Cisco 877 Port Forwarding
I’ve been using the Cisco 877 Integrated Services router for a few months now and have recently come across a strange quirk that may catch a few people out.
I host a few websites on a virtual machine within my internal network, now to make these sites viewable to the world I need to direct any traffic on port 80 heading to my external static IP address to the internal virtual web server. To do this I added a static NAT rule to the running configuration of the router.
Router(config)# ip nat inside source static tcp xxx.xxx.xxx.xxx 80 interface Dialer1 80
What I didn’t realise was that from the internal network you cannot open a connection to the port you have just forwarded using the above rule. This caused me to scratch my head, it wasn’t until I telnet’d to the external IP on port 80 from the Cisco router that I realised the static NAT rule was actually working.
So lesson learnt today, don’t assume that Cisco router port forwarding will work in the same way as your conventional home DSL router.
