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dhcp relay?

Hell0,

Attempting to break up a flat design and introduce a router and subnetting. The router/switch is an 8510csr and we are a windows 2000 network. My question is this; how can I get a workstation on one subnet to get dhcp from the dhcp server on another subnet without putting a dhcp server on every subnetted segment? I am using the 'ip helper-address ' on each subnetted etherport.

TIA,

Gary

9 REPLIES
Silver

Re: dhcp relay?

Gary,

Two things.

1. ip helper which you are doing to get your client's DHCP request to the DHCP server. Ensure the ip you specify in your helper statement is the ip of your DHCP server.

2. Create a scope on your DHCP server for the clients subnetwork. Since the DHCP request is wrapped up by the primary IP address of the clients routed interface you'll need to ensure you make a scope to service that specific network.

You'll not need DHCP servers on each subnetwork. Doing the above should work fine for you.

Hope this helps you,

Don

Anonymous
N/A

Re: dhcp relay?

Thanks Don. I set the scope to cover the workstations subnet and did give the ip helper-address of the dhcp server.. hmm. I must be doing something else incorrectly. Thanks so much for confirming the ip helper should traverse subnets! Helps a lot!

Gary

Silver

Re: dhcp relay?

Gary,

Depending on the DHCP server implementation you are using (assume NT) make sure you enable the scope that you've created as well. I think, by default , they are disabled.

Regards,

Don

Anonymous
N/A

Re: dhcp relay?

Yes, the scope is enabled. I must be doing something really stupid. I have in testing, two windows servers, one a dc with dhcp. These two servers are on 10.0.0.1 255.255.255.0 subnet. The test workstation is on 10.0.1.1 255.255.255.0. The ip helper-address is the dc's at 10.0.0.2. Both ports on the 8510csr have this ip helper. I cannot even ping 10.0.0.2 from the workstation on 10.0.1.1 subnet with it having a fixed ip. The setup is simple.

???

Gary

Silver

Re: dhcp relay?

Gary,

Ip routing is enabled? If you can't even ping with an assigned 1.1 address you've got other things stopping this from working.

Don

Anonymous
N/A

Re: dhcp relay?

Hi Don,

Yes, ip routing is enabled on the router and the dhcp server has dhcp relay turned on. I think your correct and will start looking at cabling etc. Strange though, because I can ping the routers ip and both etherports.. just can't across the subnet to the dhcp server. At least I know it is not an ip helper issue.

Gary

Silver

Re: dhcp relay?

Gary,

For one, you don't need DHCP relay enabled on your DHCP server. The router with "ip helper" is providing this function. Other than that I'd say you've got a physical or other issue.

Regards,

Don

Anonymous
N/A

Re: dhcp relay?

I just turned off the dhcp relay on the server. We continue to dig into this one. Must be some sort of physical issue. I will be sure and let you know what I discover and really appreicate your valuable input and time!

Thanks Don,

Gary

Anonymous
N/A

Re: dhcp relay?

Don,

Got it working. It appears to have been the order of which I had my straight-thru cable and my cross-over cable connected to the port, switch and punch down block. Thanks so much for your help!

Gary

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