Chapter 18 ALG

Table 108 Network > ALG (continued)

LABEL

DESCRIPTION

Enable FTP

Turn on the FTP ALG to allow FTP sessions to pass through the ZyWALL. FTP (File

Transformations

Transfer Program) enables fast transfer of files, including large files that may not be

 

possible by e-mail.

 

Using the FTP ALG allows you to use bandwidth management on FTP traffic.

 

 

FTP Signaling

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

Port

 

 

 

Additional FTP

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

Signaling port

 

for

 

transformations

 

 

 

Apply

Click Apply to save your changes back to the ZyWALL.

 

 

Reset

Click Reset to begin configuring this screen afresh.

 

 

18.3 ALG Technical Reference

Here is more detailed information about the Application Layer Gateway.

ALG

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.

ALG and Trunks

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 connections to the second (passive) interface when the active interface’s connection goes down. When the active interface’s connection fails, the client needs to re-initialize the connection through the second interface (that was set to passive) in order to have the connection go through the second interface. VoIP clients usually re-register automatically at set intervals or the users can manually force them to re-register.

FTP

File Transfer Protocol (FTP) is an Internet file transfer service that operates on the Internet and over TCP/IP networks. A system running the FTP server accepts commands from a system running an FTP client. The service allows users to send commands to the server for uploading and downloading files.

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ZyWALL USG 100/200 Series User’s Guide