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 whose IP address is, with a web server running on port 80, the local computer would connect to the remote computer using the socket address :

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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