On Tue, 17 Feb 2026 20:13:02 +0100
Ondrej Zajicek <[email protected]> wrote:
> On Tue, Feb 17, 2026 at 07:16:03PM +0100, Mariusz Gronczewski wrote:
> > > Hi
> > >
> > > Isn't that just mismatched ptp/broadcast mode? BIRD defaults to
> > > ptp mode for /30 and similar networks, but i thought that in
> > > mismatch mode it would not even make an adjacency. But perhaps it
> > > makes adjacency, just not work correctly.
> > >
> > > Try setting explicitly broadcast mode (or ptp mode on the other
> > > side).
> >
> > First, thanks for help, I didn't thought about trying to change
> > stuff on the router/switch side ("it was working fine before") and
> > forcing Juniper/Brocade side to PtP was enough.
> >
> > I tried every option on Bird side, didn't help, setting
> > it to p2p on the router/switch side worked, but I'm more confused
> > than before because:
>
> Setting 'type broadcast' for the interface on BIRD side (when
> router/switch side was not set to ptp) with /30 did not work?
>
> (i am not sure about /31)
I've checked it now and it worked when forcing broadcast on Bird (I
think I forgot to check broadcast before).
So in short when Bird auto-defaulted to PtP and other router did
broadcast I had Full/PtP state on Bird side and Full state on the
Juniper (but no routes put into Bird routing table)
But in reverse situation, when I forced Juniper to run PtP and forced
Bird to run brodcast, the connection did not establish at all.
So I'm confused why it even established in the first place
> You can also use 'show ospf interface' to see which mode (type) is
> used on the interface.
>
>
> > * the other devices talked between them just fine (in similar /31
> > vlans without PtP being explicitly set)
> > * the same setup in FRR worked just fine (not needing to set PtP
> > there too)
> > * the same setup with 2 Bird instances (albeit thru wireguard
> > tunnels) also works fine (PtP mode is enabled automatically)
>
> I think other devices always defaults to broadcast mode on ethernet,
> while BIRD defaults to ptp mode when an opposite address is known
> (i.e. /30, /31, /32 with peer address).
>
Yeah I just kinda assumed the other devices did the logical thing here
Cheers
Mariusz
--
Mariusz Gronczewski (XANi) <[email protected]>
GnuPG: 0xEA8ACE64
https://devrandom.eu
