For setting up the environment, I was following this really in-depth guide from former Data Platform MVP and current Microsoft employee Ryan J. Adams: Build a SQL Cluster Lab Part 1
The guide is generally fantastic, and provides a lot of good insight into the non-SQL Server related aspects of setting up an Availability Group. I’d highly recommend checking it out if you’re interested in that sort of thing.
Relevant to this post, he has provided a diagram of how the different networks are configured:
If you’re very experienced with networking, you may already have some idea of what the problem is going to be. Don’t spoil it for everyone else okay?
I’ll admit I did not have an idea of what the problem was.