Setting Up Port Triggering (In Nat Mode) - NETGEAR ProSafe Quad WAN FR538G Reference Manual

Setting Up Port Triggering (in NAT mode)

This screen is used when the router is in NAT mode to configure port triggering for applications.
Some applications require that, when external devices connect to them, they receive data on a
specific port or range of ports in order to function properly. The router must send all incoming data
for that application only on the required port or range of ports.
Port triggering allows computers on the private network (LAN or DMZ) to request one or more
ports to be forwarded to them. Unlike basic port forwarding which forwards ports to only one IP
address, port triggering waits for an outbound request from the private network on one of the
defined outgoing ports. It then automatically sets up forwarding to the IP address from where the
request was made. When the application ceases to transmit data over the port, the router waits for a
timeout interval and then closes the port or range of ports, making them available to other
computers on the private network.
Port triggering allows some applications running on a LAN network to be available to external
applications that would otherwise be partially blocked by the firewall. Using this feature requires
that you know the port numbers used by the Application.
Once configured, Port Triggering operates as follows:
1. A PC makes an outgoing connection using a port number defined in the Port Triggering table.
2. The quad WAN gigabit firewall records this connection, opens the additional INCOMING port
or ports associated with this entry in the Port Triggering table, and associates them with the
PC.
3. The remote system receives the PCs request and responds using the different port numbers that
you have now opened.
4. The quad WAN gigabit firewall matches the response to the previous request, and forwards the
response to the PC.
Without Port Triggering, this response would be treated as a new connection request rather than a
response. As such, it would be handled in accordance with the Port Forwarding rules:
• Only one PC can use a Port Triggering application at any time.
Firewall Protection and Content Filtering
ProSafe Quad WAN Gigabit Firewall FR538G Reference Manual
v1.0, November 2007
4-31