IPv6 OSPFv3 MTU Quirk with Brocade and Quagga

One of the things learned in my time at previous job, was the interoperability between IPv6 routing protocols and platforms. I ran into a quirk when deploying some Quagga boxes (0.99.x version) talking OSPFv3 with some Brocade routers running NetIron 5.x. The issue was that if MTU wasn’t specifically configured on the Brocade interface facing the Quagga box, OSPFv3 wouldn’t properly negotiate and was pretty much useless. However setting the MTU on the Brocade interface to 1500 fixed this. It is possible that this would also work with jumbo frame MTU settings, however the machines weren’t getting configured or deployed for that. Just something to look out for in the lab or production, if OSPFv3 appears configured correctly everywhere, but won’t establish. Quagga’s BGP had no issue with communicating properly with a Brocade router that didn’t specify MTU on its interface, it was only OSPFv3 that appeared to be affected.