ZyXEL Communications P-2302HWL-P1 Series - Manual (Page 133)

P-2302HW/HWL-P1 Series User’s Guide
Chapter 8 NAT 133
1 Jane requests a file from the Real Audio server (port 7070).
2 Port 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 6970-7170.
3 The Real Audio server responds using a port number ranging between 6970-7170.
4 The ZyXEL Device forwards the traffic to Jane’s computer IP address.
5 Only 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).
8.1.2.2 Two Points To Remember About Trigger Ports
1 Trigger events only happen on data that is coming from inside the ZyXEL Device and
going to the outside.
2 If 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.