User`s guide

Chapter 9 The NAT Configuration Screens
User’s Guide
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3 The Real Audio server responds using a port number ranging between 6970-7170.
4 The WiMAX Modem forwards the traffic to Jane’s computer IP address.
5 Only Jane can connect to the Real Audio server until the connection is closed or times
out. The WiMAX Modem times out in three minutes with UDP (User Datagram
Protocol), or two hours with TCP/IP (Transfer Control Protocol/Internet Protocol).
Two points to remember about trigger ports:
1 Trigger events only happen on data that is coming from inside the WiMAX Modem and
going to the outside.
2 If an application needs a continuous data stream, that port (range) will be tied up so that
another computer on the LAN can’t trigger it.
9.5 ALG
Some applications, such as SIP, cannot operate through NAT (are NAT un-friendly) because
they embed IP addresses and port numbers in their packets’ data payload.
Some NAT routers may include a SIP Application Layer Gateway (ALG). An Application
Layer Gateway (ALG) manages a specific protocol (such as SIP, H.323 or FTP) at the
application layer.
A SIP ALG allows SIP calls to pass through NAT by examining and translating IP addresses
embedded in the data stream.
Click ADVANCED > NAT Configuration > ALG to enable and disable SIP (VoIP), FTP
(file transfer), and H.323 (audio-visual) ALG in the WiMAX Modem.
Figure 56 ADVANCED > NAT Configuration > ALG
The following table describes the labels in this screen.
Table 38 ADVANCED > NAT Configuration > ALG
LABEL DESCRIPTION
Enable SIP ALG
Select this to make sure SIP (VoIP) works correctly with port-forwarding and port-
triggering rules.
Enable FTP ALG
Select this to make sure FTP (file transfer) works correctly with port-forwarding
and port-triggering rules.
Enable H.323
ALG
Select this to make sure H.323 (audio-visual programs, such as NetMeeting)
works correctly with port-forwarding and port-triggering rules.
Apply
Click to save your changes.
Cancel Click to return to the previous screen without saving your changes.