OSPFv2: PtP stub interface

6 Jul 2026

      hello,

i'm using BIRD 3.2.0 on FreeBSD 15.0.  i have a PPPoE interface with a
point-to-point IPv4 address configured:

	ng0: flags=10088d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
		options=0
		inet 81.187.73.117 --> 81.187.81.187/32
		inet6 2001:8b0:aab5:1::1/128
		inet6 fe80::227c:14ff:fef3:d8f7%ng0/64 scopeid 0x12
		groups: arpa
		nd6 options=1<PERFORMNUD>

i would like to advertise this in OSPF as a passive interface, so i configured
the OSPF protocol:

	define OSPF_V6_EXPORT = [
	];

	define OSPF_V4_EXPORT = [
		0.0.0.0/0
	];

	filter ospf_export {
		if (net ~ OSPF_V6_EXPORT) then accept;
		if (net ~ OSPF_V4_EXPORT) then accept;
		reject;
	};

	protocol ospf v2 core4 {
		ipv4 {
			export filter ospf_export;
			import all;
		};

		area 0 {
			interface "ng0" {
				stub yes;
			};
			[... other config elided ...]
		};
	}

however, BIRD does not advertise 81.187.73.117/32 in OSPF.  it *does* advertise
81.187.81.187/32, which is the remote side of the interface.

the interface looks fine in BIRD:

	bird> show ospf interface "ng0"
	core6:

	core4:
	Interface ng0 (peer 81.187.81.187)
		Type: ptp
		Area: 0.0.0.0 (0)
		State: PtP (stub)
		Priority: 1
		Cost: 10
		ECMP weight: 1
		Hello timer: 10
		Wait timer: 40
		Dead timer: 40
		Retransmit timer: 5

the route:

	bird> show route for 81.187.73.117/32
	Table master4:
	0.0.0.0/0            unicast [kernel4 2026-07-04] ! (10)
		via 81.187.81.187 on ng0
	81.187.73.117/32     unicast [kernel4 2026-07-04] ! (10)
		dev lo0

if i add 81.187.73.117/32 to OSPF_V4_EXPORT, then it is correctly advertised as
an E2 route, which is fine as a workaround, but i would like to understand why
the interface configuration doesn't work.

OSPFv2: PtP stub interface

Lexi Winter