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12.1 Overview
Application Layer Gateway (ALG) allows the following application to operate properly through the
NXC's NAT.
• FTP - File Transfer Protocol - an Internet file transfer service.
The ALG feature is only needed for traffic that goes through the NXC's NAT.
12.1.1 What You Can Do in this Chapter
The ALG screen
12.1.2 What You Need to Know
The following terms and concepts may help as you read this chapter.
Application Layer Gateway (ALG) and NAT
The NXC can function as an Application Layer Gateway (ALG) to allow certain NAT un-friendly
applications to operate properly through the NXC's NAT. The NXC dynamically creates an implicit
NAT session for the application's traffic from the WAN to the LAN. The ALG on the NXC supports all
of the NXC'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) rules if you want to allow
access to the server from the WAN.
12.1.3 Before You Begin
You must also enable NAT in the NXC to allow sessions initiated from the WAN.
NXC2500 User's Guide
(Section 12.2 on page
148) configures the FTP ALG settings.
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HAPTER
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ALG
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Troubleshooting
