Actually, Benzene & Lundy are talking about a different, but very similar problem.
There are two IP addresses involved here: one "WAN" IP address; this is the address that your ISP assigns to your modem, and one "LAN" IP address; this is the IP address that your router assigns to your Mac. The "WAN" address is the one that other people on the internet can "see", all computers connected to your home network will appear to have the same IP address from the outside world, due to the magic of NAT
To aid in explanation, let's say that your WAN IP address (given to your modem by your ISP) is 64.324.67.89 and your LAN IP address (given to your Mac by your router) is 192.168.0.2.
When you set up port forwarding on your belkin (in the firewall -> virtual server area), you instructed any requests on port 80 of the 64.324.67.89 IP address to be forwarded to the 192.168.0.2 IP address of your Mac. However, under default settings, routers use DHCP to assign LAN IP addresses).
This means that if your Mac loses its network connection to the router, when it regains a connection, it may well be given an address other than 192.168.0.2. e.g. 192.168.0.5. However, the port forwarding is setup to forward port 80 requests to 192.168.0.2, so the forwarding will cease to work. DynDNS.org cannot solve this problem for you.
To solve this problem, you have to consult your router intructions and find out how to assign static LAN IP addresses. This may involve turning off the DHCP server altogether (which would then require you to set the IP address of any machines connecting to your network manually), or setting the DHCP server a restricted range of IP address (e.g. set the DHCP server to assign addresses in the range 192.168.0.10 to 192.168.0.255, reserving 192.168.0.2 to 192.168.0.9 for manually assigned IP address.
Once the router is configured, you then need to go to system preferences on your Mac and change the "configure IPv4" option under TCP/IP tab of the "network settings" pane to "manually", then enter the desired fixed IP address. You then use this IP address to forward port 80 requests to.
On to the second problem:
The second problem is that your WAN IP (e.g. 64.324.67.89) will almost certainly not always be the same. If your modem drops its connection, your modem will probably get a new IP address from the ISP. So if you told your friends they can get you on http://64.324.67.89
, now they would not be able to do so. Even worse, someone else may have been assigned the address you used to have, and if they're running a web server too, people will see entirely the wrong site, rather than just nothing.
This is where dynDNS.org can help. You register something like www.mylovelywebsite.com
, and when someone enters that into a webbrowser, a DNS server translates the words into an IP address. Using the dynDNS.org service, you can ensure that this IP address is always the one that has been assigned to you by your ISP.