FAQ.md

   1 Frequently Asked Questions
   2 ==========================
   3
   4 Open vSwitch <http://openvswitch.org>
   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
  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
  18    management protocol.
  19
  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.
  26
  27 ### Q: What virtualization platforms can use Open vSwitch?
  28
  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
  35    platforms.
  36
  37 ### Q: How can I try Open vSwitch?
  38
  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.
  43
  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
  48    vSwitch release.
  49
  50 ### Q: Does Open vSwitch only work on Linux?
  51
  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.
  57
  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.
  61
  62 ### Q: What's involved with porting Open vSwitch to a new platform or switching ASIC?
  63
  64 A: The [PORTING.md] document describes how one would go about
  65    porting Open 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
  72    [WHY-OVS.md] for a more detailed description of how Open vSwitch
  73    relates to the Linux Bridge.
  74
  75 ### Q: How is Open vSwitch related to distributed virtual switches like the VMware vNetwork distributed switch or the Cisco Nexus 1000V?
  76
  77 A: Distributed vswitch applications (e.g., VMware vNetwork distributed
  78    switch, Cisco Nexus 1000V) provide a centralized way to configure and
  79    monitor the network state of VMs that are spread across many physical
  80    hosts.  Open vSwitch is not a distributed vswitch itself, rather it
  81    runs on each physical host and supports remote management in a way
  82    that makes it easier for developers of virtualization/cloud
  83    management platforms to offer distributed vswitch capabilities.
  84
  85    To aid in distribution, Open vSwitch provides two open protocols that
  86    are specially designed for remote management in virtualized network
  87    environments: OpenFlow, which exposes flow-based forwarding state,
  88    and the OVSDB management protocol, which exposes switch port state.
  89    In addition to the switch implementation itself, Open vSwitch
  90    includes tools (ovs-ofctl, ovs-vsctl) that developers can script and
  91    extend to provide distributed vswitch capabilities that are closely
  92    integrated with their virtualization management platform.
  93
  94 ### Q: Why doesn't Open vSwitch support distribution?
  95
  96 A: Open vSwitch is intended to be a useful component for building
  97    flexible network infrastructure. There are many different approaches
  98    to distribution which balance trade-offs between simplicity,
  99    scalability, hardware compatibility, convergence times, logical
 100    forwarding model, etc. The goal of Open vSwitch is to be able to
 101    support all as a primitive building block rather than choose a
 102    particular point in the distributed design space.
 103
 104 ### Q: How can I contribute to the Open vSwitch Community?
 105
 106 A: You can start by joining the mailing lists and helping to answer
 107    questions.  You can also suggest improvements to documentation.  If
 108    you have a feature or bug you would like to work on, send a mail to
 109    one of the mailing lists:
 110
 111    http://openvswitch.org/mlists/
 112
 113
 114 Releases
 115 --------
 116
 117 ### Q: What does it mean for an Open vSwitch release to be LTS (long-term support)?
 118
 119 A: All official releases have been through a comprehensive testing
 120    process and are suitable for production use.  Planned releases will
 121    occur several times a year.  If a significant bug is identified in an
 122    LTS release, we will provide an updated release that includes the
 123    fix.  Releases that are not LTS may not be fixed and may just be
 124    supplanted by the next major release.  The current LTS release is
 125    1.9.x.
 126
 127 ### Q: What Linux kernel versions does each Open vSwitch release work with?
 128
 129 A: The following table lists the Linux kernel versions against which the
 130    given versions of the Open vSwitch kernel module will successfully
 131    build.  The Linux kernel versions are upstream kernel versions, so
 132    Linux kernels modified from the upstream sources may not build in
 133    some cases even if they are based on a supported version.  This is
 134    most notably true of Red Hat Enterprise Linux (RHEL) kernels, which
 135    are extensively modified from upstream.
 136
 137 | Open vSwitch | Linux kernel
 138 |:------------:|:-------------:
 139 |    1.4.x     | 2.6.18 to 3.2
 140 |    1.5.x     | 2.6.18 to 3.2
 141 |    1.6.x     | 2.6.18 to 3.2
 142 |    1.7.x     | 2.6.18 to 3.3
 143 |    1.8.x     | 2.6.18 to 3.4
 144 |    1.9.x     | 2.6.18 to 3.8
 145 |    1.10.x    | 2.6.18 to 3.8
 146 |    1.11.x    | 2.6.18 to 3.8
 147 |    2.0.x     | 2.6.32 to 3.10
 148 |    2.1.x     | 2.6.32 to 3.11
 149 |    2.3.x     | 2.6.32 to 3.14
 150
 151    Open vSwitch userspace should also work with the Linux kernel module
 152    built into Linux 3.3 and later.
 153
 154    Open vSwitch userspace is not sensitive to the Linux kernel version.
 155    It should build against almost any kernel, certainly against 2.6.32
 156    and later.
 157
 158 ### Q: I get an error like this when I configure Open vSwitch:
 159
 160        configure: error: Linux kernel in <dir> is version <x>, but
 161        version newer than <y> is not supported (please refer to the
 162        FAQ for advice)
 163
 164    What should I do?
 165
 166 A: If there is a newer version of Open vSwitch, consider building that
 167    one, because it may support the kernel that you are building
 168    against.  (To find out, consult the table in the previous answer.)
 169
 170    Otherwise, use the Linux kernel module supplied with the kernel
 171    that you are using.  All versions of Open vSwitch userspace are
 172    compatible with all versions of the Open vSwitch kernel module, so
 173    this will also work.  See also the following question.
 174
 175 ### Q: What features are not available in the Open vSwitch kernel datapath that ships as part of the upstream Linux kernel?
 176
 177 A: The kernel module in upstream Linux does not include support for
 178    LISP. Work is in progress to add support for LISP to the upstream
 179    Linux version of the Open vSwitch kernel module. For now, if you
 180    need this feature, use the kernel module from the Open vSwitch
 181    distribution instead of the upstream Linux kernel module.
 182
 183    Certain features require kernel support to function or to have
 184    reasonable performance. If the ovs-vswitchd log file indicates that
 185    a feature is not supported, consider upgrading to a newer upstream
 186    Linux release or using the kernel module paired with the userspace
 187    distribution.
 188
 189 ### Q: Why do tunnels not work when using a kernel module other than the one packaged with Open vSwitch?
 190
 191 A: Support for tunnels was added to the upstream Linux kernel module
 192    after the rest of Open vSwitch. As a result, some kernels may contain
 193    support for Open vSwitch but not tunnels. The minimum kernel version
 194    that supports each tunnel protocol is:
 195
 196 | Protocol |  Linux Kernel
 197 |:--------:|:-------------:
 198 | GRE      |    3.11
 199 | VXLAN    |    3.12
 200 | LISP     | <not upstream>
 201
 202    If you are using a version of the kernel that is older than the one
 203    listed above, it is still possible to use that tunnel protocol. However,
 204    you must compile and install the kernel module included with the Open
 205    vSwitch distribution rather than the one on your machine. If problems
 206    persist after doing this, check to make sure that the module that is
 207    loaded is the one you expect.
 208
 209 ### Q: What features are not available when using the userspace datapath?
 210
 211 A: Tunnel virtual ports are not supported, as described in the
 212    previous answer.  It is also not possible to use queue-related
 213    actions.  On Linux kernels before 2.6.39, maximum-sized VLAN packets
 214    may not be transmitted.
 215
 216 ### Q: What Linux kernel versions does IPFIX flow monitoring work with?
 217
 218 A: IPFIX flow monitoring requires the Linux kernel module from Open
 219    vSwitch version 1.10.90 or later.
 220
 221 ### Q: Should userspace or kernel be upgraded first to minimize downtime?
 222
 223    In general, the Open vSwitch userspace should be used with the
 224    kernel version included in the same release or with the version
 225    from upstream Linux.  However, when upgrading between two releases
 226    of Open vSwitch it is best to migrate userspace first to reduce
 227    the possibility of incompatibilities.
 228
 229 ### Q: What happened to the bridge compatibility feature?
 230
 231 A: Bridge compatibility was a feature of Open vSwitch 1.9 and earlier.
 232    When it was enabled, Open vSwitch imitated the interface of the
 233    Linux kernel "bridge" module.  This allowed users to drop Open
 234    vSwitch into environments designed to use the Linux kernel bridge
 235    module without adapting the environment to use Open vSwitch.
 236
 237    Open vSwitch 1.10 and later do not support bridge compatibility.
 238    The feature was dropped because version 1.10 adopted a new internal
 239    architecture that made bridge compatibility difficult to maintain.
 240    Now that many environments use OVS directly, it would be rarely
 241    useful in any case.
 242
 243    To use bridge compatibility, install OVS 1.9 or earlier, including
 244    the accompanying kernel modules (both the main and bridge
 245    compatibility modules), following the instructions that come with
 246    the release.  Be sure to start the ovs-brcompatd daemon.
 247
 248
 249 Terminology
 250 -----------
 251
 252 ### Q: I thought Open vSwitch was a virtual Ethernet switch, but the documentation keeps talking about bridges.  What's a bridge?
 253
 254 A: In networking, the terms "bridge" and "switch" are synonyms.  Open
 255    vSwitch implements an Ethernet switch, which means that it is also
 256    an Ethernet bridge.
 257
 258 ### Q: What's a VLAN?
 259
 260 A: See the "VLAN" section below.
 261
 262
 263 Basic Configuration
 264 -------------------
 265
 266 ### Q: How do I configure a port as an access port?
 267
 268 A: Add "tag=VLAN" to your "ovs-vsctl add-port" command.  For example,
 269    the following commands configure br0 with eth0 as a trunk port (the
 270    default) and tap0 as an access port for VLAN 9:
 271
 272        ovs-vsctl add-br br0
 273        ovs-vsctl add-port br0 eth0
 274        ovs-vsctl add-port br0 tap0 tag=9
 275
 276    If you want to configure an already added port as an access port,
 277    use "ovs-vsctl set", e.g.:
 278
 279        ovs-vsctl set port tap0 tag=9
 280
 281 ### Q: How do I configure a port as a SPAN port, that is, enable mirroring of all traffic to that port?
 282
 283 A: The following commands configure br0 with eth0 and tap0 as trunk
 284    ports.  All traffic coming in or going out on eth0 or tap0 is also
 285    mirrored to tap1; any traffic arriving on tap1 is dropped:
 286
 287        ovs-vsctl add-br br0
 288        ovs-vsctl add-port br0 eth0
 289        ovs-vsctl add-port br0 tap0
 290        ovs-vsctl add-port br0 tap1 \
 291            -- --id=@p get port tap1 \
 292            -- --id=@m create mirror name=m0 select-all=true output-port=@p \
 293            -- set bridge br0 mirrors=@m
 294
 295    To later disable mirroring, run:
 296
 297        ovs-vsctl clear bridge br0 mirrors
 298
 299 ### Q: Does Open vSwitch support configuring a port in promiscuous mode?
 300
 301 A: Yes.  How you configure it depends on what you mean by "promiscuous
 302    mode":
 303
 304   - Conventionally, "promiscuous mode" is a feature of a network
 305     interface card.  Ordinarily, a NIC passes to the CPU only the
 306     packets actually destined to its host machine.  It discards
 307     the rest to avoid wasting memory and CPU cycles.  When
 308     promiscuous mode is enabled, however, it passes every packet
 309     to the CPU.  On an old-style shared-media or hub-based
 310     network, this allows the host to spy on all packets on the
 311     network.  But in the switched networks that are almost
 312     everywhere these days, promiscuous mode doesn't have much
 313     effect, because few packets not destined to a host are
 314     delivered to the host's NIC.
 315
 316     This form of promiscuous mode is configured in the guest OS of
 317     the VMs on your bridge, e.g. with "ifconfig".
 318
 319   - The VMware vSwitch uses a different definition of "promiscuous
 320     mode".  When you configure promiscuous mode on a VMware vNIC,
 321     the vSwitch sends a copy of every packet received by the
 322     vSwitch to that vNIC.  That has a much bigger effect than just
 323     enabling promiscuous mode in a guest OS.  Rather than getting
 324     a few stray packets for which the switch does not yet know the
 325     correct destination, the vNIC gets every packet.  The effect
 326     is similar to replacing the vSwitch by a virtual hub.
 327
 328     This "promiscuous mode" is what switches normally call "port
 329     mirroring" or "SPAN".  For information on how to configure
 330     SPAN, see "How do I configure a port as a SPAN port, that is,
 331     enable mirroring of all traffic to that port?"
 332
 333 ### Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable mirroring of all traffic to that VLAN?
 334
 335 A: The following commands configure br0 with eth0 as a trunk port and
 336    tap0 as an access port for VLAN 10.  All traffic coming in or going
 337    out on tap0, as well as traffic coming in or going out on eth0 in
 338    VLAN 10, is also mirrored to VLAN 15 on eth0.  The original tag for
 339    VLAN 10, in cases where one is present, is dropped as part of
 340    mirroring:
 341
 342        ovs-vsctl add-br br0
 343        ovs-vsctl add-port br0 eth0
 344        ovs-vsctl add-port br0 tap0 tag=10
 345        ovs-vsctl \
 346            -- --id=@m create mirror name=m0 select-all=true select-vlan=10 \
 347                                     output-vlan=15 \
 348            -- set bridge br0 mirrors=@m
 349
 350    To later disable mirroring, run:
 351
 352        ovs-vsctl clear bridge br0 mirrors
 353
 354    Mirroring to a VLAN can disrupt a network that contains unmanaged
 355    switches.  See ovs-vswitchd.conf.db(5) for details.  Mirroring to a
 356    GRE tunnel has fewer caveats than mirroring to a VLAN and should
 357    generally be preferred.
 358
 359 ### Q: Can I mirror more than one input VLAN to an RSPAN VLAN?
 360
 361 A: Yes, but mirroring to a VLAN strips the original VLAN tag in favor
 362    of the specified output-vlan.  This loss of information may make
 363    the mirrored traffic too hard to interpret.
 364
 365    To mirror multiple VLANs, use the commands above, but specify a
 366    comma-separated list of VLANs as the value for select-vlan.  To
 367    mirror every VLAN, use the commands above, but omit select-vlan and
 368    its value entirely.
 369
 370    When a packet arrives on a VLAN that is used as a mirror output
 371    VLAN, the mirror is disregarded.  Instead, in standalone mode, OVS
 372    floods the packet across all the ports for which the mirror output
 373    VLAN is configured.  (If an OpenFlow controller is in use, then it
 374    can override this behavior through the flow table.)  If OVS is used
 375    as an intermediate switch, rather than an edge switch, this ensures
 376    that the RSPAN traffic is distributed through the network.
 377
 378    Mirroring to a VLAN can disrupt a network that contains unmanaged
 379    switches.  See ovs-vswitchd.conf.db(5) for details.  Mirroring to a
 380    GRE tunnel has fewer caveats than mirroring to a VLAN and should
 381    generally be preferred.
 382
 383 ### Q: How do I configure mirroring of all traffic to a GRE tunnel?
 384
 385 A: The following commands configure br0 with eth0 and tap0 as trunk
 386    ports.  All traffic coming in or going out on eth0 or tap0 is also
 387    mirrored to gre0, a GRE tunnel to the remote host 192.168.1.10; any
 388    traffic arriving on gre0 is dropped:
 389
 390        ovs-vsctl add-br br0
 391        ovs-vsctl add-port br0 eth0
 392        ovs-vsctl add-port br0 tap0
 393        ovs-vsctl add-port br0 gre0 \
 394            -- set interface gre0 type=gre options:remote_ip=192.168.1.10 \
 395            -- --id=@p get port gre0 \
 396            -- --id=@m create mirror name=m0 select-all=true output-port=@p \
 397            -- set bridge br0 mirrors=@m
 398
 399    To later disable mirroring and destroy the GRE tunnel:
 400
 401        ovs-vsctl clear bridge br0 mirrors
 402        ovs-vcstl del-port br0 gre0
 403
 404 ### Q: Does Open vSwitch support ERSPAN?
 405
 406 A: No.  ERSPAN is an undocumented proprietary protocol.  As an
 407    alternative, Open vSwitch supports mirroring to a GRE tunnel (see
 408    above).
 409
 410 ### Q: How do I connect two bridges?
 411
 412 A: First, why do you want to do this?  Two connected bridges are not
 413    much different from a single bridge, so you might as well just have
 414    a single bridge with all your ports on it.
 415
 416    If you still want to connect two bridges, you can use a pair of
 417    patch ports.  The following example creates bridges br0 and br1,
 418    adds eth0 and tap0 to br0, adds tap1 to br1, and then connects br0
 419    and br1 with a pair of patch ports.
 420
 421        ovs-vsctl add-br br0
 422        ovs-vsctl add-port br0 eth0
 423        ovs-vsctl add-port br0 tap0
 424        ovs-vsctl add-br br1
 425        ovs-vsctl add-port br1 tap1
 426        ovs-vsctl \
 427            -- add-port br0 patch0 \
 428            -- set interface patch0 type=patch options:peer=patch1 \
 429            -- add-port br1 patch1 \
 430            -- set interface patch1 type=patch options:peer=patch0
 431
 432    Bridges connected with patch ports are much like a single bridge.
 433    For instance, if the example above also added eth1 to br1, and both
 434    eth0 and eth1 happened to be connected to the same next-hop switch,
 435    then you could loop your network just as you would if you added
 436    eth0 and eth1 to the same bridge (see the "Configuration Problems"
 437    section below for more information).
 438
 439    If you are using Open vSwitch 1.9 or an earlier version, then you
 440    need to be using the kernel module bundled with Open vSwitch rather
 441    than the one that is integrated into Linux 3.3 and later, because
 442    Open vSwitch 1.9 and earlier versions need kernel support for patch
 443    ports.  This also means that in Open vSwitch 1.9 and earlier, patch
 444    ports will not work with the userspace datapath, only with the
 445    kernel module.
 446
 447 ### Q: How do I configure a bridge without an OpenFlow local port?  (Local port in the sense of OFPP_LOCAL)
 448
 449 A: Open vSwitch does not support such a configuration.
 450    Bridges always have their local ports.
 451
 452
 453 Implementation Details
 454 ----------------------
 455
 456 ### Q: I hear OVS has a couple of kinds of flows.  Can you tell me about them?
 457
 458 A: Open vSwitch uses different kinds of flows for different purposes:
 459
 460   - OpenFlow flows are the most important kind of flow.  OpenFlow
 461     controllers use these flows to define a switch's policy.
 462     OpenFlow flows support wildcards, priorities, and multiple
 463     tables.
 464
 465     When in-band control is in use, Open vSwitch sets up a few
 466     "hidden" flows, with priority higher than a controller or the
 467     user can configure, that are not visible via OpenFlow.  (See
 468     the "Controller" section of the FAQ for more information
 469     about hidden flows.)
 470
 471   - The Open vSwitch software switch implementation uses a second
 472     kind of flow internally.  These flows, called "datapath" or
 473     "kernel" flows, do not support priorities and comprise only a
 474     single table, which makes them suitable for caching.  (Like
 475     OpenFlow flows, datapath flows do support wildcarding, in Open
 476     vSwitch 1.11 and later.)  OpenFlow flows and datapath flows
 477     also support different actions and number ports differently.
 478
 479     Datapath flows are an implementation detail that is subject to
 480     change in future versions of Open vSwitch.  Even with the
 481     current version of Open vSwitch, hardware switch
 482     implementations do not necessarily use this architecture.
 483
 484    Users and controllers directly control only the OpenFlow flow
 485    table.  Open vSwitch manages the datapath flow table itself, so
 486    users should not normally be concerned with it.
 487
 488 ### Q: Why are there so many different ways to dump flows?
 489
 490 A: Open vSwitch has two kinds of flows (see the previous question), so
 491    it has commands with different purposes for dumping each kind of
 492    flow:
 493
 494   - `ovs-ofctl dump-flows <br>` dumps OpenFlow flows, excluding
 495     hidden flows.  This is the most commonly useful form of flow
 496     dump.  (Unlike the other commands, this should work with any
 497     OpenFlow switch, not just Open vSwitch.)
 498
 499   - `ovs-appctl bridge/dump-flows <br>` dumps OpenFlow flows,
 500     including hidden flows.  This is occasionally useful for
 501     troubleshooting suspected issues with in-band control.
 502
 503   - `ovs-dpctl dump-flows [dp]` dumps the datapath flow table
 504     entries for a Linux kernel-based datapath.  In Open vSwitch
 505     1.10 and later, ovs-vswitchd merges multiple switches into a
 506     single datapath, so it will show all the flows on all your
 507     kernel-based switches.  This command can occasionally be
 508     useful for debugging.
 509
 510   - `ovs-appctl dpif/dump-flows <br>`, new in Open vSwitch 1.10,
 511     dumps datapath flows for only the specified bridge, regardless
 512     of the type.
 513
 514 ### Q: How does multicast snooping works with VLANs?
 515
 516 A: Open vSwitch maintains snooping tables for each VLAN.
 517
 518
 519 Performance
 520 -----------
 521
 522 ### Q: I just upgraded and I see a performance drop.  Why?
 523
 524 A: The OVS kernel datapath may have been updated to a newer version than
 525    the OVS userspace components.  Sometimes new versions of OVS kernel
 526    module add functionality that is backwards compatible with older
 527    userspace components but may cause a drop in performance with them.
 528    Especially, if a kernel module from OVS 2.1 or newer is paired with
 529    OVS userspace 1.10 or older, there will be a performance drop for
 530    TCP traffic.
 531
 532    Updating the OVS userspace components to the latest released
 533    version should fix the performance degradation.
 534
 535    To get the best possible performance and functionality, it is
 536    recommended to pair the same versions of the kernel module and OVS
 537    userspace.
 538
 539
 540 Configuration Problems
 541 ----------------------
 542
 543 ### Q: I created a bridge and added my Ethernet port to it, using commands
 544    like these:
 545
 546        ovs-vsctl add-br br0
 547        ovs-vsctl add-port br0 eth0
 548
 549    and as soon as I ran the "add-port" command I lost all connectivity
 550    through eth0.  Help!
 551
 552 A: A physical Ethernet device that is part of an Open vSwitch bridge
 553    should not have an IP address.  If one does, then that IP address
 554    will not be fully functional.
 555
 556    You can restore functionality by moving the IP address to an Open
 557    vSwitch "internal" device, such as the network device named after
 558    the bridge itself.  For example, assuming that eth0's IP address is
 559    192.168.128.5, you could run the commands below to fix up the
 560    situation:
 561
 562        ifconfig eth0 0.0.0.0
 563        ifconfig br0 192.168.128.5
 564
 565    (If your only connection to the machine running OVS is through the
 566    IP address in question, then you would want to run all of these
 567    commands on a single command line, or put them into a script.)  If
 568    there were any additional routes assigned to eth0, then you would
 569    also want to use commands to adjust these routes to go through br0.
 570
 571    If you use DHCP to obtain an IP address, then you should kill the
 572    DHCP client that was listening on the physical Ethernet interface
 573    (e.g. eth0) and start one listening on the internal interface
 574    (e.g. br0).  You might still need to manually clear the IP address
 575    from the physical interface (e.g. with "ifconfig eth0 0.0.0.0").
 576
 577    There is no compelling reason why Open vSwitch must work this way.
 578    However, this is the way that the Linux kernel bridge module has
 579    always worked, so it's a model that those accustomed to Linux
 580    bridging are already used to.  Also, the model that most people
 581    expect is not implementable without kernel changes on all the
 582    versions of Linux that Open vSwitch supports.
 583
 584    By the way, this issue is not specific to physical Ethernet
 585    devices.  It applies to all network devices except Open vSwitch
 586    "internal" devices.
 587
 588 ### Q: I created a bridge and added a couple of Ethernet ports to it,
 589 ### using commands like these:
 590
 591        ovs-vsctl add-br br0
 592        ovs-vsctl add-port br0 eth0
 593        ovs-vsctl add-port br0 eth1
 594
 595    and now my network seems to have melted: connectivity is unreliable
 596    (even connectivity that doesn't go through Open vSwitch), all the
 597    LEDs on my physical switches are blinking, wireshark shows
 598    duplicated packets, and CPU usage is very high.
 599
 600 A: More than likely, you've looped your network.  Probably, eth0 and
 601    eth1 are connected to the same physical Ethernet switch.  This
 602    yields a scenario where OVS receives a broadcast packet on eth0 and
 603    sends it out on eth1, then the physical switch connected to eth1
 604    sends the packet back on eth0, and so on forever.  More complicated
 605    scenarios, involving a loop through multiple switches, are possible
 606    too.
 607
 608    The solution depends on what you are trying to do:
 609
 610    - If you added eth0 and eth1 to get higher bandwidth or higher
 611      reliability between OVS and your physical Ethernet switch,
 612      use a bond.  The following commands create br0 and then add
 613      eth0 and eth1 as a bond:
 614
 615          ovs-vsctl add-br br0
 616          ovs-vsctl add-bond br0 bond0 eth0 eth1
 617
 618      Bonds have tons of configuration options.  Please read the
 619      documentation on the Port table in ovs-vswitchd.conf.db(5)
 620      for all the details.
 621
 622    - Perhaps you don't actually need eth0 and eth1 to be on the
 623      same bridge.  For example, if you simply want to be able to
 624      connect each of them to virtual machines, then you can put
 625      each of them on a bridge of its own:
 626
 627          ovs-vsctl add-br br0
 628          ovs-vsctl add-port br0 eth0
 629
 630          ovs-vsctl add-br br1
 631          ovs-vsctl add-port br1 eth1
 632
 633      and then connect VMs to br0 and br1.  (A potential
 634      disadvantage is that traffic cannot directly pass between br0
 635      and br1.  Instead, it will go out eth0 and come back in eth1,
 636      or vice versa.)
 637
 638    - If you have a redundant or complex network topology and you
 639      want to prevent loops, turn on spanning tree protocol (STP).
 640      The following commands create br0, enable STP, and add eth0
 641      and eth1 to the bridge.  The order is important because you
 642      don't want have to have a loop in your network even
 643      transiently:
 644
 645          ovs-vsctl add-br br0
 646          ovs-vsctl set bridge br0 stp_enable=true
 647          ovs-vsctl add-port br0 eth0
 648          ovs-vsctl add-port br0 eth1
 649
 650      The Open vSwitch implementation of STP is not well tested.
 651      Please report any bugs you observe, but if you'd rather avoid
 652      acting as a beta tester then another option might be your
 653      best shot.
 654
 655 ### Q: I can't seem to use Open vSwitch in a wireless network.
 656
 657 A: Wireless base stations generally only allow packets with the source
 658    MAC address of NIC that completed the initial handshake.
 659    Therefore, without MAC rewriting, only a single device can
 660    communicate over a single wireless link.
 661
 662    This isn't specific to Open vSwitch, it's enforced by the access
 663    point, so the same problems will show up with the Linux bridge or
 664    any other way to do bridging.
 665
 666 ### Q: I can't seem to add my PPP interface to an Open vSwitch bridge.
 667
 668 A: PPP most commonly carries IP packets, but Open vSwitch works only
 669    with Ethernet frames.  The correct way to interface PPP to an
 670    Ethernet network is usually to use routing instead of switching.
 671
 672 ### Q: Is there any documentation on the database tables and fields?
 673
 674 A: Yes.  ovs-vswitchd.conf.db(5) is a comprehensive reference.
 675
 676 ### Q: When I run ovs-dpctl I no longer see the bridges I created.  Instead,
 677    I only see a datapath called "ovs-system".  How can I see datapath
 678    information about a particular bridge?
 679
 680 A: In version 1.9.0, OVS switched to using a single datapath that is
 681    shared by all bridges of that type.  The "ovs-appctl dpif/*"
 682    commands provide similar functionality that is scoped by the bridge.
 683
 684 ### Q: I created a GRE port using ovs-vsctl so why can't I send traffic or
 685    see the port in the datapath?
 686
 687 A: On Linux kernels before 3.11, the OVS GRE module and Linux GRE module
 688    cannot be loaded at the same time. It is likely that on your system the
 689    Linux GRE module is already loaded and blocking OVS (to confirm, check
 690    dmesg for errors regarding GRE registration). To fix this, unload all
 691    GRE modules that appear in lsmod as well as the OVS kernel module. You
 692    can then reload the OVS module following the directions in
 693    [INSTALL.md], which will ensure that dependencies are satisfied.
 694
 695 ### Q: Open vSwitch does not seem to obey my packet filter rules.
 696
 697 A: It depends on mechanisms and configurations you want to use.
 698
 699    You cannot usefully use typical packet filters, like iptables, on
 700    physical Ethernet ports that you add to an Open vSwitch bridge.
 701    This is because Open vSwitch captures packets from the interface at
 702    a layer lower below where typical packet-filter implementations
 703    install their hooks.  (This actually applies to any interface of
 704    type "system" that you might add to an Open vSwitch bridge.)
 705
 706    You can usefully use typical packet filters on Open vSwitch
 707    internal ports as they are mostly ordinary interfaces from the point
 708    of view of packet filters.
 709
 710    For example, suppose you create a bridge br0 and add Ethernet port
 711    eth0 to it.  Then you can usefully add iptables rules to affect the
 712    internal interface br0, but not the physical interface eth0.  (br0
 713    is also where you would add an IP address, as discussed elsewhere
 714    in the FAQ.)
 715
 716    For simple filtering rules, it might be possible to achieve similar
 717    results by installing appropriate OpenFlow flows instead.
 718
 719    If the use of a particular packet filter setup is essential, Open
 720    vSwitch might not be the best choice for you.  On Linux, you might
 721    want to consider using the Linux Bridge.  (This is the only choice if
 722    you want to use ebtables rules.)  On NetBSD, you might want to
 723    consider using the bridge(4) with BRIDGE_IPF option.
 724
 725 ### Q: It seems that Open vSwitch does nothing when I removed a port and
 726    then immediately put it back.  For example, consider that p1 is
 727    a port of type=internal:
 728
 729        ovs-vsctl del-port br0 p1 -- \
 730            add-port br0 p1 -- \
 731            set interface p1 type=internal
 732
 733 A: It's an expected behaviour.
 734
 735    If del-port and add-port happen in a single OVSDB transaction as
 736    your example, Open vSwitch always "skips" the intermediate steps.
 737    Even if they are done in multiple transactions, it's still allowed
 738    for Open vSwitch to skip the intermediate steps and just implement
 739    the overall effect.  In both cases, your example would be turned
 740    into a no-op.
 741
 742    If you want to make Open vSwitch actually destroy and then re-create
 743    the port for some side effects like resetting kernel setting for the
 744    corresponding interface, you need to separate operations into multiple
 745    OVSDB transactions and ensure that at least the first one does not have
 746    --no-wait.  In the following example, the first ovs-vsctl will block
 747    until Open vSwitch reloads the new configuration and removes the port:
 748
 749        ovs-vsctl del-port br0 p1
 750        ovs-vsctl add-port br0 p1 -- \
 751            set interface p1 type=internal
 752
 753 Quality of Service (QoS)
 754 ------------------------
 755
 756 ### Q: How do I configure Quality of Service (QoS)?
 757
 758 A: Suppose that you want to set up bridge br0 connected to physical
 759    Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
 760    vif1.0 and vif2.0, and that you want to limit traffic from vif1.0
 761    to eth0 to 10 Mbps and from vif2.0 to eth0 to 20 Mbps.  Then, you
 762    could configure the bridge this way:
 763
 764        ovs-vsctl -- \
 765            add-br br0 -- \
 766            add-port br0 eth0 -- \
 767            add-port br0 vif1.0 -- set interface vif1.0 ofport_request=5 -- \
 768            add-port br0 vif2.0 -- set interface vif2.0 ofport_request=6 -- \
 769            set port eth0 qos=@newqos -- \
 770            --id=@newqos create qos type=linux-htb \
 771                other-config:max-rate=1000000000 \
 772                queues:123=@vif10queue \
 773                queues:234=@vif20queue -- \
 774            --id=@vif10queue create queue other-config:max-rate=10000000 -- \
 775            --id=@vif20queue create queue other-config:max-rate=20000000
 776
 777    At this point, bridge br0 is configured with the ports and eth0 is
 778    configured with the queues that you need for QoS, but nothing is
 779    actually directing packets from vif1.0 or vif2.0 to the queues that
 780    we have set up for them.  That means that all of the packets to
 781    eth0 are going to the "default queue", which is not what we want.
 782
 783    We use OpenFlow to direct packets from vif1.0 and vif2.0 to the
 784    queues reserved for them:
 785
 786        ovs-ofctl add-flow br0 in_port=5,actions=set_queue:123,normal
 787        ovs-ofctl add-flow br0 in_port=6,actions=set_queue:234,normal
 788
 789    Each of the above flows matches on the input port, sets up the
 790    appropriate queue (123 for vif1.0, 234 for vif2.0), and then
 791    executes the "normal" action, which performs the same switching
 792    that Open vSwitch would have done without any OpenFlow flows being
 793    present.  (We know that vif1.0 and vif2.0 have OpenFlow port
 794    numbers 5 and 6, respectively, because we set their ofport_request
 795    columns above.  If we had not done that, then we would have needed
 796    to find out their port numbers before setting up these flows.)
 797
 798    Now traffic going from vif1.0 or vif2.0 to eth0 should be
 799    rate-limited.
 800
 801    By the way, if you delete the bridge created by the above commands,
 802    with:
 803
 804        ovs-vsctl del-br br0
 805
 806    then that will leave one unreferenced QoS record and two
 807    unreferenced Queue records in the Open vSwich database.  One way to
 808    clear them out, assuming you don't have other QoS or Queue records
 809    that you want to keep, is:
 810
 811        ovs-vsctl -- --all destroy QoS -- --all destroy Queue
 812
 813    If you do want to keep some QoS or Queue records, or the Open
 814    vSwitch you are using is older than version 1.8 (which added the
 815    --all option), then you will have to destroy QoS and Queue records
 816    individually.
 817
 818 ### Q: I configured Quality of Service (QoS) in my OpenFlow network by
 819    adding records to the QoS and Queue table, but the results aren't
 820    what I expect.
 821
 822 A: Did you install OpenFlow flows that use your queues?  This is the
 823    primary way to tell Open vSwitch which queues you want to use.  If
 824    you don't do this, then the default queue will be used, which will
 825    probably not have the effect you want.
 826
 827    Refer to the previous question for an example.
 828
 829 ### Q: I'd like to take advantage of some QoS feature that Open vSwitch
 830    doesn't yet support.  How do I do that?
 831
 832 A: Open vSwitch does not implement QoS itself.  Instead, it can
 833    configure some, but not all, of the QoS features built into the
 834    Linux kernel.  If you need some QoS feature that OVS cannot
 835    configure itself, then the first step is to figure out whether
 836    Linux QoS supports that feature.  If it does, then you can submit a
 837    patch to support Open vSwitch configuration for that feature, or
 838    you can use "tc" directly to configure the feature in Linux.  (If
 839    Linux QoS doesn't support the feature you want, then first you have
 840    to add that support to Linux.)
 841
 842 ### Q: I configured QoS, correctly, but my measurements show that it isn't
 843    working as well as I expect.
 844
 845 A: With the Linux kernel, the Open vSwitch implementation of QoS has
 846    two aspects:
 847
 848    - Open vSwitch configures a subset of Linux kernel QoS
 849      features, according to what is in OVSDB.  It is possible that
 850      this code has bugs.  If you believe that this is so, then you
 851      can configure the Linux traffic control (QoS) stack directly
 852      with the "tc" program.  If you get better results that way,
 853      you can send a detailed bug report to bugs@openvswitch.org.
 854
 855      It is certain that Open vSwitch cannot configure every Linux
 856      kernel QoS feature.  If you need some feature that OVS cannot
 857      configure, then you can also use "tc" directly (or add that
 858      feature to OVS).
 859
 860    - The Open vSwitch implementation of OpenFlow allows flows to
 861      be directed to particular queues.  This is pretty simple and
 862      unlikely to have serious bugs at this point.
 863
 864    However, most problems with QoS on Linux are not bugs in Open
 865    vSwitch at all.  They tend to be either configuration errors
 866    (please see the earlier questions in this section) or issues with
 867    the traffic control (QoS) stack in Linux.  The Open vSwitch
 868    developers are not experts on Linux traffic control.  We suggest
 869    that, if you believe you are encountering a problem with Linux
 870    traffic control, that you consult the tc manpages (e.g. tc(8),
 871    tc-htb(8), tc-hfsc(8)), web resources (e.g. http://lartc.org/), or
 872    mailing lists (e.g. http://vger.kernel.org/vger-lists.html#netdev).
 873
 874 ### Q: Does Open vSwitch support OpenFlow meters?
 875
 876 A: Since version 2.0, Open vSwitch has OpenFlow protocol support for
 877    OpenFlow meters.  There is no implementation of meters in the Open
 878    vSwitch software switch (neither the kernel-based nor userspace
 879    switches).
 880
 881
 882 VLANs
 883 -----
 884
 885 ### Q: What's a VLAN?
 886
 887 A: At the simplest level, a VLAN (short for "virtual LAN") is a way to
 888    partition a single switch into multiple switches.  Suppose, for
 889    example, that you have two groups of machines, group A and group B.
 890    You want the machines in group A to be able to talk to each other,
 891    and you want the machine in group B to be able to talk to each
 892    other, but you don't want the machines in group A to be able to
 893    talk to the machines in group B.  You can do this with two
 894    switches, by plugging the machines in group A into one switch and
 895    the machines in group B into the other switch.
 896
 897    If you only have one switch, then you can use VLANs to do the same
 898    thing, by configuring the ports for machines in group A as VLAN
 899    "access ports" for one VLAN and the ports for group B as "access
 900    ports" for a different VLAN.  The switch will only forward packets
 901    between ports that are assigned to the same VLAN, so this
 902    effectively subdivides your single switch into two independent
 903    switches, one for each group of machines.
 904
 905    So far we haven't said anything about VLAN headers.  With access
 906    ports, like we've described so far, no VLAN header is present in
 907    the Ethernet frame.  This means that the machines (or switches)
 908    connected to access ports need not be aware that VLANs are
 909    involved, just like in the case where we use two different physical
 910    switches.
 911
 912    Now suppose that you have a whole bunch of switches in your
 913    network, instead of just one, and that some machines in group A are
 914    connected directly to both switches 1 and 2.  To allow these
 915    machines to talk to each other, you could add an access port for
 916    group A's VLAN to switch 1 and another to switch 2, and then
 917    connect an Ethernet cable between those ports.  That works fine,
 918    but it doesn't scale well as the number of switches and the number
 919    of VLANs increases, because you use up a lot of valuable switch
 920    ports just connecting together your VLANs.
 921
 922    This is where VLAN headers come in.  Instead of using one cable and
 923    two ports per VLAN to connect a pair of switches, we configure a
 924    port on each switch as a VLAN "trunk port".  Packets sent and
 925    received on a trunk port carry a VLAN header that says what VLAN
 926    the packet belongs to, so that only two ports total are required to
 927    connect the switches, regardless of the number of VLANs in use.
 928    Normally, only switches (either physical or virtual) are connected
 929    to a trunk port, not individual hosts, because individual hosts
 930    don't expect to see a VLAN header in the traffic that they receive.
 931
 932    None of the above discussion says anything about particular VLAN
 933    numbers.  This is because VLAN numbers are completely arbitrary.
 934    One must only ensure that a given VLAN is numbered consistently
 935    throughout a network and that different VLANs are given different
 936    numbers.  (That said, VLAN 0 is usually synonymous with a packet
 937    that has no VLAN header, and VLAN 4095 is reserved.)
 938
 939 ### Q: VLANs don't work.
 940
 941 A: Many drivers in Linux kernels before version 3.3 had VLAN-related
 942    bugs.  If you are having problems with VLANs that you suspect to be
 943    driver related, then you have several options:
 944
 945    - Upgrade to Linux 3.3 or later.
 946
 947    - Build and install a fixed version of the particular driver
 948      that is causing trouble, if one is available.
 949
 950    - Use a NIC whose driver does not have VLAN problems.
 951
 952    - Use "VLAN splinters", a feature in Open vSwitch 1.4 and later
 953      that works around bugs in kernel drivers.  To enable VLAN
 954      splinters on interface eth0, use the command:
 955
 956        ovs-vsctl set interface eth0 other-config:enable-vlan-splinters=true
 957
 958      For VLAN splinters to be effective, Open vSwitch must know
 959      which VLANs are in use.  See the "VLAN splinters" section in
 960      the Interface table in ovs-vswitchd.conf.db(5) for details on
 961      how Open vSwitch infers in-use VLANs.
 962
 963      VLAN splinters increase memory use and reduce performance, so
 964      use them only if needed.
 965
 966    - Apply the "vlan workaround" patch from the XenServer kernel
 967      patch queue, build Open vSwitch against this patched kernel,
 968      and then use ovs-vlan-bug-workaround(8) to enable the VLAN
 969      workaround for each interface whose driver is buggy.
 970
 971      (This is a nontrivial exercise, so this option is included
 972      only for completeness.)
 973
 974    It is not always easy to tell whether a Linux kernel driver has
 975    buggy VLAN support.  The ovs-vlan-test(8) and ovs-test(8) utilities
 976    can help you test.  See their manpages for details.  Of the two
 977    utilities, ovs-test(8) is newer and more thorough, but
 978    ovs-vlan-test(8) may be easier to use.
 979
 980 ### Q: VLANs still don't work.  I've tested the driver so I know that it's OK.
 981
 982 A: Do you have VLANs enabled on the physical switch that OVS is
 983    attached to?  Make sure that the port is configured to trunk the
 984    VLAN or VLANs that you are using with OVS.
 985
 986 ### Q: Outgoing VLAN-tagged traffic goes through OVS to my physical switch
 987    and to its destination host, but OVS seems to drop incoming return
 988    traffic.
 989
 990 A: It's possible that you have the VLAN configured on your physical
 991    switch as the "native" VLAN.  In this mode, the switch treats
 992    incoming packets either tagged with the native VLAN or untagged as
 993    part of the native VLAN.  It may also send outgoing packets in the
 994    native VLAN without a VLAN tag.
 995
 996    If this is the case, you have two choices:
 997
 998    - Change the physical switch port configuration to tag packets
 999      it forwards to OVS with the native VLAN instead of forwarding
1000      them untagged.
1001
1002    - Change the OVS configuration for the physical port to a
1003      native VLAN mode.  For example, the following sets up a
1004      bridge with port eth0 in "native-tagged" mode in VLAN 9:
1005
1006          ovs-vsctl add-br br0
1007          ovs-vsctl add-port br0 eth0 tag=9 vlan_mode=native-tagged
1008
1009      In this situation, "native-untagged" mode will probably work
1010      equally well.  Refer to the documentation for the Port table
1011      in ovs-vswitchd.conf.db(5) for more information.
1012
1013 ### Q: I added a pair of VMs on different VLANs, like this:
1014
1015        ovs-vsctl add-br br0
1016        ovs-vsctl add-port br0 eth0
1017        ovs-vsctl add-port br0 tap0 tag=9
1018        ovs-vsctl add-port br0 tap1 tag=10
1019
1020     but the VMs can't access each other, the external network, or the
1021     Internet.
1022
1023 A: It is to be expected that the VMs can't access each other.  VLANs
1024    are a means to partition a network.  When you configured tap0 and
1025    tap1 as access ports for different VLANs, you indicated that they
1026    should be isolated from each other.
1027
1028    As for the external network and the Internet, it seems likely that
1029    the machines you are trying to access are not on VLAN 9 (or 10) and
1030    that the Internet is not available on VLAN 9 (or 10).
1031
1032 ### Q: I added a pair of VMs on the same VLAN, like this:
1033
1034        ovs-vsctl add-br br0
1035        ovs-vsctl add-port br0 eth0
1036        ovs-vsctl add-port br0 tap0 tag=9
1037        ovs-vsctl add-port br0 tap1 tag=9
1038
1039     The VMs can access each other, but not the external network or the
1040     Internet.
1041
1042 A: It seems likely that the machines you are trying to access in the
1043    external network are not on VLAN 9 and that the Internet is not
1044    available on VLAN 9.  Also, ensure VLAN 9 is set up as an allowed
1045    trunk VLAN on the upstream switch port to which eth0 is connected.
1046
1047 ### Q: Can I configure an IP address on a VLAN?
1048
1049 A: Yes.  Use an "internal port" configured as an access port.  For
1050    example, the following configures IP address 192.168.0.7 on VLAN 9.
1051    That is, OVS will forward packets from eth0 to 192.168.0.7 only if
1052    they have an 802.1Q header with VLAN 9.  Conversely, traffic
1053    forwarded from 192.168.0.7 to eth0 will be tagged with an 802.1Q
1054    header with VLAN 9:
1055
1056        ovs-vsctl add-br br0
1057        ovs-vsctl add-port br0 eth0
1058        ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
1059        ifconfig vlan9 192.168.0.7
1060
1061    See also the following question.
1062
1063 ### Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
1064    this:
1065
1066        ovs-vsctl add-br br0
1067        ovs-vsctl add-port br0 eth0
1068        ifconfig br0 192.168.0.5
1069        ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
1070        ifconfig vlan9 192.168.0.9
1071
1072    but other hosts that are only on VLAN 0 can reach the IP address
1073    configured on VLAN 9.  What's going on?
1074
1075 A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
1076    approaches to IP address handling in Internet hosts:
1077
1078    - In the "Strong ES Model", where an ES is a host ("End
1079      System"), an IP address is primarily associated with a
1080      particular interface.  The host discards packets that arrive
1081      on interface A if they are destined for an IP address that is
1082      configured on interface B.  The host never sends packets from
1083      interface A using a source address configured on interface B.
1084
1085    - In the "Weak ES Model", an IP address is primarily associated
1086      with a host.  The host accepts packets that arrive on any
1087      interface if they are destined for any of the host's IP
1088      addresses, even if the address is configured on some
1089      interface other than the one on which it arrived.  The host
1090      does not restrict itself to sending packets from an IP
1091      address associated with the originating interface.
1092
1093    Linux uses the weak ES model.  That means that when packets
1094    destined to the VLAN 9 IP address arrive on eth0 and are bridged to
1095    br0, the kernel IP stack accepts them there for the VLAN 9 IP
1096    address, even though they were not received on vlan9, the network
1097    device for vlan9.
1098
1099    To simulate the strong ES model on Linux, one may add iptables rule
1100    to filter packets based on source and destination address and
1101    adjust ARP configuration with sysctls.
1102
1103    BSD uses the strong ES model.
1104
1105 ### Q: My OpenFlow controller doesn't see the VLANs that I expect.
1106
1107 A: The configuration for VLANs in the Open vSwitch database (e.g. via
1108    ovs-vsctl) only affects traffic that goes through Open vSwitch's
1109    implementation of the OpenFlow "normal switching" action.  By
1110    default, when Open vSwitch isn't connected to a controller and
1111    nothing has been manually configured in the flow table, all traffic
1112    goes through the "normal switching" action.  But, if you set up
1113    OpenFlow flows on your own, through a controller or using ovs-ofctl
1114    or through other means, then you have to implement VLAN handling
1115    yourself.
1116
1117    You can use "normal switching" as a component of your OpenFlow
1118    actions, e.g. by putting "normal" into the lists of actions on
1119    ovs-ofctl or by outputting to OFPP_NORMAL from an OpenFlow
1120    controller.  In situations where this is not suitable, you can
1121    implement VLAN handling yourself, e.g.:
1122
1123    - If a packet comes in on an access port, and the flow table
1124      needs to send it out on a trunk port, then the flow can add
1125      the appropriate VLAN tag with the "mod_vlan_vid" action.
1126
1127    - If a packet comes in on a trunk port, and the flow table
1128      needs to send it out on an access port, then the flow can
1129      strip the VLAN tag with the "strip_vlan" action.
1130
1131 ### Q: I configured ports on a bridge as access ports with different VLAN
1132    tags, like this:
1133
1134        ovs-vsctl add-br br0
1135        ovs-vsctl set-controller br0 tcp:192.168.0.10:6633
1136        ovs-vsctl add-port br0 eth0
1137        ovs-vsctl add-port br0 tap0 tag=9
1138        ovs-vsctl add-port br0 tap1 tag=10
1139
1140    but the VMs running behind tap0 and tap1 can still communicate,
1141    that is, they are not isolated from each other even though they are
1142    on different VLANs.
1143
1144 A: Do you have a controller configured on br0 (as the commands above
1145    do)?  If so, then this is a variant on the previous question, "My
1146    OpenFlow controller doesn't see the VLANs that I expect," and you
1147    can refer to the answer there for more information.
1148
1149 ### Q: How MAC learning works with VLANs?
1150
1151 A: Open vSwitch implements Independent VLAN Learning (IVL) for
1152    OFPP_NORMAL action.  I.e. it logically has separate learning tables
1153    for each VLANs.
1154
1155
1156 VXLANs
1157 -----
1158
1159 ### Q: What's a VXLAN?
1160
1161 A: VXLAN stands for Virtual eXtensible Local Area Network, and is a means
1162    to solve the scaling challenges of VLAN networks in a multi-tenant
1163    environment. VXLAN is an overlay network which transports an L2 network
1164    over an existing L3 network. For more information on VXLAN, please see
1165    the IETF draft available here:
1166
1167    http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-03
1168
1169 ### Q: How much of the VXLAN protocol does Open vSwitch currently support?
1170
1171 A: Open vSwitch currently supports the framing format for packets on the
1172    wire. There is currently no support for the multicast aspects of VXLAN.
1173    To get around the lack of multicast support, it is possible to
1174    pre-provision MAC to IP address mappings either manually or from a
1175    controller.
1176
1177 ### Q: What destination UDP port does the VXLAN implementation in Open vSwitch
1178    use?
1179
1180 A: By default, Open vSwitch will use the assigned IANA port for VXLAN, which
1181    is 4789. However, it is possible to configure the destination UDP port
1182    manually on a per-VXLAN tunnel basis. An example of this configuration is
1183    provided below.
1184
1185        ovs-vsctl add-br br0
1186        ovs-vsctl add-port br0 vxlan1 -- set interface vxlan1
1187        type=vxlan options:remote_ip=192.168.1.2 options:key=flow
1188        options:dst_port=8472
1189
1190
1191 Using OpenFlow (Manually or Via Controller)
1192 -------------------------------------------
1193
1194 ### Q: What versions of OpenFlow does Open vSwitch support?
1195
1196 A: The following table lists the versions of OpenFlow supported by
1197    each version of Open vSwitch:
1198
1199        Open vSwitch      OF1.0  OF1.1  OF1.2  OF1.3  OF1.4  OF1.5
1200        ###============   =====  =====  =====  =====  =====  =====
1201        1.9 and earlier    yes    ---    ---    ---    ---    ---
1202        1.10               yes    ---    [*]    [*]    ---    ---
1203        1.11               yes    ---    [*]    [*]    ---    ---
1204        2.0                yes    [*]    [*]    [*]    ---    ---
1205        2.1                yes    [*]    [*]    [*]    ---    ---
1206        2.2                yes    [*]    [*]    [*]    [%]    [*]
1207        2.3                yes    yes    yes    yes    [*]    [*]
1208
1209        [*] Supported, with one or more missing features.
1210        [%] Experimental, unsafe implementation.
1211
1212    Open vSwitch 2.3 enables OpenFlow 1.0, 1.1, 1.2, and 1.3 by default
1213    in ovs-vswitchd.  In Open vSwitch 1.10 through 2.2, OpenFlow 1.1,
1214    1.2, and 1.3 must be enabled manually in ovs-vswitchd.  OpenFlow
1215    1.4 and 1.5 are also supported, with missing features, in Open
1216    vSwitch 2.3 and later, but not enabled by default.  In any case,
1217    the user may override the default:
1218
1219    - To enable OpenFlow 1.0, 1.1, 1.2, and 1.3 on bridge br0:
1220
1221      ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13
1222
1223    - To enable OpenFlow 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5 on bridge br0:
1224
1225      ovs-vsctl set bridge br0 protocols=OpenFlow10,OpenFlow11,OpenFlow12,OpenFlow13,OpenFlow14,OpenFlow15
1226
1227    - To enable only OpenFlow 1.0 on bridge br0:
1228
1229      ovs-vsctl set bridge br0 protocols=OpenFlow10
1230
1231    All current versions of ovs-ofctl enable only OpenFlow 1.0 by
1232    default.  Use the -O option to enable support for later versions of
1233    OpenFlow in ovs-ofctl.  For example:
1234
1235        ovs-ofctl -O OpenFlow13 dump-flows br0
1236
1237    (Open vSwitch 2.2 had an experimental implementation of OpenFlow
1238    1.4 that could cause crashes.  We don't recommend enabling it.)
1239
1240    [OPENFLOW-1.1+.md] in the Open vSwitch source tree tracks support for
1241    OpenFlow 1.1 and later features.  When support for OpenFlow 1.4 and
1242    1.5 is solidly implemented, Open vSwitch will enable those version
1243    by default.  Also, the OpenFlow 1.5 specification is still under
1244    development and thus subject to change.
1245
1246 ### Q: Does Open vSwitch support MPLS?
1247
1248 A: Before version 1.11, Open vSwitch did not support MPLS.  That is,
1249    these versions can match on MPLS Ethernet types, but they cannot
1250    match, push, or pop MPLS labels, nor can they look past MPLS labels
1251    into the encapsulated packet.
1252
1253    Open vSwitch versions 1.11, 2.0, and 2.1 have very minimal support
1254    for MPLS.  With the userspace datapath only, these versions can
1255    match, push, or pop a single MPLS label, but they still cannot look
1256    past MPLS labels (even after popping them) into the encapsulated
1257    packet.  Kernel datapath support is unchanged from earlier
1258    versions.
1259
1260    Open vSwitch version 2.3 can match, push, or pop up to 3 MPLS
1261    labels.  Looking past MPLS labels into the encapsulated packet will
1262    still be unsupported.  Both userspace and kernel datapaths will be
1263    supported, but MPLS processing always happens in userspace either
1264    way, so kernel datapath performance will be disappointing.
1265
1266    Open vSwitch version 2.4 will have kernel support for MPLS,
1267    yielding improved performance.
1268
1269 ### Q: I'm getting "error type 45250 code 0".  What's that?
1270
1271 A: This is a Open vSwitch extension to OpenFlow error codes.  Open
1272    vSwitch uses this extension when it must report an error to an
1273    OpenFlow controller but no standard OpenFlow error code is
1274    suitable.
1275
1276    Open vSwitch logs the errors that it sends to controllers, so the
1277    easiest thing to do is probably to look at the ovs-vswitchd log to
1278    find out what the error was.
1279
1280    If you want to dissect the extended error message yourself, the
1281    format is documented in include/openflow/nicira-ext.h in the Open
1282    vSwitch source distribution.  The extended error codes are
1283    documented in lib/ofp-errors.h.
1284
1285 Q1: Some of the traffic that I'd expect my OpenFlow controller to see
1286     doesn't actually appear through the OpenFlow connection, even
1287     though I know that it's going through.
1288 Q2: Some of the OpenFlow flows that my controller sets up don't seem
1289     to apply to certain traffic, especially traffic between OVS and
1290     the controller itself.
1291
1292 A: By default, Open vSwitch assumes that OpenFlow controllers are
1293    connected "in-band", that is, that the controllers are actually
1294    part of the network that is being controlled.  In in-band mode,
1295    Open vSwitch sets up special "hidden" flows to make sure that
1296    traffic can make it back and forth between OVS and the controllers.
1297    These hidden flows are higher priority than any flows that can be
1298    set up through OpenFlow, and they are not visible through normal
1299    OpenFlow flow table dumps.
1300
1301    Usually, the hidden flows are desirable and helpful, but
1302    occasionally they can cause unexpected behavior.  You can view the
1303    full OpenFlow flow table, including hidden flows, on bridge br0
1304    with the command:
1305
1306        ovs-appctl bridge/dump-flows br0
1307
1308    to help you debug.  The hidden flows are those with priorities
1309    greater than 65535 (the maximum priority that can be set with
1310    OpenFlow).
1311
1312    The DESIGN file at the top level of the Open vSwitch source
1313    distribution describes the in-band model in detail.
1314
1315    If your controllers are not actually in-band (e.g. they are on
1316    localhost via 127.0.0.1, or on a separate network), then you should
1317    configure your controllers in "out-of-band" mode.  If you have one
1318    controller on bridge br0, then you can configure out-of-band mode
1319    on it with:
1320
1321        ovs-vsctl set controller br0 connection-mode=out-of-band
1322
1323 ### Q: I configured all my controllers for out-of-band control mode but
1324    "ovs-appctl bridge/dump-flows" still shows some hidden flows.
1325
1326 A: You probably have a remote manager configured (e.g. with "ovs-vsctl
1327    set-manager").  By default, Open vSwitch assumes that managers need
1328    in-band rules set up on every bridge.  You can disable these rules
1329    on bridge br0 with:
1330
1331        ovs-vsctl set bridge br0 other-config:disable-in-band=true
1332
1333    This actually disables in-band control entirely for the bridge, as
1334    if all the bridge's controllers were configured for out-of-band
1335    control.
1336
1337 ### Q: My OpenFlow controller doesn't see the VLANs that I expect.
1338
1339 A: See answer under "VLANs", above.
1340
1341 ### Q: I ran "ovs-ofctl add-flow br0 nw_dst=192.168.0.1,actions=drop"
1342    but I got a funny message like this:
1343
1344        ofp_util|INFO|normalization changed ofp_match, details:
1345        ofp_util|INFO| pre: nw_dst=192.168.0.1
1346        ofp_util|INFO|post:
1347
1348    and when I ran "ovs-ofctl dump-flows br0" I saw that my nw_dst
1349    match had disappeared, so that the flow ends up matching every
1350    packet.
1351
1352 A: The term "normalization" in the log message means that a flow
1353    cannot match on an L3 field without saying what L3 protocol is in
1354    use.  The "ovs-ofctl" command above didn't specify an L3 protocol,
1355    so the L3 field match was dropped.
1356
1357    In this case, the L3 protocol could be IP or ARP.  A correct
1358    command for each possibility is, respectively:
1359
1360        ovs-ofctl add-flow br0 ip,nw_dst=192.168.0.1,actions=drop
1361
1362    and
1363
1364        ovs-ofctl add-flow br0 arp,nw_dst=192.168.0.1,actions=drop
1365
1366    Similarly, a flow cannot match on an L4 field without saying what
1367    L4 protocol is in use.  For example, the flow match "tp_src=1234"
1368    is, by itself, meaningless and will be ignored.  Instead, to match
1369    TCP source port 1234, write "tcp,tp_src=1234", or to match UDP
1370    source port 1234, write "udp,tp_src=1234".
1371
1372 ### Q: How can I figure out the OpenFlow port number for a given port?
1373
1374 A: The OFPT_FEATURES_REQUEST message requests an OpenFlow switch to
1375    respond with an OFPT_FEATURES_REPLY that, among other information,
1376    includes a mapping between OpenFlow port names and numbers.  From a
1377    command prompt, "ovs-ofctl show br0" makes such a request and
1378    prints the response for switch br0.
1379
1380    The Interface table in the Open vSwitch database also maps OpenFlow
1381    port names to numbers.  To print the OpenFlow port number
1382    associated with interface eth0, run:
1383
1384        ovs-vsctl get Interface eth0 ofport
1385
1386    You can print the entire mapping with:
1387
1388        ovs-vsctl -- --columns=name,ofport list Interface
1389
1390    but the output mixes together interfaces from all bridges in the
1391    database, so it may be confusing if more than one bridge exists.
1392
1393    In the Open vSwitch database, ofport value -1 means that the
1394    interface could not be created due to an error.  (The Open vSwitch
1395    log should indicate the reason.)  ofport value [] (the empty set)
1396    means that the interface hasn't been created yet.  The latter is
1397    normally an intermittent condition (unless ovs-vswitchd is not
1398    running).
1399
1400 ### Q: I added some flows with my controller or with ovs-ofctl, but when I
1401    run "ovs-dpctl dump-flows" I don't see them.
1402
1403 A: ovs-dpctl queries a kernel datapath, not an OpenFlow switch.  It
1404    won't display the information that you want.  You want to use
1405    "ovs-ofctl dump-flows" instead.
1406
1407 ### Q: It looks like each of the interfaces in my bonded port shows up
1408    as an individual OpenFlow port.  Is that right?
1409
1410 A: Yes, Open vSwitch makes individual bond interfaces visible as
1411    OpenFlow ports, rather than the bond as a whole.  The interfaces
1412    are treated together as a bond for only a few purposes:
1413
1414    - Sending a packet to the OFPP_NORMAL port.  (When an OpenFlow
1415      controller is not configured, this happens implicitly to
1416      every packet.)
1417
1418    - Mirrors configured for output to a bonded port.
1419
1420    It would make a lot of sense for Open vSwitch to present a bond as
1421    a single OpenFlow port.  If you want to contribute an
1422    implementation of such a feature, please bring it up on the Open
1423    vSwitch development mailing list at dev@openvswitch.org.
1424
1425 ### Q: I have a sophisticated network setup involving Open vSwitch, VMs or
1426    multiple hosts, and other components.  The behavior isn't what I
1427    expect.  Help!
1428
1429 A: To debug network behavior problems, trace the path of a packet,
1430    hop-by-hop, from its origin in one host to a remote host.  If
1431    that's correct, then trace the path of the response packet back to
1432    the origin.
1433
1434    Usually a simple ICMP echo request and reply ("ping") packet is
1435    good enough.  Start by initiating an ongoing "ping" from the origin
1436    host to a remote host.  If you are tracking down a connectivity
1437    problem, the "ping" will not display any successful output, but
1438    packets are still being sent.  (In this case the packets being sent
1439    are likely ARP rather than ICMP.)
1440
1441    Tools available for tracing include the following:
1442
1443    - "tcpdump" and "wireshark" for observing hops across network
1444      devices, such as Open vSwitch internal devices and physical
1445      wires.
1446
1447    - "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
1448      later or "ovs-dpctl dump-flows <br>" in earlier versions.
1449      These tools allow one to observe the actions being taken on
1450      packets in ongoing flows.
1451
1452      See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
1453      documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
1454      documentation, and "Why are there so many different ways to
1455      dump flows?" above for some background.
1456
1457    - "ovs-appctl ofproto/trace" to observe the logic behind how
1458      ovs-vswitchd treats packets.  See ovs-vswitchd(8) for
1459      documentation.  You can out more details about a given flow
1460      that "ovs-dpctl dump-flows" displays, by cutting and pasting
1461      a flow from the output into an "ovs-appctl ofproto/trace"
1462      command.
1463
1464    - SPAN, RSPAN, and ERSPAN features of physical switches, to
1465      observe what goes on at these physical hops.
1466
1467    Starting at the origin of a given packet, observe the packet at
1468    each hop in turn.  For example, in one plausible scenario, you
1469    might:
1470
1471    1. "tcpdump" the "eth" interface through which an ARP egresses
1472       a VM, from inside the VM.
1473
1474    2. "tcpdump" the "vif" or "tap" interface through which the ARP
1475       ingresses the host machine.
1476
1477    3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
1478       the host interface through which the ARP egresses the
1479       physical machine.  You may need to use "ovs-dpctl show" to
1480       interpret the port numbers.  If the output seems surprising,
1481       you can use "ovs-appctl ofproto/trace" to observe details of
1482       how ovs-vswitchd determined the actions in the "ovs-dpctl
1483       dump-flows" output.
1484
1485    4. "tcpdump" the "eth" interface through which the ARP egresses
1486       the physical machine.
1487
1488    5. "tcpdump" the "eth" interface through which the ARP
1489       ingresses the physical machine, at the remote host that
1490       receives the ARP.
1491
1492    6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
1493       remote host that receives the ARP and observe the VM "vif"
1494       or "tap" interface to which the flow is directed.  Again,
1495       "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
1496
1497    7. "tcpdump" the "vif" or "tap" interface to which the ARP is
1498       directed.
1499
1500    8. "tcpdump" the "eth" interface through which the ARP
1501       ingresses a VM, from inside the VM.
1502
1503    It is likely that during one of these steps you will figure out the
1504    problem.  If not, then follow the ARP reply back to the origin, in
1505    reverse.
1506
1507 ### Q: How do I make a flow drop packets?
1508
1509 A: To drop a packet is to receive it without forwarding it.  OpenFlow
1510    explicitly specifies forwarding actions.  Thus, a flow with an
1511    empty set of actions does not forward packets anywhere, causing
1512    them to be dropped.  You can specify an empty set of actions with
1513    "actions=" on the ovs-ofctl command line.  For example:
1514
1515        ovs-ofctl add-flow br0 priority=65535,actions=
1516
1517    would cause every packet entering switch br0 to be dropped.
1518
1519    You can write "drop" explicitly if you like.  The effect is the
1520    same.  Thus, the following command also causes every packet
1521    entering switch br0 to be dropped:
1522
1523        ovs-ofctl add-flow br0 priority=65535,actions=drop
1524
1525    "drop" is not an action, either in OpenFlow or Open vSwitch.
1526    Rather, it is only a way to say that there are no actions.
1527
1528 ### Q: I added a flow to send packets out the ingress port, like this:
1529
1530        ovs-ofctl add-flow br0 in_port=2,actions=2
1531
1532    but OVS drops the packets instead.
1533
1534 A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
1535    out its ingress port.  The rationale is that dropping these packets
1536    makes it harder to loop the network.  Sometimes this behavior can
1537    even be convenient, e.g. it is often the desired behavior in a flow
1538    that forwards a packet to several ports ("floods" the packet).
1539
1540    Sometimes one really needs to send a packet out its ingress port
1541    ("hairpin"). In this case, output to OFPP_IN_PORT, which in
1542    ovs-ofctl syntax is expressed as just "in_port", e.g.:
1543
1544        ovs-ofctl add-flow br0 in_port=2,actions=in_port
1545
1546    This also works in some circumstances where the flow doesn't match
1547    on the input port.  For example, if you know that your switch has
1548    five ports numbered 2 through 6, then the following will send every
1549    received packet out every port, even its ingress port:
1550
1551        ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
1552
1553    or, equivalently:
1554
1555        ovs-ofctl add-flow br0 actions=all,in_port
1556
1557    Sometimes, in complicated flow tables with multiple levels of
1558    "resubmit" actions, a flow needs to output to a particular port
1559    that may or may not be the ingress port.  It's difficult to take
1560    advantage of OFPP_IN_PORT in this situation.  To help, Open vSwitch
1561    provides, as an OpenFlow extension, the ability to modify the
1562    in_port field.  Whatever value is currently in the in_port field is
1563    the port to which outputs will be dropped, as well as the
1564    destination for OFPP_IN_PORT.  This means that the following will
1565    reliably output to port 2 or to ports 2 through 6, respectively:
1566
1567        ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
1568        ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
1569
1570    If the input port is important, then one may save and restore it on
1571    the stack:
1572
1573         ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
1574                                        load:0->NXM_OF_IN_PORT[],\
1575                                        2,3,4,5,6,\
1576                                        pop:NXM_OF_IN_PORT[]
1577
1578 ### Q: My bridge br0 has host 192.168.0.1 on port 1 and host 192.168.0.2
1579    on port 2.  I set up flows to forward only traffic destined to the
1580    other host and drop other traffic, like this:
1581
1582       priority=5,in_port=1,ip,nw_dst=192.168.0.2,actions=2
1583       priority=5,in_port=2,ip,nw_dst=192.168.0.1,actions=1
1584       priority=0,actions=drop
1585
1586    But it doesn't work--I don't get any connectivity when I do this.
1587    Why?
1588
1589 A: These flows drop the ARP packets that IP hosts use to establish IP
1590    connectivity over Ethernet.  To solve the problem, add flows to
1591    allow ARP to pass between the hosts:
1592
1593       priority=5,in_port=1,arp,actions=2
1594       priority=5,in_port=2,arp,actions=1
1595
1596    This issue can manifest other ways, too.  The following flows that
1597    match on Ethernet addresses instead of IP addresses will also drop
1598    ARP packets, because ARP requests are broadcast instead of being
1599    directed to a specific host:
1600
1601       priority=5,in_port=1,dl_dst=54:00:00:00:00:02,actions=2
1602       priority=5,in_port=2,dl_dst=54:00:00:00:00:01,actions=1
1603       priority=0,actions=drop
1604
1605    The solution already described above will also work in this case.
1606    It may be better to add flows to allow all multicast and broadcast
1607    traffic:
1608
1609       priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
1610       priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
1611
1612 ### Q: My bridge disconnects from my controller on add-port/del-port.
1613
1614 A: Reconfiguring your bridge can change your bridge's datapath-id because
1615    Open vSwitch generates datapath-id from the MAC address of one of its ports.
1616    In that case, Open vSwitch disconnects from controllers because there's
1617    no graceful way to notify controllers about the change of datapath-id.
1618
1619    To avoid the behaviour, you can configure datapath-id manually.
1620
1621       ovs-vsctl set bridge br0 other-config:datapath-id=0123456789abcdef
1622
1623
1624 Development
1625 -----------
1626
1627 ### Q: How do I implement a new OpenFlow message?
1628
1629 A: Add your new message to "enum ofpraw" and "enum ofptype" in
1630    lib/ofp-msgs.h, following the existing pattern.  Then recompile and
1631    fix all of the new warnings, implementing new functionality for the
1632    new message as needed.  (If you configure with --enable-Werror, as
1633    described in [INSTALL.md], then it is impossible to miss any warnings.)
1634
1635    If you need to add an OpenFlow vendor extension message for a
1636    vendor that doesn't yet have any extension messages, then you will
1637    also need to edit build-aux/extract-ofp-msgs.
1638
1639 ### Q: How do I add support for a new field or header?
1640
1641 A: Add new members for your field to "struct flow" in lib/flow.h, and
1642    add new enumerations for your new field to "enum mf_field_id" in
1643    lib/meta-flow.h, following the existing pattern.  Then recompile
1644    and fix all of the new warnings, implementing new functionality for
1645    the new field or header as needed.  (If you configure with
1646    --enable-Werror, as described in [INSTALL.md], then it is
1647    impossible to miss any warnings.)
1648
1649 ### Q: How do I add support for a new OpenFlow action?
1650
1651 A: Add your new action to "enum ofp_raw_action_type" in
1652    lib/ofp-actions.c, following the existing pattern.  Then recompile
1653    and fix all of the new warnings, implementing new functionality for
1654    the new action as needed.  (If you configure with --enable-Werror,
1655    as described in [INSTALL.md], then it is impossible to miss any
1656    warnings.)
1657
1658    If you need to add an OpenFlow vendor extension action for a vendor
1659    that doesn't yet have any extension actions, then you will also
1660    need to edit build-aux/extract-ofp-actions.
1661
1662
1663 Contact
1664 -------
1665
1666 bugs@openvswitch.org
1667 http://openvswitch.org/
1668
1669 [PORTING.md]:PORTING.md
1670 [WHY-OVS.md]:WHY-OVS.md
1671 [INSTALL.md]:INSTALL.md
1672 [OPENFLOW-1.1+.md]:OPENFLOW-1.1+.md