Port Numbers

A port number is part of the addressing information used to identify the senders and receivers of messages. Port numbers are most commonly used with TCP/IP connections. Home network routers and computer software work with ports and sometimes allow you to configure port number settings. These port numbers allow different applications on the same computer to share network resources simultaneously.

Port numbers are from 0 to 65536. Ports 0 to 1024 are reserved for use by certain privileged services. For the HTTP service, port 80 is defined as a default and it does not have to be specified in the Uniform Resource Locator (URL). Port Numbers are typically found in the services file on your system. List below is an example.


# This file contains port numbers for well-known services as defined by
# RFC 1060 (Assigned Numbers).
#
# Format:
#
# / [aliases...] [#]

echo	7/tcp
echo	7 /udp
discard	9/tcp sink null
discard	9/udp sink null
systat	11/tcp
systat	11/tcp users
daytime	13/tcp
daytime	13/udp
netstat	15/tcp
qotd	17/tcp quote
qotd	17/udp quote
chargen	19/tcp ttytst source
chargen	19/udp ttytst source
ftp-data	20/tcp
ftp	21/tcp
telnet	23/tcp
smtp	25/tcp mail
time	37/tcp timserver
time	37/udp timserver
rlp	39/udp resource # resource location
name	42/tcp nameserver
name	42/udp nameserver
whois	43/tcp nicname # usually to sri-nic
domain	53/tcp nameserver # name-domain server
domain	53/udp nameserver
nameserver	53/tcp domain # name-domain server
nameserver	53/udp domain
mtp	57/tcp # deprecated
bootp	67/udp # boot program server
tftp	69/udp
rje	77/tcp netrjs
finger	79/tcp
link	87/tcp ttylink
supdup	95/tcp
hostnames	101/tcp hostname # usually from sri-nic
iso-tsap	102/tcp
dictionary	103/tcp webster
x400	103/tcp # ISO Mail
x400-snd	104/tcp
csnet-ns	105/tcp
pop	109/tcp postoffice
pop2	109/tcp # Post Office
pop3	110/tcp postoffice
portmap	111/tcp
portmap	111/udp