Alg; Technical Reference; Nat Port Forwarding: Services And Port Numbers - ZyXEL Communications LTE3316-M604 User Manual

11.5 ALG

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.
To enable and disable the SIP ALG in the Zyxel Device, click Configuration > Network > NAT > ALG. The
screen appears as shown.
Figure 52 Configuration > Network > NAT > ALG
The following table describes the labels in this screen.
Table 38 Configuration > Network > NAT > ALG
LABEL
ALG-SIP
Apply
Cancel

11.6 Technical Reference

The following section contains additional technical information about the Zyxel Device features
described in this chapter.

11.6.1 NAT Port Forwarding: Services and Port Numbers

A port forwarding set is a list of inside (behind NAT on the LAN) servers, for example, web or FTP, that you
can make accessible to the outside world even though NAT makes your whole inside network appear
as a single machine to the outside world.
Use the Port Forwarding screen to forward incoming service requests to the server(s) on your local
network. You may enter a single port number or a range of port numbers to be forwarded, and the local
IP address of the desired server. The port number identifies a service; for example, web service is on port
80 and FTP on port 21. In some cases, such as for unknown services or where one server can support
Chapter 11 NAT
DESCRIPTION
Select Enable to make sure SIP (VoIP) works correctly with port-forwarding and address-
mapping rules. Otherwise, select Disable to turn off the SIP ALG.
Click Apply to save your changes back to the Zyxel Device.
Click Cancel to begin configuring this screen afresh.
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