I recently saw a post about Babel getting up unnumbered, and AFAIK OSPF and IS-IS have both had it for a while.

Implementations are spotty on support of unnumbered, there’s still quite a few, mostly older OSPF devices that require an IP interface to communicate with another device for OSPF.

I’ve been trying to get a functional IP unnumbered lab up and running but there’s a lot of unknown-unknowns for me still… At least when it comes to implementation.

Of course, a router ID is still a requirement, foreign devices still need a way to uniquely identify what device they’re talking to.

Maybe I should try the lab with IS-IS, but I know less about IS-IS than I do about OSPF at the moment. I should change that.