ZyXEL ZyWALL USG 2000 User Guide - Page 407
ALG Technical Reference
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Chapter 21 ALG Table 101 Configuration > Network > ALG (continued) LABEL DESCRIPTION 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 Chapter 32 on page 521). 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. FTP Signaling Port Additional FTP Signaling Port for Transformations Apply Reset 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. If you are using a custom TCP port number (not 21) for FTP traffic, enter it here. 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. 21.3 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 ZyWALL USG 2000 User's Guide 407
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