33
Web User Interface
Answer
:
Internal Port means which port the local server is listening to. External Port means
which port the router is listening to. For example, local station John’s running Telnet Daemon
on port 64623, then internal port is 64623, external port is 23. Suppose Internet user
initializes a Telnet connection request to this router’s public IP address, router will recognize
that this is a Telnet Connection request to a station. According to existing forwarding rule,
router will first translate the packet’s destination port to be 64623, and then forward this
request to host John. If we designed “External port” only, then we’ll have trouble to setup two
FTP servers locally simultaneously, since there will be 2 FTP daemons running, and that’s
hard for router to figure out which connection request should be redirected to which FTP
daemon.
6.2.12 Advanced - Port Triggering
This page allows configuration of dynamic triggers to specific devices on the LAN. This allows
for special applications that require specific port numbers with bi-directional traffic to function
properly. Applications such as video conferencing, voice, gaming, and some messaging
program features may require these special settings.
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 port in NAT to
forward a service to the IP address of LAN side host. The problem is that port forwarding
only forwards a service to a single LAN IP address. In order to use the same service on a
different LAN computer, you have to manually replace the LAN computer's IP address in the
forwarding port with another LAN computer's IP address.
Here 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 clients host to listen. So, server
will return response to these ports.
Let’s give an application scenario to get a clear concept.
U10C019/U10C020
