Chapter 11 Network Address Translation (NAT)
VMG3925-B10A 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 VMG registers with the SIP register server, the SIP ALG translates the VMG’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 VMG is behind a SIP ALG.
Use this screen to enable and disable the NAT and SIP (VoIP) ALG in the VMG. To access this
screen, click Network Setting > NAT > ALG.
Figure 85 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 VMG applies the rules in the order that you specify.
When a rule matches the current packet, the VMG takes the corresponding action and the
remaining rules are ignored.
Click Network Setting > NAT > Address Mapping to display the following screen.
Figure 86 Network Setting > NAT > Address Mapping
Table 63 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.
RTSP ALG
Enable this to have the VMG detect RTSP traffic and help build RTSP sessions through its
NAT. The Real Time Streaming (media control) Protocol (RTSP) is a remote control for
multimedia on the Internet.
PPTP ALG
Enable this to turn on the PPTP ALG on the VMG to detect PPTP traffic and helps build PPTP
sessions through the VMG’s NAT.
IPSEC ALG
Enable this to turn on the IPsec ALG on the VMG to detect IPsec traffic and helps build IPsec
sessions through the VMG’s NAT.
Apply Click Apply to save your changes.
Cancel Click Cancel to restore your previously saved settings.
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