Network/DHCP issues after modem reboot

Question

We had some power issues and our modem rebooted. After it came back up, our internet quit working thru the local area network and users were unable to logon to the server. I noticed on the server our IP had changed to 10.1.... from 192.168.....

It seems like the server got its IP from the Cable Modem.

After disabling DHCP on the server and assigning static 10.1.... IPs to the clients, users are able to log on and use internet. If I change the cliet to Obtain an IP address automatically, clients start getting 192.168.... addresses and are unable to log on to the server.

If I change the server IP to 192.168... which is what it was before, no one can log on to the server and connect to Internet.

Also none of my wireless router connected to the network are currently working.

Should the DHCP services be running from the Cable Modem or the Server or both?

What could have changed that any time I assign 192.168.. to the server, nothing works?

Any suggestions/help will be highly appreciated.

CMH · Answer

Thanks for a quick response

1. Our server is not directly connected to the Comcast gateway and it does not use a Comcast static IP. They are connected thru a switch.

2. All the intranetwork users connect to the server thru the Network switch.

VBSSP-RICH · Answer

Hello CMH and welcome,

It would be helpful if you could answer the following questions:

1. Is you server directly plugged into the Comcast Gateway and does it use a Comcast static IP address?

2. How are all of your intranetworked users connected?

Look forward to hearing from you.

VBSSP-RICH · Answer

Hello CMH,

According to your network interconnect, you should simply just connect everything to the Comcast Gateway (CG) using the network switch and use the CG internal DHCP server and this will work with no problems.

CMH · Answer

Hi Rich,

I think that is what we have, from both server and CG we connect to the swith.

Currently DHCP is enabled on CG and disabled on the server.

DHCP on CG is unable to assign IPs (not sure why) so we have to assign them manualy.

I am trying to figutre out why CG can not assign IPs automatically? Am I missing some setting.

Thanks

VBSSP-RICH · Answer

The ONLY reason why the CG is not doling out 10.1.10.XX dynamic IPs is if the DHCP server is disabled. Typically most CG are setup for their dynamic IP address range to be 10.1.10.10 and go to 10.1.10.199. So, with 189 dynamic IP addresses this is usually plenty for most businesses.

CMH · Answer

Thank you VBSSP-RICH.

I went and checked our CG Domain Controller and found the following:

1. The IP address of the domain controller is 10.1.10.XX

2. The scope under IPV4 setting for the DHCP server is showing as 192.168.0.0

But none of the computers in our domain are able to get the IPs automatically from CG DC (domain controller). It only works when we assign the IPs ( in 10.1.10.XX range) manually on the computers. Atleast we have seen the internet working when the address is 10.1.10.XX but when we give 192.168.0.XX, the internet stops working.

Is this problem happening becuase our scope is incorrect? And if yes, how do I change the scope?

Or is there any issue with the modem?

Another question:

Who should be assigning the IPs to the computers joining our domain? Is it the DC (domain controller) or is it the Comcast router?

Thanks for your help.