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Chapter 10 Network Address Translation (NAT)
EMG5324-D10A User’s Guide
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10.6 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 Device registers with the SIP register server, the SIP ALG translates the 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 Device is behind a SIP ALG.
Use this screen to enable or disable the SIP (VoIP) ALG in the Device. To access this screen, click
Network Setting > NAT > ALG.
Figure 78 Network Setting > NAT > ALG
The following table describes the fields in this screen.
10.7 Technical Reference
This section provides some technical background information about the topics covered in this
chapter.
10.7.1 NAT Definitions
Inside/outside denotes where a host is located relative to the Device, for example, the computers
of your subscribers are the inside hosts, while the web servers on the Internet are the outside
hosts.
Global Start IP Enter the starting Inside Global IP Address (IGA). Enter 0.0.0.0 here if you have a dynamic
IP address from your ISP. You can only do this for the Many-to-One mapping type.
Global End IP Enter the ending Inside Global IP Address (IGA). This field is blank for One-to-One and
Many-to-One mapping types.
MAP Set Select the number of the mapping set for which you want to configure.
OK Click OK to save your changes.
Cancel Click Cancel to exit this screen without saving.
Table 45 Address Mapping: Add/Edit (continued)
LABEL DESCRIPTION
Table 46 Network Setting > NAT > ALG
LABEL DESCRIPTION
ALG Enable this to make sure SIP (VoIP) works correctly with port-forwarding and address-
mapping rules.
Apply Click Apply to save your changes.