ovn-bgp-agent — Scenarios

sequenceDiagram
  autonumber
  participant AG as Agent
  participant OVSDB as Local OVSDB
  participant SB as OVN SB
  participant K as Kernel
  participant OVS as OVS (ofctl)
  participant FRR as FRR
  AG->>OVSDB: monitor Open_vSwitch (system-id, ovn-remote, ovn-bridge-mappings)
  AG->>K: ensure VRF bgp-vrf (table 10), dummy bgp-nic in the VRF
  AG->>FRR: vtysh -f (router bgp AS: import vrf bgp-vrf; router bgp AS vrf bgp-vrf: redistribute connected)
  AG->>SB: monitor_cond (Port_Binding, Load_Balancer, Chassis_Private name==system-id, …)
  SB-->>AG: initial rows (ChassisPrivateCreateEvent: first_time only)
  loop every reconcile_interval (300 s), first run at start
    AG->>K: rt_tables entry + default routes per bridge, 169.254.x.y / fd53:… on bridges, proxy_arp/ndp
    AG->>OVS: dump-flows cookie=999, add MAC-tweak flows, delete extra ones
    AG->>SB: (local cache) ports bound here, cr-lrps here, patch ports, LBs
    AG->>K: ip rule / ip route / ip addr on bgp-nic for every expected IP
    AG->>K: delete leftover IPs, rules, routes, VLAN devices
  end
  loop every frr_reconcile_interval (15 s)
    AG->>K: ensure bgp-vrf and bgp-nic
    AG->>FRR: vtysh -f (same VRF-leak fragment)
  end

sequenceDiagram
  autonumber
  participant N as Neutron
  participant NB as OVN NB
  participant OC as ovn-controller
  participant AG as Agent (compute)
  participant K as Kernel
  participant OVS as OVS
  participant FRR as FRR
  participant F as Fabric
  N->>NB: LSP add (addresses "mac ip", requested-chassis=compute, neutron:network_name)
  OC->>NB: (via northd/SB) LSP up=true after binding
  NB-->>AG: update LSP up false→true
  Note over AG: LogicalSwitchPortProviderCreateEvent matches: bound here, up, provider switch, not yet exposed
  AG->>NB: (local cache) localnet port of the switch → network_name, tag
  AG->>K: ip rule to IP/32 table br-ex; ip route IP dev br-ex[.vlan] table br-ex
  AG->>OVS: get Interface patch-provnet-…-to-br-int ofport; add MAC-tweak flow if missing
  alt patch port not yet created on this node
    OVS-->>AG: ofport [] for 5 s → PortNotFound
    Note over AG: logged "Unexpected exception while wiring provider port"; IP not announced until next sync (defect D1)
  else
    AG->>K: ip addr add IP/32 dev bgp-nic
    K->>FRR: zebra: connected route in vrf bgp-vrf
    FRR->>F: BGP UPDATE IP/32 (leaked into the default instance)
  end

sequenceDiagram
  autonumber
  participant N as Neutron
  participant SB as OVN SB
  participant AG as Agent (net1)
  participant K as Kernel (net1)
  participant FRR as FRR (net1)
  N->>SB: (via NB/northd) patch port nat_addresses += "mac FIP is_chassis_resident(\"cr-lrp-X\")"
  SB-->>AG: Port_Binding update (patch, chassis empty, nat_addresses changed)
  Note over AG: FIPSetEvent: IPs new for cr-lrp-X
  AG->>SB: (cache) cr-lrp-X bound to net1? patch datapath has a localnet?
  alt cr-lrp-X on this node and provider network
    AG->>K: ip rule to FIP/32 table br-ex; ip route FIP dev br-ex table br-ex
    AG->>K: ip addr add FIP/32 dev bgp-nic
    K->>FRR: connected route → BGP UPDATE FIP/32
  else gateway elsewhere
    Note over AG: nothing; the node hosting cr-lrp-X does it
  end

sequenceDiagram
  autonumber
  participant SB as OVN (northd/controller)
  participant NB as OVN NB
  participant A1 as Agent (old gateway node)
  participant A2 as Agent (new gateway node)
  participant K2 as Kernel (new)
  participant F as Fabric
  SB->>NB: LRP lrp-gw status:hosting-chassis = node2
  NB-->>A1: LRP update (hosting-chassis node1 → node2)
  Note over A1: ChassisRedirectDeleteEvent
  A1->>A1: withdraw subnets (unwire rules/routes, delete table-10 subnet routes), LBs, gateway IP
  NB-->>A2: LRP update (… → node2)
  Note over A2: ChassisRedirectCreateEvent
  A2->>K2: rule + route GW_IP table br-ex; ip neigh GW_IP lladdr ROUTER_MAC permanent; ip addr GW_IP/32 dev bgp-nic
  A2->>NB: (cache) router-interface LSPs of the router (up, device_owner=network:router_interface)
  loop each subnet CIDR (SNAT/addr-scope filters)
    A2->>K2: ip rule to CIDR table br-ex; ip route CIDR via GW_IP dev br-ex table br-ex
    A2->>K2: ip route CIDR via GW_IP dev bgp-nic table 10
  end
  K2->>F: FRR (redistribute kernel) BGP UPDATE CIDR, GW_IP/32
  A2->>A2: expose LB VIPs / VIP-FIPs / PF FIPs of the router

sequenceDiagram
  autonumber
  participant N as Neutron
  participant NB as OVN NB
  participant A1 as Agent (cmp1)
  participant A2 as Agent (cmp2)
  N->>NB: LSP options:requested-chassis = "cmp1,cmp2"
  Note over A1,A2: no match: FIP unchanged, port still up on cmp1
  NB-->>A1: LSP up true→false (port set down on source)
  Note over A1: LogicalSwitchPortFIPDeleteEvent → withdraw FIP (ip addr del, rule/route del)
  N->>NB: requested-chassis = "cmp2", neutron:host_id = cmp2
  NB-->>A2: LSP up false→true (bound on cmp2)
  Note over A2: LogicalSwitchPortFIPCreateEvent → read NAT (external_ip, external_mac, fip_network_id)
  A2->>A2: wire FIP on provider switch neutron-<fip_network_id>, ip addr add FIP/32 dev bgp-nic

sequenceDiagram
  autonumber
  participant SB as OVN SB
  participant AG as Agent
  SB--xAG: connection lost (SB restart, network)
  AG->>SB: reconnect, monitor_cond again
  SB-->>AG: all rows as CREATE (incl. own Chassis_Private)
  Note over AG: events fire for replayed rows; ChassisPrivateCreateEvent (not first time)
  AG->>AG: "Connection to OVSDB established, doing a full sync" → sync()