21

ALG

21.1 ALG Overview

Application Layer Gateway (ALG) allows the following applications to operate properly through the ZyWALL’s NAT.

•SIP - Session Initiation Protocol (SIP) - An application-layer protocol that can be used to create voice and multimedia sessions over Internet.

•H.323 - A teleconferencing protocol suite that provides audio, data and video conferencing.

•FTP - File Transfer Protocol - an Internet file transfer service.

The following example shows SIP signaling (1) and audio (2) sessions between SIP clients A and B and the SIP server.

Figure 299 SIP ALG Example

The ALG feature is only needed for traffic that goes through the ZyWALL’s NAT.

21.1.1 What You Can Do in this Chapter

Use the ALG screen (Section 21.2 on page 405) to set up SIP, H.323, and FTP ALG settings.

 

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ZyWALL USG 2000 User’s Guide