Network Address Translation (NAT)
20 NN40011-046 Issue 1.2 BCM50 Rls 6.0
Trigger Port
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 (coming in from the server
on the WAN) to the IP address of a computer on the client side (LAN). 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, Trigger port forwarding solves
this problem by allowing computers on the LAN to dynamically take turns
using the service. The BCM50 Integrated Router records the IP address of a
LAN computer that sends traffic to the WAN to request a service with a
specific port number and protocol (a "trigger" port). When the BCM50
Integrated Router’s WAN port receives a response with a specific port number
and protocol ("incoming" port), the BCM50 Integrated Router forwards the
traffic to the LAN IP address of the computer that sent the request. After that
computer’s connection for that service closes, another computer on the LAN
can use the service in the same manner. This way you do not need to
configure a new IP address each time you want a different LAN computer to
use the application.
For example:
1. Jane requests a file from the Real Audio server (port 7070).
2. Port 7070 is a “trigger” port and causes the BCM50 Integrated Router
to record Jane’s computer IP address. The BCM50 Integrated Router
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 BCM50 Integrated Router 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 Business Secure Router times out in three
minutes with UDP (User Datagram Protocol) or two hours with TCP/IP
(Transfer Control Protocol/Internet Protocol).
