Public IP problem

[Skatan]

OKay so here is my problem.
We changed our DSL company recentley which forced us to switch modem to a Speedtouch 510v5.
This new modem has a built in router with only 1 port, so behind that we have a second router from which we conenct our PC's.
Now, Seeing how I play alot of XBOXlive games I want to bypass the modems router so that I don't have to give my 360 a hard time with double NAT translations.
the 360 has 3 diffrent types of connections it's "Strict" "Moderate" and "Open".
When I have to double NAT I get the Strict one.

So, to solve the problem I tried assigning my public IP to my D-link 804 router.
Which solved to NAT problem giving me a status of "open".
But here is the tricky part.
Our company is a PPPoE one so after a while, about 15 minutes, the internet dies when the public IP is handled by the router, which leaves me no choice but to go out there and release and renew the IP's all the time.

So the question is, how do I fix this?

[YeOldeStonecat]

You don't want to double NAT things...which is what you're doing.

Instead..if you need to use your own router, you should log into your ISPs provided gateway...and disable it's PPPoE and routing....flipping it over to pure bridged modem (basically now only using the modem part of the unit)...and setup your own router for the PPPoE duties, and the only instance of NAT.

If you can't find where do to that on your Speedtouch...calling the ISP and telling them what you wish to do...I've never had a problem doing that, they'll say they won't support your router...which is fine, they shouldn't have to. Just tell them you'l deal with your router, just help you flip your Speedtouch to pure bridged mode.

[Skatan]

That didn't work as I wanted it to, because for some reason I couldn't connect to alot of people in xbox live.

The only solution I can find is to make this whole "Assign a public IP" thing work.
So what I need to know is how do I make my router understand that it's IP will change often and it needs to check on that on a timley basis?
Or if there is any other way to make Assigning a public IP possible.

I really don't want to shell out about 25$ to buy a switch.