ZyXEL Communications MAX-200HW2, User Manual

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Chapter 10 NAT
MAX-200HW2 Series User ’ s Guide
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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.
10.1.3 SIP 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. See Section 10.2.5 on page 135 for information on configuring
the ZyXEL Device ’ s ALG.
10.2 NAT Screens
10.2.1 NAT General Screen
Use this screen to enable and disable NAT and to allocate memory for NAT and firewall rules.
To access this screen, click Network > NAT > General .
Figure 83 Network > NAT > General
Each field is described in the following table.
Table 46 Network > NAT > General
LABEL DESCRIPTION
NAT Setup
Enable Network
Address
Translation
Select this if you want to use port forwarding, trigger ports, or any of the ALG.