamically created | |
150 | through the OVSDB protocol or set the tunnel ids as a flow | |
151 | action. | |
152 | ||
153 | Work is in progress in adding these features to the upstream | |
154 | Linux version of the Open vSwitch kernel module. For now, if | |
155 | you need these features, use the kernel module from the Open | |
156 | vSwitch distribution instead of the upstream Linux kernel | |
157 | module. | |
158 | ||
159 | Q: What features are not available when using the userspace datapath? | |
160 | ||
161 | A: Tunnel and patch virtual ports are not supported, as described in the | |
162 | previous answer. It is also not possible to use queue-related | |
163 | actions. On Linux kernels before 2.6.39, maximum-sized VLAN packets | |
164 | may not be transmitted. | |
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165 | |
166 | ||
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167 | Configuration Problems |
168 | ---------------------- | |
169 | ||
170 | Q: I created a bridge and added my Ethernet port to it, using commands | |
171 | like these: | |
172 | ||
173 | ovs-vsctl add-br br0 | |
174 | ovs-vsctl add-port br0 eth0 | |
175 | ||
176 | and as soon as I ran the "add-port" command I lost all connectivity | |
177 | through eth0. Help! | |
178 | ||
179 | A: A physical Ethernet device that is part of an Open vSwitch bridge | |
180 | should not have an IP address. If one does, then that IP address | |
181 | will not be fully functional. | |
182 | ||
183 | You can restore functionality by moving the IP address to an Open | |
184 | vSwitch "internal" device, such as the network device named after | |
185 | the bridge itself. For example, assuming that eth0's IP address is | |
186 | 192.168.128.5, you could run the commands below to fix up the | |
187 | situation: | |
188 | ||
189 | ifconfig eth0 0.0.0.0 | |
190 | ifconfig br0 192.168.128.5 | |
191 | ||
192 | (If your only connection to the machine running OVS is through the | |
193 | IP address in question, then you would want to run all of these | |
194 | commands on a single command line, or put them into a script.) If | |
195 | there were any additional routes assigned to eth0, then you would | |
196 | also want to use commands to adjust these routes to go through br0. | |
197 | ||
198 | If you use DHCP to obtain an IP address, then you should kill the | |
199 | DHCP client that was listening on the physical Ethernet interface | |
200 | (e.g. eth0) and start one listening on the internal interface | |
201 | (e.g. br0). You might still need to manually clear the IP address | |
202 | from the physical interface (e.g. with "ifconfig eth0 0.0.0.0"). | |
203 | ||
204 | There is no compelling reason why Open vSwitch must work this way. | |
205 | However, this is the way that the Linux kernel bridge module has | |
206 | always worked, so it's a model that those accustomed to Linux | |
207 | bridging are already used to. Also, the model that most people | |
208 | expect is not implementable without kernel changes on all the | |
209 | versions of Linux that Open vSwitch supports. | |
210 | ||
211 | By the way, this issue is not specific to physical Ethernet | |
212 | devices. It applies to all network devices except Open vswitch | |
213 | "internal" devices. | |
214 | ||
215 | Q: I created a bridge and added a couple of Ethernet ports to it, | |
216 | using commands like these: | |
217 | ||
218 | ovs-vsctl add-br br0 | |
219 | ovs-vsctl add-port br0 eth0 | |
220 | ovs-vsctl add-port br0 eth1 | |
221 | ||
222 | and now my network seems to have melted: connectivity is unreliable | |
223 | (even connectivity that doesn't go through Open vSwitch), all the | |
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224 | LEDs on my physical switches are blinking, wireshark shows |
225 | duplicated packets, and CPU usage is very high. | |
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226 | |
227 | A: More than likely, you've looped your network. Probably, eth0 and | |
228 | eth1 are connected to the same physical Ethernet switch. This | |
229 | yields a scenario where OVS receives a broadcast packet on eth0 and | |
230 | sends it out on eth1, then the physical switch connected to eth1 | |
231 | sends the packet back on eth0, and so on forever. More complicated | |
232 | scenarios, involving a loop through multiple switches, are possible | |
233 | too. | |
234 | ||
235 | The solution depends on what you are trying to do: | |
236 | ||
237 | - If you added eth0 and eth1 to get higher bandwidth or higher | |
238 | reliability between OVS and your physical Ethernet switch, | |
239 | use a bond. The following commands create br0 and then add | |
240 | eth0 and eth1 as a bond: | |
241 | ||
242 | ovs-vsctl add-br br0 | |
243 | ovs-vsctl add-bond br0 bond0 eth0 eth1 | |
244 | ||
245 | Bonds have tons of configuration options. Please read the | |
246 | documentation on the Port table in ovs-vswitchd.conf.db(5) | |
247 | for all the details. | |
248 | ||
249 | - Perhaps you don't actually need eth0 and eth1 to be on the | |
250 | same bridge. For example, if you simply want to be able to | |
251 | connect each of them to virtual machines, then you can put | |
252 | each of them on a bridge of its own: | |
253 | ||
254 | ovs-vsctl add-br br0 | |
255 | ovs-vsctl add-port br0 eth0 | |
256 | ||
257 | ovs-vsctl add-br br1 | |
258 | ovs-vsctl add-port br1 eth1 | |
259 | ||
260 | and then connect VMs to br0 and br1. (A potential | |
261 | disadvantage is that traffic cannot directly pass between br0 | |
262 | and br1. Instead, it will go out eth0 and come back in eth1, | |
263 | or vice versa.) | |
264 | ||
265 | - If you have a redundant or complex network topology and you | |
266 | want to prevent loops, turn on spanning tree protocol (STP). | |
267 | The following commands create br0, enable STP, and add eth0 | |
268 | and eth1 to the bridge. The order is important because you | |
269 | don't want have to have a loop in your network even | |
270 | transiently: | |
271 | ||
272 | ovs-vsctl add-br br0 | |
273 | ovs-vsctl set bridge br0 stp_enable=true | |
274 | ovs-vsctl add-port br0 eth0 | |
275 | ovs-vsctl add-port br0 eth1 | |
276 | ||
277 | The Open vSwitch implementation of STP is not well tested. | |
278 | Please report any bugs you observe, but if you'd rather avoid | |
279 | acting as a beta tester then another option might be your | |
280 | best shot. | |
281 | ||
282 | Q: I can't seem to use Open vSwitch in a wireless network. | |
283 | ||
284 | A: Wireless base stations generally only allow packets with the source | |
285 | MAC address of NIC that completed the initial handshake. | |
286 | Therefore, without MAC rewriting, only a single device can | |
287 | communicate over a single wireless link. | |
288 | ||
289 | This isn't specific to Open vSwitch, it's enforced by the access | |
290 | point, so the same problems will show up with the Linux bridge or | |
291 | any other way to do bridging. | |
292 | ||
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293 | Q: Is there any documentation on the database tables and fields? |
294 | ||
295 | A: Yes. ovs-vswitchd.conf.db(5) is a comprehensive reference. | |
296 | ||
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297 | |
298 | VLANs | |
299 | ----- | |
300 | ||
301 | Q: VLANs don't work. | |
302 | ||
303 | A: Many drivers in Linux kernels before version 3.3 had VLAN-related | |
304 | bugs. If you are having problems with VLANs that you suspect to be | |
305 | driver related, then you have several options: | |
306 | ||
307 | - Upgrade to Linux 3.3 or later. | |
308 | ||
309 | - Build and install a fixed version of the particular driver | |
310 | that is causing trouble, if one is available. | |
311 | ||
312 | - Use a NIC whose driver does not have VLAN problems. | |
313 | ||
314 | - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later | |
315 | that works around bugs in kernel drivers. To enable VLAN | |
316 | splinters on interface eth0, use the command: | |
317 | ||
7b287e99 | 318 | ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true |
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319 | |
320 | For VLAN splinters to be effective, Open vSwitch must know | |
321 | which VLANs are in use. See the "VLAN splinters" section in | |
322 | the Interface table in ovs-vswitchd.conf.db(5) for details on | |
323 | how Open vSwitch infers in-use VLANs. | |
324 | ||
325 | VLAN splinters increase memory use and reduce performance, so | |
326 | use them only if needed. | |
327 | ||
328 | - Apply the "vlan workaround" patch from the XenServer kernel | |
329 | patch queue, build Open vSwitch against this patched kernel, | |
330 | and then use ovs-vlan-bug-workaround(8) to enable the VLAN | |
331 | workaround for each interface whose driver is buggy. | |
332 | ||
333 | (This is a nontrivial exercise, so this option is included | |
334 | only for completeness.) | |
335 | ||
336 | It is not always easy to tell whether a Linux kernel driver has | |
337 | buggy VLAN support. The ovs-vlan-test(8) and ovs-test(8) utilities | |
338 | can help you test. See their manpages for details. Of the two | |
339 | utilities, ovs-test(8) is newer and more thorough, but | |
340 | ovs-vlan-test(8) may be easier to use. | |
341 | ||
342 | Q: VLANs still don't work. I've tested the driver so I know that it's OK. | |
343 | ||
344 | A: Do you have VLANs enabled on the physical switch that OVS is | |
345 | attached to? Make sure that the port is configured to trunk the | |
346 | VLAN or VLANs that you are using with OVS. | |
347 | ||
348 | Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch | |
349 | and to its destination host, but OVS seems to drop incoming return | |
350 | traffic. | |
351 | ||
352 | A: It's possible that you have the VLAN configured on your physical | |
353 | switch as the "native" VLAN. In this mode, the switch treats | |
354 | incoming packets either tagged with the native VLAN or untagged as | |
355 | part of the native VLAN. It may also send outgoing packets in the | |
356 | native VLAN without a VLAN tag. | |
357 | ||
358 | If this is the case, you have two choices: | |
359 | ||
360 | - Change the physical switch port configuration to tag packets | |
361 | it forwards to OVS with the native VLAN instead of forwarding | |
362 | them untagged. | |
363 | ||
364 | - Change the OVS configuration for the physical port to a | |
365 | native VLAN mode. For example, the following sets up a | |
366 | bridge with port eth0 in "native-tagged" mode in VLAN 9: | |
367 | ||
368 | ovs-vsctl add-br br0 | |
369 | ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged | |
370 | ||
371 | In this situation, "native-untagged" mode will probably work | |
372 | equally well. Refer to the documentation for the Port table | |
373 | in ovs-vswitchd.conf.db(5) for more information. | |
374 | ||
375 | Q: Can I configure an IP address on a VLAN? | |
376 | ||
377 | A: Yes. Use an "internal port" configured as an access port. For | |
378 | example, the following configures IP address 192.168.0.7 on VLAN 9. | |
379 | That is, OVS will forward packets from eth0 to 192.168.0.7 only if | |
380 | they have an 802.1Q header with VLAN 9. Conversely, traffic | |
381 | forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q | |
382 | header with VLAN 9: | |
383 | ||
384 | ovs-vsctl add-br br0 | |
385 | ovs-vsctl add-port br0 eth0 | |
386 | ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal | |
387 | ifconfig vlan9 192.168.0.7 | |
388 | ||
389 | Q: My OpenFlow controller doesn't see the VLANs that I expect. | |
390 | ||
391 | A: The configuration for VLANs in the Open vSwitch database (e.g. via | |
392 | ovs-vsctl) only affects traffic that goes through Open vSwitch's | |
393 | implementation of the OpenFlow "normal switching" action. By | |
394 | default, when Open vSwitch isn't connected to a controller and | |
395 | nothing has been manually configured in the flow table, all traffic | |
396 | goes through the "normal switching" action. But, if you set up | |
397 | OpenFlow flows on your own, through a controller or using ovs-ofctl | |
398 | or through other means, then you have to implement VLAN handling | |
399 | yourself. | |
400 | ||
401 | You can use "normal switching" as a component of your OpenFlow | |
402 | actions, e.g. by putting "normal" into the lists of actions on | |
403 | ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow | |
404 | controller. This will only be suitable for some situations, | |
405 | though. | |
406 | ||
407 | ||
408 | Controllers | |
409 | ----------- | |
410 | ||
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411 | Q: What versions of OpenFlow does Open vSwitch support? |
412 | ||
413 | A: Open vSwitch supports OpenFlow 1.0. It also includes a number of | |
414 | extensions that bring many of the features from later versions of | |
415 | OpenFlow. Work is underway to provide support for later versions and | |
416 | can be tracked here: | |
417 | ||
418 | http://openvswitch.org/development/openflow-1-x-plan/ | |
419 | ||
c483d489 BP |
420 | Q: I'm getting "error type 45250 code 0". What's that? |
421 | ||
422 | A: This is a Open vSwitch extension to OpenFlow error codes. Open | |
423 | vSwitch uses this extension when it must report an error to an | |
424 | OpenFlow controller but no standard OpenFlow error code is | |
425 | suitable. | |
426 | ||
427 | Open vSwitch logs the errors that it sends to controllers, so the | |
428 | easiest thing to do is probably to look at the ovs-vswitchd log to | |
429 | find out what the error was. | |
430 | ||
431 | If you want to dissect the extended error message yourself, the | |
432 | format is documented in include/openflow/nicira-ext.h in the Open | |
433 | vSwitch source distribution. The extended error codes are | |
434 | documented in lib/ofp-errors.h. | |
435 | ||
436 | Q1: Some of the traffic that I'd expect my OpenFlow controller to see | |
437 | doesn't actually appear through the OpenFlow connection, even | |
438 | though I know that it's going through. | |
439 | Q2: Some of the OpenFlow flows that my controller sets up don't seem | |
440 | to apply to certain traffic, especially traffic between OVS and | |
441 | the controller itself. | |
442 | ||
443 | A: By default, Open vSwitch assumes that OpenFlow controllers are | |
444 | connected "in-band", that is, that the controllers are actually | |
445 | part of the network that is being controlled. In in-band mode, | |
446 | Open vSwitch sets up special "hidden" flows to make sure that | |
447 | traffic can make it back and forth between OVS and the controllers. | |
448 | These hidden flows are higher priority than any flows that can be | |
449 | set up through OpenFlow, and they are not visible through normal | |
450 | OpenFlow flow table dumps. | |
451 | ||
452 | Usually, the hidden flows are desirable and helpful, but | |
453 | occasionally they can cause unexpected behavior. You can view the | |
454 | full OpenFlow flow table, including hidden flows, on bridge br0 | |
455 | with the command: | |
456 | ||
457 | ovs-appctl bridge/dump-flows br0 | |
458 | ||
459 | to help you debug. The hidden flows are those with priorities | |
460 | greater than 65535 (the maximum priority that can be set with | |
461 | OpenFlow). | |
462 | ||
463 | The DESIGN file at the top level of the Open vSwitch source | |
464 | distribution describes the in-band model in detail. | |
465 | ||
466 | If your controllers are not actually in-band (e.g. they are on | |
467 | localhost via 127.0.0.1, or on a separate network), then you should | |
468 | configure your controllers in "out-of-band" mode. If you have one | |
469 | controller on bridge br0, then you can configure out-of-band mode | |
470 | on it with: | |
471 | ||
472 | ovs-vsctl set controller br0 connection-mode=out-of-band | |
473 | ||
474 | Q: I configured all my controllers for out-of-band control mode but | |
475 | "ovs-appctl bridge/dump-flows" still shows some hidden flows. | |
476 | ||
477 | A: You probably have a remote manager configured (e.g. with "ovs-vsctl | |
478 | set-manager"). By default, Open vSwitch assumes that managers need | |
479 | in-band rules set up on every bridge. You can disable these rules | |
480 | on bridge br0 with: | |
481 | ||
482 | ovs-vsctl set bridge br0 other-config:disable-in-band=true | |
483 | ||
484 | This actually disables in-band control entirely for the bridge, as | |
485 | if all the bridge's controllers were configured for out-of-band | |
486 | control. | |
487 | ||
488 | Q: My OpenFlow controller doesn't see the VLANs that I expect. | |
489 | ||
490 | A: See answer under "VLANs", above. | |
491 | ||
7b287e99 | 492 | |
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493 | Contact |
494 | ------- | |
495 | ||
496 | bugs@openvswitch.org | |
497 | http://openvswitch.org/ |