Chapter 10 Network Address Translation (NAT)

The most often used port numbers and services are shown in Appendix D on page 219. Please refer to RFC 1700 for further information about port numbers.

Note: Many residential broadband ISP accounts do not allow you to run any server processes (such as a Web or FTP server) from your location. Your ISP may periodically check for servers and may suspend your account if it discovers any active services at your location. If you are unsure, refer to your ISP.

10.4.1Configuring Servers Behind 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.

Figure 36 Multiple Servers Behind NAT Example

A=192.168.1.33 LAN

 

WAN

B=192.168.1.34

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

192.168.1.1

C=192.168.1.35

IP Address assigned by ISP

The following table summarizes the settings described in the above example.

Table 23 Multiple Servers Behind NAT Example

 

SERVERS

PORTS

DEFAULT SERVER

 

IP

 

 

 

A

FTP

21-22

192.168.1.33

 

 

 

 

B

Telnet

23

192.168.1.34

 

 

 

 

C

SMTP

25

192.168.1.35

 

 

 

 

 

93

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