I was setting up an availability group listener recently and when I tried to connect to the listener I got an error message to say “The host cannot be found” after the usual 15 seconds connection delay.
I checked the usual thing like TCP was enabled on the replicas and that routing was configured, but every time I tried I kept getting the “The host cannot be found” error. Now, I don't know about you, but I find error messages like this completely infuriating especially when I knew the hostname of the listener resolved because I could ping the damn thing (and then connect straight to the IP address.