Quick Reference Guide

Table Of Contents
Chapter 4: Firewall Protection and Content Filtering | 67
ProSafe Dual WAN Gigabit Firewall with SSL & IPsec VPN FVS336Gv2 Reference Manual
range of ports. Using this feature requires that you know the port numbers used by the
application.
Port triggering allows computers on the private network (LAN) to request that one or more
ports be forwarded to them. Unlike basic port forwarding which forwards ports to only one
preconfigured 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 that sent the request. When the application ceases to transmit data over the port,
the VPN firewall waits for a timeout interval and then closes the port or range of ports, making
them available to other computers on the private network.
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 VPN 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 PC’s request and responds using the different port
numbers that you have now opened.
4. The VPN 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 inbound service rules.
Note these restrictions with port triggering:
Only one PC can use a port triggering application at any time.
After a PC has finished using a port triggering application, there is a time-out period
before the application can be used by another PC. This is required because the VPN
firewall cannot be sure when the application has terminated.
Note: For additional ways of allowing inbound traffic, see “See
“Configuring Source MAC Filtering” on page 64 for yet another way
to block outbound traffic from selected PCs that would otherwise be
allowed by the VPN firewall.” on page 45.