ZyXEL Communications 1000 ユーザーズマニュアル

 Chapter 21 ALG

ZyWALL USG 1000 User’s Guide

Here is more detailed information about the Application Layer Gateway.

Some applications cannot operate through NAT (are NAT un-friendly) because 
they embed IP addresses and port numbers in their packets’ data payload. The 
ZyWALL examines and uses IP address and port number information embedded in 
the VoIP traffic’s data stream. When a device behind the ZyWALL uses an 
application for which the ZyWALL has VoIP pass through enabled, the ZyWALL 
translates the device’s private IP address inside the data stream to a public IP 
address. It also records session port numbers and allows the related sessions to 
go through the firewall so the application’s traffic can come in from the WAN to the 
LAN. 

If you send your ALG-managed traffic through an interface trunk and all of the 
interfaces are set to active, you can configure routing policies to specify which 
interface the ALG-managed traffic uses.

You could also have a trunk with one interface set to active and a second interface 
set to passive. The ZyWALL does not automatically change ALG-managed 

Enable FTP ALG

Turn on the FTP ALG to detect FTP (File Transfer Program) traffic and 
help build FTP sessions through the ZyWALL’s NAT. Enabling the FTP 
ALG also allows you to use the application patrol to detect FTP traffic 
and manage the FTP traffic’s bandwidth (see 

).

Enable FTP 
Transformations

Select this option to have the ZyWALL modify IP addresses and port 
numbers embedded in the FTP data payload to match the ZyWALL’s 
NAT environment. 

Clear this option if you have an FTP device or server that will modify IP 
addresses and port numbers embedded in the FTP data payload to 
match the ZyWALL’s NAT environment.

FTP Signaling 
Port 

If you are using a custom TCP port number (not 21) for FTP traffic, 
enter it here. 

Additional FTP 
Signaling Port  
for 
Transformations

If you are also using FTP on an additional TCP port number, enter it 
here. 

Apply

Click Apply to

 

save your changes back to the ZyWALL.

Reset

Click Reset to return the screen to its last-saved settings. 

Table 101   Configuration > Network > ALG (continued)