ZyXEL Communications NXC Series - Overview; What You Can Do in this Chapter; What You Need to Know; Alg

NXC Series User’s Guide
196
CHAPTER 13
ALG
13.1 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.
13.1.1 What You Can Do in this Chapter
The ALG screen (Section 13.2 on page 196) configures the FTP ALG settings.
13.1.2 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 unfriendly
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.
13.1.3 Before You Begin
You must also enable NAT in the NXC to allow sessions initiated from the WAN.
13.2 ALG
Click Configuration > Network > ALG to open this screen. Use this screen to turn the ALG off or on,
configure the port numbers to which it applies.