Technical Reference - ZyXEL Communications NXC5200 User Manual

Chapter 15 ALG
Table 79 Configuration > Network > ALG (continued)
LABEL
Enable FTP ALG
Enable FTP
Transformations
FTP Signaling
Port
Additional FTP
Signaling Port
for
Transformations
Apply
Reset

15.3 Technical Reference

The following section contains additional technical information about the features
described in this chapter.
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
NXC examines and uses IP address and port number information embedded in the
VoIP traffic's data stream. When a device behind the NXC uses an application for
which the NXC has VoIP pass through enabled, the NXC 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.
FTP
File Transfer Protocol (FTP) is an Internet file transfer service that operates on the
Internet and over TCP/IP networks. A system running the FTP server accepts
commands from a system running an FTP client. The service allows users to send
commands to the server for uploading and downloading files.
230
DESCRIPTION
Turn on the FTP ALG to detect FTP (File Transfer Program) traffic and
help build FTP sessions through the NXC'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.
Select this option to have the NXC modify IP addresses and port
numbers embedded in the FTP data payload to match the NXC's NAT
environment.
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 NXC'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 NXC.
Click Reset to return the screen to its last-saved settings.
NXC5200 User's Guide