Blocking computers from getting IP address with DHCP 1

[dprichard]

Is there anyway to block computers on the network from grabbing an IP address with DHCP. I have a computer that is using one of the IP addresses in the scope I have assigned, but I don't want it to occupy one of the IP addresses.

 

[Davetoo]

Assign an IP directly to the computer in question and it won't poll for a DHCP server.

 

[dmandell]

Is this a rogue computer that you cannot find and don't want on your network? If so, here is a cute little trick to kill it off.

Create a DHCP scope for an IP range that does not exist on your network. i.e. if your network is 192.168.0.xxx make it 10.0.0.xxx or anything that is not used or routed on your network. This scope will have only one address in it.

Find the computer's MAC address from your current DHCP scope database. Create a reservation in the nonexistant network scope for that MAC address for the one IP.

Enable the new scope. Terminate the lease on the rogue computer from your "good" DHCP scope. When the "bad" computer asks for a new IP, it will receive the "bad" IP from the unroutable (on your network) scope.

This works, I have done it when tracking down security issues on our network.

 

[sambusa]

u are greate brother

Thanks

 

[dprichard]

I am not having a problem with a rogue machine. It is more of just a can it be done and if so how. I am setting up my first network and noticed that my IP address are automatically grabbed by machines as they come on. I was trying to make it so I can assign IP addresses for certain machines and then that machine would grab that address, but a machine that is not given one cannot. Thank you in advance for your help! David A. Prichard

http://www.citrusparkcomputers.com

 

[jtb]

David,

It's a "simple" matter of assigning a scope, reserving addresses for the "approved machines", and building an exclusion for the rest of the addresses... JTB
Solutions Architect
MCSE-NT4, MCP+I, MCP-W2K, CCNA, CCDA,
CTE, MCIWD, i-Net+, Network+
(MCSA, MCSE-W2K, MCIWA, SCSA, SCNA in progress)

 

[dmandell]

So the quick answer is, if you want a specific computer to have a specific address, you will need to setup a reservation for each machine. This will be time consuming, as you will need to manually enter in the MAC address of each machine for each reservation.

If you fill up the complete scope with reservations, then no other computers will be able to get DHCP adresses from the server.

Hope this helps,
Dana