Announcements

This page describes the peer options that control which routes are exported (announced) to a peer.

Restricting announcements by prefix

dont-announce and only-announce take a list of prefixes in BIRD prefix pattern syntax, so each entry may be a plain prefix (192.0.2.0/24), a prefix with a length range (192.0.2.0/24{24,32}), or a prefix followed by + (the prefix and all more specifics) or - (the prefix and all less specifics).

• dont-announce rejects matching routes before any other export policy is evaluated.
• only-announce rejects every route that doesn't match the list.

IPv4 and IPv6 prefixes can be mixed in the same list. Pathvector splits each list by address family and every BGP channel only checks the prefixes of its own family, so a single peer with both IPv4 and IPv6 neighbors (or with mp-unicast-46) can share one list:

peers:
  Downstream:
    asn: 65510
    neighbors:
      - 192.0.2.10
      - 2001:db8::10
    only-announce:
      - 198.51.100.0/24
      - 2001:db8:1000::/36+
    dont-announce:
      - 198.51.100.128/25
      - 2001:db8:1fff::/48

If only-announce is set but contains no prefixes of an address family, nothing is announced in that address family (for example, an only-announce list with only IPv4 prefixes means no IPv6 routes are announced to the peer). only-announce cannot be combined with announce-all.

Locally originated routes

announce-originated (enabled by default) announces locally originated routes to the peer. A route is considered locally originated when it is

• within one of the global prefixes (the matching local-communities are added to it), or
• tagged with one of the global origin-communities, for example routes originated by another router in your network and learned over iBGP.

If neither prefixes nor origin-communities are configured, there is nothing to originate and announce-originated is disabled for all peers. A router without local prefixes can therefore still announce routes originated elsewhere in the network by tagging them with an origin community:

asn: 65530
origin-communities:
  - 65530:0:1  # added to originated routes by the router that originates them
peers:
  Transit:
    asn: 64496
    neighbors:
      - 203.0.113.1

Default route

announce-default: true announces a default route to the peer. The announced route is the best default route in BIRD's table: the locally originated default4/default6 route (requires the global default-route, enabled by default), or a default route learned from another peer when the global accept-default is enabled. See Kernel for how accept-default affects route selection.