4.2.14 Additional Information - Port Triggering
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DDW2600 Wireless & DDC2700 Commercial Cable Modem/Router Subscriber User Guide • May, 2010
4.2.14
Additional Information - Port Triggering
Some services use a dedicated range of ports on the client side and a dedicated
range of ports on the server side. With regular port forwarding you set a forwarding
rule to forward a service to the IP address of a LAN side host. The problem is that port
forwarding forwards a service to a
single
LAN IP address.
With port triggering, we define 2 kinds of ports: Trigger Port and Target Port. Trigger
port is defined as the service request with a specific destination port number sent from
a LAN side host. Target Port is defined as the ports this specific application requires a
LAN host to listen to. Thus, the server returns responses to these ports.
Example:
1. John requests a file from the Real Audio server (port 7070).
Port 7070 is a “trigger”
port and causes the cable modem to record John’s computer IP address. The
cable modem associates John's computer IP address with the "target" port range
of 6970-7170.
2. The Real Audio server responds to a port number ranging between 6970-7170.
3. The cable modem forwards the traffic to John’s computer IP address.
4. Only John can connect to the Real Audio server until the connection is closed or
times out.
