Bananananananana - Who is your DSL provider and what magic box did they give you in your home?
I had a problem with my AT&T DSL/Motorola Modem because the modem was playing at router and giving my machine a private "hidden" address. (stupid setting when you consider its a single port modem but prolly helps protect the confused)
I tweaked a setting to stop that and I had the address directly on the net, and boom stuff worked right.
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How do I do what he did? LOL

 

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Not sure on the "tweak" that was done, but I am guessing your modem is a Motorola Netopia as it seems to be the most common. A bit more information is required though to help you.

Model of Modem (e.g. Motorola Netopia 2210)
ISP
Type of Router

Some "Reading Material" for you in the meantime.

 

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I'm sorry.. WHAT? You quoted someone elses post and expect us to tell you how to fix your problem? How about giving us some details about your situation..

 

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Sounds to me like they disabled the DHCP Server in the modem and enabled what they call "bridge mode". This only works well if you have a single PC in the house. If you have more than 1 PC then usually ISPs will charge you a small fortune to get other IP addresses beyond the first.

Most systems don't require having a public IP to work correctly however as long as they have proper routing protocols in place. At worst case, you would just have to set up port forwarding to allow the ports you're expecting to be forwarded directly to your machine.

I'm not familiar with that type of DSL modem, but I can only think that the possibilities which could be incorrectly configured would be the internal firewall might be set up incorrectly, or you may need to set up Port Forwarding if the DSL modem isn't properly handling the UDP traffic. I'd say if the DSL modem was made after 2008 it should work properly with UDP however.

Just for posterity

On the connection page for the version of the motorla modem I have it has a setting for use the private or public ip address.

On the private the modem gives you an internal address which has problems connecting.
On the public you get the ip address directly from the interwebs.

As always YMMV

 

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Normally I'd recommend setting it on "Public" (**read the next paragraph for disclaimer**) as that basically will put it into what they call "Bridge Mode" meaning that it is acting as a gateway between your PC and the ISP. It shouldn't do anything with the packets except forward them. That's why they call it a "Bridge". It is like a bridge over the water.. it transports from one side to the other and back.

If you do this however, I would HIGHLY recommend getting a real "Router" that includes some basic firewall in it as well so that you can set up an internal network that has a little more protection in addition to allowing you to set up more than one computer without paying the ISP a whole bunch of IP lease fees. Normally most ISPs will give you a single IP address for free with your account, but any more require additional fees. If you use a router, then the Router is the one that is assigned the IP by the ISP and then it is responsible for handing out private IPs to the other computers on the network (in addition to routing packets and protecting your network if it is set up to do so).