If wonder what ports are the default for a given service, you can look
them up by inspecting the /etc/services file which is present on
most Unix systems, including macOS. E.g. if you wonder which port is
the default for SSH, you can do:
$ grep -w ssh /etc/services
ssh 22/tcp
ssh 22/udp
ssh 22/sctp
..
The other way works too. Say you wonder which services are related to
389 and 636, you can do:
$ egrep -w '389|636' /etc/services
ldap 389/tcp
ldap 389/udp
ldaps 636/tcp
ldaps 636/udp
I find having /etc/services at my fingertips extremely useful, hope
you do too!
