ZyXEL Communications Network Card unified security gateway Manuel d'utilisateur télécharger pdf (Page 357)

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101

Chapter 19 ALG

ZyWALL USG 20/20W User’s Guide

357

19.3 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

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 98 Configuration > Network > ALG (continued)

LABEL DESCRIPTION

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