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Modem and Router DHCP giving out wrong Default Gateway

Last response: in Networking
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November 6, 2012 5:50:35 PM

So network was running fine for about a year or so. Network consists of 1 Motorola SB6120 cable modem attached to a D-Link DIR-601 wireless router. All settings were default except for SSID and WPA password. One day I just couldn't access internet anymore. I've narrowed it down to the default gateway that is being given out through DHCP. The default gateway that is being given out is the IP of the modem (192.168.100.1) and not of the Router (192.168.0.1). I can't find any option on Wireless router to be able to force the gateway address when handing out the gateway IP. Theoretically I thought I should be able to put router on same subnet as modem as 192.168.100.2 but that still doesn't work. If I set the IP adresses statically on the PCs and give it the Gateway of the Router everything works fine. I should mention this is for my boss' house and basically I dont want him calling me everytime he has a friend come over and I have to talk em through setting up a Static IP.

And just for an example this is what I get if I use DHCP:

IP Address: 192.168.0.155
Mask: 255.255.255.0
DNS: 192.168.0.1
Default Gateway: 192.168.100.1

And If I want it to work I have to change the default gateway to 192.168.0.1

I've tried updating routers firmware and reset to factory default numerous times. Is it possible for a router DHCP stop working? I've never heard of that. ISP is Comcast and when I talk to them all they can suggest is unplugging everything.......like 500 times.
November 6, 2012 6:48:50 PM

under the Network settings what is the router's IP address and what is the DHCP IP range? do the IP schemes match?
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November 13, 2012 5:37:43 PM

For anyone that has the same problem, I have found the cause of the problem but no solution yet. The Motorola SB has a feature where when its not synced with the ISP (comcast) it turns on DHCP. When it is synced with ISP the DHCP is disabled and the the routers DHCP is used. The problem is that I am synced with comcast but for some reason the Modem's DHCP is not turning off so I am getting conflicting Default Gateways. There is no way to disable DHCP in the Modem. Putting both the router and the modem in the same address range does not work since the router see's the LAN and Internet as 2 diferent networks. I believe if I could setup the Dlink as a switch or put it in bridge mode that would work but since the router is very cheap it lacks any of these features.
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