Chapter 11 Network Address Translation (NAT)
PMG5317-T20A User’s Guide
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Figure 81 NAT Application With IP Alias
Port Forwarding: Services and Port Numbers
The most often used port numbers are shown in the following table. Please refer to RFC 1700 for
further information about port numbers..
Port Forwarding Example
Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (A in the example),
port 80 to another (B in the example) and assign a default server IP address of 192.168.1.35 to a
third (C in the example). You assign the LAN IP addresses and the ISP assigns the WAN IP address.
The NAT network appears as a single host on the Internet.
Table 58 Services and 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
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