I have just recently encountered a problem on two different dlink routers (DI-825) and (DI-635)
After a clean setup and install of the routers, setup with wireless and wired clients.
The wireless clients can attach, but the wired clients cannot. When I log off with one of the wireless clients and reconnect the router throws an address such as 192.168.100.13. w/ a default gateway of 192.168.100.1.. yes the dhcp range I have is 192.168.0.50 to 192.168.0.100.. with a normal gateway of 192.168.0.1 I cannot figure out how the router is assigning an address outside of this range when I set all clients to be managed by dhcp.
This is even more of an issue as of my 5 devices on the network only two get addresses with the dhcp range while the others do not.
The odd part is I have tried this with two new (different) routers and the same thing occurs.. The modem appears to be functioning fine and after a few ours with comcast trying to break this problem down further it appears (for now) to not be the modem.
I need to know, are you using TWO routers at the same time, or only one?
Btw, many cable modems use that 192.168.100.x IP range, and many can be configured as gateways w/ their own DHCP service! IOW, it appears that you may have configured your devices in such a way that some clients are getting their IP assignment from the cable modem rather than the router. Don't ask me how at this point, but it sure seems that way. That's why I asked about the possibility you might be using multiple routers. I thought perhaps you were picking up DHCP from the wrong router. But that 192.168.100.x network is often associated w/ the cable modem. In fact, you can probably bring up the web interface of your cable modem w/ http://192.168.100.1
Anyway, the more details you provide on how things are hooked up, the easier it will be to determine the problem.