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Chapter 4: Configuration
Virtual Server (“Port Forwarding”)
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
will usually need to configure your router to forward these incoming connection attempts using
specific ports to the PC on your network running the application. You will also need to use port
forwarding if you want to host an online game server.
The reason for this is that when using NAT, your publicly accessible IP address will be used by
and point to your router, which then needs to deliver all traffic to the private IP addresses used
by your PCs. Please see the WAN configuration section of this manual for more 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
ports 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 in Table 4, for further
information, please see IANA’s website at:
http://www.iana.org/assignments/port-numbers
For help on determining which private port numbers are used by common applications on this
list, please see the FAQs (Frequently Asked Questions) at:
http://www.billion.com
Table 4: Well-know 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)
103