FAQ

   1                  Open vSwitch <http://openvswitch.org>
   2
   3 Frequently Asked Questions
   4 ==========================
   5
   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
  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.
  42
  43    You may also download and run a virtualization platform that already
  44    has Open vSwitch integrated.  For example, download a recent ISO for
  45    XenServer or Xen Cloud Platform.  Be aware that the version
  46    integrated with a particular platform may not be the most recent Open
  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.
  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
  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.
  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
 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
 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)?
 122
 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 virtual ports, that is, interfaces with type "gre",
 147          "ipsec_gre", "capwap".  It is possible to create tunnels in
 148          Linux and attach them to Open vSwitch as system devices.
 149          However, they cannot be dynamically created through the OVSDB
 150          protocol or set the tunnel ids as a flow action.
 151
 152          Work is in progress in adding these features to the upstream
 153          Linux version of the Open vSwitch kernel module.  For now, if
 154          you need these features, use the kernel module from the Open
 155          vSwitch distribution instead of the upstream Linux kernel
 156          module.
 157
 158        - Patch virtual ports, that is, interfaces with type "patch".
 159          You can use Linux "veth" devices as a substitute.
 160
 161          We don't have any plans to add patch ports upstream.
 162
 163 Q: What features are not available when using the userspace datapath?
 164
 165 A: Tunnel and patch virtual ports are not supported, as described in the
 166    previous answer.  It is also not possible to use queue-related
 167    actions.  On Linux kernels before 2.6.39, maximum-sized VLAN packets
 168    may not be transmitted.
 169
 170
 171 Configuration Problems
 172 ----------------------
 173
 174 Q: I created a bridge and added my Ethernet port to it, using commands
 175    like these:
 176
 177        ovs-vsctl add-br br0
 178        ovs-vsctl add-port br0 eth0
 179
 180    and as soon as I ran the "add-port" command I lost all connectivity
 181    through eth0.  Help!
 182
 183 A: A physical Ethernet device that is part of an Open vSwitch bridge
 184    should not have an IP address.  If one does, then that IP address
 185    will not be fully functional.
 186
 187    You can restore functionality by moving the IP address to an Open
 188    vSwitch "internal" device, such as the network device named after
 189    the bridge itself.  For example, assuming that eth0's IP address is
 190    192.168.128.5, you could run the commands below to fix up the
 191    situation:
 192
 193        ifconfig eth0 0.0.0.0
 194        ifconfig br0 192.168.128.5
 195
 196    (If your only connection to the machine running OVS is through the
 197    IP address in question, then you would want to run all of these
 198    commands on a single command line, or put them into a script.)  If
 199    there were any additional routes assigned to eth0, then you would
 200    also want to use commands to adjust these routes to go through br0.
 201
 202    If you use DHCP to obtain an IP address, then you should kill the
 203    DHCP client that was listening on the physical Ethernet interface
 204    (e.g. eth0) and start one listening on the internal interface
 205    (e.g. br0).  You might still need to manually clear the IP address
 206    from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
 207
 208    There is no compelling reason why Open vSwitch must work this way.
 209    However, this is the way that the Linux kernel bridge module has
 210    always worked, so it's a model that those accustomed to Linux
 211    bridging are already used to.  Also, the model that most people
 212    expect is not implementable without kernel changes on all the
 213    versions of Linux that Open vSwitch supports.
 214
 215    By the way, this issue is not specific to physical Ethernet
 216    devices.  It applies to all network devices except Open vswitch
 217    "internal" devices.
 218
 219 Q: I created a bridge and added a couple of Ethernet ports to it,
 220    using commands like these:
 221
 222        ovs-vsctl add-br br0
 223        ovs-vsctl add-port br0 eth0
 224        ovs-vsctl add-port br0 eth1
 225
 226    and now my network seems to have melted: connectivity is unreliable
 227    (even connectivity that doesn't go through Open vSwitch), all the
 228    LEDs on my physical switches are blinking, wireshark shows
 229    duplicated packets, and CPU usage is very high.
 230
 231 A: More than likely, you've looped your network.  Probably, eth0 and
 232    eth1 are connected to the same physical Ethernet switch.  This
 233    yields a scenario where OVS receives a broadcast packet on eth0 and
 234    sends it out on eth1, then the physical switch connected to eth1
 235    sends the packet back on eth0, and so on forever.  More complicated
 236    scenarios, involving a loop through multiple switches, are possible
 237    too.
 238
 239    The solution depends on what you are trying to do:
 240
 241        - If you added eth0 and eth1 to get higher bandwidth or higher
 242          reliability between OVS and your physical Ethernet switch,
 243          use a bond.  The following commands create br0 and then add
 244          eth0 and eth1 as a bond:
 245
 246              ovs-vsctl add-br br0
 247              ovs-vsctl add-bond br0 bond0 eth0 eth1
 248
 249          Bonds have tons of configuration options.  Please read the
 250          documentation on the Port table in ovs-vswitchd.conf.db(5)
 251          for all the details.
 252
 253        - Perhaps you don't actually need eth0 and eth1 to be on the
 254          same bridge.  For example, if you simply want to be able to
 255          connect each of them to virtual machines, then you can put
 256          each of them on a bridge of its own:
 257
 258              ovs-vsctl add-br br0
 259              ovs-vsctl add-port br0 eth0
 260
 261              ovs-vsctl add-br br1
 262              ovs-vsctl add-port br1 eth1
 263
 264          and then connect VMs to br0 and br1.  (A potential
 265          disadvantage is that traffic cannot directly pass between br0
 266          and br1.  Instead, it will go out eth0 and come back in eth1,
 267          or vice versa.)
 268
 269        - If you have a redundant or complex network topology and you
 270          want to prevent loops, turn on spanning tree protocol (STP).
 271          The following commands create br0, enable STP, and add eth0
 272          and eth1 to the bridge.  The order is important because you
 273          don't want have to have a loop in your network even
 274          transiently:
 275
 276              ovs-vsctl add-br br0
 277              ovs-vsctl set bridge br0 stp_enable=true
 278              ovs-vsctl add-port br0 eth0
 279              ovs-vsctl add-port br0 eth1
 280
 281          The Open vSwitch implementation of STP is not well tested.
 282          Please report any bugs you observe, but if you'd rather avoid
 283          acting as a beta tester then another option might be your
 284          best shot.
 285
 286 Q: I can't seem to use Open vSwitch in a wireless network.
 287
 288 A: Wireless base stations generally only allow packets with the source
 289    MAC address of NIC that completed the initial handshake.
 290    Therefore, without MAC rewriting, only a single device can
 291    communicate over a single wireless link.
 292
 293    This isn't specific to Open vSwitch, it's enforced by the access
 294    point, so the same problems will show up with the Linux bridge or
 295    any other way to do bridging.
 296
 297 Q: Is there any documentation on the database tables and fields?
 298
 299 A: Yes.  ovs-vswitchd.conf.db(5) is a comprehensive reference.
 300
 301
 302 VLANs
 303 -----
 304
 305 Q: What's a VLAN?
 306
 307 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
 308    partition a single switch into multiple switches.  Suppose, for
 309    example, that you have two groups of machines, group A and group B.
 310    You want the machines in group A to be able to talk to each other,
 311    and you want the machine in group B to be able to talk to each
 312    other, but you don't want the machines in group A to be able to
 313    talk to the machines in group B.  You can do this with two
 314    switches, by plugging the machines in group A into one switch and
 315    the machines in group B into the other switch.
 316
 317    If you only have one switch, then you can use VLANs to do the same
 318    thing, by configuring the ports for machines in group A as VLAN
 319    "access ports" for one VLAN and the ports for group B as "access
 320    ports" for a different VLAN.  The switch will only forward packets
 321    between ports that are assigned to the same VLAN, so this
 322    effectively subdivides your single switch into two independent
 323    switches, one for each group of machines.
 324
 325    So far we haven't said anything about VLAN headers.  With access
 326    ports, like we've described so far, no VLAN header is present in
 327    the Ethernet frame.  This means that the machines (or switches)
 328    connected to access ports need not be aware that VLANs are
 329    involved, just like in the case where we use two different physical
 330    switches.
 331
 332    Now suppose that you have a whole bunch of switches in your
 333    network, instead of just one, and that some machines in group A are
 334    connected directly to both switches 1 and 2.  To allow these
 335    machines to talk to each other, you could add an access port for
 336    group A's VLAN to switch 1 and another to switch 2, and then
 337    connect an Ethernet cable between those ports.  That works fine,
 338    but it doesn't scale well as the number of switches and the number
 339    of VLANs increases, because you use up a lot of valuable switch
 340    ports just connecting together your VLANs.
 341
 342    This is where VLAN headers come in.  Instead of using one cable and
 343    two ports per VLAN to connect a pair of switches, we configure a
 344    port on each switch as a VLAN "trunk port".  Packets sent and
 345    received on a trunk port carry a VLAN header that says what VLAN
 346    the packet belongs to, so that only two ports total are required to
 347    connect the switches, regardless of the number of VLANs in use.
 348    Normally, only switches (either physical or virtual) are connected
 349    to a trunk port, not individual hosts, because individual hosts
 350    don't expect to see a VLAN header in the traffic that they receive.
 351
 352    None of the above discussion says anything about particular VLAN
 353    numbers.  This is because VLAN numbers are completely arbitrary.
 354    One must only ensure that a given VLAN is numbered consistently
 355    throughout a network and that different VLANs are given different
 356    numbers.  (That said, VLAN 0 is usually synonymous with a packet
 357    that has no VLAN header, and VLAN 4095 is reserved.)
 358
 359 Q: VLANs don't work.
 360
 361 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
 362    bugs.  If you are having problems with VLANs that you suspect to be
 363    driver related, then you have several options:
 364
 365        - Upgrade to Linux 3.3 or later.
 366
 367        - Build and install a fixed version of the particular driver
 368          that is causing trouble, if one is available.
 369
 370        - Use a NIC whose driver does not have VLAN problems.
 371
 372        - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
 373          that works around bugs in kernel drivers.  To enable VLAN
 374          splinters on interface eth0, use the command:
 375
 376            ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
 377
 378          For VLAN splinters to be effective, Open vSwitch must know
 379          which VLANs are in use.  See the "VLAN splinters" section in
 380          the Interface table in ovs-vswitchd.conf.db(5) for details on
 381          how Open vSwitch infers in-use VLANs.
 382
 383          VLAN splinters increase memory use and reduce performance, so
 384          use them only if needed.
 385
 386        - Apply the "vlan workaround" patch from the XenServer kernel
 387          patch queue, build Open vSwitch against this patched kernel,
 388          and then use ovs-vlan-bug-workaround(8) to enable the VLAN
 389          workaround for each interface whose driver is buggy.
 390
 391          (This is a nontrivial exercise, so this option is included
 392          only for completeness.)
 393
 394    It is not always easy to tell whether a Linux kernel driver has
 395    buggy VLAN support.  The ovs-vlan-test(8) and ovs-test(8) utilities
 396    can help you test.  See their manpages for details.  Of the two
 397    utilities, ovs-test(8) is newer and more thorough, but
 398    ovs-vlan-test(8) may be easier to use.
 399
 400 Q: VLANs still don't work.  I've tested the driver so I know that it's OK.
 401
 402 A: Do you have VLANs enabled on the physical switch that OVS is
 403    attached to?  Make sure that the port is configured to trunk the
 404    VLAN or VLANs that you are using with OVS.
 405
 406 Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
 407    and to its destination host, but OVS seems to drop incoming return
 408    traffic.
 409
 410 A: It's possible that you have the VLAN configured on your physical
 411    switch as the "native" VLAN.  In this mode, the switch treats
 412    incoming packets either tagged with the native VLAN or untagged as
 413    part of the native VLAN.  It may also send outgoing packets in the
 414    native VLAN without a VLAN tag.
 415
 416    If this is the case, you have two choices:
 417
 418        - Change the physical switch port configuration to tag packets
 419          it forwards to OVS with the native VLAN instead of forwarding
 420          them untagged.
 421
 422        - Change the OVS configuration for the physical port to a
 423          native VLAN mode.  For example, the following sets up a
 424          bridge with port eth0 in "native-tagged" mode in VLAN 9:
 425
 426              ovs-vsctl add-br br0
 427              ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
 428
 429          In this situation, "native-untagged" mode will probably work
 430          equally well.  Refer to the documentation for the Port table
 431          in ovs-vswitchd.conf.db(5) for more information.
 432
 433 Q: Can I configure an IP address on a VLAN?
 434
 435 A: Yes.  Use an "internal port" configured as an access port.  For
 436    example, the following configures IP address 192.168.0.7 on VLAN 9.
 437    That is, OVS will forward packets from eth0 to 192.168.0.7 only if
 438    they have an 802.1Q header with VLAN 9.  Conversely, traffic
 439    forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
 440    header with VLAN 9:
 441
 442        ovs-vsctl add-br br0
 443        ovs-vsctl add-port br0 eth0
 444        ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
 445        ifconfig vlan9 192.168.0.7
 446
 447 Q: My OpenFlow controller doesn't see the VLANs that I expect.
 448
 449 A: The configuration for VLANs in the Open vSwitch database (e.g. via
 450    ovs-vsctl) only affects traffic that goes through Open vSwitch's
 451    implementation of the OpenFlow "normal switching" action.  By
 452    default, when Open vSwitch isn't connected to a controller and
 453    nothing has been manually configured in the flow table, all traffic
 454    goes through the "normal switching" action.  But, if you set up
 455    OpenFlow flows on your own, through a controller or using ovs-ofctl
 456    or through other means, then you have to implement VLAN handling
 457    yourself.
 458
 459    You can use "normal switching" as a component of your OpenFlow
 460    actions, e.g. by putting "normal" into the lists of actions on
 461    ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
 462    controller.  This will only be suitable for some situations,
 463    though.
 464
 465 Q: I configured ports on a bridge as access ports with different VLAN
 466    tags, like this:
 467
 468        ovs-vsctl add-br br0
 469        ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
 470        ovs-vsctl add-port br0 eth0
 471        ovs-vsctl add-port br0 tap0 tag=9
 472        ovs-vsctl add-port br0 tap1 tag=10
 473
 474    but the VMs running behind tap0 and tap1 can still communicate,
 475    that is, they are not isolated from each other even though they are
 476    on different VLANs.
 477
 478 A: Do you have a controller configured on br0 (as the commands above
 479    do)?  If so, then this is a variant on the previous question, "My
 480    OpenFlow controller doesn't see the VLANs that I expect," and you
 481    can refer to the answer there for more information.
 482
 483
 484 Controllers
 485 -----------
 486
 487 Q: What versions of OpenFlow does Open vSwitch support?
 488
 489 A: Open vSwitch supports OpenFlow 1.0.  It also includes a number of
 490    extensions that bring many of the features from later versions of
 491    OpenFlow.  Work is underway to provide support for later versions and
 492    can be tracked here:
 493
 494        http://openvswitch.org/development/openflow-1-x-plan/
 495
 496 Q: I'm getting "error type 45250 code 0".  What's that?
 497
 498 A: This is a Open vSwitch extension to OpenFlow error codes.  Open
 499    vSwitch uses this extension when it must report an error to an
 500    OpenFlow controller but no standard OpenFlow error code is
 501    suitable.
 502
 503    Open vSwitch logs the errors that it sends to controllers, so the
 504    easiest thing to do is probably to look at the ovs-vswitchd log to
 505    find out what the error was.
 506
 507    If you want to dissect the extended error message yourself, the
 508    format is documented in include/openflow/nicira-ext.h in the Open
 509    vSwitch source distribution.  The extended error codes are
 510    documented in lib/ofp-errors.h.
 511
 512 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
 513     doesn't actually appear through the OpenFlow connection, even
 514     though I know that it's going through.
 515 Q2: Some of the OpenFlow flows that my controller sets up don't seem
 516     to apply to certain traffic, especially traffic between OVS and
 517     the controller itself.
 518
 519 A: By default, Open vSwitch assumes that OpenFlow controllers are
 520    connected "in-band", that is, that the controllers are actually
 521    part of the network that is being controlled.  In in-band mode,
 522    Open vSwitch sets up special "hidden" flows to make sure that
 523    traffic can make it back and forth between OVS and the controllers.
 524    These hidden flows are higher priority than any flows that can be
 525    set up through OpenFlow, and they are not visible through normal
 526    OpenFlow flow table dumps.
 527
 528    Usually, the hidden flows are desirable and helpful, but
 529    occasionally they can cause unexpected behavior.  You can view the
 530    full OpenFlow flow table, including hidden flows, on bridge br0
 531    with the command:
 532
 533        ovs-appctl bridge/dump-flows br0
 534
 535    to help you debug.  The hidden flows are those with priorities
 536    greater than 65535 (the maximum priority that can be set with
 537    OpenFlow).
 538
 539    The DESIGN file at the top level of the Open vSwitch source
 540    distribution describes the in-band model in detail.
 541
 542    If your controllers are not actually in-band (e.g. they are on
 543    localhost via 127.0.0.1, or on a separate network), then you should
 544    configure your controllers in "out-of-band" mode.  If you have one
 545    controller on bridge br0, then you can configure out-of-band mode
 546    on it with:
 547
 548        ovs-vsctl set controller br0 connection-mode=out-of-band
 549
 550 Q: I configured all my controllers for out-of-band control mode but
 551    "ovs-appctl bridge/dump-flows" still shows some hidden flows.
 552
 553 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
 554    set-manager").  By default, Open vSwitch assumes that managers need
 555    in-band rules set up on every bridge.  You can disable these rules
 556    on bridge br0 with:
 557
 558        ovs-vsctl set bridge br0 other-config:disable-in-band=true
 559
 560    This actually disables in-band control entirely for the bridge, as
 561    if all the bridge's controllers were configured for out-of-band
 562    control.
 563
 564 Q: My OpenFlow controller doesn't see the VLANs that I expect.
 565
 566 A: See answer under "VLANs", above.
 567
 568 Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
 569    but I got a funny message like this:
 570
 571        ofp_util|INFO|normalization changed ofp_match, details:
 572        ofp_util|INFO| pre: nw_dst=192.168.0.1
 573        ofp_util|INFO|post:
 574
 575    and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
 576    match had disappeared, so that the flow ends up matching every
 577    packet.
 578
 579 A: The term "normalization" in the log message means that a flow
 580    cannot match on an L3 field without saying what L3 protocol is in
 581    use.  The "ovs-ofctl" command above didn't specify an L3 protocol,
 582    so the L3 field match was dropped.
 583
 584    In this case, the L3 protocol could be IP or ARP.  A correct
 585    command for each possibility is, respectively:
 586
 587        ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
 588
 589    and
 590
 591        ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
 592
 593    Similarly, a flow cannot match on an L4 field without saying what
 594    L4 protocol is in use.  For example, the flow match "tp_src=1234"
 595    is, by itself, meaningless and will be ignored.  Instead, to match
 596    TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
 597    source port 1234, write "udp,tp_src=1234".
 598
 599 Q: How can I figure out the OpenFlow port number for a given port?
 600
 601 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
 602    respond with an OFPT_FEATURES_REPLY that, among other information,
 603    includes a mapping between OpenFlow port names and numbers.  From a
 604    command prompt, "ovs-ofctl show br0" makes such a request and
 605    prints the response for switch br0.
 606
 607    The Interface table in the Open vSwitch database also maps OpenFlow
 608    port names to numbers.  To print the OpenFlow port number
 609    associated with interface eth0, run:
 610
 611        ovs-vsctl get Interface eth0 ofport
 612
 613    You can print the entire mapping with:
 614
 615        ovs-vsctl -- --columns=name,ofport list Interface
 616
 617    but the output mixes together interfaces from all bridges in the
 618    database, so it may be confusing if more than one bridge exists.
 619
 620    In the Open vSwitch database, ofport value -1 means that the
 621    interface could not be created due to an error.  (The Open vSwitch
 622    log should indicate the reason.)  ofport value [] (the empty set)
 623    means that the interface hasn't been created yet.  The latter is
 624    normally an intermittent condition (unless ovs-vswitchd is not
 625    running).
 626
 627 Contact
 628 -------
 629
 630 bugs@openvswitch.org
 631 http://openvswitch.org/