postgresql definitive list of network resources used/needed?

I'm currently standing up a number of PostgreSQL 14 servers. There is a
question concerning ports and protocols required or used by PostgreSQL.
Unfortunately, I can't seem to find any such listing. Most references only
mention the primary connection port, ex: tcp 5432.

Apparently, I've discovered that PostgreSQL connects to itself over UDP.
I've also discovered, while looking at the network while one of our server
was running PostgreSQL, that while there were a number of connections
between local 5432 and a random remote port, there was also a connection
from a local random port to a remote 5432. If these ports were closed and
only 5432 left open, this connection would have failed.

Does anyone know where I might find the definitive listing of ports and
protocols used by PostgreSQL?

Thanks,
rik.