I received an email from a client who is having issues with third-party applications connecting to their three-subnet SQL Server Availability Group. After an exchange with Microsoft Support, they discovered that the applications weren’t specifying MultiSubNetFailover = True in their connection strings. As a result, because RegisterAllProvidersIP = 1 in the cluster, connections were randomly experiencing high latency upon connecting, as client-side DNS queries over time had a 66% chance of returning the wrong IP from the listener.
They set RegisterAllProvidersIP = 0, but before you take that as advice keep reading.
Read on to learn why this is not a first-best solution.