OK, a friend of mine has 4 web based CCTV cameras, they are set up at fixed ip addresses on his LAN so for example 192.168.0.10, 11, 12 and 13.

You can access them on the LAN via port 80 and Internet Explorer or Firefox to those IP addresses, this asks you for the user and password to access the camera.

We have got one working so that you can access it from anywhere on the Internet by creating a rule in the router to forward incoming port 80 requests from WAN to 192.168.0.10 on the LAN. We've even conqured DynDNS too as the ISP doesn't provide static IP.

How, though, do we get the other three cameras so you can access them from the WAN?

My idea is to change the port numbers on the three others to, say, 81, 82, and 83. The camera config application looks like it lets this be done. Then just create more rules in the router's firewall to forward these specific ports to the cameras LAN IP addresses.

Is it as simple as that and is that a valid thing to do? Perhaps port 81, 82 and 83 might not be able to be used from 'anywhere' on the internet due to firewalls?

Anyway, enough rambling, just be interested in anyone's thoughts. Ta

Yes, changing the ports and then setting up appropriate forwarding rules on the router will work. But you should really use high random port numbers to avoid interfering with other network services, and reduce the risk of a portscanner seeing them.