ZyXEL ZyWALL USG 20 User Guide - Page 357
ALG Technical Reference
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Chapter 19 ALG Table 98 Configuration > Network > ALG (continued) LABEL DESCRIPTION Additional FTP Signaling Port for Transformations Apply Reset If you are also using FTP on an additional TCP port number, enter it here. Click Apply to save your changes back to the ZyWALL. Click Reset to return the screen to its last-saved settings. 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 ZyWALL USG 20/20W User's Guide 357