ZyXEL Communications ZyWALL 2 Plus - Manual (Page 341)

Chapter 17 Network Address Translation (NAT)
ZyWALL 2 Plus User’s Guide
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If you do not assign a Default Server IP address, the ZyWALL discards all
packets received for ports that are not specified here or in the remote
management setup.
17.5.2 Port Forwarding: Services and Port Numbers
Use the Port Forwarding screen to forward incoming service requests to the server(s) on your
local network. See
Appendix D on page 653 for a list of commonly used services and port
numbers.
The ZyWALL provides the additional safety of the DMZ ports for connecting your publicly
accessible servers. This makes the LAN more secure by physically separating it from your
public servers.
17.5.3 Configuring 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 221 Multiple Servers Behind NAT Example
17.5.4 Port Translation
The ZyWALL can translate the destination port number or a range of port numbers of packets
coming from the WAN to another destination port number or range of port numbers on the
local network. When you use port forwarding without port translation, a single server on the
local network can use a specific port number and be accessible to the outside world through a
single WAN IP address. When you use port translation with port forwarding, multiple servers
on the local network can use the same port number and still be accessible to the outside world
through a single WAN IP address.