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4.2.12 Additional Information - Forwarding
DDW2600 Wireless & DDC2700 Commercial Cable Modem/Router Subscriber User Guide • May, 2010
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4.2.12
Additional Information - Forwarding
Internal Ports are the ports that local servers listen to. External Ports are the ports that
the cable modem listens to. For example, a local user on your network (e.g. John) is
running a Telnet Daemon on port 64623; the internal port is 64623, the external port is
23. If an
internet user
initializes a Telnet connection request to this router’s public IP
address, the router recognizes that this is a Telnet connection request to a station.
According to existing forwarding rules, the router first translates the packet’s
destination port to be 64623, and then forward this request to John’s Telnet host.
In summary, when you have port forwarding rules set up, your router takes the data off
of the external IP address:port number and sends that data to an internal
IP address:port number. Port Forwarding rules are created per port. So a rule set up
for port 53 will only work for port 53. A port can only be used by one program at a
time.
