User's Manual

Chapter 9 Network Address Translation (NAT)

P-660HW-Tx v3 Series User’s Guide

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9.5 The SIP ALG Screen

Some NAT routers may include a SIP Application Layer Gateway (ALG). A SIP ALG

allows SIP calls to pass through NAT by examining and translating IP addresses

embedded in the data stream. When the ZyXEL Device registers with the SIP

inside the SIP data stream to a public IP address. You do not need to use STUN or

an outbound proxy if your ZyXEL Device is behind a SIP ALG.

Use this screen to enable and disable the SIP (VoIP) ALG in the ZyXEL Device. To

access this screen, click Network > NAT > ALG.

Figure 73 Network > NAT > ALG

The following table describes the fields in this screen.

9.6 NAT Technical Reference

This chapter contains more information regarding NAT.

9.6.1 NAT Definitions

Inside/outside denotes where a host is located relative to the ZyXEL Device, for

example, the computers of your subscribers are the inside hosts, while the web

servers on the Internet are the outside hosts.

Global/local denotes the IP address of a host in a packet as the packet traverses a

router, for example, the local address refers to the IP address of a host when the

Table 49 Network > NAT > ALG

LABEL DESCRIPTION

Enable SIP ALG Select this to make sure SIP (VoIP) works correctly with port-

forwarding and address-mapping rules.

Apply Click this to save your changes.

Reset Click this to restore your previously saved settings.