Chapter 11 Network Address Translation (NAT)
VMG8825-B 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 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 92 Network Setting > NAT > ALG
The following table describes the fields in this screen.
Apply Click Apply to save your changes.
Cancel Click Cancel to restore your previously saved settings.
Table 63 Network Setting > NAT > DMZ (continued)
LABEL DESCRIPTION
Table 64 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 help 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 help 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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