ovn-nb.xml

<?xml version="1.0" encoding="utf-8"?>
<database name="ovn-nb" title="OVN Northbound Database">
  <p>
    This database is the interface between OVN and the cloud management system
    (CMS), such as OpenStack, running above it.  The CMS produces almost all of
    the contents of the database.  The <code>ovn-northd</code> program
    monitors the database contents, transforms it, and stores it into the <ref
    db="OVN_Southbound"/> database.
  </p>

  <p>
    We generally speak of ``the'' CMS, but one can imagine scenarios in
    which multiple CMSes manage different parts of an OVN deployment.
  </p>

  <h2>External IDs</h2>

  <p>
    Each of the tables in this database contains a special column, named
    <code>external_ids</code>.  This column has the same form and purpose each
    place it appears.
  </p>

  <dl>
    <dt><code>external_ids</code>: map of string-string pairs</dt>
    <dd>
      Key-value pairs for use by the CMS.  The CMS might use certain pairs, for
      example, to identify entities in its own configuration that correspond to
      those in this database.
    </dd>
  </dl>

  <table name="Logical_Switch" title="L2 logical switch">
    <p>
      Each row represents one L2 logical switch.
    </p>

    <p>
      There are two kinds of logical switches, that is, ones that fully
      virtualize the network (overlay logical switches) and ones that provide
      simple connectivity to a physical network (bridged logical switches).
      They work in the same way when providing connectivity between logical
      ports on same chasis, but differently when connecting remote logical
      ports.  Overlay logical switches connect remote logical ports by tunnels,
      while bridged logical switches provide connectivity to remote ports by
      bridging the packets to directly connected physical L2 segment with the
      help of <code>localnet</code> ports.  Each bridged logical switch has
      one and only one <code>localnet</code> port, which has only one special
      address <code>unknown</code>.
    </p>

    <column name="name">
      <p>
        A name for the logical switch.  This name has no special meaning or purpose
        other than to provide convenience for human interaction with the ovn-nb
        database.  There is no requirement for the name to be unique.  The
        logical switch's UUID should be used as the unique identifier.
      </p>
    </column>

    <column name="ports">
      <p>
        The logical ports connected to the logical switch.
      </p>

      <p>
        It is an error for multiple logical switches to include the same
        logical port.
      </p>
    </column>

    <column name="load_balancer">
      Load balance a virtual ipv4 address to a set of logical port endpoint
      ipv4 addresses.
    </column>

    <column name="acls">
      Access control rules that apply to packets within the logical switch.
    </column>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="Logical_Switch_Port" title="L2 logical switch port">
    <p>
      A port within an L2 logical switch.
    </p>

    <group title="Core Features">
      <column name="name">
        <p>
          The logical port name.
        </p>

        <p>
          For entities (VMs or containers) that are spawned in the hypervisor,
          the name used here must match those used in the <ref key="iface-id"
          table="Interface" column="external_ids" db="Open_vSwitch"/> in the
          <ref db="Open_vSwitch"/> database's <ref table="Interface"
          db="Open_vSwitch"/> table, because hypervisors use <ref key="iface-id"
          table="Interface" column="external_ids" db="Open_vSwitch"/> as a lookup
          key to identify the network interface of that entity.
        </p>

        <p>
          For containers that share a VIF within a VM, the name can be any
          unique identifier.  See <code>Containers</code>, below, for more
          information.
        </p>
      </column>

      <column name="type">
        <p>
          Specify 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:
        </p>

        <dl>
          <dt>(empty string)</dt>
          <dd>
            A VM (or VIF) interface.
          </dd>

          <dt><code>router</code></dt>
          <dd>
            A connection to a logical router.
          </dd>

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

          <dt><code>l2gateway</code></dt>
          <dd>
            A connection to a physical network.
          </dd>

          <dt><code>vtep</code></dt>
          <dd>
            A port to a logical switch on a VTEP gateway.
          </dd>
        </dl>
      </column>
    </group>

    <group title="Options">
      <column name="options">
        This column provides key/value settings specific to the logical port
        <ref column="type"/>.  The type-specific options are described
        individually below.
      </column>

      <group title="Options for router ports">
        <p>
          These options apply when <ref column="type"/> is <code>router</code>.
        </p>

        <column name="options" key="router-port">
          Required.  The <ref column="name"/> of the <ref
          table="Logical_Router_Port"/> to which this logical switch port is
          connected.
        </column>
      </group>

      <group title="Options for localnet ports">
        <p>
          These options apply when <ref column="type"/> is
          <code>localnet</code>.
        </p>

        <column name="options" key="network_name">
          Required.  The name of the network to which the <code>localnet</code>
          port is connected.  Each hypervisor, via <code>ovn-controller</code>,
          uses its local configuration to determine exactly how to connect to
          this locally accessible network.
        </column>
      </group>

      <group title="Options for l2gateway ports">
        <p>
          These options apply when <ref column="type"/> is
          <code>l2gateway</code>.
        </p>

        <column name="options" key="network_name">
          Required.  The name of the network to which the <code>l2gateway</code>
          port is connected.  The L2 gateway, via <code>ovn-controller</code>,
          uses its local configuration to determine exactly how to connect to
          this network.
        </column>

        <column name="options" key="l2gateway-chassis">
          Required. The chassis on which the <code>l2gateway</code> logical
          port should be bound to. <code>ovn-controller</code> running on the
          defined chassis will connect this logical port to the physical network.
        </column>

      </group>

      <group title="Options for vtep ports">
        <p>
          These options apply when <ref column="type"/> is <code>vtep</code>.
        </p>

        <column name="options" key="vtep-physical-switch">
          Required.  The name of the VTEP gateway.
        </column>

        <column name="options" key="vtep-logical-switch">
          Required.  A logical switch name connected by the VTEP gateway.
        </column>
      </group>

      <group title="VMI (or VIF) Options">
        <p>
          These options apply to logical ports with <ref column="type"/> having
          (empty string)
        </p>

        <column name="options" key="policing_rate">
          If set, indicates the maximum rate for data sent from this interface,
          in kbps. Data exceeding this rate is dropped.
        </column>

        <column name="options" key="policing_burst">
          If set, indicates the maximum burst size for data sent from this
          interface, in kb.
        </column>
      </group>
    </group>

    <group title="Containers">
      <p>
        When a large number of containers are nested within a VM, it may be too
        expensive to dedicate a VIF to each container.  OVN can use VLAN tags
        to support such cases.  Each container is assigned a VLAN ID and each
        packet that passes between the hypervisor and the VM is tagged with the
        appropriate ID for the container.  Such VLAN IDs never appear on a
        physical wire, even inside a tunnel, so they need not be unique except
        relative to a single VM on a hypervisor.
      </p>

      <p>
        These columns are used for VIFs that represent nested containers using
        shared VIFs.  For VMs and for containers that have dedicated VIFs, they
        are empty.
      </p>

      <column name="parent_name">
        The VM interface through which the nested container sends its network
        traffic.  This must match the <ref column="name"/> column for some
        other <ref table="Logical_Switch_Port"/>.
      </column>

      <column name="tag">
        <p>
          The VLAN tag in the network traffic associated with a container's
          network interface.
        </p>

        <p>
          When <ref column="type"/> is set to <code>localnet</code>, this can
          be set to indicate 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.
        </p>
      </column>
    </group>

    <group title="Port State">
      <column name="up">
        This column is populated by <code>ovn-northd</code>, rather than by the
        CMS plugin as is most of this database.  When a logical port is bound
        to a physical location in the OVN Southbound database <ref
        db="OVN_Southbound" table="Binding"/> table, <code>ovn-northd</code>
        sets this column to <code>true</code>; otherwise, or if the port
        becomes unbound later, it sets it to <code>false</code>.  This allows
        the CMS to wait for a VM's (or container's) networking to become active
        before it allows the VM (or container) to start.
      </column>

      <column name="enabled">
        This column is used to administratively set port state.  If this column
        is empty or is set to <code>true</code>, the port is enabled.  If this
        column is set to <code>false</code>, the port is disabled.  A disabled
        port has all ingress and egress traffic dropped.
      </column>

    </group>

    <group title="Addressing">
      <column name="addresses">
        <p>
          Addresses owned by the logical port.
        </p>

        <p>
          Each element in the set must take one of the following forms:
        </p>

        <dl>
          <dt><code>Ethernet address followed by zero or more IPv4 or IPv6 addresses (or both)</code></dt>
          <dd>
            <p>
              An Ethernet address defined is owned by the logical port.
              Like a physical Ethernet NIC, a logical port ordinarily has
              a single fixed Ethernet address.
            </p>

            <p>
              When a OVN logical switch processes a unicast Ethernet frame
              whose destination MAC address is in a logical port's <ref
              column="addresses"/> column, it delivers it only to that port, as
              if a MAC learning process had learned that MAC address on the
              port.
            </p>

            <p>
              If IPv4 or IPv6 address(es) (or both) are defined, it indicates
              that the logical port owns the given IP addresses.
            </p>

            <p>
              If IPv4 address(es) are defined, the OVN logical switch uses this
              information to synthesize responses to ARP requests without
              traversing the physical network. The OVN logical router connected
              to the logical switch, if any, uses this information to avoid
              issuing ARP requests for logical switch ports.
            </p>

            <p>
              Note that the order here is important. The Ethernet address must
              be listed before the IP address(es) if defined.
            </p>

            <p>
              Examples:
            </p>

            <dl>
              <dt><code>80:fa:5b:06:72:b7</code></dt>
              <dd>
                This indicates that the logical port owns the above mac address.
              </dd>

              <dt><code>80:fa:5b:06:72:b7 10.0.0.4 20.0.0.4</code></dt>
              <dd>
                This indicates that the logical port owns the mac address and two
                IPv4 addresses.
              </dd>

              <dt><code>80:fa:5b:06:72:b7 fdaa:15f2:72cf:0:f816:3eff:fe20:3f41</code></dt>
              <dd>
                This indicates that the logical port owns the mac address and
                1 IPv6 address.
              </dd>

              <dt><code>80:fa:5b:06:72:b7 10.0.0.4 fdaa:15f2:72cf:0:f816:3eff:fe20:3f41</code></dt>
              <dd>
                This indicates that the logical port owns the mac address and
                1 IPv4 address and 1 IPv6 address.
              </dd>
            </dl>
          </dd>

          <dt><code>unknown</code></dt>
          <dd>
            This indicates that the logical port has an unknown set of Ethernet
            addresses.  When an OVN logical switch processes a unicast Ethernet
            frame whose destination MAC address is not in any logical port's
            <ref column="addresses"/> column, it delivers it to the port (or
            ports) whose <ref column="addresses"/> columns include
            <code>unknown</code>.
          </dd>
        </dl>
      </column>

      <column name="port_security">
        <p>
          This column controls the addresses from which the host attached to the
          logical port (``the host'') is allowed to send packets and to which it
          is allowed to receive packets.  If this column is empty, all addresses
          are permitted.
        </p>

        <p>
          Each element in the set must begin with one Ethernet address.
          This would restrict the host to sending packets from and receiving
          packets to the ethernet addresses defined in the logical port's
          <ref column="port_security"/> column. It also restricts the inner
          source MAC addresses that the host may send in ARP and IPv6
          Neighbor Discovery packets. The host is always allowed to receive packets
          to multicast and broadcast Ethernet addresses.
        </p>

        <p>
          Each element in the set may additionally contain one or more IPv4 or
          IPv6 addresses (or both), with optional masks.  If a mask is given, it
          must be a CIDR mask.  In addition to the restrictions described for
          Ethernet addresses above, such an element restricts the IPv4 or IPv6
          addresses from which the host may send and to which it may receive
          packets to the specified addresses.  A masked address, if the host part
          is zero, indicates that the host is allowed to use any address in the
          subnet; if the host part is nonzero, the mask simply indicates the size
          of the subnet. In addition:
        </p>

        <ul>
          <li>
            <p>
              If any IPv4 address is given, the host is also allowed to receive
              packets to the IPv4 local broadcast address 255.255.255.255 and to
              IPv4 multicast addresses (224.0.0.0/4).  If an IPv4 address with a
              mask is given, the host is also allowed to receive packets to the
              broadcast address in that specified subnet.
            </p>

            <p>
              If any IPv4 address is given, the host is additionally restricted
              to sending ARP packets with the specified source IPv4 address.
              (RARP is not restricted.)
            </p>
          </li>

          <li>
            <p>
              If any IPv6 address is given, the host is also allowed to receive
              packets to IPv6 multicast addresses (ff00::/8).
            </p>

            <p>
              If any IPv6 address is given, the host is additionally restricted
              to sending IPv6 Neighbor Discovery Solicitation or Advertisement
              packets with the specified source address or, for solicitations,
              the unspecified address.
            </p>
          </li>
        </ul>

        <p>
          If an element includes an IPv4 address, but no IPv6 addresses, then
          IPv6 traffic is not allowed.  If an element includes an IPv6 address,
          but no IPv4 address, then IPv4 and ARP traffic is not allowed.
        </p>

        <p>
          This column uses the same lexical syntax as the <ref column="match"
          table="Pipeline" db="OVN_Southbound"/> column in the OVN Southbound
          database's <ref table="Pipeline" db="OVN_Southbound"/> table.  Multiple
          addresses within an element may be space or comma separated.
        </p>

        <p>
          This column is provided as a convenience to cloud management systems,
          but all of the features that it implements can be implemented as ACLs
          using the <ref table="ACL"/> table.
        </p>

        <p>
          Examples:
        </p>

        <dl>
          <dt><code>80:fa:5b:06:72:b7</code></dt>
          <dd>
            The host may send traffic from and receive traffic to the specified
            MAC address, and to receive traffic to Ethernet multicast and
            broadcast addresses, but not otherwise.  The host may not send ARP or
            IPv6 Neighbor Discovery packets with inner source Ethernet addresses
            other than the one specified.
          </dd>

          <dt><code>80:fa:5b:06:72:b7 192.168.1.10/24</code></dt>
          <dd>
            This adds further restrictions to the first example.  The host may
            send IPv4 packets from or receive IPv4 packets to only 192.168.1.10,
            except that it may also receive IPv4 packets to 192.168.1.255 (based
            on the subnet mask), 255.255.255.255, and any address in 224.0.0.0/4.
            The host may not send ARPs with a source Ethernet address other than
            80:fa:5b:06:72:b7 or source IPv4 address other than 192.168.1.10.
            The host may not send or receive any IPv6 (including IPv6 Neighbor
            Discovery) traffic.
          </dd>

          <dt><code>"80:fa:5b:12:42:ba", "80:fa:5b:06:72:b7 192.168.1.10/24"</code></dt>
          <dd>
            The host may send traffic from and receive traffic to the
            specified MAC addresses, and
            to receive traffic to Ethernet multicast and broadcast addresses,
            but not otherwise.   With MAC 80:fa:5b:12:42:ba, the host may
            send traffic from and receive traffic to any L3 address.
            With MAC 80:fa:5b:06:72:b7, the host may send IPv4 packets from or
            receive IPv4 packets to only 192.168.1.10, except that it may also
            receive IPv4 packets to 192.168.1.255 (based on the subnet mask),
            255.255.255.255, and any address in 224.0.0.0/4.  The host may not
            send or receive any IPv6 (including IPv6 Neighbor Discovery) traffic.
          </dd>
        </dl>
      </column>
    </group>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="Address_Set" title="Address Sets">
    <p>
      Each row in this table represents a named set of addresses.
      An address set may contain Ethernet, IPv4, or IPv6 addresses
      with optional bitwise or CIDR masks.
      Address set may ultimately be used in ACLs to compare against
      fields such as <code>ip4.src</code> or <code>ip6.src</code>.
      A single address set must contain addresses of the
      same type. As an example, the following would create an address set
      with three IP addresses:
    </p>

    <pre>
      ovn-nbctl create Address_Set name=set1 addresses='10.0.0.1 10.0.0.2 10.0.0.3'
    </pre>

    <p>
      Address sets may be used in the <ref column="match" table="ACL"/> column
      of the <ref table="ACL"/> table.  For syntax information, see the details
      of the expression language used for the <ref column="match"
      table="Logical_Flow" db="OVN_Southbound"/> column in the <ref
      table="Logical_Flow" db="OVN_Southbound"/> table of the <ref
      db="OVN_Southbound"/> database.
    </p>

    <column name="name">
      A name for the address set.  This must be unique among all address sets.
    </column>

    <column name="addresses">
      The set of addresses in string form.
    </column>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="Load_Balancer" title="load balancer">
    <p>
      Each row represents one load balancer.
    </p>

    <column name="vips">
      <p>
        A map of virtual IPv4 addresses (and an optional port number with
        <code>:</code> as a separator) associated with this load balancer and
        their corresponding endpoint IPv4 addresses (and optional port numbers
        with <code>:</code> as separators) separated by commas.  If
        the destination IP address (and port number) of a packet leaving a
        container or a VM matches the virtual IPv4 address (and port number)
        provided here as a key, then OVN will statefully replace the
        destination IP address by one of the provided IPv4 address (and port
        number) in this map as a value.  Examples for keys are "192.168.1.4"
        and "172.16.1.8:80".  Examples for value are "10.0.0.1, 10.0.0.2" and
        "20.0.0.10:8800, 20.0.0.11:8800".
      </p>
    </column>

    <column name="protocol">
      <p>
        Valid protocols are <code>tcp</code> or <code>udp</code>.  This column
        is useful when a port number is provided as part of the
        <code>vips</code> column.  If this column is empty and a port number
        is provided as part of <code>vips</code> column, OVN assumes the
        protocol to be <code>tcp</code>.
      </p>
    </column>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="ACL" title="Access Control List (ACL) rule">
    <p>
      Each row in this table represents one ACL rule for a logical switch
      that points to it through its <ref column="acls"/> column.  The <ref
      column="action"/> column for the highest-<ref column="priority"/>
      matching row in this table determines a packet's treatment.  If no row
      matches, packets are allowed by default.  (Default-deny treatment is
      possible: add a rule with <ref column="priority"/> 0, <code>0</code> as
      <ref column="match"/>, and <code>deny</code> as <ref column="action"/>.)
    </p>

    <column name="priority">
      <p>
        The ACL rule's priority.  Rules with numerically higher priority
        take precedence over those with lower.  If two ACL rules with
        the same priority both match, then the one actually applied to a
        packet is undefined.
      </p>

      <p>
        Return traffic from an <code>allow-related</code> flow is always
        allowed and cannot be changed through an ACL.
      </p>
    </column>

    <column name="direction">
      <p>Direction of the traffic to which this rule should apply:</p>
      <ul>
        <li>
          <code>from-lport</code>: Used to implement filters on traffic
          arriving from a logical port.  These rules are applied to the
          logical switch's ingress pipeline.
        </li>
        <li>
          <code>to-lport</code>: Used to implement filters on traffic
          forwarded to a logical port.  These rules are applied to the
          logical switch's egress pipeline.
        </li>
      </ul>
    </column>

    <column name="match">
      <p>
        The packets that the ACL should match, in the same expression
        language used for the <ref column="match" table="Logical_Flow"
        db="OVN_Southbound"/> column in the OVN Southbound database's
        <ref table="Logical_Flow" db="OVN_Southbound"/> table.  The
        <code>outport</code> logical port is only available in the
        <code>to-lport</code> direction (the <code>inport</code> is
        available in both directions).
      </p>

      <p>
        By default all traffic is allowed.  When writing a more
        restrictive policy, it is important to remember to allow flows
        such as ARP and IPv6 neighbor discovery packets.
      </p>

      <p>
        Note that you can not create an ACL matching on a port with
        type=router.
      </p>

      <p>
        Note that when <code>localnet</code> port exists in a lswitch, for
        <code>to-lport</code> direction, the <code>inport</code> works only if
        the <code>to-lport</code> is located on the same chassis as the
        <code>inport</code>.
      </p>
    </column>

    <column name="action">
      <p>The action to take when the ACL rule matches:</p>
      <ul>
        <li>
          <code>allow</code>: Forward the packet.
        </li>

        <li>
          <code>allow-related</code>: Forward the packet and related traffic
          (e.g. inbound replies to an outbound connection).
        </li>

        <li>
          <code>drop</code>: Silently drop the packet.
        </li>

        <li>
          <code>reject</code>: Drop the packet, replying with a RST for TCP or
          ICMP unreachable message for other IP-based protocols.
          <code>Not implemented--currently treated as drop</code>
        </li>
      </ul>
    </column>

    <column name="log">
      <p>
        If set to <code>true</code>, packets that match the ACL will trigger a
        log message on the transport node or nodes that perform ACL processing.
        Logging may be combined with any <ref column="action"/>.
      </p>

      <p>
        Logging is not yet implemented.
      </p>
    </column>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="Logical_Router" title="L3 logical router">
    <p>
      Each row represents one L3 logical router.
    </p>

    <column name="name">
      <p>
        A name for the logical router.  This name has no special meaning or purpose
        other than to provide convenience for human interaction with the ovn-nb
        database.  There is no requirement for the name to be unique.  The
        logical router's UUID should be used as the unique identifier.
      </p>
    </column>

    <column name="ports">
      The router's ports.
    </column>

    <column name="static_routes">
      One or more static routes for the router.
    </column>

    <column name="enabled">
      This column is used to administratively set router state.  If this column
      is empty or is set to <code>true</code>, the router is enabled.  If this
      column is set to <code>false</code>, the router is disabled.  A disabled
      router has all ingress and egress traffic dropped.
    </column>

    <column name="nat">
      One or more NAT rules for the router. NAT rules only work on the
      Gateway routers.
    </column>

    <group title="Options">
      <p>
        Additional options for the logical router.
      </p>

      <column name="options" key="chassis">
        <p>
          If set, indicates that the logical router in question is a Gateway
          router (which is centralized) and resides in the set chassis.  The
          same value is also used by <code>ovn-controller</code> to
          uniquely identify the chassis in the OVN deployment and
          comes from <code>external_ids:system-id</code> in the
          <code>Open_vSwitch</code> table of Open_vSwitch database.
        </p>

        <p>
          The Gateway router can only be connected to a distributed router
          via a switch if SNAT and DNAT are to be configured in the Gateway
          router.
        </p>
      </column>
    </group>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="Logical_Router_Port" title="L3 logical router port">
    <p>
      A port within an L3 logical router.
    </p>

    <p>
      Exactly one <ref table="Logical_Router"/> row must reference a given
      logical router port.
    </p>

    <column name="name">
      <p>
        A name for the logical router port.
      </p>

      <p>
        In addition to provide convenience for human interaction with the
        ovn-nb database, this column is used as reference by its patch port in
        <ref table="Logical_Switch_Port"/> or another logical router port in
        <ref table="Logical_Router_Port"/>.
      </p>
    </column>

    <column name="networks">
      <p>
        The IP addresses and netmasks of the router.  For example,
        <code>192.168.0.1/24</code> indicates that the router's IP
        address is 192.168.0.1 and that packets destined to
        192.168.0.<var>x</var> should be routed to this port.
      </p>
    </column>

    <column name="mac">
      The Ethernet address that belongs to this router port.
    </column>

    <column name="enabled">
      This column is used to administratively set port state.  If this column
      is empty or is set to <code>true</code>, the port is enabled.  If this
      column is set to <code>false</code>, the port is disabled.  A disabled
      port has all ingress and egress traffic dropped.
    </column>

    <group title="Attachment">
      <p>
        A given router port serves one of two purposes:
      </p>

      <ul>
        <li>
          To attach a logical switch to a logical router.  A logical router
          port of this type is referenced by exactly one <ref
          table="Logical_Switch_Port"/> of type <code>router</code>.
          The value of <ref column="name"/> is set as
          <code>router-port</code> in column <ref column="options"/> of
          <ref table="Logical_Switch_Port"/>.  In this case <ref
          column="peer"/> column is empty.
        </li>

        <li>
          To connect one logical router to another.  This requires a pair of
          logical router ports, each connected to a different router.  Each
          router port in the pair specifies the other in its <ref
          column="peer"/> column.  No <ref table="Logical_Switch"/> refers to
          the router port.
        </li>
      </ul>

      <column name="peer">
        <p>
          For a router port used to connect two logical routers, this
          identifies the other router port in the pair by <ref column="name"/>.
        </p>

        <p>
          For a router port attached to a logical switch, this column is empty.
        </p>
      </column>
    </group>

    <group title="Common Columns">
      <column name="external_ids">
        See <em>External IDs</em> at the beginning of this document.
      </column>
    </group>
  </table>

  <table name="Logical_Router_Static_Route" title="Logical router static routes">
    <p>
      Each record represents a static route.
    </p>

    <column name="ip_prefix">
      <p>
        IP prefix of this route (e.g. 192.168.100.0/24).
      </p>
    </column>

    <column name="nexthop">
      <p>
        Nexthop IP address for this route.  Nexthop IP address should be the IP
        address of a connected router port or the IP address of a logical port.
      </p>
    </column>

    <column name="output_port">
      <p>
        The name of the <ref table="Logical_Router_Port"/> via which the packet
        needs to be sent out.  This is optional and when not specified,
        OVN will automatically figure this out based on the
        <ref column="nexthop"/>.
      </p>
    </column>
  </table>

  <table name="NAT" title="NAT rules for a Gateway router.">
    <p>
      Each record represents a NAT rule in a Gateway router.
    </p>

    <column name="type">
      <p>Type of the NAT rule.</p>
      <ul>
        <li>
          When <ref column="type"/> is <code>dnat</code>, the externally
          visible IP address <ref column="external_ip"/> is DNATted to the IP
          address <ref column="logical_ip"/> in the logical space.
        </li>
        <li>
          When <ref column="type"/> is <code>snat</code>, IP packets
          with their source IP address that either matches the IP address
          in <ref column="logical_ip"/> or is in the network provided by
          <ref column="logical_ip"/> is SNATed into the IP address in
          <ref column="external_ip"/>.
        </li>
        <li>
          When <ref column="type"/> is <code>dnat_and_snat</code>, the
          externally visible IP address <ref column="external_ip"/> is
          DNATted to the IP address <ref column="logical_ip"/> in the
          logical space. In addition, IP packets with the source IP
          address that matches <ref column="logical_ip"/> is SNATed into
          the IP address in <ref column="external_ip"/>.
        </li>
      </ul>
    </column>

    <column name="external_ip">
      An IPv4 address.
    </column>

    <column name="logical_ip">
      An IPv4 network (e.g 192.168.1.0/24) or an IPv4 address.
    </column>
  </table>

</database>