ZyXEL Communications Prestige 623ME-T User Manual

Page 59

Prestige 623ME-T User’s Guide

NAT

5-3

Figure 5-2 Multiple Servers Behind NAT Example

Please note that a server can support more than one service, e.g., a server can provide both FTP and DNS
service, while another provides only web service. Also, since you need to specify the IP address of a server
in the Prestige, a server must have a fixed IP address and not be a DHCP client whose IP address potentially
changes each time it is powered on.
In addition to the servers for specific services, SUA 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 server is not
defined, the service request is simply discarded.
The most often used port numbers are described in the following table:

Table 5-1 NAT Mode

SERVICES PORT

NUMBER

FTP (File Transfer Protocol)

Telnet 23

SMTP (Simple Mail Transfer Protocol)

DNS(Domain Name System)

HTTP (Hyper Text Transfer Protocol or WWW, Web)

PPTP (Point-to-Point Tunneling Protocol)

1723