OSPF unexpectedly adds /128 interface route

[Ondrej Zajicek]

On Sun, May 10, 2026 at 01:42:07PM +0100, Lexi Winter wrote:
> hello,
> 
> i have an interface with a /64 address configured:
> 
> 	# ifconfig bridge0.500
> 	bridge0.500: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
> 		options=0
> 		ether 58:9c:fc:10:8d:b4
> 		inet6 fe80::1%bridge0.500/64 scopeid 0x1c
> 		inet6 fd13:480d:2ffa:3::1/64
> 		groups: vlan
> 		vlan: 500 vlanproto: 802.1q vlanpcp: 0 parent interface: bridge0
> 		nd6 options=1<PERFORMNUD>
> 
> this is configured as an OSPF stub interface in BIRD:
> 
> 	protocol ospf v3 core {
> 		area 0 {
> 			interface "bridge0.500" {
> 				stub yes;
> 			};
> 			...
> 
> however, BIRD only adds a /128 route into the OSPF database:
> 
> 	# birdc show route in fd13:480d:2ffa:3::/64
> 	BIRD 3.2.0 ready.
> 	Table master6:
> 	fd13:480d:2ffa:3::1/128 unicast [core 13:25:02.965] ! I (150/0) [176.126.243.164]
> 		dev bridge0.500
> 	fd13:480d:2ffa:3::/64 unicast [direct1 13:38:01.578] * (240)
> 		dev bridge0.500
> 
> i would have expected it to add the /64 route instead.  filtering the /64
> route in the direct protocol does not make any difference, except that the
> direct route disappears from 'show route'.

Hello

There are two reasons why it could generate /128 route instead of /64.
Either BIRD thinks there is link down in the interface, or it is
confused by its type and handles the interface as PtMP.

You can try 'show ospf interface' command, it should give you type and
state. You could disable link-down check, or force broadcast type.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
"To err is human -- to blame it on a computer is even more so."