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This article is from the Firewalls FAQ, by Matt Curtin cmcurtin@interhack.net and Marcus J. Ranum mjr@nfr.com with numerous contributions by others.

56 How do I know which application uses what port? (Firewalls - TCP and UDP Ports)

There are several lists outlining the ``reserved'' and ``well known''
ports, as well as ``commonly used'' ports, and the best one is:
ftp://ftp.isi.edu/in-notes/iana/assignments/port-numbers. For those of you
still reading RFC 1700 to find out what port number does what, STOP DOING
IT. It is horribly out of date, and it won't be less so tomorrow. Now, as
for trusting this information: These lists do not, in any way, constitute
any kind of holy bible on which ports do what.

Wait, let me rephrase that: THERE IS NO WAY OF RELIABLY DETERMINING WHAT
PORT DOES WHAT SIMPLY BY LOOKING IN A LIST.

 

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security, Internet, firewalls, ssl, port, protection, application layer, proxy server, packet screening, filtering rules, viruses, terms