OSPFv2 Unnumbered -- Am I doing it right?

[Bernd Naumann]

Hi Users of BIRD!

I have only heard about "OSPF Unnumbered" a couple of times, and never 
have seen any clear explanation or specific details. And based on that, 
I had the false assumption that "unnumbered" would imply "having no 
address on the interfaces"; maybe only an IPv4 address used as a 
router-id as an `/32' assignment on loopback.


But without an address on an interface I have not seen any packets sent 
to 224.0.0.5.

So I just gave it a try and added the `/32` from loopback on each 
interface, too, and from the BIRD documentation I concluded I must set 
`type ptp;` in the ospf area interface stanza... and.... Bingo.
It just works.

Later I discovered, that's the way how Cumulus recommends it with FRR. 
[1] But couldn't have anyone told me this earlier? Next time maybe :)


So basically my question is: Is this the correct way as it is intended? 
Is OSPFv2 unnumbered --how ever-- properly specified, or just a clever 
way, which just happens to work? And: Is this compatible with NOS from 
various vendors?
(As IPv6 offers link-local addresses, there is no need for OSPFv3 
unnumbered, right?)
Are there any issues with that approach I'm unaware of?


Thanks for your time, and
have a nice Friday evening and weekend.

Bernd

PS: I tried this on Debian 11 with kernel 5.10 and bird 2.0.9


[1] 
https://docs.nvidia.com/networking-ethernet-software/cumulus-linux-50/Layer-3/OSPF/Open-Shortest-Path-First-v2-OSPFv2/#ospfv2-unnumbered