Routing

This is a story about six months of work that didn’t ship, and what I’m still figuring out about why. The surface story is technical: I implemented RFC 8362 Extended LSA support for FRR’s ospf6d. The code works. The tests pass. It wasn’t accepted upstream. The deeper story is about what happens when…

On a good day, my day job involves building networking tools in python. Too many python networking tools look like shell scripts, spawning subprocesses for basic tools like ‘ping’ or ‘ip’ - often resulting in a fragile mess due to poor, or inconsistent error handling.

I was quite excited to find icmplib. It provides a much simpler, less fragile way to do things like reachability tests, RTT measurements, path discovery and path MTU discovery in python code. Hopefully it finds its way into Fedora soon!

Armed with icmplib, I went on a journey of discovery to develop my understanding of Path MTU. I specifically wanted to understand the differences between IPv4 and IPv6, and the effect of VETH, VLAN and Bridge virtual devices.

Sometimes there is good reason to talk to yourself. You might be doing a sound check, for example. Likewise, it can be useful to route IP packets between two interfaces on the same machine using an external path. One reason to do this is to test other network devices like routers or switches. For ma…