On Mon, Jul 06, 2026 at 09:42:35PM +0100, Lexi Winter wrote:
> 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:
> 
> 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.
> 
> 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.

Hello

This is somewhat idiosyncratic BIRD behavior. For point-to-point IPv4
addresses, BIRD do *not* announce the local one (while the remote one is
announced only in case of stub interface). This works when one configures
point-to-point addresses with existing/loopback address of the router. E.g.:

eth0: 192.168.1.0/24
eth1: 192.168.1.0/32 --> 192.168.2.0/32

This is something that i always wanted to fix in some more
generic/configurable way, but never got to that.

The workaround is to set the same IP address as /32 on a dummy/loopback
interface and announce it as a stub.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: [email protected])
"To err is human -- to blame it on a computer is even more so."

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