Dhcp Troubleshooting

Dhcp Troubleshooting

Dear IT Admin:
I am working at a branch office and have been tasked with changing out the DHCP scope to match the overall corporate IP address scheme. The main office assigned me an IP address range of 192.168.0.200 through 192.168.0.225. I changed the scope on Friday afternoon and came in on Monday morning to discover that only some of the workstations had picked up new leases from the new DHCP scope. Any ideas as to what may be happening, what I might check or adjust?
Thank you,
Junior Admin
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Dear Junior Admin,
A common problem that happens more often than not is assuming as soon as DHCP options are changed that all PCs will automatically implement them.   It sounds like this may be an example of that exactly.
With DHCP when the computer comes online it does a broadcast search for a DHCP server.   The server responds with a message offering an IP address, subnet mask, and default gateway as well as some DNS options and WINS if that is configured.
Once the pc accepts it the DHCP server will send an acknowledgement message.   At that point the PC will send back a message that it will take it and the DHCP server will send a message indicating that an IP address has been reserved for the lease period.
At this point the PC will not contact the DHCP server again until halfway through the lease time, which is usually a default period of 8 days.
If you want to force all of the PCs to grab a new IP address then you will have to go to each computer, open a DOS prompt, and do an “ipconfig/release” and “ipconfig/renew”.
Now if that fixes the problem, then great.   If not then you may need to check your scope configuration and make sure the network/subnet mask match what is configured on the router that you have connected to that particular LAN.
I hope this information helps you with your problem.

Sincerely,
IT Admin

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