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network. You may enter a single port number or a range of port numbers to be forwarded, and
the local IP address of the desired server. The port number identifies a service; for example,
web service is on port 80 and FTP on port 21. In some cases, such as for unknown services or
where one server can support more than one service (for example both FTP and web service),
it might be better to specify a range of port numbers.
In addition to the servers for specified services, NAT supports a default server. A service
request that does not have a server explicitly designated for it is forwarded to the default server.
If the default is not defined, the service request is simply discarded.
The most often used port numbers are shown in the following table. Please refer to RFC 1700
for further information about port numbers.
SERVICES PORT NUMBER
ECHO 7
FTP (File Transfer Protocol) 21
SMTP (Simple Mail Transfer Protocol) 25
DNS (Domain Name System) 53
Finger 79
HTTP (Hyper Text Transfer protocol or WWW, Web) 80
POP3 (Post Office Protocol) 110
NNTP (Network News Transport Protocol) 119
SNMP (Simple Network Management Protocol) 161
SNMP trap 162
PPTP (Point-to-Point Tunneling Protocol) 1723
6.3.2 Configuring Servers Behind SUA (Example)
Let's say you want to assign ports 22-25 to one server, port 80 to another and assign a default
server IP address of 192.168.1.35 as shown in the next figure.