1Jane requests a file from the Real Audio server (port 7070).
2Port 7070 is a “trigger” port and causes the ZyXEL Device to record Jane’s computer IP address. The ZyXEL Device associates Jane's computer IP address with the "incoming" port range of
3The Real Audio server responds using a port number ranging between
4The ZyXEL Device forwards the traffic to Jane’s computer IP address.
5Only Jane can connect to the Real Audio server until the connection is closed or times out. The ZyXEL Device times out in three minutes with UDP (User Datagram Protocol), or two hours with TCP/IP (Transfer Control Protocol/Internet Protocol).
8.1.2.2Two Points To Remember About Trigger Ports
1Trigger events only happen on data that is coming from inside the ZyXEL Device and going to the outside.
2If an application needs a continuous data stream, that port (range) will be tied up so that another computer on the LAN can’t trigger it.
8.1.3 SIP 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 (see Chapter 9 on page 139) if your ZyXEL Device is behind a SIP ALG.
8.2 NAT Screens
8.2.1 NAT General Screen
Use this screen to enable and disable NAT and to allocate memory for NAT and firewall rules. To access this screen, click Network > NAT > General.
Chapter 8 NAT | 133 |