Chapter 8 Network Address Translation (NAT)
P-660HN-51 User’s Guide
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8.6 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 Settings > NAT > ALG.
Figure 51 Network Settings > NAT > ALG
The following table describes the fields in this screen.
8.7 The Sessions Screen
Use the Sessions screen to limit the number of concurrent NAT sessions all clients can use.
Click Network Settings > NAT > Sessions to display the following screen.
Figure 52 Network Settings > NAT > Sessions
Table 34 Network Settings > 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 Apply to save your changes.
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