Operation Manual

Cerberus ADSL2 Wi-Fi Plus (P6331-6)
50
Configuration / Virtual Server
In TCP/IP and UDP networks a port is a 16-bit number used to identify which application
program (usually a server) incoming connections should be delivered to. Some ports have
numbers that are pre-assigned to them by the IANA (the Internet Assigned Numbers
Authority), and these are referred to as “well-known ports”. Servers follow the well-known port
assignments so clients can locate them.
If you wish to run a server on your network that can be accessed from the WAN (i.e. from
other machines on the Internet that are outside your local network), or any application that can
accept incoming connections (e.g. Peer-to-peer/P2P software such as instant messaging
applications and P2P file-sharing applications) and are using NAT (Network Address
Translation), then you need to configure your router to forward these incoming connection
attempts using specific ports to the PC on your network running the application. You also need
to use port forwarding if you wish to host an online game server.
The reason is that when using NAT, your publicly accessible IP address is used by and points
to your router, which needs to deliver all traffic to the private IP addresses used by your PCs.
Please see the WAN configuration section of this manual for information on NAT.
The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment
of unique parameter values for Internet protocols. Port numbers range from 0 to 65535, but
only port numbers 0 to 1023 are reserved for privileged services and are designated as “well-
known ports”. The registered ports are numbered from 1024 through 49151. The remaining
ports, referred to as dynamic ports, or private ports, are numbered from 49152 through 65535.
Examples of well-known and registered port numbers are shown below, for further
information, please see IANA’s website at: http://www.iana.org/assignments/port-numbers
Well-known and Registered Ports
Port
Number
Protocol Description
20 TCP FTP Data
21 TCP FTP Control
22 TCP & UDP SSH Remote Login Protocol
23 TCP Telnet
25 TCP SMTP (Simple Mail Transfer Protocol)
53 TCP & UDP DNS (Domain Name Server)
69 UDP TFTP (Trivial File Transfer Protocol)
80 TCP World Wide Web HTTP
110 TCP POP3 (Post Office Protocol Version 3)
119 TCP NEWS (Network News Transfer Protocol)
123 UDP NTP (Network Time Protocol)
161 TCP SNMP
443 TCP & UDP HTTPS
1503 TCP T.120
1720 TCP H.323
4000 TCP ICQ
7070 UDP RealAudio