---
# Configures BIRD2 on the D-Link as an iBGP peer of the MikroTik CRS418.
#
# Route exchange:
#   D-Link → CRS: announces 0.0.0.0/0 and 2000::/3 when wwan0 is up.
#                 CRS installs these at BGP distance 200 (below the GPON
#                 static default at distance 1 — activates only on GPON failure).
#
#   CRS → D-Link: announces connected routes (VLAN subnets), static routes
#                 (Tailscale, GPON default), and reflects k8s BGP routes.
#                 BIRD2 installs all of these into the kernel at metric 10.
#
# D-Link's own routing:
#   - Kernel metric 10: BGP-learned routes from CRS (preferred)
#   - Kernel metric 100: wwan QMI-assigned routes (fallback)
#   No static default gateway on uplink — the default comes from BGP.
#   When GPON fails, CRS withdraws the BGP default; D-Link falls back to wwan.

- name: Write BIRD2 configuration
  community.openwrt.copy:
    dest: /etc/bird.conf
    mode: '0640'
    owner: root
    group: root
    content: |
      # BIRD2 — LTE failover BGP peer for MikroTik CRS418
      # iBGP session, AS 65000, peer: 192.168.6.1 (CRS vlan6)

      router id 192.168.6.2;

      protocol device {
        # Tracks interface up/down state via netlink.
        # scan time is a periodic reconciliation fallback; real events are
        # netlink-driven and processed immediately.
        scan time 5;
      }

      # Announce directly connected prefixes into BIRD2's RIB so that
      # next-hop resolution works for BGP routes received from CRS.
      # Without this, 192.168.6.1 (CRS uplink) is unresolvable and all
      # IPv4 BGP routes appear unreachable. Same for IPv6 uplink prefix.
      protocol direct {
        ipv4;
        ipv6;
        interface "eth0.6";
      }

      # Install BGP-learned routes from CRS into the kernel at metric 10.
      # This is lower than the wwan QMI default (metric 100), so D-Link
      # prefers the CRS path for its own outbound traffic when GPON is up.
      # import none: BIRD2 does not read the kernel table, preventing
      # wwan kernel routes from leaking into BGP.
      protocol kernel k4 {
        ipv4 {
          import none;
          export filter {
            if proto = "crs" then {
              krt_metric = 10;
              accept;
            }
            reject;
          };
        };
      }

      protocol kernel k6 {
        ipv6 {
          import none;
          export filter {
            if proto = "crs" then {
              krt_metric = 10;
              accept;
            }
            reject;
          };
        };
      }

      # LTE default routes — exist only while wwan0 is up.
      # BIRD2's device protocol tracks wwan0 via netlink; when the interface
      # goes down the routes become unreachable and BGP withdraws them.
      # Uses interface-name routing (no explicit gateway IP) which is correct
      # for QMI raw-ip POINTOPOINT NOARP interfaces.
      #
      # Preference 50 is below BGP's default of 100 — these routes are only
      # used by BIRD2 internally as a presence signal for BGP export, NOT for
      # installing into the kernel as our active default route. The kernel
      # already gets the wwan default at metric 100 via netifd/qmi.sh, and
      # we want the BGP-learned default via CRS (kernel metric 10) to be
      # preferred for D-Link's own outbound traffic when GPON is up.
      protocol static lte_default {
        ipv4 {
          preference 50;
        };
        route 0.0.0.0/0 via "wwan0";
      }

      protocol static lte_default6 {
        ipv6 {
          preference 50;
        };
        route 2000::/3 via "wwan0";
      }

      protocol bgp crs {
        description "MikroTik CRS418 — LTE failover signalling";
        local 192.168.6.2 as 65000;
        neighbor 192.168.6.1 as 65000;
        hold time 30;
        keepalive time 10;

        ipv4 {
          # Import all prefixes CRS announces (VLAN subnets, static routes,
          # k8s BGP routes reflected via RR). Installed into kernel via k4.
          import all;
          # Export only the wwan-sourced LTE default route.
          # BGP-learned CRS routes are never re-exported (iBGP split-horizon
          # applies; BIRD2 also does not import CRS routes into its RIB from
          # the kernel, so they cannot appear here).
          export where proto = "lte_default";
        };

        ipv6 {
          # CRS uses Extended Next Hop (RFC 5549) for IPv6 routes, advertising
          # them with the IPv4 next-hop 192.168.6.1. The Linux kernel cannot
          # install IPv6 routes with IPv4 next-hops. Accept the routes from BGP
          # (we negotiated ENHE via "extended next hop yes") but rewrite the
          # next-hop in the import filter to the CRS's native IPv6 address on
          # vlan6 before they reach the kernel.
          extended next hop yes;
          import filter {
            gw = 2001:470:61a3:600::1;
            accept;
          };
          # Force our own native IPv6 address as the next-hop when advertising
          # to CRS, otherwise BIRD2 also uses ENHE and CRS receives a route
          # with ::ffff:192.168.6.2 which it can't resolve as an IPv6 next-hop.
          export filter {
            if proto = "lte_default6" then {
              bgp_next_hop = 2001:470:61a3:600::2;
              accept;
            }
            reject;
          };
        };
      }
  notify: Reload bird

- name: Enable and start BIRD2 service
  community.openwrt.service:
    name: bird
    enabled: true
    state: started