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          ovn-trace(8)                  Open vSwitch Manual                 ovn-trace(8)
                 ovn-trace - Open Virtual Network logical network tracing utility
                 ovn-trace [options] datapath microflow
                 ovn-trace [options] --detach
                 This utility simulates packet forwarding within an OVN logical network.
                 It can be used to run through ``what-if’’ scenarios: if a packet origi‐
                 nates at a logical port, what will happen to it and where will it ulti‐
                 mately end up?  Users  already  familiar  with  the  Open  vSwitch  of
                 proto/trace  command described in ovs-vswitch(8) will find ovn-trace to
                 be a similar tool for logical networks.
                 ovn-trace works by reading the Logical_Flow and other tables  from  the
                 OVN  southbound  database (see ovn-sb(5)). It simulates a packet’s path
                 through logical networks by repeatedly looking it  up  in  the  logical
                 flow table, following the entire tree of possibilities.
                 ovn-trace  simulates only the OVN logical network. It does not simulate
                 the physical elements on which the logical  network  is  layered.  This
                 means  that,  for  example,  it  is unimportant how VMs are distributed
                 among hypervisors, or whether their  hypervisors  are  functioning  and
                 reachable,  so  ovn-trace will yield the same results regardless. There
                 is one important exception: ovn-northd, the daemon that  generates  the
                 logical  flows  that  ovn-trace simulates, treats logical ports differ‐
                 ently based on whether they are up or down. Thus, if you see surprising
                 results, ensure that the ports involved in a simulation are up.
                 The  simplest way to use ovn-trace is to provide datapath and microflow
                 arguments on the command line. In this case, it simulates the  behavior
                 of  a single packet and exits. For an alternate usage model, see Daemon
                 Mode below.
                 The datapath argument specifies the name of a logical datapath. Accept‐
                 able  names  are  the  name from the northbound Logical_Switch or Logi
                 cal_Router table, the UUID of a record from one of those tables, or the
                 UUID of a record from the southbound Datapath_Binding table.
                 The  microflow  argument describes the packet whose forwarding is to be
                 simulated, in the syntax of an OVN logical expression, as described  in
                 ovn-sb(5),  to  express  constraints.  The parser understands prerequi‐
                 sites; for example, if the expression refers to ip4.src,  there  is  no
                 need to explicitly state ip4 or eth.type == 0x800.
                 For  reasonable  L2 behavior, the microflow should include at least in
                 port and eth.dst, plus eth.src if port security is enabled.  For  exam‐
                     inport == "lp11" &&&& eth.src == 00:01:02:03:04:05 &&&& eth.dst == ff:ff:ff:ff:ff:ff
                 For  reasonable  L3 behavior, microflow should also include ip4.src and
                 ip4.dst (or ip6.src and ip6.dst) and ip.ttl. For example:
                     inport == "lp111" &&&& eth.src == f0:00:00:00:01:11 &&&& eth.dst == 00:00:00:00:ff:11
                     &&&& ip4.src == &&&& ip4.dst == &&&& ip.ttl == 64
                 Here’s an ARP microflow example:
                     inport == "lp123"
                     &&&& eth.dst == ff:ff:ff:ff:ff:ff &&&& eth.src == f0:00:00:00:01:11
                     &&&& arp.op == 1 &&&& arp.sha == f0:00:00:00:01:11 &&&& arp.spa ==
                     &&&& arp.tha == ff:ff:ff:ff:ff:ff &&&& arp.tpa ==
                 ovn-trace will reject erroneous  microflow  expressions,  which  beyond
                 syntax  errors  fall into two categories. First, they can be ambiguous.
                 For example, tcp.src == 80 is ambiguous because it does not state  IPv4
                 or  IPv6  as the Ethernet type. ip4 &&&& tcp.src >gt;>gt; 1024 is also ambiguous
                 because it does not constrain bits of  tcp.src  to  particular  values.
                 Second, they can be contradictory, e.g. ip4 &&&& ip6.
                 ovn-trace  supports the three different forms of output, each described
                 in a separate section below. Regardless of the selected output  format,
                 ovn-trace  starts the output with a line that shows the microflow being
                 traced in OpenFlow syntax.
             Detailed Output
                 The detailed form of output is also the default form. This form  groups
                 output  into sections headed up by the ingress or egress pipeline being
                 traversed. Each pipeline lists each table that was visited  (by  number
                 and  name), the ovn-northd source file and line number of the code that
                 added the flow, the match expression and priority of the  logical  flow
                 that was matched, and the actions that were executed.
                 The  execution  of  OVN  logical  actions  naturally  forms a ``control
                 stack’’ that resembles that of a program  in  conventional  programming
                 languages  such  as  C or Java. Because the next action that calls into
                 another logical flow table for a lookup is a recursive  construct,  OVN
                 ``programs’’  in  practice  tend to form deep control stacks that, dis‐
                 played in the obvious way using additional indentation for each  level,
                 quickly  use up the horizontal space on all but the widest displays. To
                 make  detailed  output  more  readable,  without  loss  of  generality,
                 ovn-trace  omits indentation for ``tail recursion,’’ that is, when next
                 is the last action in a logical flow, it does not indent details of the
                 next table lookup more deeply. Output still uses indentation when it is
                 needed for clarity.
                 OVN ``programs’’ traces also tend to encounter long strings of  logical
                 flows with match expression 1 (which matches every packet) and the sin‐
                 gle action next;. These are uninteresting and merely clutter output, so
                 ovn-trace omits them entirely even from detailed output.
                 The  following  excerpt  from detailed ovn-trace output shows a section
                 for a packet traversing the ingress pipeline of  logical  datapath  ls1
                 with  ingress  logical port lp111. The packet matches a logical flow in
                 table 0 (aka ls_in_port_sec_l2) with priority 50 and executes  next(1);
                 to pass to table 1. Tables 1 through 11 are trivial and omitted. In ta‐
                 ble 12 (aka ls_in_l2_lkup), the packet matches a flow with priority  50
                 based on its Ethernet destination address and the flow’s actions output
                 the packet to the lrp11-attachement logical port.
                     ingress(dp="ls1", inport="lp111")
                     0. ls_in_port_sec_l2: inport == "lp111", priority 50
                     12. ls_in_l2_lkup: eth.dst == 00:00:00:00:ff:11, priority 50
                     outport = "lrp11-attachment";
             Summary Output
                 Summary output includes the logical pipelines visited by a  packet  and
                 the  logical  actions  executed on it. Compared to the detailed output,
                 however, it removes details of tables and logical flows traversed by  a
                 packet.  It  uses a format closer to that of a programming language and
                 does not attempt to avoid indentation. The summary output equivalent to
                 the above detailed output fragment is:
                     ingress(dp="ls1", inport="lp111") {
                     outport = "lrp11-attachment";
             Minimal Output
                 Minimal  output  includes only actions that modify packet data (not in‐
                 cluding OVN registers or metadata such as outport) and  output  actions
                 that  actually  deliver  a  packet  to  a logical port (excluding patch
                 ports). The operands of actions that modify packet data  are  displayed
                 reduced  to  constants, e.g. ip4.dst = reg0; might be show as ip4.dst =
       ; if that was the value actually loaded. This yields  output
                 even simpler than the summary format. (Users familiar with Open vSwitch
                 may recognize this as similar in spirit to the datapath actions  listed
                 at the bottom of ofproto/trace output.)
                 The  minimal output format reflects the externally seen behavior of the
                 logical networks more than it does the implementation. This makes  this
                 output format the most suitable for use in regression tests, because it
                 is least likely to change when logical flow tables are rearranged with‐
                 out semantic change.
                 Some  OVN  logical actions use or update state that is not available in
                 the southbound database. ovn-trace handles these actions  as  described
                               By  default  ovn-trace  treats  flows  as ``tracked’’ and
                               ``established.’’ See the description of the  --ct  option
                               for a way to override this behavior.
                        ct_dnat (without an argument)
                               Forks the pipeline. In one fork, advances to the next ta‐
                               ble as if next; were executed. The packet is not changed,
                               on the assumption that no NAT state was available. In the
                               other fork, the pipeline continues without  change  after
                               the ct_dnat action.
                        ct_snat (without an argument)
                               This  action  distinguishes  between  gateway routers and
                               distributed routers. A gateway router  is  defined  as  a
                               logical  datapath  that  contains  an l3gateway port; any
                               other logical datapath is  a  distributed  router.  On  a
                               gateway router, ct_snat; is treated as a no-op. On a dis‐
                               tributed router, it is treated the same way as ct_dnat;.
                             Forks the pipeline. In one fork, sets ip4.dst (or  ip4.src)
                             to  ip  and  ct.dnat  (or ct.snat) to 1 and advances to the
                             next table as if next; were executed. In  the  other  fork,
                             the pipeline continues without change after the ct_dnat (or
                             ct_snat) action.
                             Forks the pipeline. In one fork, sets ip4.dst (or  ip6.dst)
                             to  one  of the load-balancer addresses and the destination
                             port to its associated port, if any, and sets ct.dnat to 1.
                             With one or more arguments, gives preference to the address
                             specified on --lb-dst, if any; without arguments, uses  the
                             address  and port specified on --lb-dst. In the other fork,
                             the pipeline continues without change after the  ct_lb  ac‐
                             These actions are treated as no-ops.
          DAEMON MODE
                 If  ovn-trace  is invoked with the --detach option (see Daemon Options,
                 below), it runs in the background as a daemon and accepts commands from
                 ovs-appctl  (or  another  JSON-RPC  client) indefinitely. The currently
                 supported commands are described below.
                        trace [options] datapath microflow
                               Traces microflow through datapath and  replies  with  the
                               results of the trace. Accepts the options described under
                               Trace Options below.
                        exit   Causes ovn-trace to gracefully terminate.
             Trace Options
                      These options control the form and level of  detail  in  ovn-trace
                      output. If more than one of these options is specified, all of the
                      selected forms are output, in the order listed above, each  headed
                      by a banner line. If none of these options is given, --detailed is
                      the default. See Output, above, for a description of each kind  of
                      Selects all three forms of output.
                      Makes  ovn-trace  attempt to obtain and display the OpenFlow flows
                      that correspond to each OVN logical flow. To do so, ovn-trace con‐
                      nects     to     remote     (by    default,    unix:/var/run/open
                      vswitch/br-int.mgmt) over OpenFlow and retrieves the flows. If re
                      mote is specified, it must be an active OpenFlow connection method
                      described in ovsdb(7).
                      To make the best use of the output, it is important to  understand
                      the relationship between logical flows and OpenFlow flows. ovn-ar
                      chitecture(7),  under  Architectural  Physical  Life  Cycle  of  a
                      Packet,  describes  this  relationship. Keep in mind the following
                      ?      ovn-trace currently shows all the OpenFlow flows to which a
                             logical  flow corresponds, even though an actual packet or‐
                             dinarily matches only one of these.
                      ?      Some logical flows can map to the Open  vSwitch  ``conjunc‐
                             tive   match’’  extension  (see  ovs-fields(7)).  Currently
                             ovn-trace cannot display the flows with conjunction actions
                             that effectively produce the conj_id match.
                      ?      Some  logical  flows may not be represented in the OpenFlow
                             tables on a given hypervisor, if they could not be used  on
                             that hypervisor.
                      ?      Some  OpenFlow  flows  do  not correspond to logical flows,
                             such as OpenFlow flows that map between physical and  logi‐
                             cal ports. These flows will never show up in a trace.
                      ?      When  ovn-trace omits uninteresting logical flows from out‐
                             put, it does not look up the corresponding OpenFlow flows.
                      This option sets the ct_state flags that a ct_next logical  action
                      will report. The flags must be a comma- or space-separated list of
                      the following connection tracking flags:
                      ?      trk: Include to  indicate  connection  tracking  has  taken
                             place. (This bit is set automatically even if not listed in
                      ?      new: Include to indicate a new flow.
                      ?      est: Include to indicate an established flow.
                      ?      rel: Include to indicate a related flow.
                      ?      rpl: Include to indicate a reply flow.
                      ?      inv: Include to indicate a connection entry in a bad state.
                      ?      dnat: Include to indicate a packet whose destination IP ad‐
                             dress has been changed.
                      ?      snat:  Include to indicate a packet whose source IP address
                             has been changed.
                      The ct_next action is used to implement the OVN distributed  fire‐
                      wall. For testing, useful flag combinations include:
                      ?      trk,new:  A  packet in a flow in either direction through a
                             firewall that has not yet been committed (with ct_commit).
                      ?      trk,est: A packet in an established flow going out  through
                             a firewall.
                      ?      trk,rpl:  A packet coming in through a firewall in reply to
                             an established flow.
                      ?      trk,inv: An invalid packet in either direction.
                      A packet might pass through the connection tracker  twice  in  one
                      trip  through  OVN:  once  following egress from a VM as it passes
                      outward through a firewall, and once preceding ingress to a second
                      VM  as  it passes inward through a firewall. Use multiple --ct op‐
                      tions to specify the flags for multiple ct_next actions.
                      When --ct is unspecified, or when there  are  fewer  --ct  options
                      than ct_next actions, the flags default to trk,est.
                      Sets  the  IP  from  VIP pool to use as destination of the packet.
                      --lb-dst is not available in daemon mode.
                      When cloud management systems such as OpenStack are layered on top
                      of  OVN, they often use long, human-unfriendly names for ports and
                      datapaths, for example, ones that include entire  UUIDs.  They  do
                      usually include friendlier names, but the long, hard-to-read names
                      are the ones that appear in matches and actions.  By  default,  or
                      with  --friendly-names,  ovn-trace  substitutes  these  friendlier
                      names for the long names in its output. Use --no-friendly-names to
                      disable  this  behavior; this option might be useful, for example,
                      if a program is going to parse ovn-trace output.
             Daemon Options
                        Causes a file (by default, program.pid) to be created indicating
                        the  PID  of the running process. If the pidfile argument is not
                        specified, or if it does not begin with /, then it is created in
                        If --pidfile is not specified, no pidfile is created.
                        By  default,  when --pidfile is specified and the specified pid‐
                        file already exists and is locked by a running process, the dae‐
                        mon refuses to start. Specify --overwrite-pidfile to cause it to
                        instead overwrite the pidfile.
                        When --pidfile is not specified, this option has no effect.
                        Runs this program as a background process.  The  process  forks,
                        and  in  the  child it starts a new session, closes the standard
                        file descriptors (which has the side effect of disabling logging
                        to  the  console), and changes its current directory to the root
                        (unless --no-chdir is specified). After the child completes  its
                        initialization, the parent exits.
                        Creates  an  additional  process  to monitor this program. If it
                        dies due to a signal that indicates a programming  error  (SIGA
                        or SIGXFSZ) then the monitor process starts a new copy of it. If
                        the daemon dies or exits for another reason, the monitor process
                        This option is normally used with --detach, but  it  also  func‐
                        tions without it.
                        By  default,  when --detach is specified, the daemon changes its
                        current working directory to the root  directory  after  it  de‐
                        taches.  Otherwise, invoking the daemon from a carelessly chosen
                        directory would prevent the administrator  from  unmounting  the
                        file system that holds that directory.
                        Specifying  --no-chdir  suppresses this behavior, preventing the
                        daemon from changing its current working directory. This may  be
                        useful for collecting core files, since it is common behavior to
                        write core dumps into the current working directory and the root
                        directory is not a good directory to use.
                        This option has no effect when --detach is not specified.
                        By  default  this daemon will try to self-confine itself to work
                        with files under well-known  directories  whitelisted  at  build
                        time.  It  is better to stick with this default behavior and not
                        to use this flag unless some other Access  Control  is  used  to
                        confine  daemon.  Note  that in contrast to other access control
                        implementations that are typically  enforced  from  kernel-space
                        (e.g.  DAC  or  MAC), self-confinement is imposed from the user-
                        space daemon itself and hence should not be considered as a full
                        confinement  strategy,  but instead should be viewed as an addi‐
                        tional layer of security.
                        Causes this program to run as  a  different  user  specified  in
                        user:group,  thus  dropping  most  of the root privileges. Short
                        forms user and :group are also allowed,  with  current  user  or
                        group  assumed,  respectively.  Only daemons started by the root
                        user accepts this argument.
                        On   Linux,   daemons   will   be   granted   CAP_IPC_LOCK   and
                        CAP_NET_BIND_SERVICES  before  dropping root privileges. Daemons
                        that interact with a datapath, such  as  ovs-vswitchd,  will  be
                        granted  three  additional  capabilities,  namely CAP_NET_ADMIN,
                        CAP_NET_BROADCAST and CAP_NET_RAW. The  capability  change  will
                        apply even if the new user is root.
                        On Windows, this option is not currently supported. For security
                        reasons, specifying this option will cause  the  daemon  process
                        not to start.
             Logging Options
                      Sets  logging levels. Without any spec, sets the log level for ev‐
                      ery module and destination to dbg. Otherwise, spec is  a  list  of
                      words separated by spaces or commas or colons, up to one from each
                      category below:
                      ?      A valid module name, as displayed by the vlog/list  command
                             on ovs-appctl(8), limits the log level change to the speci‐
                             fied module.
                      ?      syslog, console, or file, to limit the log level change  to
                             only  to  the system log, to the console, or to a file, re‐
                             spectively. (If --detach is specified,  the  daemon  closes
                             its  standard  file  descriptors, so logging to the console
                             will have no effect.)
                             On Windows platform, syslog is accepted as a  word  and  is
                             only useful along with the --syslog-target option (the word
                             has no effect otherwise).
                      ?      off, emer, err, warn, info, or  dbg,  to  control  the  log
                             level.  Messages  of  the  given severity or higher will be
                             logged, and messages of lower  severity  will  be  filtered
                             out.  off filters out all messages. See ovs-appctl(8) for a
                             definition of each log level.
                      Case is not significant within spec.
                      Regardless of the log levels set for file, logging to a file  will
                      not take place unless --log-file is also specified (see below).
                      For compatibility with older versions of OVS, any is accepted as a
                      word but has no effect.
                      Sets the maximum logging verbosity  level,  equivalent  to  --ver
                      Sets  the log pattern for destination to pattern. Refer to ovs-ap
                      pctl(8) for a description of the valid syntax for pattern.
                      Sets the RFC5424 facility of the log message. facility can be  one
                      of kern, user, mail, daemon, auth, syslog, lpr, news, uucp, clock,
                      ftp, ntp, audit, alert, clock2, local0,  local1,  local2,  local3,
                      local4, local5, local6 or local7. If this option is not specified,
                      daemon is used as the default for the local system syslog and  lo
                      cal0  is  used  while sending a message to the target provided via
                      the --syslog-target option.
                      Enables logging to a file. If file is specified, then it  is  used
                      as the exact name for the log file. The default log file name used
                      if file is omitted is /var/log/openvswitch/program.log.
                      Send syslog messages to UDP port on host, in addition to the  sys‐
                      tem  syslog.  The host must be a numerical IP address, not a host‐
                      Specify method as how syslog messages should  be  sent  to  syslog
                      daemon. The following forms are supported:
                      ?      libc,  to use the libc syslog() function. Downside of using
                             this options is that libc adds fixed prefix to  every  mes‐
                             sage  before  it is actually sent to the syslog daemon over
                             /dev/log UNIX domain socket.
                      ?      unix:file, to use a UNIX domain socket directly. It is pos‐
                             sible to specify arbitrary message format with this option.
                             However, rsyslogd 8.9 and older  versions  use  hard  coded
                             parser  function anyway that limits UNIX domain socket use.
                             If you want to use  arbitrary  message  format  with  older
                             rsyslogd  versions, then use UDP socket to localhost IP ad‐
                             dress instead.
                      ?      udp:ip:port, to use a UDP socket. With this  method  it  is
                             possible  to  use  arbitrary message format also with older
                             rsyslogd. When sending syslog messages over UDP socket  ex‐
                             tra precaution needs to be taken into account, for example,
                             syslog daemon needs to be configured to listen on the spec‐
                             ified  UDP  port, accidental iptables rules could be inter‐
                             fering with local syslog traffic and there are  some  secu‐
                             rity  considerations  that apply to UDP sockets, but do not
                             apply to UNIX domain sockets.
                      ?      null, to discard all messages logged to syslog.
                      The default is taken from the OVS_SYSLOG_METHOD environment  vari‐
                      able; if it is unset, the default is libc.
             PKI Options
                 PKI  configuration  is  required  to  use SSL for the connection to the
                 database (and the switch, if --ovs is specified).
                        -p privkey.pem
                             Specifies a PEM file containing the  private  key  used  as
                             identity for outgoing SSL connections.
                        -c cert.pem
                             Specifies  a  PEM file containing a certificate that certi‐
                             fies the private key specified on -p or --private-key to be
                             trustworthy. The certificate must be signed by the certifi‐
                             cate authority (CA) that the peer in SSL  connections  will
                             use to verify it.
                        -C cacert.pem
                             Specifies a PEM file containing the CA certificate for ver‐
                             ifying certificates presented to this program by SSL peers.
                             (This  may  be  the  same certificate that SSL peers use to
                             verify the certificate specified on -c or --certificate, or
                             it  may  be a different one, depending on the PKI design in
                        -C none
                             Disables verification  of  certificates  presented  by  SSL
                             peers.  This  introduces  a security risk, because it means
                             that certificates cannot be verified to be those  of  known
                             trusted hosts.
             Other Options
                 --db database
                        The  OVSDB database remote to contact. If the OVN_SB_DB environ‐
                        ment variable is set, its value is used as the  default.  Other‐
                        wise, the default is unix:/var/run/openvswitch/db.sock, but this
                        default is unlikely to be useful outside of  single-machine  OVN
                        test environments.
                             Prints a brief help message to the console.
                             Prints version information to the console.
          Open vSwitch 2.10.90               ovn-trace                      ovn-trace(8)