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Ports

What is a port? Well, a port is used by TCP (Transmission Control Protocol) to provide a connection for commonly occurring or standard traffic. An example would be e-mail.

Before I explain this and show you how it works, I want to make clear that these port numbers are not carved in stone. If you have a fairly configurable piece of software, you can change these port numbers to anything you want. For purposes of explanation, I will be using the default/common port numbers.

You open up your e-mail program and check your mail (Ok, another explanation. There are a few ways you can check your e-mail. Some examples are POP, Kerberos and IMAP. They vary in degrees of security for the authentication procedure and options that the server will allow you to use to control your e-mail. For now, I'm just going to stick with straight POP3 ident and auth.) Ok, where were we? Oh yeah, you open up your e-mail and check for new mail. Well, you use port 113 to do the identification and authorization for your account info and password, you receive your e-mail on port 110, and you send your outgoing mail on port 25.

Why all the different ports? Well, they mainly serve to help sort out all the traffic coming into/out of your computer. If you're anything like me, I download files, browse internet sites (I really dislike the term "Surfing the Net"), chat in ICQ, and upload files to my web page server, all at the same time. That's a lot of data to keep track of. Ports help to keep all that data separate and going to the right places.

I've listed below some standard port numbers for the common types of activities. In addition to the basic usage ports which are numbered 0 - 1023 called Well Known Ports (BTW, these are assigned by IANA (Internet Assigned Numbers Authority)), there are two more categories of ports. Registered Ports which are 1024 - 49151, and Dynamic/Private Ports numbered 49152 - 65535.

Name # Function
ftp-data
ftp
telnet
smtp
domain
whois++
gopher
finger
http
kerberos
pop2
pop3
ident
auth
sftp
nntp
ntp
imap
irc
qmtp
softpc
imap3
openport
ldap
genie
imsp
infoseek
snpp
appleqtc
ph
mynet
who
irc-serv
klogin
whoami
eudora-set
doom
kerberos-adm

20
21
23
25
53
63
70
79
80
88
109
110
113
113
115
119
123
143
194
209
215
220
260
389
402
406
414
444
458
481
511
513
529
543
565
592
666
749

File Transfer [Default Data]
File Transfer [Control]
Telnet
Simple Mail Transfer Protocol
Domain Name Server
whois++
Gopher
Finger
WWW/http (Internet connection)

Post Office Protocol 2
Post Office Protocol 3

Simple File Transfer Protocol
Network News Transfer Protocol
Network Time Protocol
Internet Message Access Protocol
Internet Relay Chat
Quick Mail Transfer Protocol
Insignia Solutions
Internet Mil Access Protocol 3
Openport
Lightweight Directory Access Protocol

Interactive Mail Support Protocol

Simple Network Paging Protocol
Apple Quick time

mynet-as
Who is logged on

Doom Id software
kerberos administration


 

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