ZyXEL NSA325 User Manual

Chapter 9 Network

Media Server User’s Guide

If your Internet gateway supports Port Address Translation (PAT is sometimes included with a port 
forwarding feature), you can have the Internet users use a different TCP port number from the one 
the NSA uses for the service.

UPnP Port Address Translation for FTP Example

In the above example, the Internet gateway uses PAT to accept Internet user FTP sessions on port 
2100, translate them to port 21, and forward them to the NSA. 

It is recommended that the NSA use a static IP address (or a static DHCP IP address) if you will 
allow access to the NSA from the Internet. The UPnP-created NAT mappings keep the IP address 
the NSA had when you applied your settings in the UPnP Port Mapping screen. They do not 
automatically update if the NSA’s IP address changes. 

Note: WAN access stops working if the NSA’s IP address changes.

For example, if the NSA’s IP address was 192.168.1.33 when you applied the UPnP Port Mapping 
screen’s settings and the NSA later gets a new IP address of 192.168.1.34 through DHCP, WAN 
access stops working because the Internet gateway still tries to forward traffic to IP address 
192.168.1.33. Since you can no longer access the NSA from the WAN, you would have to access 
the NSA from the LAN and re-apply your UPnP Port Mapping screen settings to update the 
Internet gateway’s UPnP port mappings. 

UPnP Using the Wrong IP Address

UPnP’s automated nature makes it easier to use than manually configuring firewall and NAT rules, 
but it is also less secure. Using UPnP may make your network more susceptible to snooping and 
hacking attacks.