port forwarding

[carl_townshend]

Why would I use port forwarding ? and what is it,

[Brandon Buffin]

Port forwarding maps a particular local port to a different remote port. One context in which to use port forwarding is with WebVPN. Please see the following document.

http://www.cisco.com/en/US/tech/tk583/tk372/technologies_white_paper0900aecd8029d630.shtml

Another example would be to use port forwarding to map incoming SMTP traffic (Port 25) to Port 26 on your internal server. A possible use is to let a spam filter receive your mail before passing it on to your mail server. If the filter and the mail server are on the same box, they can't both receive on Port 25. You could let the filter receive on Port 26 in which case you would need to forward external Port 25 traffic to Port 26 internally.

Hope this helps.

Brandon

[carl_townshend]

Can anyone eleborate a little, Why would we need to set up this ?

[cisco_trouble]

hey carl,

i guess port forwarding is to direct traffic from where you receiving it, to you want it...

- A port can only be used by one program at a time.

- Every IP address is divided up into many ports. When one computer sends data to another computer, it sends it from a port on an ip address to a port on an ip address.

- Port Forwarding simply tells the router which computer on the local area network to send the data to. 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.

hope this helps...

[carl_townshend]

what commands on the router would do this ?

[cisco_trouble]

e.g.

set nat entry add x.x.x.x 80 tcp

It also depends on the router being used.