Chapter 8 Network Address Translation (NAT)

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. Please also refer to the Supporting CD for more examples and details on port forwarding and NAT.

Table 43 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

 

 

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 69 Multiple Servers Behind NAT Example

A=192.168.1.33

192.168.1.1

B=192.168.1.34

IP address assigned by ISP

C=192.168.1.35 D=192.168.1.36

 

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P-870HN-51D User’s Guide