I have been cleaning up the code and checking the specification for the Ethernet Router Hello message to make sure I have implemented it fully. In doing so I realised that I was not setting the router information in the router list correctly to indicate that I had established two-way communication with the routers that had sent Ethernet Router Hello messages to me. This is why the simulated VAX780 was immediately saying that the adjacency was down after saying it was up. Now that I am reporting the status and priority correctly the 780 says the adjacency is up and it stays up.