Most Commonly Used Ports assigned by IANA

A port is an extension of an address, similar to adding an apartment or room number to a street address. A letter with a street address will arrive at the correct apartment building, but without the apartment number, it will not be delivered to the correct recipient. Ports work in much the same way. A packet can be delivered to the correct IP address, but without the associated port, there is no way to determine which application should act on the packet.

Once the ports have been defined, it is possible for the different types of information that are sent to one IP address to then be sent to the appropriate applications. By using ports, a service running on a remote computer can determine what type of information a local client is requesting, can determine the protocol needed to send that information, and maintain simultaneous communication with a number of different clients.

For example, if a local computer attempts to connect to the website www.example.com whose IP address is 192.168.1.10, with a web server running on port 80, the local computer would connect to the remote computer using the socket address : 192.168.1.10:80

In order to maintain a level of standardization among the most commonly used ports, IANA (Internet Assigned Numbers Authority) has established that the ports numbered from 0 to 1024 are to be used for common services. The remaining ports up through 65535 are used for dynamic allocations or particular services.

The most commonly used ports as assigned by the IANA (Internet Assigned Numbers Authority) are listed here:

Decimals	Keywords	Description
0		Reserved
1-4		Unassigned
5	rje	Remote Job Entry
7	echo	Echo
9	discard	Discard
11	systat	Active Users
13	daytime	Daytime
15	netstat	Who is Up or NETSTAT
17	qotd	Quote of the Day
19	chargen	Character Generator
20	ftp-data	File Transfer [Default Data]
21	ftp	File Transfer [Control]
22	ssh	SSH Remote Login Protocol
23	telnet	Telnet
25	smtp	Simple Mail Transfer Protocol
37	time	Time
39	rlp	Resource Location Protocol
42	nameserver	Host Name Server
43	nicname	Who Is
53	domain	Domain Name Server
67	bootps	Bootstrap Protocol Server
68	bootpc	Bootstrap Protocol Client
69	tftp	Trivial File Transfer
70	gopher	Gopher
75		any private dial out service
77		any private RJE service
79	finger	Finger
80	www-http	World Wide Web HTTP
95	supdup	SUPDUP
101	hostname	NIC Host Name Server
102	iso-tsap	ISO-TSAP Class 0
110	pop3	Post Office Protocol – Version 3
113	auth	Authentication Service
117	uucp-path	UUCP Path Service
119	nntp	Network News Transfer Protocol
123	ntp	Network Time Protocol
137	netbios-ns	NETBIOS Name Service
138	netbios-dgm	NETBIOS Datagram Service
139	netbios-ssn	NETBIOS Session Service
140-159		Unassigned
160-223		Reserved

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