/Cisco Nat Port Forwarding

Cisco Nat Port Forwarding

We are trying to replace a Netgear ADSL router with a Cisco ADSL Router – we’ve used the GUI configuration tool to get it working but we don’t how to configure port forwarding like we had on the netgear! So we can forward smtp, http and such like to our Windows server. Can you help?
This depends on the model of router you have but basically if it’s an IOS sytle router then I’m guessing you have used something like the SDM to configure the router? I’m also guessing that you are using NAT (network address translation) on your router which is probably configured on a dialer0 interface. Have a look through the config and you should see a line like:

ip nat inside source list 100 dialer0 overload

If you do then you are use using NAT. You can configure port forwarding (PAT) with a command like:

ip nat inside source static tcp [internal ip] [port number] interface [interface with nat outside] [port number]


ip nat inside source static tcp 25 interface dialer0 25

be careful if using this type of command because if you have http enabled on your router then you won’t be able to forward port 80 to your server. You’ll have to disable it first!

alternatively if you have a fixed ip address on your adsl interface or you have a range of ip addresses on your adsl interface then you can do this:

ip nat inside source static tcp 25 25

where is your static ip address or one of the range of addresses you have allocated by your ISP.

you can also leave out the port number to have everything passed directly to you internal this is useful for debugging or if your internal system has a firewall of it’s own!

ip nat inside source static tcp

Hope this help.