Can't connect gateway DHCP ADSL Modem using Windows 2008 DC

[RamaHH]

Dear Friends,

I had a problem with my internet connection trough my DHCP ADSL Modem (gateway).
First we using ADSL modem(DHCP) to connect as a gateway to internet, we using windows 2000 DC for server. The connection is ok, our server and client can ping and browsing through gateway (192.168.1.77).

Then we've tried to develop using windows 2008 as a DC, but after domain create it the internet gateway can't access the internet gateway.

This is the configuration
DC/DNS Win 2000 = 192.168.1.12/16
Gt 192.168.1.77
DNS1 192.168.1.12
DNS2 202.x.x.x

DC/DNS win 2008 = ip 192.168.1.247/16
Gt 192.168.1.77
DNS1 192.168.1.247
DNS2 202.x.x.x

PC with ADSL Modem =
eth01 (LAN) not join domain
IP 192.168.1.77/16
Default G/W not set
Subnet Mask 255.255.0.0

eth02 (ADSL Modem) #DHCP 192.168.1.x - 254#
IP 192.168.1.6/24
Default Gateway 192.168.1.1
DHCP Server 192.168.1.1
DNS Servers 192.168.1.1

PC Client : ip 192.168.5.9/16
Gt 192.168.1.77
DNS1 192.168.1.247
DNS2 202.x.x.x

Before promote server to Domain 2008,PC Client and server can access gateway (internet) locally and can ping the gateway 192.168.1.77

But after promote server to windows 2008 domain & DNS sever, the server and client can't ping the ip gateway 192.168.1.77, but still can ping another DC (2000) and Clients.

Is it the problem cause by ADSL modem using DHCP? but before it, we using windows 2000 domain the ip gateway can ping the ADSL PC gateway and it's ok for internet. (the Firewall not configure yet)

Is there something with windows 2008 domain behaviour (firewall set turn off)?

Thx All

[Zachary]

I think that something is unusual with Windows 2008 domain.! Since you were using the ADSL modem before for the Windows 2000 Domain, I don't think that your ADSL modem using DHCP is causing some issue. You might have not developed Windows 2008 as a DC properly. That can be the reason of this issue. I would like to suggest you to try to develop the Windows 2008 as a DC properly and then reset your DNS configuration. Doing this might fix the problem.