I want to make my local server visible over the internet. I've learnt that I'll be able to achieve this through NAT. I'm using a D-Link router, DIR-600. In the application rules it asks me for Firewall port number. However, firewall is not configured on my router. Do I have to configure firewall first in order to NAT?
closed as off topic by Michael Hampton♦, Magellan, HopelessN00b Genius of network, RobM, Ward Oct 29 '12 at 13:56
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The normal way is to get one or more public IPs from your provider. Then you can give all your devices a IP number and connect them to the Internet. No firewall or NATting is needed, though you really want a properly configured firewall before you connect anything to the Internet.
If you do not have a few assigned IPs (e.g. because we have almost run out of unassigned numbers) but only one IP then you have two options:
1) Get a modem in bridge mode (no IP used) and connect your server to the internet.
With NAT all connections are made to your D-link. It is the only device directly reachable from the outside. I suspect it is asking you if it needs to forward a connection to a specific port on it to another computer (e.g. your server).
However do answer this we really need more detail.
So you have a router connected to your internet with no firewall rules? You might want to rethink that. (regardless of using NAT or not).
NAT is a sort of firewalling. A firewall usual setting is 'deny all, except for this and this. Do that and that with those packets'. NAT only way of working is 'Deny all except forward this'. Those are quite similar. They may be lumped together in your modem.
But seriously, assuming you posted in the right place you are a professional admin. You should know all this. Either you need to learn networking 101, or you need to read this sites FAQ.
In your case your NAT is likely acting as your firewall (insert debate as to whether or not NAT is actually a firewall), in that if traffic reaches your network and doesn't know where to go it will be dropped. For instance, if traffic goes to your network destined for port 80 and you haven't set up a rule to forward port 80 to a specific machine, your router won't know what to do with the traffic and will drop it.
That said, what you'll need to do is configure the NAT on your router to point to the server ports that the server will be listening on.
A great tool to help troubleshoot NAT and firewall problems is Canyouseeme.org. This tool will determine whether or not you have ports open on your router.