ovn-northd(8)                 Open vSwitch Manual                ovn-northd(8)



NAME
       ovn-northd - Open Virtual Network central control daemon

SYNOPSIS
       ovn-northd [options]

DESCRIPTION
       ovn-northd  is  a  centralized  daemon  responsible for translating the
       high-level OVN configuration into logical configuration  consumable  by
       daemons  such as ovn-controller. It translates the logical network con‐
       figuration in terms of conventional network concepts,  taken  from  the
       OVN Northbound Database (see ovn-nb(5)), into logical datapath flows in
       the OVN Southbound Database (see ovn-sb(5)) below it.

OPTIONS
       --ovnnb-db=database
              The OVSDB database containing the OVN  Northbound  Database.  If
              the  OVN_NB_DB environment variable is set, its value is used as
              the  default.  Otherwise,  the  default  is  unix:/var/run/open
              vswitch/ovnnb_db.sock.

       --ovnsb-db=database
              The  OVSDB  database  containing the OVN Southbound Database. If
              the OVN_SB_DB environment variable is set, its value is used  as
              the  default.  Otherwise,  the  default  is  unix:/var/run/open
              vswitch/ovnsb_db.sock.

       database in the above options must be an OVSDB active or  passive  con‐
       nection method, as described in ovsdb(7).

   Daemon Options
       --pidfile[=pidfile]
              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
              /var/run/openvswitch.

              If --pidfile is not specified, no pidfile is created.

       --overwrite-pidfile
              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.

       --detach
              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.

       --monitor
              Creates an additional process to monitor  this  program.  If  it
              dies  due  to a signal that indicates a programming error (SIGA
              BRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV, SIGXCPU,
              or SIGXFSZ) then the monitor process starts a new copy of it. If
              the daemon dies or exits for another reason, the monitor process
              exits.

              This  option  is  normally used with --detach, but it also func‐
              tions without it.

       --no-chdir
              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.

       --no-self-confinement
              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.

       --user=user:group
              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
       -v[spec]
       --verbose=[spec]
            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.

       -v
       --verbose
            Sets  the  maximum  logging  verbosity level, equivalent to --ver
            bose=dbg.

       -vPATTERN:destination:pattern
       --verbose=PATTERN:destination:pattern
            Sets the log pattern for destination to pattern. Refer to  ovs-ap
            pctl(8) for a description of the valid syntax for pattern.

       -vFACILITY:facility
       --verbose=FACILITY:facility
            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.

       --log-file[=file]
            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.

       --syslog-target=host:port
            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‐
            name.

       --syslog-method=method
            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 in order to use SSL for  the  connections
       to the Northbound and Southbound databases.

              -p privkey.pem
              --private-key=privkey.pem
                   Specifies  a  PEM  file  containing the private key used as
                   identity for outgoing SSL connections.

              -c cert.pem
              --certificate=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
              --ca-cert=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
                   use.)

              -C none
              --ca-cert=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
       --unixctl=socket
              Sets the name of the control socket on which program listens for
              runtime  management  commands  (see RUNTIME MANAGEMENT COMMANDS,
              below). If socket does not begin with /, it  is  interpreted  as
              relative  to  /var/run/openvswitch.  If --unixctl is not used at
              all, the default socket is /var/run/openvswitch/program.pid.ctl,
              where pid is program’s process ID.

              On Windows a local named pipe is used to listen for runtime man‐
              agement commands. A file is created  in  the  absolute  path  as
              pointed  by socket or if --unixctl is not used at all, a file is
              created as program in the configured OVS_RUNDIR  directory.  The
              file exists just to mimic the behavior of a Unix domain socket.

              Specifying none for socket disables the control socket feature.



       -h
       --help
            Prints a brief help message to the console.

       -V
       --version
            Prints version information to the console.

RUNTIME MANAGEMENT COMMANDS
       ovs-appctl  can send commands to a running ovn-northd process. The cur‐
       rently supported commands are described below.

              exit   Causes ovn-northd to gracefully terminate.

ACTIVE-STANDBY FOR HIGH AVAILABILITY
       You may run ovn-northd more than once in an OVN  deployment.  OVN  will
       automatically ensure that only one of them is active at a time. If mul‐
       tiple instances of ovn-northd are running  and  the  active  ovn-northd
       fails,  one  of  the hot standby instances of ovn-northd will automati‐
       cally take over.

LOGICAL FLOW TABLE STRUCTURE
       One of the main purposes of ovn-northd is to populate the  Logical_Flow
       table  in  the  OVN_Southbound  database.  This  section  describes how
       ovn-northd does this for switch and router logical datapaths.

   Logical Switch Datapaths
     Ingress Table 0: Admission Control and Ingress Port Security - L2

       Ingress table 0 contains these logical flows:

              •      Priority 100 flows to drop packets with VLAN tags or mul‐
                     ticast Ethernet source addresses.

              •      Priority  50  flows  that implement ingress port security
                     for each enabled logical port. For logical ports on which
                     port  security is enabled, these match the inport and the
                     valid eth.src address(es) and advance only those  packets
                     to  the  next flow table. For logical ports on which port
                     security is not enabled, these advance all  packets  that
                     match the inport.

       There  are no flows for disabled logical ports because the default-drop
       behavior of logical flow tables causes packets that ingress  from  them
       to be dropped.

     Ingress Table 1: Ingress Port Security - IP

       Ingress table 1 contains these logical flows:

              •      For  each  element in the port security set having one or
                     more IPv4 or IPv6 addresses (or both),

                     •      Priority 90 flow to allow IPv4 traffic if  it  has
                            IPv4  addresses  which  match  the  inport,  valid
                            eth.src and valid ip4.src address(es).

                     •      Priority 90 flow  to  allow  IPv4  DHCP  discovery
                            traffic  if it has a valid eth.src. This is neces‐
                            sary since DHCP discovery messages are  sent  from
                            the  unspecified  IPv4 address (0.0.0.0) since the
                            IPv4 address has not yet been assigned.

                     •      Priority 90 flow to allow IPv6 traffic if  it  has
                            IPv6  addresses  which  match  the  inport,  valid
                            eth.src and valid ip6.src address(es).

                     •      Priority 90 flow to allow IPv6 DAD (Duplicate  Ad‐
                            dress   Detection)  traffic  if  it  has  a  valid
                            eth.src. This is is necessary  since  DAD  include
                            requires  joining  an  multicast group and sending
                            neighbor solicitations for the newly assigned  ad‐
                            dress. Since no address is yet assigned, these are
                            sent from the unspecified IPv6 address (::).

                     •      Priority 80 flow to drop IP (both IPv4  and  IPv6)
                            traffic which match the inport and valid eth.src.

              •      One priority-0 fallback flow that matches all packets and
                     advances to the next table.

     Ingress Table 2: Ingress Port Security - Neighbor discovery

       Ingress table 2 contains these logical flows:

              •      For each element in the port security set,

                     •      Priority 90 flow to allow ARP traffic which  match
                            the  inport  and valid eth.src and arp.sha. If the
                            element has one or more IPv4  addresses,  then  it
                            also matches the valid arp.spa.

                     •      Priority  90 flow to allow IPv6 Neighbor Solicita‐
                            tion and Advertisement traffic which match the in
                            port, valid eth.src and nd.sll/nd.tll. If the ele‐
                            ment has one or more IPv6 addresses, then it  also
                            matches the valid nd.target address(es) for Neigh‐
                            bor Advertisement traffic.

                     •      Priority 80 flow to drop ARP and IPv6 Neighbor So‐
                            licitation  and  Advertisement traffic which match
                            the inport and valid eth.src.

              •      One priority-0 fallback flow that matches all packets and
                     advances to the next table.

     Ingress Table 3: from-lport Pre-ACLs

       This  table  prepares  flows  for  possible  stateful ACL processing in
       ingress table ACLs. It contains a priority-0  flow  that  simply  moves
       traffic  to  the  next  table. If stateful ACLs are used in the logical
       datapath, a priority-100 flow is added that sets a hint (with reg0[0] =
       1;  next;)  for table Pre-stateful to send IP packets to the connection
       tracker before eventually advancing to ingress table ACLs.  If  special
       ports  such  as  route ports or localnet ports can’t use ct(), a prior‐
       ity-110 flow is added to skip over stateful ACLs.

     Ingress Table 4: Pre-LB

       This table prepares flows for possible stateful load balancing process‐
       ing  in  ingress  table  LB and Stateful. It contains a priority-0 flow
       that simply moves traffic to the next table.  Moreover  it  contains  a
       priority-110  flow  to move IPv6 Neighbor Discovery traffic to the next
       table. If load balancing rules with virtual IP  addresses  (and  ports)
       are  configured  in  OVN_Northbound database for a logical switch data‐
       path, a priority-100 flow is added for each configured virtual  IP  ad‐
       dress  VIP.  For IPv4 VIPs, the match is ip &&&& ip4.dst == VIP. For IPv6
       VIPs, the match is ip &&&& ip6.dst  ==  VIP.  The  flow  sets  an  action
       reg0[0]  =  1; next; to act as a hint for table Pre-stateful to send IP
       packets to the connection tracker for  packet  de-fragmentation  before
       eventually advancing to ingress table LB.

     Ingress Table 5: Pre-stateful

       This  table prepares flows for all possible stateful processing in next
       tables. It contains a priority-0 flow that simply moves traffic to  the
       next table. A priority-100 flow sends the packets to connection tracker
       based on a hint provided by the  previous  tables  (with  a  match  for
       reg0[0] == 1) by using the ct_next; action.

     Ingress table 6: from-lport ACLs

       Logical flows in this table closely reproduce those in the ACL table in
       the OVN_Northbound database for the from-lport direction. The  priority
       values  from  the ACL table have a limited range and have 1000 added to
       them to leave room for OVN default flows at both higher and lower  pri‐
       orities.

              •      allow  ACLs  translate  into logical flows with the next;
                     action. If there are any stateful ACLs on this  datapath,
                     then allow ACLs translate to ct_commit; next; (which acts
                     as a hint for the next tables to commit the connection to
                     conntrack),

              •      allow-related  ACLs translate into logical flows with the
                     ct_commit(ct_label=0/1); next; actions  for  new  connec‐
                     tions and reg0[1] = 1; next; for existing connections.

              •      Other  ACLs  translate to drop; for new or untracked con‐
                     nections and ct_commit(ct_label=1/1); for  known  connec‐
                     tions.  Setting  ct_label  marks a connection as one that
                     was previously allowed, but should no longer  be  allowed
                     due to a policy change.

       This  table  also contains a priority 0 flow with action next;, so that
       ACLs allow packets by default. If the logical datapath has a  statetful
       ACL, the following flows will also be added:

              •      A priority-1 flow that sets the hint to commit IP traffic
                     to the connection  tracker  (with  action  reg0[1]  =  1;
                     next;).  This  is needed for the default allow policy be‐
                     cause, while the initiator’s direction may not  have  any
                     stateful  rules,  the  server’s  may  and then its return
                     traffic would not be known and marked as invalid.

              •      A priority-65535 flow that allows any traffic in the  re‐
                     ply direction for a connection that has been committed to
                     the connection tracker (i.e., established flows), as long
                     as the committed flow does not have ct_label.blocked set.
                     We only handle traffic in the reply  direction  here  be‐
                     cause  we want all packets going in the request direction
                     to still go through the flows  that  implement  the  cur‐
                     rently  defined  policy based on ACLs. If a connection is
                     no longer allowed by policy,  ct_label.blocked  will  get
                     set  and packets in the reply direction will no longer be
                     allowed, either.

              •      A priority-65535 flow that allows  any  traffic  that  is
                     considered  related to a committed flow in the connection
                     tracker (e.g., an ICMP Port Unreachable from  a  non-lis‐
                     tening  UDP port), as long as the committed flow does not
                     have ct_label.blocked set.

              •      A priority-65535 flow that drops all  traffic  marked  by
                     the connection tracker as invalid.

              •      A  priority-65535 flow that drops all trafic in the reply
                     direction with ct_label.blocked set meaning that the con‐
                     nection  should  no  longer  be  allowed  due to a policy
                     change. Packets in the request direction are skipped here
                     to let a newly created ACL re-allow this connection.

     Ingress Table 7: from-lport QoS Marking

       Logical  flows  in  this table closely reproduce those in the QoS table
       with the action column set  in  the  OVN_Northbound  database  for  the
       from-lport direction.

              •      For  every  qos_rules entry in a logical switch with DSCP
                     marking enabled, a flow will be  added  at  the  priority
                     mentioned in the QoS table.

              •      One priority-0 fallback flow that matches all packets and
                     advances to the next table.

     Ingress Table 8: from-lport QoS Meter

       Logical flows in this table closely reproduce those in  the  QoS  table
       with  the  bandwidth  column set in the OVN_Northbound database for the
       from-lport direction.

              •      For every qos_rules entry in a logical switch with meter‐
                     ing  enabled,  a flow will be added at the priorirty men‐
                     tioned in the QoS table.

              •      One priority-0 fallback flow that matches all packets and
                     advances to the next table.

     Ingress Table 9: LB

       It contains a priority-0 flow that simply moves traffic to the next ta‐
       ble. For established connections a priority 100 flow matches on  ct.est
       &&&&  !ct.rel &&&& !ct.new &&&& !ct.inv and sets an action reg0[2] = 1; next;
       to act as a hint for table Stateful to send packets through  connection
       tracker  to  NAT the packets. (The packet will automatically get DNATed
       to the same IP address as the first packet in that connection.)

     Ingress Table 10: Stateful

              •      For all the configured load balancing rules for a  switch
                     in  OVN_Northbound  database that includes a L4 port PORT
                     of protocol P and IP address VIP, a priority-120 flow  is
                     added.  For  IPv4 VIPs , the flow matches ct.new &&&& ip &&&&
                     ip4.dst == VIP &&&& P &&&& P.dst == PORT. For IPv6 VIPs,  the
                     flow matches ct.new &&&& ip &&&& ip6.dst == VIP &&&& P &&&& P.dst
                     == PORT. The flow’s action is ct_lb(args)  ,  where  args
                     contains  comma separated IP addresses (and optional port
                     numbers) to load balance to. The address family of the IP
                     addresses  of  args  is the same as the address family of
                     VIP

              •      For all the configured load balancing rules for a  switch
                     in  OVN_Northbound  database that includes just an IP ad‐
                     dress VIP to match on, OVN adds a priority-110 flow.  For
                     IPv4  VIPs,  the  flow matches ct.new &&&& ip &&&& ip4.dst ==
                     VIP. For IPv6 VIPs, the flow  matches  ct.new  &&&&  ip  &&&&
                     ip6.dst  ==  VIP. The action on this flow is ct_lb(args),
                     where args contains comma separated IP addresses  of  the
                     same address family as VIP.

              •      A priority-100 flow commits packets to connection tracker
                     using ct_commit; next; action based on a hint provided by
                     the previous tables (with a match for reg0[1] == 1).

              •      A  priority-100  flow  sends  the  packets  to connection
                     tracker using ct_lb; as the action based on a  hint  pro‐
                     vided by the previous tables (with a match for reg0[2] ==
                     1).

              •      A priority-0 flow that simply moves traffic to  the  next
                     table.

     Ingress Table 11: ARP/ND responder

       This  table  implements  ARP/ND responder in a logical switch for known
       IPs. The advantage of the ARP responder flow is to limit ARP broadcasts
       by locally responding to ARP requests without the need to send to other
       hypervisors. One common case is when the inport is a logical port asso‐
       ciated with a VIF and the broadcast is responded to on the local hyper‐
       visor rather than broadcast across the whole network and  responded  to
       by the destination VM. This behavior is proxy ARP.

       ARP  requests  arrive from VMs from a logical switch inport of type de‐
       fault. For this case, the logical switch proxy ARP  rules  can  be  for
       other  VMs  or logical router ports. Logical switch proxy ARP rules may
       be programmed both for mac binding of IP  addresses  on  other  logical
       switch  VIF  ports  (which are of the default logical switch port type,
       representing connectivity to VMs or containers), and for mac binding of
       IP  addresses  on  logical switch router type ports, representing their
       logical router port peers. In order to support proxy  ARP  for  logical
       router  ports,  an  IP address must be configured on the logical switch
       router type port, with the same value as the peer logical router  port.
       The configured MAC addresses must match as well. When a VM sends an ARP
       request for a distributed logical router port and if  the  peer  router
       type  port  of  the attached logical switch does not have an IP address
       configured, the ARP request will be broadcast on  the  logical  switch.
       One of the copies of the ARP request will go through the logical switch
       router type port to the logical  router  datapath,  where  the  logical
       router  ARP  responder will generate a reply. The MAC binding of a dis‐
       tributed logical router, once learned by an associated VM, is used  for
       all  that VM’s communication needing routing. Hence, the action of a VM
       re-arping for the mac binding of the  logical  router  port  should  be
       rare.

       Logical  switch  ARP responder proxy ARP rules can also be hit when re‐
       ceiving ARP requests externally on a L2 gateway port. In this case, the
       hypervisor  acting as an L2 gateway, responds to the ARP request on be‐
       half of a destination VM.

       Note that ARP requests received from localnet or vtep  logical  inports
       can either go directly to VMs, in which case the VM responds or can hit
       an ARP responder for a logical router port if the packet is used to re‐
       solve  a  logical router port next hop address. In either case, logical
       switch ARP responder rules will not be hit. It contains  these  logical
       flows:

              •      Priority-100 flows to skip the ARP responder if inport is
                     of type localnet or vtep and  advances  directly  to  the
                     next  table.  ARP requests sent to localnet or vtep ports
                     can be received by multiple hypervisors. Now, because the
                     same mac binding rules are downloaded to all hypervisors,
                     each of the multiple hypervisors will respond. This  will
                     confuse  L2  learning  on the source of the ARP requests.
                     ARP requests received on an inport of type router are not
                     expected  to  hit any logical switch ARP responder flows.
                     However, no skip flows are installed for  these  packets,
                     as  there would be some additional flow cost for this and
                     the value appears limited.

              •      Priority-50 flows that match ARP requests to  each  known
                     IP  address  A  of every logical switch port, and respond
                     with ARP replies directly with corresponding Ethernet ad‐
                     dress E:

                     eth.dst = eth.src;
                     eth.src = E;
                     arp.op = 2; /* ARP reply. */
                     arp.tha = arp.sha;
                     arp.sha = E;
                     arp.tpa = arp.spa;
                     arp.spa = A;
                     outport = inport;
                     flags.loopback = 1;
                     output;


                     These  flows  are  omitted  for logical ports (other than
                     router ports or localport ports) that are down.

              •      Priority-50 flows that match IPv6 ND  neighbor  solicita‐
                     tions  to each known IP address A (and A’s solicited node
                     address) of every logical  switch  port  except  of  type
                     router, and respond with neighbor advertisements directly
                     with corresponding Ethernet address E:

                     nd_na {
                         eth.src = E;
                         ip6.src = A;
                         nd.target = A;
                         nd.tll = E;
                         outport = inport;
                         flags.loopback = 1;
                         output;
                     };


                     Priority-50 flows that match IPv6 ND  neighbor  solicita‐
                     tions  to each known IP address A (and A’s solicited node
                     address) of logical switch port of type router,  and  re‐
                     spond  with  neighbor advertisements directly with corre‐
                     sponding Ethernet address E:

                     nd_na_router {
                         eth.src = E;
                         ip6.src = A;
                         nd.target = A;
                         nd.tll = E;
                         outport = inport;
                         flags.loopback = 1;
                         output;
                     };


                     These flows are omitted for  logical  ports  (other  than
                     router ports or localport ports) that are down.

              •      Priority-100  flows  with match criteria like the ARP and
                     ND flows above, except that they only match packets  from
                     the  inport  that owns the IP addresses in question, with
                     action next;. These flows prevent OVN from  replying  to,
                     for  example,  an ARP request emitted by a VM for its own
                     IP address. A VM only makes this kind of request  to  at‐
                     tempt  to  detect  a  duplicate IP address assignment, so
                     sending a reply will prevent the VM from accepting the IP
                     address that it owns.

                     In  place  of  next;, it would be reasonable to use drop;
                     for the flows’ actions. If everything is working as it is
                     configured,  then  this would produce equivalent results,
                     since no host should reply to the request. But ARPing for
                     one’s  own  IP  address  is intended to detect situations
                     where the network is not working as configured, so  drop‐
                     ping the request would frustrate that intent.

              •      One priority-0 fallback flow that matches all packets and
                     advances to the next table.

     Ingress Table 12: DHCP option processing

       This table adds the DHCPv4 options to a DHCPv4 packet from the  logical
       ports  configured  with  IPv4 address(es) and DHCPv4 options, and simi‐
       larly for DHCPv6 options.

              •      A priority-100 logical flow is added  for  these  logical
                     ports which matches the IPv4 packet with udp.src = 68 and
                     udp.dst = 67 and applies the action put_dhcp_opts and ad‐
                     vances the packet to the next table.

                     reg0[3] = put_dhcp_opts(offer_ip = ip, options...);
                     next;


                     For  DHCPDISCOVER  and  DHCPREQUEST,  this transforms the
                     packet into a DHCP reply, adds the DHCP offer IP  ip  and
                     options  to  the  packet,  and stores 1 into reg0[3]. For
                     other kinds of packets, it just stores  0  into  reg0[3].
                     Either way, it continues to the next table.

              •      A  priority-100  logical  flow is added for these logical
                     ports which matches the IPv6 packet with  udp.src  =  546
                     and  udp.dst = 547 and applies the action put_dhcpv6_opts
                     and advances the packet to the next table.

                     reg0[3] = put_dhcpv6_opts(ia_addr = ip, options...);
                     next;


                     For DHCPv6 Solicit/Request/Confirm packets,  this  trans‐
                     forms  the packet into a DHCPv6 Advertise/Reply, adds the
                     DHCPv6 offer IP ip and options to the packet, and  stores
                     1  into  reg0[3].  For  other  kinds  of packets, it just
                     stores 0 into reg0[3]. Either way, it  continues  to  the
                     next table.

              •      A priority-0 flow that matches all packets to advances to
                     table 11.

     Ingress Table 13: DHCP responses

       This table implements DHCP responder for the DHCP replies generated  by
       the previous table.

              •      A  priority  100  logical  flow  is added for the logical
                     ports configured with DHCPv4 options which  matches  IPv4
                     packets with udp.src == 68 &&&& udp.dst == 67 &&&& reg0[3] ==
                     1 and responds back to the inport  after  applying  these
                     actions. If reg0[3] is set to 1, it means that the action
                     put_dhcp_opts was successful.

                     eth.dst = eth.src;
                     eth.src = E;
                     ip4.dst = A;
                     ip4.src = S;
                     udp.src = 67;
                     udp.dst = 68;
                     outport = P;
                     flags.loopback = 1;
                     output;


                     where E is the server MAC address and  S  is  the  server
                     IPv4  address  defined in the DHCPv4 options and A is the
                     IPv4 address defined in the logical port’s addresses col‐
                     umn.

                     (This  terminates  ingress  packet processing; the packet
                     does not go to the next ingress table.)

              •      A priority 100 logical flow  is  added  for  the  logical
                     ports  configured  with DHCPv6 options which matches IPv6
                     packets with udp.src == 546 &&&& udp.dst == 547 &&&&  reg0[3]
                     == 1 and responds back to the inport after applying these
                     actions. If reg0[3] is set to 1, it means that the action
                     put_dhcpv6_opts was successful.

                     eth.dst = eth.src;
                     eth.src = E;
                     ip6.dst = A;
                     ip6.src = S;
                     udp.src = 547;
                     udp.dst = 546;
                     outport = P;
                     flags.loopback = 1;
                     output;


                     where  E  is  the  server MAC address and S is the server
                     IPv6 LLA address generated from the server_id defined  in
                     the  DHCPv6  options and A is the IPv6 address defined in
                     the logical port’s addresses column.

                     (This terminates packet processing; the packet  does  not
                     go on the next ingress table.)

              •      A priority-0 flow that matches all packets to advances to
                     table 12.

     Ingress Table 14 DNS Lookup

       This table looks up and resolves the DNS  names  to  the  corresponding
       configured IP address(es).

              •      A priority-100 logical flow for each logical switch data‐
                     path if it is configured with DNS records, which  matches
                     the  IPv4  and IPv6 packets with udp.dst = 53 and applies
                     the action dns_lookup and advances the packet to the next
                     table.

                     reg0[4] = dns_lookup(); next;


                     For  valid DNS packets, this transforms the packet into a
                     DNS reply if the DNS name can be resolved, and  stores  1
                     into reg0[4]. For failed DNS resolution or other kinds of
                     packets, it just stores 0 into reg0[4].  Either  way,  it
                     continues to the next table.

     Ingress Table 15 DNS Responses

       This  table  implements  DNS responder for the DNS replies generated by
       the previous table.

              •      A priority-100 logical flow for each logical switch data‐
                     path  if it is configured with DNS records, which matches
                     the IPv4 and IPv6 packets with udp.dst = 53 &&&& reg0[4] ==
                     1  and  responds  back to the inport after applying these
                     actions. If reg0[4] is set to 1, it means that the action
                     dns_lookup was successful.

                     eth.dst ->gt;>gt; eth.src;
                     ip4.src ->gt;>gt; ip4.dst;
                     udp.dst = udp.src;
                     udp.src = 53;
                     outport = P;
                     flags.loopback = 1;
                     output;


                     (This  terminates  ingress  packet processing; the packet
                     does not go to the next ingress table.)

     Ingress Table 16 Destination Lookup

       This table implements switching behavior.  It  contains  these  logical
       flows:

              •      A priority-100 flow that outputs all packets with an Eth‐
                     ernet broadcast or multicast eth.dst to the MC_FLOOD mul‐
                     ticast group, which ovn-northd populates with all enabled
                     logical ports.

              •      One priority-50 flow that matches each known Ethernet ad‐
                     dress  against eth.dst and outputs the packet to the sin‐
                     gle associated output port.

                     For the Ethernet address on a logical switch port of type
                     router,  when that logical switch port’s addresses column
                     is set to router and the connected  logical  router  port
                     specifies a redirect-chassis:

                     •      The  flow  for the connected logical router port’s
                            Ethernet address is only programmed on  the  redi
                            rect-chassis.

                     •      If  the  logical router has rules specified in nat
                            with external_mac, then those addresses  are  also
                            used  to  populate the switch’s destination lookup
                            on the chassis where logical_port is resident.

                     For the Ethernet address on a logical switch port of type
                     router,  when that logical switch port’s addresses column
                     is set to router and the connected  logical  router  port
                     specifies  a  reside-on-redirect-chassis  and the logical
                     router to which the connected logical router port belongs
                     to  has  a  redirect-chassis  distributed gateway logical
                     router port:

                     •      The flow for the connected logical  router  port’s
                            Ethernet  address  is only programmed on the redi
                            rect-chassis.

              •      One priority-0 fallback flow that matches all packets and
                     outputs  them  to  the  MC_UNKNOWN multicast group, which
                     ovn-northd populates with all enabled logical ports  that
                     accept  unknown destination packets. As a small optimiza‐
                     tion, if no  logical  ports  accept  unknown  destination
                     packets,  ovn-northd omits this multicast group and logi‐
                     cal flow.

     Egress Table 0: Pre-LB

       This table is similar to ingress table Pre-LB. It contains a priority-0
       flow  that simply moves traffic to the next table. Moreover it contains
       a priority-110 flow to move IPv6 Neighbor Discovery traffic to the next
       table.  If  any  load  balancing rules exist for the datapath, a prior‐
       ity-100 flow is added with a match of ip and action  of  reg0[0]  =  1;
       next; to act as a hint for table Pre-stateful to send IP packets to the
       connection tracker for packet de-fragmentation.

     Egress Table 1: to-lport Pre-ACLs

       This is similar to ingress table Pre-ACLs except for to-lport traffic.

     Egress Table 2: Pre-stateful

       This is similar to ingress table Pre-stateful.

     Egress Table 3: LB

       This is similar to ingress table LB.

     Egress Table 4: to-lport ACLs

       This is similar to ingress table ACLs except for to-lport ACLs.

       In addition, the following flows are added.

              •      A priority 34000 logical flow is added for  each  logical
                     port which has DHCPv4 options defined to allow the DHCPv4
                     reply packet and which has DHCPv6 options defined to  al‐
                     low  the  DHCPv6  reply packet from the Ingress Table 13:
                     DHCP responses.

              •      A priority 34000 logical flow is added for  each  logical
                     switch  datapath  configured  with  DNS  records with the
                     match udp.dst = 53 to allow the DNS reply packet from the
                     Ingress Table 15:DNS responses.

     Egress Table 5: to-lport QoS Marking

       This  is  similar  to  ingress  table  QoS marking except they apply to
       to-lport QoS rules.

     Egress Table 6: to-lport QoS Meter

       This is similar to  ingress  table  QoS  meter  except  they  apply  to
       to-lport QoS rules.

     Egress Table 7: Stateful

       This  is  similar  to  ingress  table Stateful except that there are no
       rules added for load balancing new connections.

     Egress Table 8: Egress Port Security - IP

       This is similar to the port security logic in table Ingress Port  Secu
       rity - IP except that outport, eth.dst, ip4.dst and ip6.dst are checked
       instead of inport, eth.src, ip4.src and ip6.src

     Egress Table 9: Egress Port Security - L2

       This is similar to the ingress port security logic in ingress table Ad
       mission Control and Ingress Port Security - L2, but with important dif‐
       ferences. Most obviously, outport and eth.dst are  checked  instead  of
       inport  and eth.src. Second, packets directed to broadcast or multicast
       eth.dst are always accepted instead of being subject to the port  secu‐
       rity  rules;  this  is  implemented  through  a  priority-100 flow that
       matches on eth.mcast with action output;. Finally, to ensure that  even
       broadcast  and  multicast packets are not delivered to disabled logical
       ports, a priority-150 flow for each disabled logical outport  overrides
       the priority-100 flow with a drop; action.

   Logical Router Datapaths
       Logical router datapaths will only exist for Logical_Router rows in the
       OVN_Northbound database that do not have enabled set to false

     Ingress Table 0: L2 Admission Control

       This table drops packets that the router shouldn’t see at all based  on
       their Ethernet headers. It contains the following flows:

              •      Priority-100 flows to drop packets with VLAN tags or mul‐
                     ticast Ethernet source addresses.

              •      For each enabled router port P with Ethernet address E, a
                     priority-50  flow  that matches inport == P &&&& (eth.mcast
                     || eth.dst == E), with action next;.

                     For the gateway port  on  a  distributed  logical  router
                     (where  one of the logical router ports specifies a redi
                     rect-chassis), the above flow matching eth.dst  ==  E  is
                     only programmed on the gateway port instance on the redi
                     rect-chassis.

              •      For each dnat_and_snat NAT rule on a  distributed  router
                     that  specifies  an external Ethernet address E, a prior‐
                     ity-50 flow that matches inport == GW &&&&  eth.dst  ==  E,
                     where  GW is the logical router gateway port, with action
                     next;.

                     This flow is only programmed on the gateway port instance
                     on  the  chassis  where the logical_port specified in the
                     NAT rule resides.

       Other packets are implicitly dropped.

     Ingress Table 1: IP Input

       This table is the core of the logical router datapath functionality. It
       contains  the following flows to implement very basic IP host function‐
       ality.

              •      L3 admission control: A priority-100 flow  drops  packets
                     that match any of the following:

                     •      ip4.src[28..31] == 0xe (multicast source)

                     •      ip4.src == 255.255.255.255 (broadcast source)

                     •      ip4.src  ==  127.0.0.0/8 || ip4.dst == 127.0.0.0/8
                            (localhost source or destination)

                     •      ip4.src == 0.0.0.0/8 || ip4.dst == 0.0.0.0/8 (zero
                            network source or destination)

                     •      ip4.src  or ip6.src is any IP address owned by the
                            router, unless the packet was recirculated due  to
                            egress    loopback    as    indicated    by   REG
                            BIT_EGRESS_LOOPBACK.

                     •      ip4.src is the broadcast address of any IP network
                            known to the router.

              •      ICMP  echo reply. These flows reply to ICMP echo requests
                     received for the router’s IP address. Let A be an IP  ad‐
                     dress owned by a router port. Then, for each A that is an
                     IPv4 address, a priority-90 flow matches on ip4.dst ==  A
                     and  icmp4.type  ==  8  &&&& icmp4.code == 0 (ICMP echo re‐
                     quest). For each A that is an IPv6 address, a priority-90
                     flow  matches  on  ip6.dst  == A and icmp6.type == 128 &&&&
                     icmp6.code == 0 (ICMPv6 echo request). The  port  of  the
                     router  that  receives  the echo request does not matter.
                     Also, the ip.ttl  of  the  echo  request  packet  is  not
                     checked,  so  it complies with RFC 1812, section 4.2.2.9.
                     Flows for ICMPv4 echo requests use the following actions:

                     ip4.dst ->gt;>gt; ip4.src;
                     ip.ttl = 255;
                     icmp4.type = 0;
                     flags.loopback = 1;
                     next;


                     Flows for ICMPv6 echo requests use the following actions:

                     ip6.dst ->gt;>gt; ip6.src;
                     ip.ttl = 255;
                     icmp6.type = 129;
                     flags.loopback = 1;
                     next;


              •      Reply to ARP requests.

                     These flows reply to ARP requests for the router’s own IP
                     address  and  populates  mac binding table of the logical
                     router port. The ARP requests are handled only if the re‐
                     questor’s  IP  belongs to the same subnets of the logical
                     router port. For each router port P that owns IP  address
                     A,  which  belongs  to subnet S with prefix length L, and
                     Ethernet address E, a priority-90 flow matches inport  ==
                     P  &&&&  arp.spa == S/L &&&& arp.op == 1 &&&& arp.tpa == A (ARP
                     request) with the following actions:

                     put_arp(inport, arp.spa, arp.sha);
                     eth.dst = eth.src;
                     eth.src = E;
                     arp.op = 2; /* ARP reply. */
                     arp.tha = arp.sha;
                     arp.sha = E;
                     arp.tpa = arp.spa;
                     arp.spa = A;
                     outport = P;
                     flags.loopback = 1;
                     output;


                     For the gateway port  on  a  distributed  logical  router
                     (where  one of the logical router ports specifies a redi
                     rect-chassis), the above flows are only programmed on the
                     gateway  port  instance on the redirect-chassis. This be‐
                     havior avoids generation of multiple ARP  responses  from
                     different  chassis,  and  allows upstream MAC learning to
                     point to the redirect-chassis.

                     For the logical router port with the option reside-on-re
                     direct-chassis  set  (which  is  centralized),  the above
                     flows are only programmed on the gateway port instance on
                     the  redirect-chassis  (if  the logical router has a dis‐
                     tributed gateway port). This behavior  avoids  generation
                     of multiple ARP responses from different chassis, and al‐
                     lows upstream MAC learning to point to the redirect-chas
                     sis.

              •      These  flows handles ARP requests not for router’s own IP
                     address. They use the SPA and SHA to populate the logical
                     router  port’s  mac  binding table, with priority 80. The
                     typical use case of these flows are  GARP  requests  han‐
                     dling.  For  the  gateway  port  on a distributed logical
                     router, these flows are only programmed  on  the  gateway
                     port instance on the redirect-chassis.

              •      These  flows reply to ARP requests for the virtual IP ad‐
                     dresses configured in the router for DNAT or load balanc‐
                     ing.  For a configured DNAT IP address or a load balancer
                     IPv4 VIP A, for each router port P with Ethernet  address
                     E,  a priority-90 flow matches inport == P &&&& arp.op == 1
                     &&&& arp.tpa == A (ARP request) with the following actions:

                     eth.dst = eth.src;
                     eth.src = E;
                     arp.op = 2; /* ARP reply. */
                     arp.tha = arp.sha;
                     arp.sha = E;
                     arp.tpa = arp.spa;
                     arp.spa = A;
                     outport = P;
                     flags.loopback = 1;
                     output;


                     For the gateway port on a distributed logical router with
                     NAT  (where  one  of the logical router ports specifies a
                     redirect-chassis):

                     •      If the corresponding NAT rule cannot be handled in
                            a  distributed manner, then this flow is only pro‐
                            grammed on the gateway port instance on the  redi
                            rect-chassis.  This  behavior avoids generation of
                            multiple ARP responses from different chassis, and
                            allows upstream MAC learning to point to the redi
                            rect-chassis.

                     •      If the corresponding NAT rule can be handled in  a
                            distributed  manner,  then  this flow is only pro‐
                            grammed on the gateway  port  instance  where  the
                            logical_port specified in the NAT rule resides.

                            Some  of  the actions are different for this case,
                            using the external_mac specified in the  NAT  rule
                            rather than the gateway port’s Ethernet address E:

                            eth.src = external_mac;
                            arp.sha = external_mac;


                            This  behavior  avoids  generation of multiple ARP
                            responses from different chassis, and  allows  up‐
                            stream  MAC learning to point to the correct chas‐
                            sis.

              •      ARP reply handling. This flow uses ARP replies  to  popu‐
                     late  the  logical router’s ARP table. A priority-90 flow
                     with  match  arp.op  ==  2  has  actions  put_arp(inport,
                     arp.spa, arp.sha);.

              •      Reply  to  IPv6 Neighbor Solicitations. These flows reply
                     to Neighbor Solicitation requests for  the  router’s  own
                     IPv6  address  and  load balancing IPv6 VIPs and populate
                     the logical router’s mac binding table.

                     For each router port P that  owns  IPv6  address  A,  so‐
                     licited  node address S, and Ethernet address E, a prior‐
                     ity-90 flow matches inport == P &&&& nd_ns  &&&&  ip6.dst  ==
                     {A, E} &&&& nd.target == A with the following actions:

                     put_nd(inport, ip6.src, nd.sll);
                     nd_na_router {
                         eth.src = E;
                         ip6.src = A;
                         nd.target = A;
                         nd.tll = E;
                         outport = inport;
                         flags.loopback = 1;
                         output;
                     };


                     For each router port P that has load balancing VIP A, so‐
                     licited node address S, and Ethernet address E, a  prior‐
                     ity-90  flow  matches  inport == P &&&& nd_ns &&&& ip6.dst ==
                     {A, E} &&&& nd.target == A with the following actions:

                     put_nd(inport, ip6.src, nd.sll);
                     nd_na {
                         eth.src = E;
                         ip6.src = A;
                         nd.target = A;
                         nd.tll = E;
                         outport = inport;
                         flags.loopback = 1;
                         output;
                     };


                     For the gateway port  on  a  distributed  logical  router
                     (where  one of the logical router ports specifies a redi
                     rect-chassis), the above flows replying to IPv6  Neighbor
                     Solicitations are only programmed on the gateway port in‐
                     stance on the redirect-chassis. This behavior avoids gen‐
                     eration  of  multiple replies from different chassis, and
                     allows upstream  MAC  learning  to  point  to  the  redi
                     rect-chassis.

              •      IPv6  neighbor  advertisement  handling.  This  flow uses
                     neighbor advertisements to populate the logical  router’s
                     mac  binding  table.  A priority-90 flow with match nd_na
                     has actions put_nd(inport, nd.target, nd.tll);.

              •      IPv6 neighbor solicitation for non-hosted addresses  han‐
                     dling.  This flow uses neighbor solicitations to populate
                     the logical router’s mac binding table  (ones  that  were
                     directed  at  the  logical  router would have matched the
                     priority-90 neighbor solicitation flow already). A prior‐
                     ity-80  flow  with match nd_ns has actions put_nd(inport,
                     ip6.src, nd.sll);.

              •      UDP port unreachable.  Priority-80  flows  generate  ICMP
                     port  unreachable  messages in reply to UDP datagrams di‐
                     rected to the router’s IP address, except in the  special
                     case  of  gateways,  which  accept  traffic directed to a
                     router IP for load balancing and NAT purposes.

                     These flows should not match IP  fragments  with  nonzero
                     offset.

              •      TCP  reset. Priority-80 flows generate TCP reset messages
                     in reply to TCP datagrams directed to the router’s IP ad‐
                     dress,  except in the special case of gateways, which ac‐
                     cept traffic directed to a router IP for  load  balancing
                     and NAT purposes.

                     These  flows  should  not match IP fragments with nonzero
                     offset.

              •      Protocol or address unreachable. Priority-70 flows gener‐
                     ate  ICMP  protocol  or  address unreachable messages for
                     IPv4 and IPv6 respectively in reply to  packets  directed
                     to  the  router’s  IP  address on IP protocols other than
                     UDP, TCP, and ICMP, except in the special case  of  gate‐
                     ways,  which  accept  traffic directed to a router IP for
                     load balancing purposes.

                     These flows should not match IP  fragments  with  nonzero
                     offset.

              •      Drop  other  IP  traffic to this router. These flows drop
                     any other traffic destined  to  an  IP  address  of  this
                     router  that  is  not already handled by one of the flows
                     above, which amounts to ICMP (other than  echo  requests)
                     and fragments with nonzero offsets. For each IP address A
                     owned by the router, a priority-60 flow  matches  ip4.dst
                     ==  A and drops the traffic. An exception is made and the
                     above flow is not added if the router port’s own  IP  ad‐
                     dress  is  used  to  SNAT  packets  passing  through that
                     router.

       The flows above handle all of the traffic that might be directed to the
       router  itself.  The following flows (with lower priorities) handle the
       remaining traffic, potentially for forwarding:

              •      Drop Ethernet local broadcast. A  priority-50  flow  with
                     match  eth.bcast drops traffic destined to the local Eth‐
                     ernet  broadcast  address.  By  definition  this  traffic
                     should not be forwarded.

              •      ICMP  time exceeded. For each router port P, whose IP ad‐
                     dress is A, a priority-40 flow with match inport == P  &&&&
                     ip.ttl  == {0, 1} &&&& !ip.later_frag matches packets whose
                     TTL has expired, with the following actions  to  send  an
                     ICMP time exceeded reply for IPv4 and IPv6 respectively:

                     icmp4 {
                         icmp4.type = 11; /* Time exceeded. */
                         icmp4.code = 0;  /* TTL exceeded in transit. */
                         ip4.dst = ip4.src;
                         ip4.src = A;
                         ip.ttl = 255;
                         next;
                     };
                     icmp6 {
                         icmp6.type = 3; /* Time exceeded. */
                         icmp6.code = 0;  /* TTL exceeded in transit. */
                         ip6.dst = ip6.src;
                         ip6.src = A;
                         ip.ttl = 255;
                         next;
                     };


              •      TTL  discard. A priority-30 flow with match ip.ttl == {0,
                     1} and actions drop; drops other packets  whose  TTL  has
                     expired, that should not receive a ICMP error reply (i.e.
                     fragments with nonzero offset).

              •      Next table. A priority-0 flows  match  all  packets  that
                     aren’t  already  handled  and  uses actions next; to feed
                     them to the next table.

     Ingress Table 2: DEFRAG

       This is to send packets to connection tracker for tracking and  defrag‐
       mentation.  It  contains a priority-0 flow that simply moves traffic to
       the next table. If load balancing rules with virtual IP addresses  (and
       ports)  are configured in OVN_Northbound database for a Gateway router,
       a priority-100 flow is added for each  configured  virtual  IP  address
       VIP.  For  IPv4  VIPs  the  flow matches ip &&&& ip4.dst == VIP. For IPv6
       VIPs, the flow matches ip &&&& ip6.dst == VIP. The flow uses  the  action
       ct_next;  to  send  IP packets to the connection tracker for packet de-
       fragmentation and tracking before sending it to the next table.

     Ingress Table 3: UNSNAT

       This is for already established  connections’  reverse  traffic.  i.e.,
       SNAT  has  already  been done in egress pipeline and now the packet has
       entered the ingress pipeline as part of a reply. It is unSNATted here.

       Ingress Table 3: UNSNAT on Gateway Routers

              •      If the Gateway router has been configured to  force  SNAT
                     any  previously DNATted packets to B, a priority-110 flow
                     matches ip &&&& ip4.dst == B with an action ct_snat; .

                     If the Gateway router has been configured to  force  SNAT
                     any previously load-balanced packets to B, a priority-100
                     flow matches ip &&&& ip4.dst == B with an action ct_snat; .

                     For each NAT configuration in the  OVN  Northbound  data‐
                     base,  that  asks  to  change  the source IP address of a
                     packet from A to B, a  priority-90  flow  matches  ip  &&&&
                     ip4.dst == B with an action ct_snat; .

                     A priority-0 logical flow with match 1 has actions next;.

       Ingress Table 3: UNSNAT on Distributed Routers

              •      For  each  configuration  in the OVN Northbound database,
                     that asks to change the source IP  address  of  a  packet
                     from A to B, a priority-100 flow matches ip &&&& ip4.dst ==
                     B &&&& inport == GW, where GW is the logical router gateway
                     port, with an action ct_snat;.

                     If  the  NAT rule cannot be handled in a distributed man‐
                     ner, then the priority-100 flow above is only  programmed
                     on the redirect-chassis.

                     For  each  configuration  in the OVN Northbound database,
                     that asks to change the source IP  address  of  a  packet
                     from  A to B, a priority-50 flow matches ip &&&& ip4.dst ==
                     B with an action REGBIT_NAT_REDIRECT  =  1;  next;.  This
                     flow  is  for east/west traffic to a NAT destination IPv4
                     address. By setting the REGBIT_NAT_REDIRECT flag, in  the
                     ingress  table Gateway Redirect this will trigger a redi‐
                     rect to the instance of the gateway  port  on  the  redi
                     rect-chassis.

                     A priority-0 logical flow with match 1 has actions next;.

     Ingress Table 4: DNAT

       Packets enter the pipeline with destination IP address that needs to be
       DNATted from a virtual IP address to a real IP address. Packets in  the
       reverse direction needs to be unDNATed.

       Ingress Table 4: Load balancing DNAT rules

       Following  load  balancing  DNAT  flows are added for Gateway router or
       Router with gateway port. These flows are programmed only on the  redi
       rect-chassis. These flows do not get programmed for load balancers with
       IPv6 VIPs.

              •      For all the configured load balancing rules for a Gateway
                     router  or  Router  with  gateway  port in OVN_Northbound
                     database that includes a L4 port PORT of protocol  P  and
                     IPv4  address  VIP,  a  priority-120 flow that matches on
                     ct.new &&&& ip &&&& ip4.dst == VIP &&&& P &&&& P.dst == PORT
                      with an action of ct_lb(args), where args contains comma
                     separated  IPv4  addresses (and optional port numbers) to
                     load balance to. If the router  is  configured  to  force
                     SNAT  any load-balanced packets, the above action will be
                     replaced by flags.force_snat_for_lb = 1; ct_lb(args);.

              •      For all the configured load balancing rules for a  router
                     in  OVN_Northbound  database that includes a L4 port PORT
                     of protocol P and IPv4 address VIP, a  priority-120  flow
                     that  matches  on  ct.est &&&& ip &&&& ip4.dst == VIP &&&& P &&&&
                     P.dst == PORT
                      with an action of ct_dnat;. If the router is  configured
                     to force SNAT any load-balanced packets, the above action
                     will  be  replaced  by   flags.force_snat_for_lb   =   1;
                     ct_dnat;.

              •      For  all the configured load balancing rules for a router
                     in OVN_Northbound database that includes just an  IP  ad‐
                     dress  VIP  to match on, a priority-110 flow that matches
                     on ct.new &&&& ip &&&& ip4.dst  ==  VIP  with  an  action  of
                     ct_lb(args), where args contains comma separated IPv4 ad‐
                     dresses. If the router is configured to  force  SNAT  any
                     load-balanced  packets, the above action will be replaced
                     by flags.force_snat_for_lb = 1; ct_lb(args);.

              •      For all the configured load balancing rules for a  router
                     in  OVN_Northbound  database that includes just an IP ad‐
                     dress VIP to match on, a priority-110 flow  that  matches
                     on  ct.est  &&&&  ip  &&&&  ip4.dst  == VIP with an action of
                     ct_dnat;. If the router is configured to force  SNAT  any
                     load-balanced  packets, the above action will be replaced
                     by flags.force_snat_for_lb = 1; ct_dnat;.

       Ingress Table 4: DNAT on Gateway Routers

              •      For each configuration in the  OVN  Northbound  database,
                     that  asks  to  change  the  destination  IP address of a
                     packet from A to B, a priority-100  flow  matches  ip  &&&&
                     ip4.dst   ==   A  with  an  action  flags.loopback  =  1;
                     ct_dnat(B);. If the Gateway router is configured to force
                     SNAT any DNATed packet, the above action will be replaced
                     by flags.force_snat_for_dnat =  1;  flags.loopback  =  1;
                     ct_dnat(B);.

              •      For  all  IP  packets  of a Gateway router, a priority-50
                     flow with an action flags.loopback = 1; ct_dnat;.

              •      A priority-0 logical flow with match 1 has actions next;.

       Ingress Table 4: DNAT on Distributed Routers

       On distributed routers, the DNAT table only handles packets with desti‐
       nation IP address that needs to be DNATted from a virtual IP address to
       a real IP address. The unDNAT processing in the  reverse  direction  is
       handled in a separate table in the egress pipeline.

              •      For  each  configuration  in the OVN Northbound database,
                     that asks to change  the  destination  IP  address  of  a
                     packet  from  A  to  B, a priority-100 flow matches ip &&&&
                     ip4.dst == B &&&& inport == GW, where  GW  is  the  logical
                     router gateway port, with an action ct_dnat(B);.

                     If  the  NAT rule cannot be handled in a distributed man‐
                     ner, then the priority-100 flow above is only  programmed
                     on the redirect-chassis.

                     For  each  configuration  in the OVN Northbound database,
                     that asks to change  the  destination  IP  address  of  a
                     packet  from  A  to  B,  a priority-50 flow matches ip &&&&
                     ip4.dst == B with  an  action  REGBIT_NAT_REDIRECT  =  1;
                     next;. This flow is for east/west traffic to a NAT desti‐
                     nation IPv4 address. By setting  the  REGBIT_NAT_REDIRECT
                     flag,  in  the  ingress  table Gateway Redirect this will
                     trigger a redirect to the instance of the gateway port on
                     the redirect-chassis.

                     A priority-0 logical flow with match 1 has actions next;.

     Ingress Table 5: IPv6 ND RA option processing

              •      A  priority-50  logical  flow  is  added for each logical
                     router port configured with  IPv6  ND  RA  options  which
                     matches  IPv6  ND  Router Solicitation packet and applies
                     the action put_nd_ra_opts and advances the packet to  the
                     next table.

                     reg0[5] = put_nd_ra_opts(options);next;


                     For a valid IPv6 ND RS packet, this transforms the packet
                     into an IPv6 ND RA reply and sets the RA options  to  the
                     packet  and  stores  1  into  reg0[5]. For other kinds of
                     packets, it just stores 0 into reg0[5].  Either  way,  it
                     continues to the next table.

              •      A priority-0 logical flow with match 1 has actions next;.

     Ingress Table 6: IPv6 ND RA responder

       This  table  implements IPv6 ND RA responder for the IPv6 ND RA replies
       generated by the previous table.

              •      A priority-50 logical flow  is  added  for  each  logical
                     router  port  configured  with  IPv6  ND RA options which
                     matches IPv6 ND RA packets and reg0[5] == 1 and  responds
                     back  to  the  inport  after  applying  these actions. If
                     reg0[5]  is  set  to  1,  it  means   that   the   action
                     put_nd_ra_opts was successful.

                     eth.dst = eth.src;
                     eth.src = E;
                     ip6.dst = ip6.src;
                     ip6.src = I;
                     outport = P;
                     flags.loopback = 1;
                     output;


                     where  E  is the MAC address and I is the IPv6 link local
                     address of the logical router port.

                     (This terminates packet processing in  ingress  pipeline;
                     the packet does not go to the next ingress table.)

              •      A priority-0 logical flow with match 1 has actions next;.

     Ingress Table 7: IP Routing

       A  packet  that  arrives  at  this table is an IP packet that should be
       routed to the address in ip4.dst or ip6.dst. This table  implements  IP
       routing,  setting  reg0 (or xxreg0 for IPv6) to the next-hop IP address
       (leaving ip4.dst or ip6.dst, the packet’s final destination, unchanged)
       and  advances  to  the next table for ARP resolution. It also sets reg1
       (or xxreg1) to the  IP  address  owned  by  the  selected  router  port
       (ingress  table  ARP  Request  will generate an ARP request, if needed,
       with reg0 as the target protocol address and reg1 as the source  proto‐
       col address).

       This table contains the following logical flows:

              •      For  distributed logical routers where one of the logical
                     router ports specifies a redirect-chassis, a priority-300
                     logical  flow with match REGBIT_NAT_REDIRECT == 1 has ac‐
                     tions ip.ttl--; next;. The outport will be set  later  in
                     the Gateway Redirect table.

              •      IPv4 routing table. For each route to IPv4 network N with
                     netmask M, on router port P with IP address A and  Ether‐
                     net  address E, a logical flow with match ip4.dst == N/M,
                     whose priority is the number of 1-bits in M, has the fol‐
                     lowing actions:

                     ip.ttl--;
                     reg0 = G;
                     reg1 = A;
                     eth.src = E;
                     outport = P;
                     flags.loopback = 1;
                     next;


                     (Ingress table 1 already verified that ip.ttl--; will not
                     yield a TTL exceeded error.)

                     If the route has a gateway, G is the gateway IP  address.
                     Instead,  if the route is from a configured static route,
                     G is the next hop IP address. Else it is ip4.dst.

              •      IPv6 routing table. For each route to IPv6 network N with
                     netmask  M, on router port P with IP address A and Ether‐
                     net address E, a logical flow with match in CIDR notation
                     ip6.dst == N/M, whose priority is the integer value of M,
                     has the following actions:

                     ip.ttl--;
                     xxreg0 = G;
                     xxreg1 = A;
                     eth.src = E;
                     outport = P;
                     flags.loopback = 1;
                     next;


                     (Ingress table 1 already verified that ip.ttl--; will not
                     yield a TTL exceeded error.)

                     If  the route has a gateway, G is the gateway IP address.
                     Instead, if the route is from a configured static  route,
                     G is the next hop IP address. Else it is ip6.dst.

                     If  the  address  A is in the link-local scope, the route
                     will be limited to sending on the ingress port.

     Ingress Table 8: ARP/ND Resolution

       Any packet that reaches this table is an IP packet whose next-hop  IPv4
       address  is  in  reg0 or IPv6 address is in xxreg0. (ip4.dst or ip6.dst
       contains the final destination.) This table resolves the IP address  in
       reg0 (or xxreg0) into an output port in outport and an Ethernet address
       in eth.dst, using the following flows:

              •      For distributed logical routers where one of the  logical
                     router ports specifies a redirect-chassis, a priority-200
                     logical flow with match REGBIT_NAT_REDIRECT == 1 has  ac‐
                     tions eth.dst = E; next;, where E is the ethernet address
                     of the router’s distributed gateway port.

              •      Static MAC bindings. MAC bindings can be known statically
                     based  on data in the OVN_Northbound database. For router
                     ports connected to logical switches, MAC bindings can  be
                     known  statically  from the addresses column in the Logi
                     cal_Switch_Port table.  For  router  ports  connected  to
                     other  logical  routers, MAC bindings can be known stati‐
                     cally from the mac  and  networks  column  in  the  Logi
                     cal_Router_Port table.

                     For  each IPv4 address A whose host is known to have Eth‐
                     ernet address E on router port  P,  a  priority-100  flow
                     with match outport === P &&&& reg0 == A has actions eth.dst
                     = E; next;.

                     For each IPv6 address A whose host is known to have  Eth‐
                     ernet  address  E  on  router port P, a priority-100 flow
                     with match outport === P  &&&&  xxreg0  ==  A  has  actions
                     eth.dst = E; next;.

                     For each logical router port with an IPv4 address A and a
                     mac address of E that is reachable via a different  logi‐
                     cal router port P, a priority-100 flow with match outport
                     === P &&&& reg0 == A has actions eth.dst = E; next;.

                     For each logical router port with an IPv6 address A and a
                     mac  address of E that is reachable via a different logi‐
                     cal router port P, a priority-100 flow with match outport
                     === P &&&& xxreg0 == A has actions eth.dst = E; next;.

              •      Dynamic MAC bindings. These flows resolve MAC-to-IP bind‐
                     ings that have become known dynamically  through  ARP  or
                     neighbor  discovery.  (The ingress table ARP Request will
                     issue an ARP or neighbor solicitation request  for  cases
                     where the binding is not yet known.)

                     A  priority-0  logical  flow  with  match ip4 has actions
                     get_arp(outport, reg0); next;.

                     A priority-0 logical flow  with  match  ip6  has  actions
                     get_nd(outport, xxreg0); next;.

     Ingress Table 9: Gateway Redirect

       For  distributed  logical routers where one of the logical router ports
       specifies a redirect-chassis, this table redirects certain  packets  to
       the distributed gateway port instance on the redirect-chassis. This ta‐
       ble has the following flows:

              •      A priority-200 logical flow with  match  REGBIT_NAT_REDI
                     RECT  ==  1  has actions outport = CR; next;, where CR is
                     the chassisredirect port representing the instance of the
                     logical  router  distributed  gateway  port  on the redi
                     rect-chassis.

              •      A priority-150 logical flow with match outport ==  GW  &&&&
                     eth.dst  ==  00:00:00:00:00:00  has actions outport = CR;
                     next;, where GW is the logical router distributed gateway
                     port  and CR is the chassisredirect port representing the
                     instance of the logical router distributed  gateway  port
                     on the redirect-chassis.

              •      For each NAT rule in the OVN Northbound database that can
                     be handled in a distributed manner, a priority-100  logi‐
                     cal  flow with match ip4.src == B &&&& outport == GW, where
                     GW is the logical router distributed gateway  port,  with
                     actions next;.

              •      A  priority-50  logical flow with match outport == GW has
                     actions outport = CR; next;,  where  GW  is  the  logical
                     router  distributed  gateway  port  and  CR  is the chas
                     sisredirect port representing the instance of the logical
                     router distributed gateway port on the redirect-chassis.

              •      A priority-0 logical flow with match 1 has actions next;.

     Ingress Table 10: ARP Request

       In  the  common  case where the Ethernet destination has been resolved,
       this table outputs the packet. Otherwise, it composes and sends an  ARP
       or IPv6 Neighbor Solicitation request. It holds the following flows:

              •      Unknown MAC address. A priority-100 flow for IPv4 packets
                     with match eth.dst == 00:00:00:00:00:00 has the following
                     actions:

                     arp {
                         eth.dst = ff:ff:ff:ff:ff:ff;
                         arp.spa = reg1;
                         arp.tpa = reg0;
                         arp.op = 1;  /* ARP request. */
                         output;
                     };


                     Unknown  MAC  address. For each IPv6 static route associ‐
                     ated with the router with the nexthop  IP:  G,  a  prior‐
                     ity-200  flow  for  IPv6  packets  with  match eth.dst ==
                     00:00:00:00:00:00 &&&& xxreg0 == G with the  following  ac‐
                     tions is added:

                     nd_ns {
                         eth.dst = E;
                         ip6.dst = I
                         nd.target = G;
                         output;
                     };


                     Where E is the multicast mac derived from the Gateway IP,
                     I is the solicited-node multicast  address  corresponding
                     to the target address G.

                     Unknown MAC address. A priority-100 flow for IPv6 packets
                     with match eth.dst == 00:00:00:00:00:00 has the following
                     actions:

                     nd_ns {
                         nd.target = xxreg0;
                         output;
                     };


                     (Ingress  table  IP  Routing initialized reg1 with the IP
                     address owned by outport and (xx)reg0 with  the  next-hop
                     IP address)

                     The  IP  packet  that triggers the ARP/IPv6 NS request is
                     dropped.

              •      Known MAC address. A priority-0 flow with match 1 has ac‐
                     tions output;.

     Egress Table 0: UNDNAT

       This  is  for  already  established connections’ reverse traffic. i.e.,
       DNAT has already been done in ingress pipeline and now the  packet  has
       entered  the  egress pipeline as part of a reply. For NAT on a distrib‐
       uted router, it is unDNATted here. For Gateway routers, the unDNAT pro‐
       cessing is carried out in the ingress DNAT table.

              •      For  all the configured load balancing rules for a router
                     with gateway port in  OVN_Northbound  database  that  in‐
                     cludes  an  IPv4  address VIP, for every backend IPv4 ad‐
                     dress B defined for the VIP a priority-120 flow  is  pro‐
                     grammed on redirect-chassis that matches ip &&&& ip4.src ==
                     B &&&& outport == GW, where GW is the logical router  gate‐
                     way port with an action ct_dnat;. If the backend IPv4 ad‐
                     dress B is also configured with L4 port PORT of  protocol
                     P,  then  the  match  also  includes P.src == PORT. These
                     flows are not added for load balancers with IPv6 VIPs.

                     If the router is configured to force SNAT  any  load-bal‐
                     anced   packets,   above   action  will  be  replaced  by
                     flags.force_snat_for_lb = 1; ct_dnat;.

              •      For each configuration in  the  OVN  Northbound  database
                     that  asks  to  change  the  destination  IP address of a
                     packet from an IP address of A to B, a priority-100  flow
                     matches  ip &&&& ip4.src == B &&&& outport == GW, where GW is
                     the logical router gateway port, with an action ct_dnat;.

                     If the NAT rule cannot be handled in a  distributed  man‐
                     ner,  then the priority-100 flow above is only programmed
                     on the redirect-chassis.

                     If the NAT rule can be handled in a  distributed  manner,
                     then  there  is an additional action eth.src = EA;, where
                     EA is the ethernet address associated with the IP address
                     A  in  the NAT rule. This allows upstream MAC learning to
                     point to the correct chassis.

              •      A priority-0 logical flow with match 1 has actions next;.

     Egress Table 1: SNAT

       Packets that are configured to be SNATed get their  source  IP  address
       changed based on the configuration in the OVN Northbound database.

       Egress Table 1: SNAT on Gateway Routers

              •      If  the Gateway router in the OVN Northbound database has
                     been configured to force SNAT a  packet  (that  has  been
                     previously  DNATted)  to  B,  a priority-100 flow matches
                     flags.force_snat_for_dnat ==  1  &&&&  ip  with  an  action
                     ct_snat(B);.

                     If  the Gateway router in the OVN Northbound database has
                     been configured to force SNAT a  packet  (that  has  been
                     previously  load-balanced)  to  B,  a  priority-100  flow
                     matches flags.force_snat_for_lb == 1 &&&& ip with an action
                     ct_snat(B);.

                     For  each  configuration  in the OVN Northbound database,
                     that asks to change the source IP  address  of  a  packet
                     from  an  IP  address of A or to change the source IP ad‐
                     dress of a packet that belongs to network A to B, a  flow
                     matches  ip  &&&&  ip4.src == A with an action ct_snat(B);.
                     The priority of the flow is calculated based on the  mask
                     of  A,  with  matches  having larger masks getting higher
                     priorities.

                     A priority-0 logical flow with match 1 has actions next;.

       Egress Table 1: SNAT on Distributed Routers

              •      For each configuration in the  OVN  Northbound  database,
                     that  asks  to  change  the source IP address of a packet
                     from an IP address of A or to change the  source  IP  ad‐
                     dress  of a packet that belongs to network A to B, a flow
                     matches ip &&&& ip4.src == A &&&& outport == GW, where GW  is
                     the   logical   router   gateway  port,  with  an  action
                     ct_snat(B);. The priority of the flow is calculated based
                     on  the  mask of A, with matches having larger masks get‐
                     ting higher priorities.

                     If the NAT rule cannot be handled in a  distributed  man‐
                     ner,  then the flow above is only programmed on the redi
                     rect-chassis.

                     If the NAT rule can be handled in a  distributed  manner,
                     then  there  is an additional action eth.src = EA;, where
                     EA is the ethernet address associated with the IP address
                     A  in  the NAT rule. This allows upstream MAC learning to
                     point to the correct chassis.

              •      A priority-0 logical flow with match 1 has actions next;.

     Egress Table 2: Egress Loopback

       For distributed logical routers where one of the logical  router  ports
       specifies a redirect-chassis.

       Earlier  in the ingress pipeline, some east-west traffic was redirected
       to the chassisredirect port, based on flows  in  the  UNSNAT  and  DNAT
       ingress  tables  setting the REGBIT_NAT_REDIRECT flag, which then trig‐
       gered a match to a flow in the Gateway Redirect ingress table. The  in‐
       tention  was  not  to actually send traffic out the distributed gateway
       port instance on the redirect-chassis. This traffic  was  sent  to  the
       distributed  gateway  port  instance in order for DNAT and/or SNAT pro‐
       cessing to be applied.

       While UNDNAT and SNAT processing have already occurred by  this  point,
       this  traffic  needs  to be forced through egress loopback on this dis‐
       tributed gateway port instance, in order for UNSNAT and DNAT processing
       to  be applied, and also for IP routing and ARP resolution after all of
       the NAT processing, so that the packet can be forwarded to the destina‐
       tion.

       This table has the following flows:

              •      For  each  NAT  rule  in the OVN Northbound database on a
                     distributed router,  a  priority-100  logical  flow  with
                     match  ip4.dst  == E &&&& outport == GW, where E is the ex‐
                     ternal IP address specified in the NAT rule,  and  GW  is
                     the  logical  router  distributed  gateway port, with the
                     following actions:

                     clone {
                         ct_clear;
                         inport = outport;
                         outport = "";
                         flags = 0;
                         flags.loopback = 1;
                         reg0 = 0;
                         reg1 = 0;
                         ...
                         reg9 = 0;
                         REGBIT_EGRESS_LOOPBACK = 1;
                         next(pipeline=ingress, table=0);
                     };


                     flags.loopback is set since in_port is unchanged and  the
                     packet may return back to that port after NAT processing.
                     REGBIT_EGRESS_LOOPBACK is set  to  indicate  that  egress
                     loopback has occurred, in order to skip the source IP ad‐
                     dress check against the router address.

              •      A priority-0 logical flow with match 1 has actions next;.

     Egress Table 3: Delivery

       Packets that reach this table are ready for delivery. It contains  pri‐
       ority-100  logical  flows  that  match  packets on each enabled logical
       router port, with action output;.



Open vSwitch 2.10.90              ovn-northd                     ovn-northd(8)