Dreamcast wont connect to servers?

[Xiden]

If you can't connect on GameCube either than I'd say it's a DNS issue. Maybe your ISP is blocking use of a custom DNS server?

Well I've been using the same ISP for all of last year (AT&T), and I haven't gotten anything like this. Unless they changed something.

What router are you using?

I've tested on both an AT&T, and Netgear routers.

Yeah I had AT&T Last year and can confirm for sure they work with the servers. Are you just using the AT&T only with the IP Passthrough? Makes me think if GC and DC don't work it maybe up the line further with a router setting.