Provided by: ovn-common_20.03.2-0ubuntu0.20.04.5_amd64 bug

NAME

       ovn-sb - OVN_Southbound database schema

       This  database  holds  logical  and  physical configuration and state for the Open Virtual
       Network (OVN) system to support virtual network abstraction. For an introduction  to  OVN,
       please see ovn-architecture(7).

       The  OVN  Southbound  database  sits  at the center of the OVN architecture. It is the one
       component that speaks both southbound directly to all the hypervisors  and  gateways,  via
       ovn-controller/ovn-controller-vtep,  and  northbound  to  the Cloud Management System, via
       ovn-northd:

   Database Structure
       The OVN Southbound database  contains  classes  of  data  with  different  properties,  as
       described in the sections below.

     Physical network

       Physical  network  tables  contain information about the chassis nodes in the system. This
       contains all the information  necessary  to  wire  the  overlay,  such  as  IP  addresses,
       supported tunnel types, and security keys.

       The  amount  of  physical  network  data  is  small (O(n) in the number of chassis) and it
       changes infrequently, so it can be replicated to every chassis.

       The Chassis and Encap tables are the physical network tables.

     Logical Network

       Logical network tables contain  the  topology  of  logical  switches  and  routers,  ACLs,
       firewall  rules, and everything needed to describe how packets traverse a logical network,
       represented as logical datapath flows (see Logical Datapath Flows, below).

       Logical network data may be large (O(n) in the number of logical ports, ACL rules,  etc.).
       Thus,  to  improve  scaling,  each  chassis  should  receive  only data related to logical
       networks in which that chassis participates.

       The logical network data is ultimately controlled by the  cloud  management  system  (CMS)
       running  northbound  of  OVN. That CMS determines the entire OVN logical configuration and
       therefore the logical network data at any given time is a deterministic  function  of  the
       CMS’s  configuration, although that happens indirectly via the OVN_Northbound database and
       ovn-northd.

       Logical network data is likely to change more quickly than physical network data. This  is
       especially true in a container environment where containers are created and destroyed (and
       therefore added to and deleted from logical switches) quickly.

       The Logical_Flow, Multicast_Group, Address_Group, DHCP_Options,  DHCPv6_Options,  and  DNS
       tables contain logical network data.

     Logical-physical bindings

       These  tables  link  logical  and  physical components. They show the current placement of
       logical components (such as VMs and VIFs) onto chassis, and map logical  entities  to  the
       values that represent them in tunnel encapsulations.

       These  tables  change  frequently, at least every time a VM powers up or down or migrates,
       and especially quickly in a container environment. The amount of data per VM (or  VIF)  is
       small.

       Each  chassis  is authoritative about the VMs and VIFs that it hosts at any given time and
       can efficiently flood that state to a central  location,  so  the  consistency  needs  are
       minimal.

       The Port_Binding and Datapath_Binding tables contain binding data.

     MAC bindings

       The MAC_Binding table tracks the bindings from IP addresses to Ethernet addresses that are
       dynamically discovered using ARP (for IPv4) and neighbor discovery  (for  IPv6).  Usually,
       IP-to-MAC  bindings  for  virtual  machines are statically populated into the Port_Binding
       table, so MAC_Binding is primarily used to discover bindings on physical networks.

   Common Columns
       Some tables contain a special column named external_ids. This column has the same form and
       purpose each place that it appears, so we describe it here to save space later.

              external_ids: map of string-string pairs
                     Key-value  pairs  for  use  by  the software that manages the OVN Southbound
                     database rather than by ovn-controller/ovn-controller-vtep.  In  particular,
                     ovn-northd  can use key-value pairs in this column to relate entities in the
                     southbound database to higher-level entities (such as entities  in  the  OVN
                     Northbound  database).  Individual  key-value  pairs  in  this column may be
                     documented in some cases to aid in understanding  and  troubleshooting,  but
                     the reader should not mistake such documentation as comprehensive.

TABLE SUMMARY

       The  following  list  summarizes  the  purpose of each of the tables in the OVN_Southbound
       database.  Each table is described in more detail on a later page.

       Table     Purpose
       SB_Global Southbound configuration
       Chassis   Physical Network Hypervisor and Gateway Information
       Encap     Encapsulation Types
       Address_Set
                 Address Sets
       Port_Group
                 Port Groups
       Logical_Flow
                 Logical Network Flows
       Multicast_Group
                 Logical Port Multicast Groups
       Meter     Meter entry
       Meter_Band
                 Band for meter entries
       Datapath_Binding
                 Physical-Logical Datapath Bindings
       Port_Binding
                 Physical-Logical Port Bindings
       MAC_Binding
                 IP to MAC bindings
       DHCP_Options
                 DHCP Options supported by native OVN DHCP
       DHCPv6_Options
                 DHCPv6 Options supported by native OVN DHCPv6
       Connection
                 OVSDB client connections.
       SSL       SSL configuration.
       DNS       Native DNS resolution
       RBAC_Role RBAC_Role configuration.
       RBAC_Permission
                 RBAC_Permission configuration.
       Gateway_Chassis
                 Gateway_Chassis configuration.
       HA_Chassis
                 HA_Chassis configuration.
       HA_Chassis_Group
                 HA_Chassis_Group configuration.
       Controller_Event
                 Controller Event table
       IP_Multicast
                 IP_Multicast configuration.
       IGMP_Group
                 IGMP_Group configuration.
       Service_Monitor
                 Service_Monitor configuration.

SB_Global TABLE

       Southbound configuration for an OVN system. This table must have exactly one row.

   Summary:
       Status:
         nb_cfg                      integer
       Common Columns:
         external_ids                map of string-string pairs
         options                     map of string-string pairs
       Common options:
         options                     map of string-string pairs
         Options for configuring BFD:
            options : bfd-min-rx     optional string
            options : bfd-decay-min-rx
                                     optional string
            options : bfd-min-tx     optional string
            options : bfd-mult       optional string
       Connection Options:
         connections                 set of Connections
         ssl                         optional SSL
       Security Configurations:
         ipsec                       boolean

   Details:
     Status:

       This column allow a client to track the overall configuration state of the system.

       nb_cfg: integer
              Sequence number for  the  configuration.  When  a  CMS  or  ovn-nbctl  updates  the
              northbound  database, it increments the nb_cfg column in the NB_Global table in the
              northbound database. In turn, when ovn-northd updates the  southbound  database  to
              bring it up to date with these changes, it updates this column to the same value.

     Common Columns:

       external_ids: map of string-string pairs
              See External IDs at the beginning of this document.

       options: map of string-string pairs

     Common options:

       options: map of string-string pairs
              This  column  provides  general  key/value  settings.  The  supported  options  are
              described individually below.

     Options for configuring BFD:

       These options apply when ovn-controller configures BFD on tunnels interfaces.

       options : bfd-min-rx: optional string
              BFD option min-rx value to use when configuring BFD on tunnel interfaces.

       options : bfd-decay-min-rx: optional string
              BFD option decay-min-rx value to use when configuring BFD on tunnel interfaces.

       options : bfd-min-tx: optional string
              BFD option min-tx value to use when configuring BFD on tunnel interfaces.

       options : bfd-mult: optional string
              BFD option mult value to use when configuring BFD on tunnel interfaces.

     Connection Options:

       connections: set of Connections
              Database clients to which the Open vSwitch database server  should  connect  or  on
              which  it  should  listen,  along  with options for how these connections should be
              configured. See the Connection table for more information.

       ssl: optional SSL
              Global SSL configuration.

     Security Configurations:

       ipsec: boolean
              Tunnel encryption configuration. If this column is set to be true, all OVN  tunnels
              will be encrypted with IPsec.

Chassis TABLE

       Each  row  in  this  table  represents a hypervisor or gateway (a chassis) in the physical
       network. Each chassis, via ovn-controller/ovn-controller-vtep, adds and  updates  its  own
       row, and keeps a copy of the remaining rows to determine how to reach other hypervisors.

       When  a chassis shuts down gracefully, it should remove its own row. (This is not critical
       because resources hosted on the chassis are equally unreachable regardless of whether  the
       row  is  present.) If a chassis shuts down permanently without removing its row, some kind
       of manual or automatic cleanup is eventually needed; we can devise a process for  that  as
       necessary.

   Summary:
       name                          string (must be unique within table)
       hostname                      string
       nb_cfg                        integer
       external_ids : ovn-bridge-mappings
                                     optional string
       external_ids : datapath-type  optional string
       external_ids : iface-types    optional string
       external_ids : ovn-cms-options
                                     optional string
       external_ids : is-interconn   optional string
       external_ids : is-remote      optional string
       transport_zones               set of strings
       external_ids : ovn-chassis-mac-mappings
                                     optional string
       Common Columns:
         external_ids                map of string-string pairs
       Encapsulation Configuration:
         encaps                      set of 1 or more Encaps
       Gateway Configuration:
         vtep_logical_switches       set of strings

   Details:
       name: string (must be unique within table)
              OVN  does  not  prescribe  a  particular  format  for chassis names. ovn-controller
              populates this column using external_ids:system-id in the  Open_vSwitch  database’s
              Open_vSwitch  table.  ovn-controller-vtep  populates  this  column with name in the
              hardware_vtep database’s Physical_Switch table.

       hostname: string
              The hostname of the chassis,  if  applicable.  ovn-controller  will  populate  this
              column  with  the  hostname  of the host it is running on. ovn-controller-vtep will
              leave this column empty.

       nb_cfg: integer
              Sequence  number  for  the   configuration.   When   ovn-controller   updates   the
              configuration  of a chassis from the contents of the southbound database, it copies
              nb_cfg from the SB_Global table into this column.

       external_ids : ovn-bridge-mappings: optional string
              ovn-controller populates this key with the set  of  bridge  mappings  it  has  been
              configured  to  use.  Other  applications  should  treat this key as read-only. See
              ovn-controller(8) for more information.

       external_ids : datapath-type: optional string
              ovn-controller populates  this  key  with  the  datapath  type  configured  in  the
              datapath_type   column   of   the   Open_vSwitch  database’s  Bridge  table.  Other
              applications should treat this key as read-only.  See  ovn-controller(8)  for  more
              information.

       external_ids : iface-types: optional string
              ovn-controller  populates  this  key  with  the  interface  types configured in the
              iface_types  column  of  the  Open_vSwitch  database’s  Open_vSwitch  table.  Other
              applications  should  treat  this  key as read-only. See ovn-controller(8) for more
              information.

       external_ids : ovn-cms-options: optional string
              ovn-controller populates this key  with  the  set  of  options  configured  in  the
              external_ids:ovn-cms-options  column  of  the  Open_vSwitch database’s Open_vSwitch
              table. See ovn-controller(8) for more information.

       external_ids : is-interconn: optional string
              ovn-controller  populates  this  key   with   the   setting   configured   in   the
              external_ids:ovn-is-interconn  column  of  the Open_vSwitch database’s Open_vSwitch
              table. If set to true, the chassis is  used  as  an  interconnection  gateway.  See
              ovn-controller(8) for more information.

       external_ids : is-remote: optional string
              ovn-ic  set  this  key to true for remote interconnection gateway chassises learned
              from the interconnection southbound database. See ovn-ic(8) for more information.

       transport_zones: set of strings
              ovn-controller populates this key  with  the  transport  zones  configured  in  the
              external_ids:ovn-transport-zones column of the Open_vSwitch database’s Open_vSwitch
              table. See ovn-controller(8) for more information.

       external_ids : ovn-chassis-mac-mappings: optional string
              ovn-controller populates this key  with  the  set  of  options  configured  in  the
              external_ids:ovn-chassis-mac-mappings   column   of   the  Open_vSwitch  database’s
              Open_vSwitch table. See ovn-controller(8) for more information.

     Common Columns:

       The overall purpose of these columns is described under Common Columns at the beginning of
       this document.

       external_ids: map of string-string pairs

     Encapsulation Configuration:

       OVN uses encapsulation to transmit logical dataplane packets between chassis.

       encaps: set of 1 or more Encaps
              Points  to  supported  encapsulation  configurations  to transmit logical dataplane
              packets to  this  chassis.  Each  entry  is  a  Encap  record  that  describes  the
              configuration.

     Gateway Configuration:

       A  gateway  is  a  chassis that forwards traffic between the OVN-managed part of a logical
       network and a physical VLAN, extending a tunnel-based  logical  network  into  a  physical
       network.  Gateways  are  typically  dedicated  nodes  that  do  not  host  VMs and will be
       controlled by ovn-controller-vtep.

       vtep_logical_switches: set of strings
              Stores all VTEP logical  switch  names  connected  by  this  gateway  chassis.  The
              Port_Binding  table entry with options:vtep-physical-switch equal Chassis name, and
              options:vtep-logical-switch  value  in  Chassis  vtep_logical_switches,   will   be
              associated with this Chassis.

Encap TABLE

       The  encaps  column  in the Chassis table refers to rows in this table to identify how OVN
       may  transmit  logical  dataplane   packets   to   this   chassis.   Each   chassis,   via
       ovn-controller(8)  or  ovn-controller-vtep(8),  adds  and updates its own rows and keeps a
       copy of the remaining rows to determine how to reach other chassis.

   Summary:
       type                          string, one of geneve, stt, or vxlan
       options                       map of string-string pairs
       options : csum                optional string, either true or false
       options : dst_port            optional string, containing an integer
       ip                            string
       chassis_name                  string

   Details:
       type: string, one of geneve, stt, or vxlan
              The encapsulation to use to transmit packets to this chassis. Hypervisors must  use
              either geneve or stt. Gateways may use vxlan, geneve, or stt.

       options: map of string-string pairs
              Options for configuring the encapsulation, which may be type specific.

       options : csum: optional string, either true or false
              csum  indicates  whether this chassis can transmit and receive packets that include
              checksums with reasonable performance. It hints to  senders  transmitting  data  to
              this chassis that they should use checksums to protect OVN metadata. ovn-controller
              populates this key with the value defined in external_ids:ovn-encap-csum column  of
              the  Open_vSwitch  database’s  Open_vSwitch  table. Other applications should treat
              this key as read-only. See ovn-controller(8) for more information.

              In terms of performance, checksumming actually significantly  increases  throughput
              in  most  common  cases  when  running on Linux based hosts without NICs supporting
              encapsulation hardware offload (around 60% for bulk traffic). The  reason  is  that
              generally  all  NICs  are  capable  of  offloading transmitted and received TCP/UDP
              checksums (viewed as ordinary data packets and not as tunnels). The  benefit  comes
              on  the receive side where the validated outer checksum can be used to additionally
              validate an inner checksum (such as TCP),  which  in  turn  allows  aggregation  of
              packets to be more efficiently handled by the rest of the stack.

              Not  all  devices see such a benefit. The most notable exception is hardware VTEPs.
              These devices are designed to not buffer entire packets in their switching  engines
              and  are therefore unable to efficiently compute or validate full packet checksums.
              In addition certain versions of the  Linux  kernel  are  not  able  to  fully  take
              advantage  of  encapsulation  NIC  offloads  in the presence of checksums. (This is
              actually a pretty narrow corner  case  though:  earlier  versions  of  Linux  don’t
              support  encapsulation offloads at all and later versions support both offloads and
              checksums well.)

              csum defaults to false for hardware VTEPs and true for all other cases.

              This option applies to geneve and vxlan encapsulations.

       options : dst_port: optional string, containing an integer
              If set, overrides the UDP (for geneve and vxlan) or TCP (for stt) destination port.

       ip: string
              The IPv4 address of the encapsulation tunnel endpoint.

       chassis_name: string
              The name of the chassis that created this encap.

Address_Set TABLE

       This table contains address sets synced from the Address_Set table in  the  OVN_Northbound
       database  and  address  sets  generated  from  the  Port_Group table in the OVN_Northbound
       database.

       See the documentation for the Address_Set table and Port_Group table in the OVN_Northbound
       database for details.

   Summary:
       name                          string (must be unique within table)
       addresses                     set of strings

   Details:
       name: string (must be unique within table)

       addresses: set of strings

Port_Group TABLE

       This table contains names for the logical switch ports in the OVN_Northbound database that
       belongs to the same group that is defined in Port_Group in the OVN_Northbound database.

   Summary:
       name                          string (must be unique within table)
       ports                         set of strings

   Details:
       name: string (must be unique within table)

       ports: set of strings

Logical_Flow TABLE

       Each row in this table represents one logical flow. ovn-northd populates this  table  with
       logical  flows  that  implement  the  L2 and L3 topologies specified in the OVN_Northbound
       database. Each hypervisor, via ovn-controller, translates the logical flows into  OpenFlow
       flows specific to its hypervisor and installs them into Open vSwitch.

       Logical  flows are expressed in an OVN-specific format, described here. A logical datapath
       flow is much like an OpenFlow flow, except that the flows are written in terms of  logical
       ports  and logical datapaths instead of physical ports and physical datapaths. Translation
       between logical and physical flows helps to ensure isolation  between  logical  datapaths.
       (The  logical flow abstraction also allows the OVN centralized components to do less work,
       since they do not have to separately compute and push out physical flows to each chassis.)

       The default action when no flow matches is to drop packets.

       Architectural Logical Life Cycle of a Packet

       This following description focuses on the  life  cycle  of  a  packet  through  a  logical
       datapath,  ignoring  physical details of the implementation. Please refer to Architectural
       Physical Life Cycle of a Packet in ovn-architecture(7) for the physical information.

       The description here is written as if OVN itself executes these steps,  but  in  fact  OVN
       (that  is,  ovn-controller) programs Open vSwitch, via OpenFlow and OVSDB, to execute them
       on its behalf.

       At a high level, OVN passes each packet through the  logical  datapath’s  logical  ingress
       pipeline,  which  may  output  the packet to one or more logical port or logical multicast
       groups. For each such logical output port, OVN passes the packet  through  the  datapath’s
       logical  egress  pipeline,  which  may  either  drop  the  packet  or  deliver  it  to the
       destination. Between the two pipelines, outputs to logical multicast groups  are  expanded
       into  logical  ports,  so  that the egress pipeline only processes a single logical output
       port at a time. Between the two pipelines is also where, when necessary, OVN  encapsulates
       a packet in a tunnel (or tunnels) to transmit to remote hypervisors.

       In  more  detail,  to  start,  OVN  searches the Logical_Flow table for a row with correct
       logical_datapath, a pipeline of ingress, a table_id of 0, and a match that is true for the
       packet. If none is found, OVN drops the packet. If OVN finds more than one, it chooses the
       match with the highest priority. Then OVN executes each of the actions  specified  in  the
       row’s actions column, in the order specified. Some actions, such as those to modify packet
       headers, require no further details. The next and output actions are special.

       The next action causes the above process to  be  repeated  recursively,  except  that  OVN
       searches for table_id of 1 instead of 0. Similarly, any next action in a row found in that
       table would cause a further search for  a  table_id  of  2,  and  so  on.  When  recursive
       processing completes, flow control returns to the action following next.

       The  output  action  also introduces recursion. Its effect depends on the current value of
       the outport field. Suppose outport designates a logical port. First, OVN  compares  inport
       to  outport;  if they are equal, it treats the output as a no-op by default. In the common
       case, where they are different, the packet enters the egress pipeline. This transition  to
       the  egress  pipeline  discards  register data, e.g. reg0 ... reg9 and connection tracking
       state, to achieve uniform behavior regardless of whether  the  egress  pipeline  is  on  a
       different hypervisor (because registers aren’t preserve across tunnel encapsulation).

       To  execute  the egress pipeline, OVN again searches the Logical_Flow table for a row with
       correct logical_datapath, a table_id of 0, a match that is true for the  packet,  but  now
       looking for a pipeline of egress. If no matching row is found, the output becomes a no-op.
       Otherwise, OVN executes the actions for the matching flow (which is chosen from  multiple,
       if necessary, as already described).

       In  the  egress  pipeline,  the  next action acts as already described, except that it, of
       course, searches for egress flows. The output action, however, now  directly  outputs  the
       packet  to  the  output  port (which is now fixed, because outport is read-only within the
       egress pipeline).

       The description earlier assumed that outport referred to a logical  port.  If  it  instead
       designates  a  logical multicast group, then the description above still applies, with the
       addition of fan-out from the logical multicast group to each logical port  in  the  group.
       For  each  member  of  the group, OVN executes the logical pipeline as described, with the
       logical output port replaced by the group member.

       Pipeline Stages

       ovn-northd populates the Logical_Flow table with the logical flows described in detail  in
       ovn-northd(8).

   Summary:
       logical_datapath              Datapath_Binding
       pipeline                      string, either egress or ingress
       table_id                      integer, in range 0 to 23
       priority                      integer, in range 0 to 65,535
       match                         string
       actions                       string
       external_ids : stage-name     optional string
       external_ids : stage-hint     optional string, containing an uuid
       external_ids : source         optional string
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       logical_datapath: Datapath_Binding
              The logical datapath to which the logical flow belongs.

       pipeline: string, either egress or ingress
              The  primary  flows  used  for  deciding  on a packet’s destination are the ingress
              flows. The egress flows implement ACLs. See Logical Life Cycle of a Packet,  above,
              for details.

       table_id: integer, in range 0 to 23
              The stage in the logical pipeline, analogous to an OpenFlow table number.

       priority: integer, in range 0 to 65,535
              The  flow’s  priority.  Flows with numerically higher priority take precedence over
              those with lower. If two logical datapath flows with the same priority both  match,
              then the one actually applied to the packet is undefined.

       match: string
              A  matching  expression. OVN provides a superset of OpenFlow matching capabilities,
              using a syntax similar to Boolean expressions in a programming language.

              The most important components of match expression are comparisons  between  symbols
              and constants, e.g. ip4.dst == 192.168.0.1, ip.proto == 6, arp.op == 1, eth.type ==
              0x800. The logical  AND  operator  &&  and  logical  OR  operator  ||  can  combine
              comparisons into a larger expression.

              Matching  expressions also support parentheses for grouping, the logical NOT prefix
              operator !, and literals 0 and 1 to express ``false’’  or  ``true,’’  respectively.
              The latter is useful by itself as a catch-all expression that matches every packet.

              Match  expressions  also support a kind of function syntax. The following functions
              are supported:

              is_chassis_resident(lport)
                     Evaluates to true on a chassis on which logical port lport (a quoted string)
                     resides, and to false elsewhere. This function was introduced in OVN 2.7.

              Symbols

              Type. Symbols have integer or string type. Integer symbols have a width in bits.

              Kinds. There are three kinds of symbols:

              •      Fields.  A  field  symbol  represents a packet header or metadata field. For
                     example, a field named vlan.tci might represent the  VLAN  TCI  field  in  a
                     packet.

                     A  field  symbol  can  have  integer  or  string type. Integer fields can be
                     nominal or ordinal (see Level of Measurement, below).

              •      Subfields. A subfield represents a subset of bits from a larger  field.  For
                     example,  a field vlan.vid might be defined as an alias for vlan.tci[0..11].
                     Subfields are provided for  syntactic  convenience,  because  it  is  always
                     possible to instead refer to a subset of bits from a field directly.

                     Only  ordinal  fields  (see Level of Measurement, below) may have subfields.
                     Subfields are always ordinal.

              •      Predicates. A predicate is shorthand for a  Boolean  expression.  Predicates
                     may  be  used  much  like  1-bit  fields.  For  example, ip4 might expand to
                     eth.type ==  0x800.  Predicates  are  provided  for  syntactic  convenience,
                     because  it  is always possible to instead specify the underlying expression
                     directly.

                     A predicate whose expansion refers to any nominal field  or  predicate  (see
                     Level of Measurement, below) is nominal; other predicates have Boolean level
                     of measurement.

              Level of Measurement. See http://en.wikipedia.org/wiki/Level_of_measurement for the
              statistical concept on which this classification is based. There are three levels:

              •      Ordinal.  In  statistics,  ordinal  values  can  be  ordered on a scale. OVN
                     considers a field (or subfield) to be ordinal if its bits  can  be  examined
                     individually.  This  is  true  for the OpenFlow fields that OpenFlow or Open
                     vSwitch makes ``maskable.’’

                     Any use of a ordinal field may specify a single bit or a range of bits, e.g.
                     vlan.tci[13..15]   refers  to  the  PCP  field  within  the  VLAN  TCI,  and
                     eth.dst[40] refers to the multicast bit in the Ethernet destination address.

                     OVN supports all the usual arithmetic relations (==, !=, <, <=, >,  and  >=)
                     on  ordinal  fields  and their subfields, because OVN can implement these in
                     OpenFlow and Open vSwitch as collections of bitwise tests.

              •      Nominal. In statistics, nominal values cannot be  usefully  compared  except
                     for  equality. This is true of OpenFlow port numbers, Ethernet types, and IP
                     protocols  are  examples:  all  of  these  are  just  identifiers   assigned
                     arbitrarily  with  no  deeper meaning. In OpenFlow and Open vSwitch, bits in
                     these fields generally aren’t individually addressable.

                     OVN only supports arithmetic tests for equality on nominal  fields,  because
                     OpenFlow and Open vSwitch provide no way for a flow to efficiently implement
                     other comparisons on them. (A test for inequality can be sort of  built  out
                     of  two flows with different priorities, but OVN matching expressions always
                     generate flows with a single priority.)

                     String fields are always nominal.

              •      Boolean. A nominal field that has only two values,  0  and  1,  is  somewhat
                     exceptional,  since it is easy to support both equality and inequality tests
                     on such a field: either one can be implemented as a test for 0 or 1.

                     Only predicates (see above) have a Boolean level of measurement.

                     This isn’t a standard level of measurement.

              Prerequisites. Any symbol can have prerequisites, which  are  additional  condition
              implied by the use of the symbol. For example, For example, icmp4.type symbol might
              have prerequisite icmp4, which would cause an expression  icmp4.type  ==  0  to  be
              interpreted  as  icmp4.type == 0 && icmp4, which would in turn expand to icmp4.type
              == 0 && eth.type == 0x800 && ip4.proto == 1 (assuming icmp4 is a predicate  defined
              as suggested under Types above).

              Relational operators

              All  of  the  standard relational operators ==, !=, <, <=, >, and >= are supported.
              Nominal fields support only == and !=, and only in a positive sense  when  outer  !
              are  taken  into  account,  e.g.  given  string  field inport, inport == "eth0" and
              !(inport != "eth0") are acceptable, but not inport != "eth0".

              The implementation of == (or != when it is negated), is more efficient than that of
              the other relational operators.

              Constants

              Integer  constants  may  be expressed in decimal, hexadecimal prefixed by 0x, or as
              dotted-quad IPv4 addresses, IPv6 addresses in their  standard  forms,  or  Ethernet
              addresses  as  colon-separated  hex digits. A constant in any of these forms may be
              followed by a slash and a second constant (the mask) in the same form,  to  form  a
              masked  constant.  IPv4  and  IPv6  masks may be given as integers, to express CIDR
              prefixes.

              String constants have the same syntax as quoted strings in  JSON  (thus,  they  are
              Unicode strings).

              Some  operators  support  sets  of  constants  written inside curly braces { ... }.
              Commas between elements of a set, and after the last elements, are  optional.  With
              ==,  ``field  ==  { constant1, constant2, ... }’’ is syntactic sugar for ``field ==
              constant1 || field  ==  constant2  ||  ....  Similarly,  ``field  !=  {  constant1,
              constant2,  ...  }’’ is equivalent to ``field != constant1 && field != constant2 &&
              ...’’.

              You may refer to a set of IPv4, IPv6, or MAC addresses stored  in  the  Address_Set
              table by its name. An Address_Set with a name of set1 can be referred to as $set1.

              You  may refer to a group of logical switch ports stored in the Port_Group table by
              its name. An  Port_Group  with  a  name  of  port_group1  can  be  referred  to  as
              @port_group1.

              Additionally, you may refer to the set of addresses belonging to a group of logical
              switch ports stored in the Port_Group table  by  its  name  followed  by  a  suffix
              ’_ip4’/’_ip6’.  The IPv4 address set of a Port_Group with a name of port_group1 can
              be referred to as $port_group1_ip4, and the IPv6 address set of the same Port_Group
              can be referred to as $port_group1_ip6

              Miscellaneous

              Comparisons may name the symbol or the constant first, e.g. tcp.src == 80 and 80 ==
              tcp.src are both acceptable.

              Tests for a range may be expressed using a syntax like 1024 <=  tcp.src  <=  49151,
              which is equivalent to 1024 <= tcp.src && tcp.src <= 49151.

              For  a one-bit field or predicate, a mention of its name is equivalent to symobl ==
              1, e.g. vlan.present is equivalent to vlan.present == 1. The same is true for  one-
              bit  subfields, e.g. vlan.tci[12]. There is no technical limitation to implementing
              the same for ordinal fields of all widths,  but  the  implementation  is  expensive
              enough  that the syntax parser requires writing an explicit comparison against zero
              to make mistakes less likely, e.g. in tcp.src != 0  the  comparison  against  0  is
              required.

              Operator  precedence  is  as  shown  below,  from  highest to lowest. There are two
              exceptions where parentheses are required even though the table would suggest  that
              they  are  not:  &&  and  || require parentheses when used together, and ! requires
              parentheses when applied to a relational expression. Thus, in (eth.type == 0x800 ||
              eth.type  ==  0x86dd)  &&  ip.proto  ==  6  or  !(arp.op == 1), the parentheses are
              mandatory.

              •      ()==   !=   <   <=   >   >=!&&   ||

              Comments may be introduced by //, which extends  to  the  next  new-line.  Comments
              within a line may be bracketed by /* and */. Multiline comments are not supported.

              Symbols

              Most  of  the  symbols below have integer type. Only inport and outport have string
              type. inport names a logical port. Thus, its value is a logical_port name from  the
              Port_Binding  table.  outport  may  name  a  logical  port, as inport, or a logical
              multicast group defined in the Multicast_Group table. For both symbols, only  names
              within the flow’s logical datapath may be used.

              The  regX  symbols  are  32-bit  integers. The xxregX symbols are 128-bit integers,
              which overlay four of the 32-bit registers: xxreg0 overlays reg0 through reg3, with
              reg0  supplying  the most-significant bits of xxreg0 and reg3 the least-signficant.
              xxreg1 similarly overlays reg4 through reg7.

              •      reg0...reg9xxreg0 xxreg1inport outportflags.loopbacketh.src eth.dst eth.typevlan.tci vlan.vid vlan.pcp vlan.presentip.proto ip.dscp ip.ecn ip.ttl ip.fragip4.src ip4.dstip6.src ip6.dst ip6.labelarp.op arp.spa arp.tpa arp.sha arp.thatcp.src tcp.dst tcp.flagsudp.src udp.dstsctp.src sctp.dsticmp4.type icmp4.codeicmp6.type icmp6.codend.target nd.sll nd.tllct_mark ct_labelct_state,  which  has  several  Boolean  subfields.   The   ct_next   action
                     initializes the following subfields:

                     •      ct.trk:  Always  set  to  true by ct_next to indicate that connection
                            tracking has taken place. All other ct subfields  have  ct.trk  as  a
                            prerequisite.

                     •      ct.new: True for a new flow

                     •      ct.est: True for an established flow

                     •      ct.rel: True for a related flow

                     •      ct.rpl: True for a reply flow

                     •      ct.inv: True for a connection entry in a bad state

                     The ct_dnat, ct_snat, and ct_lb actions initialize the following subfields:

                     •      ct.dnat:  True  for  a  packet  whose destination IP address has been
                            changed.

                     •      ct.snat: True for a packet whose source IP address has been changed.

              The following predicates are supported:

              •      eth.bcast expands to eth.dst == ff:ff:ff:ff:ff:ffeth.mcast expands to eth.dst[40]vlan.present expands to vlan.tci[12]ip4 expands to eth.type == 0x800ip4.src_mcast expands to ip4.src[28..31] == 0xeip4.mcast expands to ip4.dst[28..31] == 0xeip6 expands to eth.type == 0x86ddip expands to ip4 || ip6icmp4 expands to ip4 && ip.proto == 1icmp6 expands to ip6 && ip.proto == 58icmp expands to icmp4 || icmp6ip.is_frag expands to ip.frag[0]ip.later_frag expands to ip.frag[1]ip.first_frag expands to ip.is_frag && !ip.later_fragarp expands to eth.type == 0x806nd expands to icmp6.type == {135, 136} && icmp6.code == 0 && ip.ttl == 255nd_ns expands to icmp6.type == 135 && icmp6.code == 0 && ip.ttl == 255nd_na expands to icmp6.type == 136 && icmp6.code == 0 && ip.ttl == 255nd_rs expands to icmp6.type == 133 && icmp6.code == 0 && ip.ttl == 255nd_ra expands to icmp6.type == 134 && icmp6.code == 0 && ip.ttl == 255tcp expands to ip.proto == 6udp expands to ip.proto == 17sctp expands to ip.proto == 132

       actions: string
              Logical datapath actions, to be executed when the logical flow represented by  this
              row is the highest-priority match.

              Actions share lexical syntax with the match column. An empty set of actions (or one
              that contains just white space or comments), or a set of actions that  consists  of
              just  drop;, causes the matched packets to be dropped. Otherwise, the column should
              contain a sequence of actions, each terminated by a semicolon.

              The following actions are defined:

              output;
                     In the ingress pipeline, this action  executes  the  egress  pipeline  as  a
                     subroutine.  If  outport  names a logical port, the egress pipeline executes
                     once; if it is a multicast group, the egress pipeline  runs  once  for  each
                     logical port in the group.

                     In  the  egress  pipeline,  this  action  performs  the actual output to the
                     outport logical port.  (In  the  egress  pipeline,  outport  never  names  a
                     multicast group.)

                     By  default, output to the input port is implicitly dropped, that is, output
                     becomes a no-op if outport == inport.  Occasionally  it  may  be  useful  to
                     override  this  behavior, e.g. to send an ARP reply to an ARP request; to do
                     so, use flags.loopback = 1 to allow the packet to  "hair-pin"  back  to  the
                     input port.

              next;
              next(table);
              next(pipeline=pipeline, table=table);
                   Executes  the  given  logical  datapath table in pipeline as a subroutine. The
                   default table is just after the current one. If pipeline is specified, it  may
                   be  ingress  or  egress;  the default pipeline is the one currently executing.
                   Actions in the both ingress and egress pipeline can use next  to  jump  across
                   the  other  pipeline.  Actions in the ingress pipeline should use next to jump
                   into the specific table of egress pipeline only if  it  is  certain  that  the
                   packets  are  local  and not tunnelled and wants to skip certain stages in the
                   packet processing.

              field = constant;
                   Sets data or metadata field field to constant value constant, e.g.  outport  =
                   "vif0";  to  set  the  logical  output port. To set only a subset of bits in a
                   field, specify a subfield for field or a masked constant,  e.g.  one  may  use
                   vlan.pcp[2] = 1; or vlan.pcp = 4/4; to set the most sigificant bit of the VLAN
                   PCP.

                   Assigning to a field with prerequisites implicitly adds those prerequisites to
                   match;  thus, for example, a flow that sets tcp.dst applies only to TCP flows,
                   regardless of whether its match mentions any TCP field.

                   Not all fields are modifiable (e.g. eth.type and ip.proto are read-only),  and
                   not all modifiable fields may be partially modified (e.g. ip.ttl must assigned
                   as a whole). The outport field is modifiable in the ingress pipeline  but  not
                   in the egress pipeline.

              ovn_field = constant;
                   Sets OVN field ovn_field to constant value constant.

                   OVN  supports setting the values of certain fields which are not yet supported
                   in OpenFlow to set or modify them.

                   Below are the supported OVN fields:

                   •      icmp4.frag_mtu

                          This field sets the low-order 16 bits of the ICMP4 header field that is
                          labelled  "unused" in the ICMP specification as defined in the RFC 1191
                          with the value specified in constant.

                          Eg. icmp4.frag_mtu = 1500;

              field1 = field2;
                   Sets data or metadata field field1 to the value  of  data  or  metadata  field
                   field2, e.g. reg0 = ip4.src; copies ip4.src into reg0. To modify only a subset
                   of a field’s bits, specify a subfield for  field1  or  field2  or  both,  e.g.
                   vlan.pcp = reg0[0..2]; copies the least-significant bits of reg0 into the VLAN
                   PCP.

                   field1 and field2 must be the same type, either both string  or  both  integer
                   fields. If they are both integer fields, they must have the same width.

                   If  field1 or field2 has prerequisites, they are added implicitly to match. It
                   is possible to write an assignment with contradictory prerequisites,  such  as
                   ip4.src  =  ip6.src[0..31];,  but  the contradiction means that a logical flow
                   with such an assignment will never be matched.

              field1 <-> field2;
                   Similar to field1 = field2; except that the two values are  exchanged  instead
                   of copied. Both field1 and field2 must modifiable.

              ip.ttl--;
                   Decrements  the IPv4 or IPv6 TTL. If this would make the TTL zero or negative,
                   then processing of the packet halts; no further  actions  are  processed.  (To
                   properly  handle  such cases, a higher-priority flow should match on ip.ttl ==
                   {0, 1};.)

                   Prerequisite: ip

              ct_next;
                   Apply connection tracking to the flow, initializing ct_state for  matching  in
                   later  tables.  Automatically  moves  on  to the next table, as if followed by
                   next.

                   As a side effect,  IP  fragments  will  be  reassembled  for  matching.  If  a
                   fragmented  packet  is  output,  then  it  will  be  sent with any overlapping
                   fragments squashed. The connection tracking state is  scoped  by  the  logical
                   port  when  the  action is used in a flow for a logical switch, so overlapping
                   addresses may be used. To allow traffic related to the matched  flow,  execute
                   ct_commit  .  Connection tracking state is scoped by the logical topology when
                   the action is used in a flow for a router.

                   It is possible to have actions follow ct_next, but they will not  have  access
                   to any of its side-effects and is not generally useful.

              ct_commit;
              ct_commit(ct_mark=value[/mask]);
              ct_commit(ct_label=value[/mask]);
              ct_commit(ct_mark=value[/mask], ct_label=value[/mask]);
                   Commit  the  flow  to  the  connection  tracking entry associated with it by a
                   previous    call    to    ct_next.    When     ct_mark=value[/mask]     and/or
                   ct_label=value[/mask] are supplied, ct_mark and/or ct_label will be set to the
                   values indicated by value[/mask] on the connection tracking entry. ct_mark  is
                   a  32-bit  field.  ct_label  is  a  128-bit  field. The value[/mask] should be
                   specified in hex string if more than 64bits are to be used.

                   Note that if you want processing to continue  in  the  next  table,  you  must
                   execute  the  next  action  after ct_commit. You may also leave out next which
                   will commit connection tracking state, and then drop the packet. This could be
                   useful  for  setting  ct_mark on a connection tracking entry before dropping a
                   packet, for example.

              ct_dnat;
              ct_dnat(IP);
                   ct_dnat sends the packet through the DNAT zone in connection tracking table to
                   unDNAT  any  packet  that  was DNATed in the opposite direction. The packet is
                   then automatically sent to to the next tables as if followed by next;  action.
                   The  next  tables  will see the changes in the packet caused by the connection
                   tracker.

                   ct_dnat(IP) sends the packet through the DNAT zone to change  the  destination
                   IP  address  of  the  packet  to  the  one provided inside the parentheses and
                   commits the connection. The packet is then  automatically  sent  to  the  next
                   tables as if followed by next; action. The next tables will see the changes in
                   the packet caused by the connection tracker.

              ct_snat;
              ct_snat(IP);
                   ct_snat sends the packet through the SNAT zone to unSNAT any packet  that  was
                   SNATed in the opposite direction. The packet is automatically sent to the next
                   tables as if followed by the next;  action.  The  next  tables  will  see  the
                   changes in the packet caused by the connection tracker.

                   ct_snat(IP)  sends  the  packet  through the SNAT zone to change the source IP
                   address of the packet to the one provided inside the parenthesis  and  commits
                   the connection. The packet is then automatically sent to the next tables as if
                   followed by next; action. The next tables will see the changes in  the  packet
                   caused by the connection tracker.

              ct_clear;
                   Clears connection tracking state.

              clone { action; ... };
                   Makes  a  copy  of  the packet being processed and executes each action on the
                   copy. Actions following the clone action,  if  any,  apply  to  the  original,
                   unmodified  packet.  This  can  be  used  as a way to ``save and restore’’ the
                   packet around a set of actions that may modify it and should not persist.

              arp { action; ... };
                   Temporarily replaces the IPv4 packet being processed  by  an  ARP  packet  and
                   executes  each  nested  action  on  the  ARP packet. Actions following the arp
                   action, if any, apply to the original, unmodified packet.

                   The ARP packet that this action operates on is initialized based on  the  IPv4
                   packet  being  processed, as follows. These are default values that the nested
                   actions will probably want to change:

                   •      eth.src unchanged

                   •      eth.dst unchanged

                   •      eth.type = 0x0806arp.op = 1 (ARP request)

                   •      arp.sha copied from eth.srcarp.spa copied from ip4.srcarp.tha = 00:00:00:00:00:00arp.tpa copied from ip4.dst

                   The ARP packet has the same VLAN header, if any, as the IP packet it replaces.

                   Prerequisite: ip4

              get_arp(P, A);
                   Parameters: logical port string field P, 32-bit IP address field A.

                   Looks up A in P’s mac binding table. If an entry is found, stores its Ethernet
                   address in eth.dst, otherwise stores 00:00:00:00:00:00 in eth.dst.

                   Example: get_arp(outport, ip4.dst);

              put_arp(P, A, E);
                   Parameters:  logical  port  string  field P, 32-bit IP address field A, 48-bit
                   Ethernet address field E.

                   Adds or updates the entry for IP address A in logical  port  P’s  mac  binding
                   table, setting its Ethernet address to E.

                   Example: put_arp(inport, arp.spa, arp.sha);

              R = lookup_arp(P, A, M);
                   Parameters: logical port string field P, 32-bit IP address field A, 48-bit MAC
                   address field M.

                   Result: stored to a 1-bit subfield R.

                   Looks up A and M in P’s mac binding table. If an entry is found, stores  1  in
                   the 1-bit subfield R, else 0.

                   Example: reg0[0] = lookup_arp(inport, arp.spa, arp.sha);

              nd_ns { action; ... };
                   Temporarily  replaces  the  IPv6  packet  being  processed by an IPv6 Neighbor
                   Solicitation packet and executes each nested action on  the  IPv6  NS  packet.
                   Actions  following the nd_ns action, if any, apply to the original, unmodified
                   packet.

                   The IPv6 NS packet that this action operates on is initialized  based  on  the
                   IPv6  packet  being  processed,  as follows. These are default values that the
                   nested actions will probably want to change:

                   •      eth.src unchanged

                   •      eth.dst set to IPv6 multicast MAC address

                   •      eth.type = 0x86ddip6.src copied from ip6.srcip6.dst set to IPv6 Solicited-Node multicast address

                   •      icmp6.type = 135 (Neighbor Solicitation)

                   •      nd.target copied from ip6.dst

                   The IPv6 NS packet has the same VLAN header, if  any,  as  the  IP  packet  it
                   replaces.

                   Prerequisite: ip6

              nd_na { action; ... };
                   Temporarily  replaces the IPv6 neighbor solicitation packet being processed by
                   an IPv6 neighbor advertisement (NA) packet and executes each nested action  on
                   the  NA  packet.  Actions  following  the  nd_na  action, if any, apply to the
                   original, unmodified packet.

                   The NA packet that this action operates on is initialized based  on  the  IPv6
                   packet  being  processed, as follows. These are default values that the nested
                   actions will probably want to change:

                   •      eth.dst exchanged with eth.srceth.type = 0x86ddip6.dst copied from ip6.srcip6.src copied from nd.targeticmp6.type = 136 (Neighbor Advertisement)

                   •      nd.target unchanged

                   •      nd.sll = 00:00:00:00:00:00nd.tll copied from eth.dst

                   The ND packet has the same  VLAN  header,  if  any,  as  the  IPv6  packet  it
                   replaces.

                   Prerequisite: nd_ns

              nd_na_router { action; ... };
                   Temporarily  replaces the IPv6 neighbor solicitation packet being processed by
                   an IPv6 neighbor advertisement (NA) packet,  sets  ND_NSO_ROUTER  in  the  RSO
                   flags  and executes each nested action on the NA packet. Actions following the
                   nd_na_router action, if any, apply to the original, unmodified packet.

                   The NA packet that this action operates on is initialized based  on  the  IPv6
                   packet  being  processed, as follows. These are default values that the nested
                   actions will probably want to change:

                   •      eth.dst exchanged with eth.srceth.type = 0x86ddip6.dst copied from ip6.srcip6.src copied from nd.targeticmp6.type = 136 (Neighbor Advertisement)

                   •      nd.target unchanged

                   •      nd.sll = 00:00:00:00:00:00nd.tll copied from eth.dst

                   The ND packet has the same  VLAN  header,  if  any,  as  the  IPv6  packet  it
                   replaces.

                   Prerequisite: nd_ns

              get_nd(P, A);
                   Parameters: logical port string field P, 128-bit IPv6 address field A.

                   Looks up A in P’s mac binding table. If an entry is found, stores its Ethernet
                   address in eth.dst, otherwise stores 00:00:00:00:00:00 in eth.dst.

                   Example: get_nd(outport, ip6.dst);

              put_nd(P, A, E);
                   Parameters: logical port string field P, 128-bit IPv6 address field A,  48-bit
                   Ethernet address field E.

                   Adds  or  updates the entry for IPv6 address A in logical port P’s mac binding
                   table, setting its Ethernet address to E.

                   Example: put_nd(inport, nd.target, nd.tll);

              R = lookup_nd(P, A, M);
                   Parameters: logical port string field P, 128-bit IP address  field  A,  48-bit
                   MAC address field M.

                   Result: stored to a 1-bit subfield R.

                   Looks  up  A and M in P’s mac binding table. If an entry is found, stores 1 in
                   the 1-bit subfield R, else 0.

                   Example: reg0[0] = lookup_nd(inport, ip6.src, eth.src);

              R = put_dhcp_opts(D1 = V1, D2 = V2, ..., Dn = Vn);
                   Parameters: one or more DHCP option/value pairs, which must include an offerip
                   option (with code 0).

                   Result: stored to a 1-bit subfield R.

                   Valid only in the ingress pipeline.

                   When  this  action  is  applied  to  a  DHCP  request  packet (DHCPDISCOVER or
                   DHCPREQUEST), it changes the packet into a DHCP reply (DHCPOFFER  or  DHCPACK,
                   respectively),  replaces  the  options  by  those specified as parameters, and
                   stores 1 in R.

                   When this action is applied to a non-DHCP packet or a DHCP packet that is  not
                   DHCPDISCOVER or DHCPREQUEST, it leaves the packet unchanged and stores 0 in R.

                   The contents of the DHCP_Option table control the DHCP option names and values
                   that this action supports.

                   Example: reg0[0]  =  put_dhcp_opts(offerip  =  10.0.0.2,  router  =  10.0.0.1,
                   netmask = 255.255.255.0, dns_server = {8.8.8.8, 7.7.7.7});

              R = put_dhcpv6_opts(D1 = V1, D2 = V2, ..., Dn = Vn);
                   Parameters: one or more DHCPv6 option/value pairs.

                   Result: stored to a 1-bit subfield R.

                   Valid only in the ingress pipeline.

                   When  this action is applied to a DHCPv6 request packet, it changes the packet
                   into a DHCPv6 reply, replaces the options by those  specified  as  parameters,
                   and stores 1 in R.

                   When  this  action  is  applied  to  a  non-DHCPv6 packet or an invalid DHCPv6
                   request packet , it leaves the packet unchanged and stores 0 in R.

                   The contents of the DHCPv6_Options table control the DHCPv6 option  names  and
                   values that this action supports.

                   Example:   reg0[3]   =   put_dhcpv6_opts(ia_addr   =   aef0::4,   server_id  =
                   00:00:00:00:10:02, dns_server={ae70::1,ae70::2});

              set_queue(queue_number);
                   Parameters: Queue number queue_number, in the range 0 to 61440.

                   This is a logical equivalent of the  OpenFlow  set_queue  action.  It  affects
                   packets  that  egress  a  hypervisor through a physical interface. For nonzero
                   queue_number, it configures packet queuing to match  the  settings  configured
                   for  the  Port_Binding with options:qdisc_queue_id matching queue_number. When
                   queue_number is zero, it resets queuing to the default strategy.

                   Example: set_queue(10);

              ct_lb;
              ct_lb(ip[:port]...);
                   With one or more  arguments,  ct_lb  commits  the  packet  to  the  connection
                   tracking table and DNATs the packet’s destination IP address (and port) to the
                   IP address or addresses (and optional  ports)  specified  in  the  string.  If
                   multiple  comma-separated  IP  addresses  are  specified,  each is given equal
                   weight for picking the DNAT address. Processing automatically moves on to  the
                   next  table, as if next; were specified, and later tables act on the packet as
                   modified by the connection tracker. Connection tracking state is scoped by the
                   logical  port  when  the  action  is  used  in a flow for a logical switch, so
                   overlapping addresses may be used. Connection tracking state is scoped by  the
                   logical topology when the action is used in a flow for a router.

                   Without  arguments, ct_lb sends the packet to the connection tracking table to
                   NAT the packets. If the packet is part of an established connection  that  was
                   previously  committed  to  the  connection  tracker  via  ct_lb(...),  it will
                   automatically get DNATed to the same IP address as the first  packet  in  that
                   connection.

              R = dns_lookup();
                   Parameters: No parameters.

                   Result: stored to a 1-bit subfield R.

                   Valid only in the ingress pipeline.

                   When  this  action  is  applied to a valid DNS request (a UDP packet typically
                   directed to port 53), it attempts to resolve the query using the  contents  of
                   the DNS table. If it is successful, it changes the packet into a DNS reply and
                   stores 1 in R. If the action is applied to a non-DNS packet,  an  invalid  DNS
                   request packet, or a valid DNS request for which the DNS table does not supply
                   an answer, it leaves the packet unchanged and stores 0 in R.

                   Regardless of success, the action does not make any of the changes to the flow
                   that  are  necessary  to  direct the packet back to the requester. The logical
                   pipeline can implement this behavior with matches and actions in later tables.

                   Example: reg0[3] = dns_lookup();

                   Prerequisite: udp

              R = put_nd_ra_opts(D1 = V1, D2 = V2, ..., Dn = Vn);
                   Parameters: The following IPv6 ND Router Advertisement option/value  pairs  as
                   defined in RFC 4861.

                   •      addr_mode

                          Mandatory  parameter which specifies the address mode flag to be set in
                          the RA flag options field. The value of this option is a string and the
                          following  values  can  be  defined  -  "slaac",  "dhcpv6_stateful" and
                          "dhcpv6_stateless".

                   •      slla

                          Mandatory parameter which  specifies  the  link-layer  address  of  the
                          interface from which the Router Advertisement is sent.

                   •      mtu

                          Optional parameter which specifies the MTU.

                   •      prefix

                          Optional  parameter  which  should  be  specified  if  the addr_mode is
                          "slaac" or "dhcpv6_stateless". The value should be an IPv6 prefix which
                          will  be used for stateless IPv6 address configuration. This option can
                          be defined multiple times.

                   Result: stored to a 1-bit subfield R.

                   Valid only in the ingress pipeline.

                   When this action is applied to an IPv6 Router solicitation request packet,  it
                   changes  the  packet  into  an  IPv6  Router  Advertisement reply and adds the
                   options specified in the parameters, and stores 1 in R.

                   When this action is applied to a non-IPv6 Router  solicitation  packet  or  an
                   invalid  IPv6  request packet , it leaves the packet unchanged and stores 0 in
                   R.

                   Example:   reg0[3]   =   put_nd_ra_opts(addr_mode   =    "slaac",    slla    =
                   00:00:00:00:10:02, prefix = aef0::/64, mtu = 1450);

              set_meter(rate);
              set_meter(rate, burst);
                   Parameters:  rate  limit  int  field rate in kbps, burst rate limits int field
                   burst in kbps.

                   This action sets the rate limit for a flow.

                   Example: set_meter(100, 1000);

              R = check_pkt_larger(L)
                   Parameters: packet length L to check for in bytes.

                   Result: stored to a 1-bit subfield R.

                   This is a logical equivalent of the OpenFlow check_pkt_larger action.  If  the
                   packet  is  larger than the length specified in L, it stores 1 in the subfield
                   R.

                   Example: reg0[6] = check_pkt_larger(1000);

              log(key=value, ...);
                     Causes ovn-controller to log the packet on the chassis  that  processes  it.
                     Packet  logging  currently  uses  the  same  logging mechanism as other Open
                     vSwitch and OVN messages, which means that whether and  where  log  messages
                     appear  depends  on  the  local logging configuration that can be configured
                     with ovs-appctl, etc.

                     The log action takes zero or more of the following key-value pair  arguments
                     that control what is logged:

                     name=string
                            An  optional  name for the ACL. The string is currently limited to 64
                            bytes.

                     severity=level
                            Indicates the severity of the event. The level is  one  of  following
                            (from  more to less serious): alert, warning, notice, info, or debug.
                            If a severity is not provided, the default is info.

                     verdict=value
                            The verdict for packets matching the flow. The value must be  one  of
                            allow, deny, or reject.

                     meter=string
                            An optional rate-limiting meter to be applied to the logs. The string
                            should reference a name entry from the Meter table.  The  only  meter
                            action that is appriopriate is drop.

              fwd_group(P);
                     Parameters: liveness, list of child ports P.

                     It  load  balances  traffic  to one or more child ports in a logical switch.
                     ovn-controller translates the fwd_group into openflow group with one  bucket
                     for  each  child  port.  If  liveness is set to true, it also integrates the
                     bucket selection with BFD status on the tunnel  interface  corresponding  to
                     child port.

                     Example: fwd_group(liveness=true, childports=p1,p2

              icmp4 { action; ... };
              icmp4_error { action; ... };
                   Temporarily  replaces  the IPv4 packet being processed by an ICMPv4 packet and
                   executes each nested action on the  ICMPv4  packet.  Actions  following  these
                   actions, if any, apply to the original, unmodified packet.

                   The  ICMPv4  packet that these actions operates on is initialized based on the
                   IPv4 packet being processed, as follows. These are  default  values  that  the
                   nested  actions  will  probably  want  to change. Ethernet and IPv4 fields not
                   listed here are not changed:

                   •      ip.proto = 1 (ICMPv4)

                   •      ip.frag = 0 (not a fragment)

                   •      ip.ttl = 255icmp4.type = 3 (destination unreachable)

                   •      icmp4.code = 1 (host unreachable)

                   icmp4_error action is expected to be used to  generate  an  ICMPv4  packet  in
                   response  to  an  error  in original IP packet. When this action generates the
                   ICMPv4 packet, it also copies the original IP datagram  following  the  ICMPv4
                   header as per RFC 1122: 3.2.2.

                   Prerequisite: ip4

              icmp6 { action; ... };
                   Temporarily  replaces  the IPv6 packet being processed by an ICMPv6 packet and
                   executes each nested action on the ICMPv6 packet. Actions following the  icmp6
                   action, if any, apply to the original, unmodified packet.

                   The  ICMPv6  packet  that  this action operates on is initialized based on the
                   IPv6 packet being processed, as follows. These are  default  values  that  the
                   nested  actions  will  probably  want  to change. Ethernet and IPv6 fields not
                   listed here are not changed:

                   •      ip.proto = 58 (ICMPv6)

                   •      ip.ttl = 255icmp6.type = 1 (destination unreachable)

                   •      icmp6.code = 1 (administratively prohibited)

                   Prerequisite: ip6

              tcp_reset;
                   This action transforms the current  TCP  packet  according  to  the  following
                   pseudocode:

                   if (tcp.ack) {
                           tcp.seq = tcp.ack;
                   } else {
                           tcp.ack = tcp.seq + length(tcp.payload);
                           tcp.seq = 0;
                   }
                   tcp.flags = RST;

                   Then,  the  action drops all TCP options and payload data, and updates the TCP
                   checksum. IP ttl is set to 255.

                   Prerequisite: tcp

              trigger_event;
                   This action is used to allow ovs-vswitchd to report CMS related events writing
                   them  in Controller_Event table. It is possible to associate a meter to a each
                   event in order to not overload pinctrl thread under heavy load; each meter  is
                   identified though a defined naming convention. Supported events:

                   •      empty_lb_backends.  This  event  is  raised  if  a  received  packet is
                          destined for a  load  balancer  VIP  that  has  no  configured  backend
                          destinations. For this event, the event info includes the load balancer
                          VIP, the load balancer UUID, and  the  transport  protocol.  Associated
                          meter: event-elb

              igmp;
                   This action sends the packet to ovn-controller for multicast snooping.

                   Prerequisite: igmp

              bind_vport(V, P);
                   Parameters:  logical  port string field V of type virtual, logical port string
                   field P.

                   Binds  the  virtual  logical  port  V  and  sets  the   chassis   column   and
                   virtual_parent of the table Port_Binding. virtual_parent is set to P.

              handle_svc_check(P);
                   Parameters: logical port string field P.

                   Handles the service monitor reply received from the VIF of the logical port P.
                   ovn-controller periodically sends out the  service  monitor  packets  for  the
                   services  configured  in the Service_Monitor table and this action updates the
                   status of those services.

                   Example: handle_svc_check(inport);

              R = select(N1[=W1], N2[=W2], ...);
                   Parameters: Integer N1, N2..., with optional weight W1, W2, ...

                   Result: stored to a logical field or subfield R.

                   Select from a list of integers N1, N2..., each within the range 0 ~ 65535, and
                   store  the  selected  one  in  the  field  R. There must be 2 or more integers
                   listed, each with an optional weight, which is an integer within the range 1 ~
                   65535. If weight is not specified, it defaults to 100. The selection method is
                   based on the 5-tuple hash of packet header.

                   Processing automatically moves  on  to  the  next  table,  as  if  next;  were
                   specified.  The  select  action  must be put as the last action of the logical
                   flow when there are multiple actions (actions put after select will  not  take
                   effect).

                   Example: reg8[16..31] = select(1=20, 2=30, 3=50);

       external_ids : stage-name: optional string
              Human-readable name for this flow’s stage in the pipeline.

       external_ids : stage-hint: optional string, containing an uuid
              UUID  of  a  OVN_Northbound  record  that  caused  this logical flow to be created.
              Currently used only for attribute of logical flows to northbound ACL records.

       external_ids : source: optional string
              Source file and line number of the code that added this flow to the pipeline.

     Common Columns:

       The overall purpose of these columns is described under Common Columns at the beginning of
       this document.

       external_ids: map of string-string pairs

Multicast_Group TABLE

       The  rows in this table define multicast groups of logical ports. Multicast groups allow a
       single packet transmitted over a tunnel to a hypervisor to be delivered to multiple VMs on
       that hypervisor, which uses bandwidth more efficiently.

       Each  row  in  this  table  defines  a  logical multicast group numbered tunnel_key within
       datapath, whose logical ports are listed in the ports column.

   Summary:
       datapath                      Datapath_Binding
       tunnel_key                    integer, in range 32,768 to 65,535
       name                          string
       ports                         set of 1 or more weak reference to Port_Bindings

   Details:
       datapath: Datapath_Binding
              The logical datapath in which the multicast group resides.

       tunnel_key: integer, in range 32,768 to 65,535
              The value used to designate this logical egress port in tunnel  encapsulations.  An
              index  forces  the  key to be unique within the datapath. The unusual range ensures
              that multicast group IDs do not overlap with logical port IDs.

       name: string
              The logical multicast group’s name. An index forces the name to  be  unique  within
              the datapath. Logical flows in the ingress pipeline may output to the group just as
              for individual logical  ports,  by  assigning  the  group’s  name  to  outport  and
              executing an output action.

              Multicast  group  names  and  logical  port names share a single namespace and thus
              should not overlap (but the database schema cannot enforce this). To try  to  avoid
              conflicts, ovn-northd uses names that begin with _MC_.

       ports: set of 1 or more weak reference to Port_Bindings
              The  logical  ports  included in the multicast group. All of these ports must be in
              the datapath logical datapath (but the database schema cannot enforce this).

Meter TABLE

       Each row in this table represents a meter that can be used for QoS or rate-limiting.

   Summary:
       name                          string (must be unique within table)
       unit                          string, either kbps or pktps
       bands                         set of 1 or more Meter_Bands

   Details:
       name: string (must be unique within table)
              A name for this meter.

              Names that begin with "__" (two underscores) are reserved for OVN internal use  and
              should not be added manually.

       unit: string, either kbps or pktps
              The  unit  for  rate  and  burst_rate parameters in the bands entry. kbps specifies
              kilobits per second, and pktps specifies packets per second.

       bands: set of 1 or more Meter_Bands
              The bands associated with this meter. Each band specifies a rate  above  which  the
              band  is to take the action action. If multiple bands’ rates are exceeded, then the
              band with the highest rate among the exceeded bands is selected.

Meter_Band TABLE

       Each row in this table represents a meter band which specifies the rate  above  which  the
       configured action should be applied. These bands are referenced by the bands column in the
       Meter table.

   Summary:
       action                        string, must be drop
       rate                          integer, in range 1 to 4,294,967,295
       burst_size                    integer, in range 0 to 4,294,967,295

   Details:
       action: string, must be drop
              The action to execute when this band matches. The only supported action is drop.

       rate: integer, in range 1 to 4,294,967,295
              The rate limit for this band, in kilobits per second or bits per second,  depending
              on whether the parent Meter entry’s unit column specified kbps or pktps.

       burst_size: integer, in range 0 to 4,294,967,295
              The maximum burst allowed for the band in kilobits or packets, depending on whether
              kbps or pktps was selected in the parent Meter entry’s unit column. If the size  is
              zero,  the  switch  is  free  to  select  some  reasonable  value  depending on its
              configuration.

Datapath_Binding TABLE

       Each row in this table represents a logical datapath, which implements a logical  pipeline
       among the ports in the Port_Binding table associated with it. In practice, the pipeline in
       a given logical datapath implements either a logical switch or a logical router.

       The main purpose of a row in this table is  provide  a  physical  binding  for  a  logical
       datapath.  A  logical  datapath does not have a physical location, so its physical binding
       information is limited: just tunnel_key. The rest of the  data  in  this  table  does  not
       affect packet forwarding.

   Summary:
       tunnel_key                    integer,  in  range  1  to 16,777,215 (must be unique within
                                     table)
       OVN_Northbound Relationship:
         external_ids : logical-switch
                                     optional string, containing an uuid
         external_ids : logical-router
                                     optional string, containing an uuid
         external_ids : interconn-ts
                                     optional string
         Naming:
            external_ids : name      optional string
            external_ids : name2     optional string
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       tunnel_key: integer, in range 1 to 16,777,215 (must be unique within table)
              The  tunnel  key  value  to  which  the  logical  datapath  is  bound.  The  Tunnel
              Encapsulation   section  in  ovn-architecture(7)  describes  how  tunnel  keys  are
              constructed for each supported encapsulation.

     OVN_Northbound Relationship:

       Each row in Datapath_Binding is associated with some  logical  datapath.  ovn-northd  uses
       these  keys  to  track  the  association  of  a  logical  datapath  with  concepts  in the
       OVN_Northbound database.

       external_ids : logical-switch: optional string, containing an uuid
              For a logical datapath that represents a logical switch, ovn-northd stores in  this
              key  the  UUID  of  the  corresponding  Logical_Switch  row  in  the OVN_Northbound
              database.

       external_ids : logical-router: optional string, containing an uuid
              For a logical datapath that represents a logical router, ovn-northd stores in  this
              key  the  UUID  of  the  corresponding  Logical_Router  row  in  the OVN_Northbound
              database.

       external_ids : interconn-ts: optional string
              For a logical datapath that represents a logical switch that represents  a  transit
              switch  for  interconnection,  ovn-northd  stores in this key the value of the same
              interconn-ts key of the external_ids column of the corresponding Logical_Switch row
              in the OVN_Northbound database.

     Naming:

       ovn-northd  copies  these from the name fields in the OVN_Northbound database, either from
       name and external_ids:neutron:router_name in the Logical_Router table  or  from  name  and
       external_ids:neutron:network_name in the Logical_Switch table.

       external_ids : name: optional string
              A name for the logical datapath.

       external_ids : name2: optional string
              Another name for the logical datapath.

     Common Columns:

       The overall purpose of these columns is described under Common Columns at the beginning of
       this document.

       external_ids: map of string-string pairs

Port_Binding TABLE

       Each row in this table binds a logical port to a realization. For most logical ports, this
       means  binding  to  some physical location, for example by binding a logical port to a VIF
       that belongs to a VM running on a particular hypervisor.  Other  logical  ports,  such  as
       logical  patch  ports,  can  be  realized  without a specific physical location, but their
       bindings are still expressed through rows in this table.

       For every Logical_Switch_Port record in  OVN_Northbound  database,  ovn-northd  creates  a
       record  in  this table. ovn-northd populates and maintains every column except the chassis
       column, which it leaves empty in new records.

       ovn-controller/ovn-controller-vtep populates the  chassis  column  for  the  records  that
       identify   the   logical   ports   that  are  located  on  its  hypervisor/gateway,  which
       ovn-controller/ovn-controller-vtep in turn finds out by monitoring the local  hypervisor’s
       Open_vSwitch  database,  which  identifies  logical ports via the conventions described in
       IntegrationGuide.rst. (The exceptions are for Port_Binding records with type of l3gateway,
       whose  locations  are identified by ovn-northd via the options:l3gateway-chassis column in
       this table. ovn-controller is still responsible to populate the chassis column.)

       When a chassis shuts down gracefully, it should  clean  up  the  chassis  column  that  it
       previously  had  populated.  (This is not critical because resources hosted on the chassis
       are equally unreachable regardless of whether their rows are present.) To handle the  case
       where a VM is shut down abruptly on one chassis, then brought up again on a different one,
       ovn-controller/ovn-controller-vtep must overwrite the chassis column with new information.

   Summary:
       Core Features:
         datapath                    Datapath_Binding
         logical_port                string (must be unique within table)
         encap                       optional weak reference to Encap
         chassis                     optional weak reference to Chassis
         gateway_chassis             set of Gateway_Chassiss
         ha_chassis_group            optional HA_Chassis_Group
         tunnel_key                  integer, in range 1 to 32,767
         mac                         set of strings
         type                        string
       Patch Options:
         options : peer              optional string
         nat_addresses               set of strings
       L3 Gateway Options:
         options : peer              optional string
         options : l3gateway-chassis
                                     optional string
         options : nat-addresses     optional string
         nat_addresses               set of strings
       Localnet Options:
         options : network_name      optional string
         tag                         optional integer, in range 1 to 4,095
       L2 Gateway Options:
         options : network_name      optional string
         options : l2gateway-chassis
                                     optional string
         tag                         optional integer, in range 1 to 4,095
       VTEP Options:
         options : vtep-physical-switch
                                     optional string
         options : vtep-logical-switch
                                     optional string
       VMI (or VIF) Options:
         options : requested-chassis
                                     optional string
         options : qos_max_rate      optional string
         options : qos_burst         optional string
         options : qdisc_queue_id    optional string, containing an integer, in range 1 to 61,440
       Chassis Redirect Options:
         options : distributed-port  optional string
         options : redirect-chassis  optional string
       Nested Containers:
         parent_port                 optional string
         tag                         optional integer, in range 1 to 4,095
       Virtual ports:
         virtual_parent              optional string
       Naming:
         external_ids : name         optional string
       Common Columns:
         external_ids                map of string-string pairs

   Details:
     Core Features:

       datapath: Datapath_Binding
              The logical datapath to which the logical port belongs.

       logical_port: string (must be unique within table)
              A   logical   port,   taken   from   name   in   the   OVN_Northbound    database’s
              Logical_Switch_Port  table.  OVN  does  not  prescribe  a particular format for the
              logical port ID.

       encap: optional weak reference to Encap
              Points to supported encapsulation  configurations  to  transmit  logical  dataplane
              packets  to  this  chassis.  Each  entry  is  a  Encap  record  that  describes the
              configuration.

       chassis: optional weak reference to Chassis
              The meaning of this column depends on the value of the type  column.  This  is  the
              meaning for each type

              (empty string)
                     The  physical  location  of  the  logical  port.  To successfully identify a
                     chassis, this column  must  be  a  Chassis  record.  This  is  populated  by
                     ovn-controller.

              vtep   The physical location of the hardware_vtep gateway. To successfully identify
                     a chassis, this column must be  a  Chassis  record.  This  is  populated  by
                     ovn-controller-vtep.

              localnet
                     Always  empty.  A  localnet  port  is  realized  on  every  chassis that has
                     connectivity to the corresponding physical network.

              localport
                     Always empty. A localport port is present on every chassis.

              l3gateway
                     The physical location of the L3 gateway. To successfully identify a chassis,
                     this  column  must  be a Chassis record. This is populated by ovn-controller
                     based on the value of the options:l3gateway-chassis column in this table.

              l2gateway
                     The physical location  of  this  L2  gateway.  To  successfully  identify  a
                     chassis,  this  column  must  be  a  Chassis  record.  This  is populated by
                     ovn-controller based on the value of the options:l2gateway-chassis column in
                     this table.

       gateway_chassis: set of Gateway_Chassiss
              A list of Gateway_Chassis.

              This  should  only  be  populated  for ports with type set to chassisredirect. This
              column defines the  list  of  chassis  used  as  gateways  where  traffic  will  be
              redirected through.

       ha_chassis_group: optional HA_Chassis_Group
              This  should  only  be  populated  for ports with type set to chassisredirect. This
              column defines the HA chassis group with a list of  HA  chassis  used  as  gateways
              where traffic will be redirected through.

       tunnel_key: integer, in range 1 to 32,767
              A  number  that represents the logical port in the key (e.g. STT key or Geneve TLV)
              field carried within tunnel protocol packets.

              The tunnel ID must be unique within the scope of a logical datapath.

       mac: set of strings
              The Ethernet address or addresses used as a source address  on  the  logical  port,
              each  in the form xx:xx:xx:xx:xx:xx. The string unknown is also allowed to indicate
              that the logical port has an unknown set of (additional) source addresses.

              A VM interface would ordinarily have a single  Ethernet  address.  A  gateway  port
              might  initially  only  have  unknown,  and then add MAC addresses to the set as it
              learns new source addresses.

       type: string
              A type for this logical port. Logical ports can be used to  model  other  types  of
              connectivity into an OVN logical switch. The following types are defined:

              (empty string)
                     VM (or VIF) interface.

              patch  One  of  a  pair of logical ports that act as if connected by a patch cable.
                     Useful for connecting two logical  datapaths,  e.g.  to  connect  a  logical
                     router to a logical switch or to another logical router.

              l3gateway
                     One  of  a  pair  of logical ports that act as if connected by a patch cable
                     across multiple chassis. Useful for  connecting  a  logical  switch  with  a
                     Gateway router (which is only resident on a particular chassis).

              localnet
                     A  connection  to  a  locally  accessible  network  from each ovn-controller
                     instance. A logical switch can only have a single  localnet  port  attached.
                     This is used to model direct connectivity to an existing network.

              localport
                     A  connection  to  a local VIF. Traffic that arrives on a localport is never
                     forwarded over a tunnel to another chassis. These ports are present on every
                     chassis  and  have  the  same  address in all of them. This is used to model
                     connectivity to local services that run on every hypervisor.

              l2gateway
                     An L2 connection to a physical network. The  chassis  this  Port_Binding  is
                     bound   to   will   serve   as  an  L2  gateway  to  the  network  named  by
                     options:network_name.

              vtep   A port to a logical switch on a VTEP gateway chassis. In order to  get  this
                     port     correctly     recognized     by    the    OVN    controller,    the
                     options:vtep-physical-switch and options:vtep-logical-switch  must  also  be
                     defined.

              chassisredirect
                     A  logical  port  that represents a particular instance, bound to a specific
                     chassis, of an otherwise distributed parent port (e.g.  of  type  patch).  A
                     chassisredirect  port  should  never  be  used as an inport. When an ingress
                     pipeline sets the outport, it may set the value to a logical  port  of  type
                     chassisredirect.  This  will  cause  the packet to be directed to a specific
                     chassis to carry out the egress pipeline. At the  beginning  of  the  egress
                     pipeline, the outport will be reset to the value of the distributed port.

              virtual
                     Represents  a  logical  port  with  an  virtual  ip.  This virtual ip can be
                     configured on a logical port (which is refered as virtual parent).

     Patch Options:

       These options apply to logical ports with type of patch.

       options : peer: optional string
              The logical_port in the Port_Binding record for the other side of  the  patch.  The
              named  logical_port must specify this logical_port in its own peer option. That is,
              the two patch logical ports must have reversed logical_port and peer values.

       nat_addresses: set of strings
              MAC address followed by a list of SNAT and DNAT external IP addresses, followed  by
              is_chassis_resident("lport"), where lport is the name of a logical port on the same
              chassis where the corresponding NAT  rules  are  applied.  This  is  used  to  send
              gratuitous  ARPs  for  SNAT  and  DNAT external IP addresses via localnet, from the
              chassis where lport resides. Example: 80:fa:5b:06:72:b7  158.36.44.22  158.36.44.24
              is_chassis_resident("foo1"). This would result in generation of gratuitous ARPs for
              IP addresses 158.36.44.22 and 158.36.44.24 with a MAC address of  80:fa:5b:06:72:b7
              from the chassis where the logical port "foo1" resides.

     L3 Gateway Options:

       These options apply to logical ports with type of l3gateway.

       options : peer: optional string
              The  logical_port  in the Port_Binding record for the other side of the ’l3gateway’
              port. The named logical_port must specify this logical_port in its own peer option.
              That is, the two ’l3gateway’ logical ports must have reversed logical_port and peer
              values.

       options : l3gateway-chassis: optional string
              The chassis in which the port resides.

       options : nat-addresses: optional string
              MAC address of the l3gateway port followed by a list of SNAT and DNAT  external  IP
              addresses.  This  is  used  to  send  gratuitous ARPs for SNAT and DNAT external IP
              addresses via localnet. Example: 80:fa:5b:06:72:b7 158.36.44.22 158.36.44.24.  This
              would  result  in  generation  of gratuitous ARPs for IP addresses 158.36.44.22 and
              158.36.44.24 with a MAC address of 80:fa:5b:06:72:b7. This is used in OVS  versions
              prior to 2.8.

       nat_addresses: set of strings
              MAC  address  of the l3gateway port followed by a list of SNAT and DNAT external IP
              addresses. This is used to send gratuitous ARPs  for  SNAT  and  DNAT  external  IP
              addresses  via localnet. Example: 80:fa:5b:06:72:b7 158.36.44.22 158.36.44.24. This
              would result in generation of gratuitous ARPs for  IP  addresses  158.36.44.22  and
              158.36.44.24  with  a MAC address of 80:fa:5b:06:72:b7. This is used in OVS version
              2.8 and later versions.

     Localnet Options:

       These options apply to logical ports with type of localnet.

       options : network_name: optional string
              Required.  ovn-controller  uses  the  configuration  entry  ovn-bridge-mappings  to
              determine  how to connect to this network. ovn-bridge-mappings is a list of network
              names mapped to a local OVS bridge that provides access to that network. An example
              of configuring ovn-bridge-mappings would be: .IP
              $ ovs-vsctl set open . external-ids:ovn-bridge-mappings=physnet1:br-eth0,physnet2:br-eth1

              When  a  logical switch has a localnet port attached, every chassis that may have a
              local vif attached to that logical switch must have a bridge mapping configured  to
              reach  that  localnet.  Traffic  that arrives on a localnet port is never forwarded
              over a tunnel to another chassis.

       tag: optional integer, in range 1 to 4,095
              If set, indicates that the port represents a connection to a  specific  VLAN  on  a
              locally  accessible  network.  The VLAN ID is used to match incoming traffic and is
              also added to outgoing traffic.

     L2 Gateway Options:

       These options apply to logical ports with type of l2gateway.

       options : network_name: optional string
              Required.  ovn-controller  uses  the  configuration  entry  ovn-bridge-mappings  to
              determine  how to connect to this network. ovn-bridge-mappings is a list of network
              names mapped to a local OVS bridge that provides access to that network. An example
              of configuring ovn-bridge-mappings would be: .IP
              $ ovs-vsctl set open . external-ids:ovn-bridge-mappings=physnet1:br-eth0,physnet2:br-eth1

              When a logical switch has a l2gateway port attached, the chassis that the l2gateway
              port is bound to must have  a  bridge  mapping  configured  to  reach  the  network
              identified by network_name.

       options : l2gateway-chassis: optional string
              Required. The chassis in which the port resides.

       tag: optional integer, in range 1 to 4,095
              If  set, indicates that the gateway is connected to a specific VLAN on the physical
              network. The VLAN ID is used to  match  incoming  traffic  and  is  also  added  to
              outgoing traffic.

     VTEP Options:

       These options apply to logical ports with type of vtep.

       options : vtep-physical-switch: optional string
              Required. The name of the VTEP gateway.

       options : vtep-logical-switch: optional string
              Required.  A  logical  switch  name connected by the VTEP gateway. Must be set when
              type is vtep.

     VMI (or VIF) Options:

       These options apply to logical ports with type having (empty string)

       options : requested-chassis: optional string
              If set, identifies a specific chassis (by name or hostname) that is allowed to bind
              this  port.  Using this option will prevent thrashing between two chassis trying to
              bind the same port during a live migration. It can also prevent  similar  thrashing
              due  to  a  mis-configuration,  if  a port is accidentally created on more than one
              chassis.

       options : qos_max_rate: optional string
              If set, indicates the maximum rate for data sent from this interface, in bit/s. The
              traffic will be shaped according to this limit.

       options : qos_burst: optional string
              If  set,  indicates  the  maximum  burst size for data sent from this interface, in
              bits.

       options : qdisc_queue_id: optional string, containing an integer, in range 1 to 61,440
              Indicates the queue number on the physical device. This is  same  as  the  queue_id
              used in OpenFlow in struct ofp_action_enqueue.

     Chassis Redirect Options:

       These options apply to logical ports with type of chassisredirect.

       options : distributed-port: optional string
              The  name  of the distributed port for which this chassisredirect port represents a
              particular instance.

       options : redirect-chassis: optional string
              The chassis that this  chassisredirect  port  is  bound  to.  This  is  taken  from
              options:redirect-chassis   in  the  OVN_Northbound  database’s  Logical_Router_Port
              table.

     Nested Containers:

       These columns support containers nested within a VM. Specifically, they are used when type
       is  empty  and  logical_port  identifies the interface of a container spawned inside a VM.
       They are empty for containers or VMs that run directly on a hypervisor.

       parent_port: optional string
              This is taken from parent_name in the OVN_Northbound database’s Logical_Switch_Port
              table.

       tag: optional integer, in range 1 to 4,095
              Identifies  the  VLAN  tag  in the network traffic associated with that container’s
              network interface.

              This column is used for a different purpose when type  is  localnet  (see  Localnet
              Options, above) or l2gateway (see L2 Gateway Options, above).

     Virtual ports:

       virtual_parent: optional string
              This   column   is   set   by  ovn-controller  with  one  of  the  value  from  the
              options:virtual-parents in the OVN_Northbound database’s Logical_Switch_Port  table
              when  the  OVN  action bind_vport is executed. ovn-controller also sets the chassis
              column when it executes this action with its chassis id.

              ovn-controller sets this column only if the type is "virtual".

     Naming:

       external_ids : name: optional string
              For    a    logical    switch     port,     ovn-northd     copies     this     from
              external_ids:neutron:port_name    in   the   Logical_Switch_Port   table   in   the
              OVN_Northbound database, if it is a nonempty string.

              For a logical switch port, ovn-northd does not currently set this key.

     Common Columns:

       external_ids: map of string-string pairs
              See External IDs at the beginning of this document.

              The ovn-northd program populates this column with all entries into the external_ids
              column of the Logical_Switch_Port table of the OVN_Northbound database.

MAC_Binding TABLE

       Each  row in this table specifies a binding from an IP address to an Ethernet address that
       has been discovered through ARP (for IPv4) or neighbor discovery (for IPv6). This table is
       primarily  used  to discover bindings on physical networks, because IP-to-MAC bindings for
       virtual machines are usually populated statically into the Port_Binding table.

       This table expresses a functional relationship: MAC_Binding(logical_port, ip) = mac.

       In outline, the lifetime of a logical router’s MAC binding looks like this:

              1.  On hypervisor 1, a logical router determines that a packet should be  forwarded
                  to  IP  address A on one of its router ports. It uses its logical flow table to
                  determine that A lacks a static IP-to-MAC binding and  the  get_arp  action  to
                  determine that it lacks a dynamic IP-to-MAC binding.

              2.  Using  an  OVN  logical  arp  action,  the logical router generates and sends a
                  broadcast ARP request to the router port. It drops the IP packet.

              3.  The logical switch attached to the router port delivers the ARP request to  all
                  of  its  ports.  (It  might make sense to deliver it only to ports that have no
                  static IP-to-MAC bindings, but this could also be surprising behavior.)

              4.  A host or VM on hypervisor 2 (which might be the same as hypervisor 1) attached
                  to the logical switch owns the IP address in question. It composes an ARP reply
                  and unicasts it to the logical router port’s Ethernet address.

              5.  The logical switch delivers the ARP reply to the logical router port.

              6.  The logical router flow table executes a put_arp action. To record  the  IP-to-
                  MAC binding, ovn-controller adds a row to the MAC_Binding table.

              7.  On hypervisor 1, ovn-controller receives the updated MAC_Binding table from the
                  OVN southbound database. The next packet destined  to  A  through  the  logical
                  router is sent directly to the bound Ethernet address.

   Summary:
       logical_port                  string
       ip                            string
       mac                           string
       datapath                      Datapath_Binding

   Details:
       logical_port: string
              The logical port on which the binding was discovered.

       ip: string
              The bound IP address.

       mac: string
              The Ethernet address to which the IP is bound.

       datapath: Datapath_Binding
              The logical datapath to which the logical port belongs.

DHCP_Options TABLE

       Each  row  in  this table stores the DHCP Options supported by native OVN DHCP. ovn-northd
       populates this table with the supported DHCP options. ovn-controller looks up  this  table
       to  get  the  DHCP codes of the DHCP options defined in the "put_dhcp_opts" action. Please
       refer to the RFC 2132 "https://tools.ietf.org/html/rfc2132" for the possible list of  DHCP
       options that can be defined here.

   Summary:
       name                          string
       code                          integer, in range 0 to 254
       type                          string,  one  of  bool,  ipv4,  static_routes,  str, uint16,
                                     uint32, or uint8

   Details:
       name: string
              Name of the DHCP option.

              Example. name="router"

       code: integer, in range 0 to 254
              DHCP option code for the DHCP option as defined in the RFC 2132.

              Example. code=3

       type: string, one of bool, ipv4, static_routes, str, uint16, uint32, or uint8
              Data type of the DHCP option code.

              value: bool
                     This indicates that the value of the DHCP option is a bool.

                     Example. "name=ip_forward_enable", "code=19", "type=bool".

                     put_dhcp_opts(..., ip_forward_enable = 1,...)

              value: uint8
                     This indicates that the value of the DHCP option  is  an  unsigned  int8  (8
                     bits)

                     Example. "name=default_ttl", "code=23", "type=uint8".

                     put_dhcp_opts(..., default_ttl = 50,...)

              value: uint16
                     This  indicates  that  the value of the DHCP option is an unsigned int16 (16
                     bits).

                     Example. "name=mtu", "code=26", "type=uint16".

                     put_dhcp_opts(..., mtu = 1450,...)

              value: uint32
                     This indicates that the value of the DHCP option is an  unsigned  int32  (32
                     bits).

                     Example. "name=lease_time", "code=51", "type=uint32".

                     put_dhcp_opts(..., lease_time = 86400,...)

              value: ipv4
                     This  indicates  that  the  value  of  the DHCP option is an IPv4 address or
                     addresses.

                     Example. "name=router", "code=3", "type=ipv4".

                     put_dhcp_opts(..., router = 10.0.0.1,...)

                     Example. "name=dns_server", "code=6", "type=ipv4".

                     put_dhcp_opts(..., dns_server = {8.8.8.8 7.7.7.7},...)

              value: static_routes
                     This indicates that the value of the DHCP option contains  a  pair  of  IPv4
                     route and next hop addresses.

                     Example. "name=classless_static_route", "code=121", "type=static_routes".

                     put_dhcp_opts(...,                  classless_static_route                 =
                     {30.0.0.0/24,10.0.0.4,0.0.0.0/0,10.0.0.1}...)

              value: str
                     This indicates that the value of the DHCP option is a string.

                     Example. "name=host_name", "code=12", "type=str".

DHCPv6_Options TABLE

       Each row in this  table  stores  the  DHCPv6  Options  supported  by  native  OVN  DHCPv6.
       ovn-northd populates this table with the supported DHCPv6 options. ovn-controller looks up
       this table to get the DHCPv6 codes of the DHCPv6 options defined  in  the  put_dhcpv6_opts
       action.  Please  refer to RFC 3315 and RFC 3646 for the list of DHCPv6 options that can be
       defined here.

   Summary:
       name                          string
       code                          integer, in range 0 to 254
       type                          string, one of ipv6, mac, or str

   Details:
       name: string
              Name of the DHCPv6 option.

              Example. name="ia_addr"

       code: integer, in range 0 to 254
              DHCPv6 option code for the DHCPv6 option as defined in the appropriate RFC.

              Example. code=3

       type: string, one of ipv6, mac, or str
              Data type of the DHCPv6 option code.

              value: ipv6
                     This indicates that the value of the DHCPv6 option is an IPv6 address(es).

                     Example. "name=ia_addr", "code=5", "type=ipv6".

                     put_dhcpv6_opts(..., ia_addr = ae70::4,...)

              value: str
                     This indicates that the value of the DHCPv6 option is a string.

                     Example. "name=domain_search", "code=24", "type=str".

                     put_dhcpv6_opts(..., domain_search = ovn.domain,...)

              value: mac
                     This indicates that the value of the DHCPv6 option is a MAC address.

                     Example. "name=server_id", "code=2", "type=mac".

                     put_dhcpv6_opts(..., server_id = 01:02:03:04L05:06,...)

Connection TABLE

       Configuration for a database connection to an Open vSwitch database (OVSDB) client.

       This table primarily configures the Open vSwitch database server (ovsdb-server).

       The Open vSwitch database server can initiate and maintain active  connections  to  remote
       clients. It can also listen for database connections.

   Summary:
       Core Features:
         target                      string (must be unique within table)
         read_only                   boolean
         role                        string
       Client Failure Detection and Handling:
         max_backoff                 optional integer, at least 1,000
         inactivity_probe            optional integer
       Status:
         is_connected                boolean
         status : last_error         optional string
         status : state              optional  string,  one of ACTIVE, BACKOFF, CONNECTING, IDLE,
                                     or VOID
         status : sec_since_connect  optional string, containing an integer, at least 0
         status : sec_since_disconnect
                                     optional string, containing an integer, at least 0
         status : locks_held         optional string
         status : locks_waiting      optional string
         status : locks_lost         optional string
         status : n_connections      optional string, containing an integer, at least 2
         status : bound_port         optional string, containing an integer
       Common Columns:
         external_ids                map of string-string pairs
         other_config                map of string-string pairs

   Details:
     Core Features:

       target: string (must be unique within table)
              Connection methods for clients.

              The following connection methods are currently supported:

              ssl:host[:port]
                     The specified SSL port on the given host, which can either be a DNS name (if
                     built with unbound library) or an IP address. A valid SSL configuration must
                     be provided when this form is used, this configuration can be specified  via
                     command-line options or the SSL table.

                     If port is not specified, it defaults to 6640.

                     SSL  support is an optional feature that is not always built as part of Open
                     vSwitch.

              tcp:host[:port]
                     The specified TCP port on the given host, which can either be a DNS name (if
                     built  with  unbound library) or an IP address (IPv4 or IPv6). If host is an
                     IPv6 address, wrap it in square brackets, e.g. tcp:[::1]:6640.

                     If port is not specified, it defaults to 6640.

              pssl:[port][:host]
                     Listens for SSL connections on the specified TCP port. Specify 0 for port to
                     have  the  kernel automatically choose an available port. If host, which can
                     either be a DNS name (if built with unbound library) or an  IP  address,  is
                     specified,  then  connections  are  restricted  to the resolved or specified
                     local IP address (either IPv4 or IPv6 address). If host is an IPv6  address,
                     wrap in square brackets, e.g. pssl:6640:[::1]. If host is not specified then
                     it listens only on IPv4 (but not IPv6) addresses. A valid SSL  configuration
                     must  be  provided  when this form is used, this can be specified either via
                     command-line options or the SSL table.

                     If port is not specified, it defaults to 6640.

                     SSL support is an optional feature that is not always built as part of  Open
                     vSwitch.

              ptcp:[port][:host]
                     Listens  for  connections  on  the specified TCP port. Specify 0 for port to
                     have the kernel automatically choose an available port. If host,  which  can
                     either  be  a  DNS name (if built with unbound library) or an IP address, is
                     specified, then connections are restricted  to  the  resolved  or  specified
                     local  IP address (either IPv4 or IPv6 address). If host is an IPv6 address,
                     wrap it in square brackets, e.g. ptcp:6640:[::1]. If host is  not  specified
                     then it listens only on IPv4 addresses.

                     If port is not specified, it defaults to 6640.

              When  multiple  clients are configured, the target values must be unique. Duplicate
              target values yield unspecified results.

       read_only: boolean
              true to restrict these connections to read-only transactions, false to  allow  them
              to modify the database.

       role: string
              String containing role name for this connection entry.

     Client Failure Detection and Handling:

       max_backoff: optional integer, at least 1,000
              Maximum  number  of  milliseconds  to  wait between connection attempts. Default is
              implementation-specific.

       inactivity_probe: optional integer
              Maximum number of milliseconds of idle time on  connection  to  the  client  before
              sending  an inactivity probe message. If Open vSwitch does not communicate with the
              client for the specified number of seconds, it will send a probe. If a response  is
              not  received  for  the  same  additional  amount of time, Open vSwitch assumes the
              connection has been broken and attempts to reconnect.  Default  is  implementation-
              specific. A value of 0 disables inactivity probes.

     Status:

       Key-value  pair  of  is_connected  is  always updated. Other key-value pairs in the status
       columns may be updated depends on the target type.

       When target specifies a connection method that listens for inbound connections (e.g. ptcp:
       or  punix:),  both  n_connections and is_connected may also be updated while the remaining
       key-value pairs are omitted.

       On the other hand, when target specifies an outbound connection, all key-value  pairs  may
       be  updated,  except  the  above-mentioned  two  key-value  pairs  associated with inbound
       connection targets. They are omitted.

       is_connected: boolean
              true if currently connected to this client, false otherwise.

       status : last_error: optional string
              A human-readable description of the last error on the connection  to  the  manager;
              i.e. strerror(errno). This key will exist only if an error has occurred.

       status : state: optional string, one of ACTIVE, BACKOFF, CONNECTING, IDLE, or VOID
              The state of the connection to the manager:

              VOID   Connection is disabled.

              BACKOFF
                     Attempting to reconnect at an increasing period.

              CONNECTING
                     Attempting to connect.

              ACTIVE Connected, remote host responsive.

              IDLE   Connection is idle. Waiting for response to keep-alive.

              These  values  may  change  in  the  future.  They  are  provided  only  for  human
              consumption.

       status : sec_since_connect: optional string, containing an integer, at least 0
              The amount of time since this client last successfully connected  to  the  database
              (in seconds). Value is empty if client has never successfully been connected.

       status : sec_since_disconnect: optional string, containing an integer, at least 0
              The  amount  of  time  since  this  client  last disconnected from the database (in
              seconds). Value is empty if client has never disconnected.

       status : locks_held: optional string
              Space-separated list of the names of OVSDB locks that the connection holds. Omitted
              if the connection does not hold any locks.

       status : locks_waiting: optional string
              Space-separated  list  of the names of OVSDB locks that the connection is currently
              waiting to acquire. Omitted if the connection is not waiting for any locks.

       status : locks_lost: optional string
              Space-separated list of the names of OVSDB locks that the connection has had stolen
              by another OVSDB client. Omitted if no locks have been stolen from this connection.

       status : n_connections: optional string, containing an integer, at least 2
              When  target  specifies  a  connection  method that listens for inbound connections
              (e.g. ptcp: or pssl:) and more than one connection is actually active, the value is
              the number of active connections. Otherwise, this key-value pair is omitted.

       status : bound_port: optional string, containing an integer
              When  target  is  ptcp: or pssl:, this is the TCP port on which the OVSDB server is
              listening. (This is particularly useful when target specifies a port of 0, allowing
              the kernel to choose any available port.)

     Common Columns:

       The overall purpose of these columns is described under Common Columns at the beginning of
       this document.

       external_ids: map of string-string pairs

       other_config: map of string-string pairs

SSL TABLE

       SSL configuration for ovn-sb database access.

   Summary:
       private_key                   string
       certificate                   string
       ca_cert                       string
       bootstrap_ca_cert             boolean
       ssl_protocols                 string
       ssl_ciphers                   string
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       private_key: string
              Name of a PEM file containing the private key used as the switch’s identity for SSL
              connections to the controller.

       certificate: string
              Name  of  a  PEM file containing a certificate, signed by the certificate authority
              (CA) used by the controller and manager, that certifies the switch’s  private  key,
              identifying a trustworthy switch.

       ca_cert: string
              Name  of a PEM file containing the CA certificate used to verify that the switch is
              connected to a trustworthy controller.

       bootstrap_ca_cert: boolean
              If set to true, then Open vSwitch will attempt to obtain the  CA  certificate  from
              the controller on its first SSL connection and save it to the named PEM file. If it
              is successful, it will immediately drop the connection and reconnect, and from then
              on  all  SSL  connections  must  be authenticated by a certificate signed by the CA
              certificate  thus  obtained.  This  option  exposes  the  SSL   connection   to   a
              man-in-the-middle  attack  obtaining  the  initial  CA certificate. It may still be
              useful for bootstrapping.

       ssl_protocols: string
              List of SSL protocols to be enabled for SSL  connections.  The  default  when  this
              option is omitted is TLSv1,TLSv1.1,TLSv1.2.

       ssl_ciphers: string
              List  of  ciphers  (in  OpenSSL  cipher  string  format)  to  be  supported for SSL
              connections. The default when this option is omitted is HIGH:!aNULL:!MD5.

     Common Columns:

       The overall purpose of these columns is described under Common Columns at the beginning of
       this document.

       external_ids: map of string-string pairs

DNS TABLE

       Each  row  in this table stores the DNS records. The OVN action dns_lookup uses this table
       for DNS resolution.

   Summary:
       records                       map of string-string pairs
       datapaths                     set of 1 or more Datapath_Bindings
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       records: map of string-string pairs
              Key-value pair of DNS records with DNS query name as the key and  a  string  of  IP
              address(es)  separated  by  comma  or space as the value. ovn-northd stores the DNS
              query name in all lowercase in order to facilitate case-insensitive lookups.

              Example:  "vm1.ovn.org" = "10.0.0.4 aef0::4"

       datapaths: set of 1 or more Datapath_Bindings
              The DNS records defined in the column records will  be  applied  only  to  the  DNS
              queries originating from the datapaths defined in this column.

     Common Columns:

       external_ids: map of string-string pairs
              See External IDs at the beginning of this document.

RBAC_Role TABLE

       Role table for role-based access controls.

   Summary:
       name                          string
       permissions                   map of string-weak reference to RBAC_Permission pairs

   Details:
       name: string
              The role name, corresponding to the role column in the Connection table.

       permissions: map of string-weak reference to RBAC_Permission pairs
              A mapping of table names to rows in the RBAC_Permission table.

RBAC_Permission TABLE

       Permissions table for role-based access controls.

   Summary:
       table                         string
       authorization                 set of strings
       insert_delete                 boolean
       update                        set of strings

   Details:
       table: string
              Name of table to which this row applies.

       authorization: set of strings
              Set  of strings identifying columns and column:key pairs to be compared with client
              ID. At least one match is required in order to be authorized. A zero-length  string
              is  treated  as  a  special  value  indicating  all  clients  should  be considered
              authorized.

       insert_delete: boolean
              When "true", row insertions and authorized row deletions are permitted.

       update: set of strings
              Set of strings identifying columns and column:key pairs that authorized clients are
              allowed to modify.

Gateway_Chassis TABLE

       Association  of  Port_Binding rows of type chassisredirect to a Chassis. The traffic going
       out through a specific chassisredirect port will be redirected to a chassis, or a  set  of
       them in high availability configurations.

   Summary:
       name                          string (must be unique within table)
       chassis                       optional weak reference to Chassis
       priority                      integer, in range 0 to 32,767
       options                       map of string-string pairs
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       name: string (must be unique within table)
              Name of the Gateway_Chassis.

              A suggested, but not required naming convention is ${port_name}_${chassis_name}.

       chassis: optional weak reference to Chassis
              The Chassis to which we send the traffic.

       priority: integer, in range 0 to 32,767
              This  is  the  priority the specific Chassis among all Gateway_Chassis belonging to
              the same Port_Binding.

       options: map of string-string pairs
              Reserved for future use.

     Common Columns:

       The overall purpose of these columns is described under Common Columns at the beginning of
       this document.

       external_ids: map of string-string pairs

HA_Chassis TABLE

   Summary:
       chassis                       optional weak reference to Chassis
       priority                      integer, in range 0 to 32,767
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       chassis: optional weak reference to Chassis
              The Chassis which provides the HA functionality.

       priority: integer, in range 0 to 32,767
              Priority of the HA chassis. Chassis with highest priority will be the master in the
              HA chassis group.

     Common Columns:

       external_ids: map of string-string pairs
              See External IDs at the beginning of this document.

HA_Chassis_Group TABLE

       Table representing a group of chassis which can provide High availability  services.  Each
       chassis  in  the group is represented by the table HA_Chassis. The HA chassis with highest
       priority will be the master of this group. If the master chassis failover is detected, the
       HA  chassis  with  the next higher priority takes over the responsibility of providing the
       HA. If ha_chassis_group column of the table Port_Binding references this table, then  this
       HA  chassis  group provides the gateway functionality and redirects the gateway traffic to
       the master of this group.

   Summary:
       name                          string (must be unique within table)
       ha_chassis                    set of HA_Chassiss
       ref_chassis                   set of weak reference to Chassiss
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       name: string (must be unique within table)
              Name of the HA_Chassis_Group. Name should be unique.

       ha_chassis: set of HA_Chassiss
              A list of HA_Chassis which belongs to this group.

       ref_chassis: set of weak reference to Chassiss
              A list of chassis which references this HA chassis group.

     Common Columns:

       external_ids: map of string-string pairs
              See External IDs at the beginning of this document.

Controller_Event TABLE

       Database table used by ovn-controller to report CMS related events. Please note  there  is
       no  guarantee a given event is written exactly once in the db. It is CMS responsibility to
       squash duplicated lines or to filter out duplicated events

   Summary:
       event_type                    string, must be empty_lb_backends
       event_info                    map of string-string pairs
       chassis                       optional weak reference to Chassis
       seq_num                       integer

   Details:
       event_type: string, must be empty_lb_backends
              Event type occurred

       event_info: map of string-string pairs
              Key-value pairs used to specify event info to the CMS. Possible values are:

              •      vip: VIP reported for the empty_lb_backends event

              •      protocol: Transport protocol reported for the empty_lb_backends event

              •      load_balancer: UUID of the load balancer reported for the  empty_lb_backends
                     event

       chassis: optional weak reference to Chassis
              This  column  is  a Chassis record to identify the chassis that has managed a given
              event.

       seq_num: integer
              Event sequence number. Global counter for controller generated events.  It  can  be
              used by the CMS to detect possible duplication of the same event.

IP_Multicast TABLE

       IP Multicast configuration options. For now only applicable to IGMP.

   Summary:
       datapath                      weak  reference  to  Datapath_Binding (must be unique within
                                     table)
       enabled                       optional boolean
       querier                       optional boolean
       table_size                    optional integer
       idle_timeout                  optional integer
       query_interval                optional integer
       seq_no                        integer
       Querier configuration options:
         eth_src                     string
         ip4_src                     string
         ip6_src                     string
         query_max_resp              optional integer

   Details:
       datapath: weak reference to Datapath_Binding (must be unique within table)
              Datapath_Binding entry for which these configuration options are defined.

       enabled: optional boolean
              Enables/disables multicast snooping. Default: disabled.

       querier: optional boolean
              Enables/disables multicast querying. If enabled then multicast querying is  enabled
              by default.

       table_size: optional integer
              Limits the number of multicast groups that can be learned. Default: 2048 groups per
              datapath.

       idle_timeout: optional integer
              Configures the idle timeout (in seconds)  for  IP  multicast  groups  if  multicast
              snooping is enabled. Default: 300 seconds.

       query_interval: optional integer
              Configures  the interval (in seconds) for sending multicast queries if snooping and
              querier are enabled. Default: idle_timeout/2 seconds.

       seq_no: integer
              ovn-controller reads this value and flushes all learned multicast  groups  when  it
              detects that seq_no was changed.

     Querier configuration options:

       The ovn-controller process that runs on OVN hypervisor nodes uses the following columns to
       determine field values in IGMP/MLD queries that it originates:

       eth_src: string
              Source Ethernet address.

       ip4_src: string
              Source IPv4 address.

       ip6_src: string
              Source IPv6 address.

       query_max_resp: optional integer
              Value (in seconds) to  be  used  as  "max-response"  field  in  multicast  queries.
              Default: 1 second.

IGMP_Group TABLE

       Contains learned IGMP groups indexed by address/datapath/chassis.

   Summary:
       address                       string
       datapath                      optional weak reference to Datapath_Binding
       chassis                       optional weak reference to Chassis
       ports                         set of weak reference to Port_Bindings

   Details:
       address: string
              Destination IPv4 address for the IGMP group.

       datapath: optional weak reference to Datapath_Binding
              Datapath to which this IGMP group belongs.

       chassis: optional weak reference to Chassis
              Chassis to which this IGMP group belongs.

       ports: set of weak reference to Port_Bindings
              The destination port bindings for this IGMP group.

Service_Monitor TABLE

       This  table montiors a service for its liveliness. The service can be an IPv4 tcp or a udp
       service. ovn-controller periodically sends out service monitor  packets  and  updates  the
       status of the service. Service monitoring for IPv6 services is not supported.

   Summary:
       ip                            string
       protocol                      optional string, either tcp or udp
       port                          integer, in range 0 to 32,767
       logical_port                  string
       status                        optional string, one of error, offline, or online
       src_mac                       string
       src_ip                        string
       Service monitor options:
         options : interval          optional string, containing an integer
         options : timeout           optional string, containing an integer
         options : success_count     optional string, containing an integer
         options : failure_count     optional string, containing an integer
       Common Columns:
         external_ids                map of string-string pairs

   Details:
       ip: string
              IP of the service to be monitored. Only IPv4 is supported.

       protocol: optional string, either tcp or udp
              The protocol of the service. It can be either tcp or udp.

       port: integer, in range 0 to 32,767
              The tcp or udp port of the service.

       logical_port: string
              The  VIF  of logical port on which the service is running. The ovn-controller which
              binds this logical_port monitors the service by sending periodic monitor packets.

       status: optional string, one of error, offline, or online
              The ovn-controller which binds  the  logical_port  updates  the  status  to  online
              offline or error.

              For tcp service, ovn-controller sends a TCP SYN packet to the service and expects a
              TCP ACK response to consider the service to be online.

              For udp service, ovn-controller sends a udp  packet  to  the  service  and  doesn’t
              expect  any  reply.  If it receives ICMP reply, then it considers the service to be
              offline.

       src_mac: string
              Source Ethernet address to use in the service monitor packet.

       src_ip: string
              Source IPv4 address to use in the service monitor packet.

     Service monitor options:

       options : interval: optional string, containing an integer
              The interval, in seconds, between service monitor checks.

       options : timeout: optional string, containing an integer
              The time, in seconds, after which the service monitor check times out.

       options : success_count: optional string, containing an integer
              The number of successful checks after which the service is considered online.

       options : failure_count: optional string, containing an integer
              The number of failure checks after which the service is considered offline.

     Common Columns:

       external_ids: map of string-string pairs
              See External IDs at the beginning of this document.