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Appendix A TCP/IP Well-Known Port
Any application or process that uses TCP for its transport is assigned a unique identification number called a
TCP port. TCP ports specify the path of communications between client and server applications. These ports
are numbered beginning with zero. Port numbers for client applications are dynamically assigned by the
operating system when there is a request for service. Port numbers for server applications are pre-assigned by
the Internet Assigned Numbers Authority (IANA) and do not change, Following is a short list of some
well-known port numbers.
Table A-1 Well-Known TCP ports
Port No.
Name (TCP)
Description
20 FTP-DATA
FTP(data)
21 FTP
FTP(command)
23 TELNET
Terminal
Connection
25 SMTP
SMTP
53
DOMAIN Name
Domain Name Server
79 FINGER
Finger
80 HTTP
Web
110 POP3
POP3
113 AUTH
Authentication
Service
139
NETBIOS-SSN
NETBIOS Session Service
1723
PPTP
Point to Point Tunneling Protocol