ZyXEL UAG4100 User Guide - Page 239
ALG Overview
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CHAPTER 18 ALG 18.1 ALG Overview Application Layer Gateway (ALG) allows the following application to operate properly through the UAG's NAT. • FTP - File Transfer Protocol - an Internet file transfer service. The ALG feature is only needed for traffic that goes through the UAG's NAT. 18.1.1 What You Can Do in this Chapter Use the ALG screen (Section 18.2 on page 240) to set up the FTP ALG settings. 18.1.2 What You Need to Know Application Layer Gateway (ALG), NAT and Security Policy The UAG can function as an Application Layer Gateway (ALG) to allow certain NAT un-friendly applications to operate properly through the UAG's NAT and security policies. The UAG dynamically creates an implicit NAT session and security policy session for the application's traffic from the WAN to the LAN. The ALG on the UAG supports all of the UAG's NAT mapping types. FTP ALG The FTP ALG allows TCP packets with a specified port destination to pass through. If the FTP server is located on the LAN, you must also configure NAT (port forwarding) and security policies if you want to allow access to the server from the WAN. 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 UAG 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. UAG Series User's Guide 239