Next hops

Every route ansage announces carries a next hop: the address the router forwards the traffic to. By default it is ansage's own address of the session.

IPv6 routes over an IPv4 session

The most common case: one session over IPv4 that carries both families. Without an IPv6 next hop, ansage cannot announce the IPv6 prefixes on it, so set the server's IPv6 address on that link:

[[neighbor]]
address = "10.0.0.1"
asn = 64501
next_hop_ipv6 = "2001:db8:0:1::10"

Without it, ansage logs once per session no next hop for this family (session runs over the other family; set next_hop_ipv4/next_hop_ipv6), its routes are not announced, and ansage show summary shows 0 sent IPv6 prefixes for that neighbor.

The router needs the same for the routes it sends back (BIRD: next hop address in the ipv6 channel), see Router configs.

IPv4 routes over an IPv6 session

The other way round: set next_hop_ipv4.

[[neighbor]]
address = "2001:db8:0:1::1"
asn = 64501
next_hop_ipv4 = "10.0.0.10"

Link-local next hops

On a link shared with the neighbor, IPv6 routes may also carry our link-local address next to the global one (RFC 2545):

[[neighbor]]
address = "2001:db8:0:1::1"
asn = 64501
next_hop_ipv6_link_local = "fe80::10"

next_hop_ipv6_link_local must be in fe80::/10, and next_hop_ipv6 must be a global address.

Rules ansage checks

• A next hop is never the neighbor's own address (RFC 4271); ansage check refuses that.
• next_hop_ipv6 is global, next_hop_ipv6_link_local is link-local.

Routes ansage learns

With [kernel], the next hops of learned routes matter too: ansage resolves each through the kernel's routing table and uses link-local next hops on a shared link. See Kernel routes.