User's Manual Part 1

Chapter 9 Network Address Translation (NAT)
AMG1202-T10A User’s Guide
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9.5 The 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 register server, the SIP ALG translates the ZyXEL
Device’s private IP address 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 70 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.
Back Click this to return to the previous screen without saving.
Apply Click this to save your changes.
Cancel Click this to restore your previously saved settings.
Table 45 Network > NAT > Address Mapping: Edit (continued)
LABEL DESCRIPTION
Table 46 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.