AWS to ASA VPN Issues

I needed to build a VPN tunnel from Threat Defence to AWS, which seemed to work fine. Until the VPN had been up for an hour that is…
After an hour, I was getting reports of tunnel traffic dropping out. This happened regularly every hour.
After a few hours of watching debugs and discussions with TAC, the answer presented itself.

Dynamic Routing and FEX

A few weeks ago I was working on a customer’s network when I found an OSPF problem. For some reason, an ASA wouldn’t peer with a Nexus switch. To make it a bit weirder, the problem only happened on the default VRF, and only with OSPFv3. On the Nexus side, I could see the ASA neighbour, but it was stuck in INIT. On the ASA side, I couldn’t see the neighbour at all.