Dan Partelly figured out that we have to configure the standard (IETF) 3-way IS-IS handshake on old IOSv images. On the other hand, all IS-IS integration tests pass for IOSv and IOSvL2. I wondered what was going on.

Fortunately, a few months ago, I spent some time installing the client-side Edgeshark components on my laptop. All I needed to do was enable the edgeshark tool in my lab topology and restart the lab.

I already had the lab topology that would replicate the problem – the “network types” IS-IS integration test – and I wanted to use it without modifying it. Obviously, I could copy it into another file and modify that one, but that’s how you end up with a thousand twisty little files, all alike.

However, there’s always another nerd knob™. netlab allows you to enable an external tool in all lab topologies with a default setting, and you can specify a default setting in an environment variable. All I had to do to enable Edgeshark integration was:

$ export NETLAB_TOOLS_EDGESHARK_ENABLED=True

A few minutes later, I had an answer to my initial question: at least FRRouting and Arista EOS ignore the missing sub-TLVs in the P2P IS-IS hello messages and happily establish adjacency with a Cisco router sending pre-standard content.