Port Numbers

____________________________________________ 

The port number system works beautifully, but naturally the hosts need to agree on what port is used for a given protocol. In the previous example, if 10.1.1.1 used TCP port 45 for Telnet and 10.1.1.2 used TCP port 55, we'd have some serious problems.

That's why most protocols use the same port number at all times, and these port numbers are referred to as well-known port numbers. All port numbers below 1024 are reserved, well-known port numbers -- but you don't have to memorize 1024 numbers for the exams!

Some Common TCP Ports :

 -  FTP :- File Transfer Protocol - Uses TCP ports 20 and 21

 -  SSH :- Secure Shell - Uses TCP port 22

 -  Telnet uses TCP port 23

 -  HTTP :- HyperText Transfer Protocol - uses TCP port 80

 -  POP3 :- Post Office Protocol 3 - uses TCP port 110

 -  SSL - Secure Socket Layer - uses TCP port 443

Some Common UDP ports:

 -  DHCP :- Dynamic Host Control Protocol - uses UDP ports 67 and 68

 -  TFTP :- Trivial File Transfer Protocol - uses UDP port 69

 -  SNMP :- Simple Network Management Protocol - uses UDP port 161

Protocols using both TCP and UDP ports

 -  DNS :- Domain Name Service - uses UDP and TCP port 53

 -  The port number 24 is reserved in both UDP and TCP for private mail systems. 

With Voice over IP (VoIP) becoming more and more commonplace in today's networks, it couldn't hurt to know that the entire range of UDp ports from 16384 - 32767 are reserved for voice traffic. 

On a CISCO router to see the list of well know ports use the following command :-

R1(config)#access-list 100 permit tcp any any eq ?

____________________________________________