Chapter 11 Network Address Translation (NAT)
SBG3500-N Series User’s Guide
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11.6 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 SBG3500-N Series registers with the SIP register server, the SIP ALG translates the
SBG3500-N Series’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 SBG3500-N Series is behind a SIP ALG.
Use this screen to enable and disable the NAT and SIP (VoIP) ALG in the SBG3500-N Series. To
access this screen, click Network Setting > NAT > ALG.
Figure 92 Network Setting > NAT > ALG
The following table describes the fields in this screen.
11.7 The Address Mapping Screen
Ordering your rules is important because the SBG3500-N Series applies the rules in the order that
you specify. When a rule matches the current packet, the SBG3500-N Series takes the
corresponding action and the remaining rules are ignored.
Click Network Setting > NAT > Address Mapping to display the following screen.
Figure 93 Network Setting > NAT > Address Mapping
Table 60 Network Setting > NAT > ALG
LABEL DESCRIPTION
NAT ALG Enable this to make sure applications such as FTP and file transfer in IM applications work
correctly with port-forwarding and address-mapping rules.
SIP ALG
Enable this to make sure SIP (VoIP) works correctly with port-forwarding and address-
mapping rules.
Apply Click Apply to save your changes.
Cancel Click Cancel to restore your previously saved settings.
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