ovn-northd(8)

NAME

ovn-northd - Open Virtual Network central control daemon

SYNOPSIS

ovn-northd [options]

DESCRIPTION

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

OPTIONS

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

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

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

  Daemon Options

--pidfile[=pidfile]
    Causes a file (by default, program.pid) to be created indicating the PID of the running process. If the pidfile argument is not specified, or if it does not begin with /, then it is created in /var/run/openvswitch.

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

--overwrite-pidfile
    By default, when --pidfile is specified and the specified pidfile already exists and is locked by a running process, the daemon refuses to start. Specify --overwrite-pidfile to cause it to instead overwrite the pidfile.

    When --pidfile is not specified, this option has no effect.

--detach
    Runs this program as a background process. The process forks, and in the child it starts a new session, closes the standard file descriptors (which has the side effect of disabling logging to the console), and changes its current directory to the root (unless --no-chdir is specified). After the child completes its initialization, the parent exits.

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

    This option is normally used with --detach, but it also functions without it.

--no-chdir
    By default, when --detach is specified, the daemon changes its current working directory to the root directory after it detaches. Otherwise, invoking the daemon from a carelessly chosen directory would prevent the administrator from unmounting the file system that holds that directory.

    Specifying --no-chdir suppresses this behavior, preventing the daemon from changing its current working directory. This may be useful for collecting core files, since it is common behavior to write core dumps into the current working directory and the root directory is not a good directory to use.

    This option has no effect when --detach is not specified.

--no-self-confinement
    By default this daemon will try to self-confine itself to work with files under well-known directories whitelisted at build time. It is better to stick with this default behavior and not to use this flag unless some other Access Control is used to confine daemon. Note that in contrast to other access control implementations that are typically enforced from kernel-space (e.g. DAC or MAC), self-confinement is imposed from the user-space daemon itself and hence should not be considered as a full confinement strategy, but instead should be viewed as an additional layer of security.

--user=user:group
    Causes this program to run as a different user specified in user:group, thus dropping most of the root privileges. Short forms user and :group are also allowed, with current user or group assumed, respectively. Only daemons started by the root user accepts this argument.

    On Linux, daemons will be granted CAP_IPC_LOCK and CAP_NET_BIND_SERVICES before dropping root privileges. Daemons that interact with a datapath, such as ovs-vswitchd, will be granted two additional capabilities, namely CAP_NET_ADMIN and CAP_NET_RAW. The capability change will apply even if the new user is root.

    On Windows, this option is not currently supported. For security reasons, specifying this option will cause the daemon process not to start.

  Logging Options

-v[spec]
--verbose=[spec]
    Sets logging levels. Without any spec, sets the log level for every module and destination to dbg. Otherwise, spec is a list of words separated by spaces or commas or colons, up to one from each category below:

    •   A valid module name, as displayed by the vlog/list command on ovs-appctl(8), limits the log level change to the specified module.

    •   syslog, console, or file, to limit the log level change to only to the system log, to the console, or to a file, respectively. (If --detach is specified, the daemon closes its standard file descriptors, so logging to the console will have no effect.)

        On Windows platform, syslog is accepted as a word and is only useful along with the --syslog-target option (the word has no effect otherwise).

    •   off, emer, err, warn, info, or dbg, to control the log level. Messages of the given severity or higher will be logged, and messages of lower severity will be filtered out. off filters out all messages. See ovs-appctl(8) for a definition of each log level.

    Case is not significant within spec.

    Regardless of the log levels set for file, logging to a file will not take place unless --log-file is also specified (see below).

    For compatibility with older versions of OVS, any is accepted as a word but has no effect.

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

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

-vFACILITY:facility
--verbose=FACILITY:facility
    Sets the RFC5424 facility of the log message. facility can be one of kern, user, mail, daemon, auth, syslog, lpr, news, uucp, clock, ftp, ntp, audit, alert, clock2, local0, local1, local2, local3, local4, local5, local6 or local7. If this option is not specified, daemon is used as the default for the local system syslog and local0 is used while sending a message to the target provided via the --syslog-target option.

--log-file[=file]
    Enables logging to a file. If file is specified, then it is used as the exact name for the log file. The default log file name used if file is omitted is /var/log/openvswitch/program.log.

--syslog-target=host:port
    Send syslog messages to UDP port on host, in addition to the system syslog. The host must be a numerical IP address, not a hostname.

--syslog-method=method
    Specify method as how syslog messages should be sent to syslog daemon. The following forms are supported:

    •   libc, to use the libc syslog() function. This is the default behavior. Downside of using this options is that libc adds fixed prefix to every message before it is actually sent to the syslog daemon over /dev/log UNIX domain socket.

    •   unix:file, to use a UNIX domain socket directly. It is possible to specify arbitrary message format with this option. However, rsyslogd 8.9 and older versions use hard coded parser function anyway that limits UNIX domain socket use. If you want to use arbitrary message format with older rsyslogd versions, then use UDP socket to localhost IP address instead.

    •   udp:ip:port, to use a UDP socket. With this method it is possible to use arbitrary message format also with older rsyslogd. When sending syslog messages over UDP socket extra precaution needs to be taken into account, for example, syslog daemon needs to be configured to listen on the specified UDP port, accidental iptables rules could be interfering with local syslog traffic and there are some security considerations that apply to UDP sockets, but do not apply to UNIX domain sockets.

  PKI Options

PKI configuration is required in order to use SSL for the connections to the Northbound and Southbound databases.

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

    -c cert.pem
    --certificate=cert.pem
        Specifies a PEM file containing a certificate that certifies the private key specified on -p or --private-key to be trustworthy. The certificate must be signed by the certificate authority (CA) that the peer in SSL connections will use to verify it.

    -C cacert.pem
    --ca-cert=cacert.pem
        Specifies a PEM file containing the CA certificate for verifying certificates presented to this program by SSL peers. (This may be the same certificate that SSL peers use to verify the certificate specified on -c or --certificate, or it may be a different one, depending on the PKI design in use.)

    -C none
    --ca-cert=none
        Disables verification of certificates presented by SSL peers. This introduces a security risk, because it means that certificates cannot be verified to be those of known trusted hosts.

  Other Options

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

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

RUNTIME MANAGEMENT COMMANDS

ovs-appctl can send commands to a running ovn-northd process. The currently supported commands are described below.

    exit
        Causes ovn-northd to gracefully terminate.

ACTIVE-STANDBY FOR HIGH AVAILABILITY

You may run ovn-northd more than once in an OVN deployment. OVN will automatically ensure that only one of them is active at a time. If multiple instances of ovn-northd are running and the active ovn-northd fails, one of the hot standby instances of ovn-northd will automatically take over.

LOGICAL FLOW TABLE STRUCTURE

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

  Logical Switch Datapaths

Ingress table 0 contains these logical flows:

    •   Priority 100 flows to drop packets with VLAN tags or multicast Ethernet source addresses.

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

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

Ingress table 1 contains these logical flows:

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

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

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

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

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

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

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

Ingress table 2 contains these logical flows:

    •   For each element in the port security set,

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

        •   Priority 90 flow to allow IPv6 Neighbor Solicitation and Advertisement traffic which match the inport, valid eth.src and nd.sll/nd.tll. If the element has one or more IPv6 addresses, then it also matches the valid nd.target address(es) for Neighbor Advertisement traffic.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    •   For every qos_rules for every logical switch a flow will be added at priorities mentioned in the QoS table.

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

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

    •   For every qos_rules for every logical switch a flow will be added at priorities mentioned in the QoS table.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        reg0[4] = dns_lookup(); next;

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

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

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

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

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

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

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

    •   One priority-50 flow that matches each known Ethernet address against eth.dst and outputs the packet to the single associated output port.

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

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

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

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

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

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

This is similar to ingress table Pre-stateful.

This is similar to ingress table LB.

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

This is similar to ingress table QoS marking except for to-lport qos rules.

This is similar to ingress table QoS meter except for to-lport qos rules.

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

Also the following flows are added.

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

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

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

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

  Logical Router Datapaths

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

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

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

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

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

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

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

Other packets are implicitly dropped.

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

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

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

        •   ip4.src == 255.255.255.255 (broadcast source)

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

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

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

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

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

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

        Flows for ICMPv6 echo requests use the following actions:

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

    •   Reply to ARP requests.

        These flows reply to ARP requests for the router’s own IP address. For each router port P that owns IP address A and Ethernet address E, a priority-90 flow matches inport == P && arp.op == 1 && arp.tpa == A (ARP request) with the following actions:

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

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

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

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

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

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

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

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

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

            This behavior avoids generation of multiple ARP responses from different chassis, and allows upstream MAC learning to point to the correct chassis.

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

    •   Reply to IPv6 Neighbor Solicitations. These flows reply to Neighbor Solicitation requests for the router’s own IPv6 address and load balancing IPv6 VIPs and populate the logical router’s mac binding table. For each router port P that owns IPv6 address or has load balancing VIP A, solicited node address S, and Ethernet address E, a priority-90 flow matches inport == P && nd_ns && ip6.dst == {A, E} && nd.target == A with the following actions:

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

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

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

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

    •   UDP port unreachable. Priority-80 flows generate ICMP port unreachable messages in reply to UDP datagrams directed to the router’s IP address. The logical router doesn’t accept any UDP traffic so it always generates such a reply.

        These flows should not match IP fragments with nonzero offset.

        Details TBD. Not yet implemented.

    •   TCP reset. Priority-80 flows generate TCP reset messages in reply to TCP datagrams directed to the router’s IP address. The logical router doesn’t accept any TCP traffic so it always generates such a reply.

        These flows should not match IP fragments with nonzero offset.

        Details TBD. Not yet implemented.

    •   Protocol unreachable. Priority-70 flows generate ICMP protocol unreachable messages in reply to packets directed to the router’s IP address on IP protocols other than UDP, TCP, and ICMP.

        These flows should not match IP fragments with nonzero offset.

        Details TBD. Not yet implemented.

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

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

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

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

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

        Not yet implemented.

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

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

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

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

Ingress Table 3: UNSNAT on Gateway Routers

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

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

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

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

Ingress Table 3: UNSNAT on Distributed Routers

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

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

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

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

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

Ingress Table 4: Load balancing DNAT rules

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

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

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

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

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

Ingress Table 4: DNAT on Gateway Routers

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

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

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

Ingress Table 4: DNAT on Distributed Routers

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

This table contains the following logical flows:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Egress Table 1: SNAT on Gateway Routers

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

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

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

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

Egress Table 1: SNAT on Distributed Routers

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

        If the NAT rule cannot be handled in a distributed manner, then the flow above is only programmed on the redirect-chassis.

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

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

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

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

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

This table has the following flows:

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

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

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

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

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