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Restricting DHCP Server

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7 replies

by reju_nair

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We have at our place two networks one of our company and second of another company the ip address range being 192.168.0.0 to 192.168.0.255 of our network and 192.168.1.0 to 192.168.1.255 of the other companies network subnet mask being 255.255.255.0we have now shared our leased line both the networks have a dhcp server and so now with both the networks connected. We face the problem that some of our clients receive dynamic ips from their dhcp server and vice versa. how can i stop this?

7 replies

by mckaytech

It depends on what your physical network setup is. If you have a router between the two subnets (and I assume you do, as opposed to a multi-homed server), you just need to tell it NOT to pass broadcast traffic.

Typically, you'll find a line in your router configuration that says something like "ip helper-address" or "ip dhcp-server" or "ip directed broadcast" that tells the router to send broadcasts (such as DHCP requests) to other a specific address on the other subnet.
The solution is usually to remove that line.

paul

by reju_nair

none of this things have been configured on my router "ip helper-address" or "ip dhcp-server" or "ip directed broadcast" so i want some other solution to restrict the dhcp server in the other company from accepting ip address request from any of my dhcp clients.

by briantruitt

You could set up superscopes on both of the DHCP servers. Set up both of the ranges on your DHCP server and exclude their range and have them do the same but exclude your range. That way you won't get any of their addresses and they won't get any of yours and neither of you should get NACKs.

by reju_nair

I read this from the Microsoft Site and indeed tried it well before i could receive this reply from you, but it doesn't help me out. I still continue to receive ip's from the other companies dhcp server and they still can receive ip's from our dhcp pool.

by grbeebeii

Hi. It sounds like your Router is acting as a DHCP Relay, sending DHCP requests into both nets. Or, you have a DHCP relay in each net and they are forwarding their requests into the other net. Either way, they shouldn?t be getting through the Router.

Another thing: In Win2K a DHCP Server has to be Authorized in Active Directory, in order for it to be allowed to dispense IP addresses, etc. Assuming of course that these are 2 separate domains. They are right. So why is their DHCP server authorized in your domain.

Sounds like you have more than one problem.

Hope this helps.

by reju_nair

Yes we have two different domains but even if their dhcp has not been authorised on my domain still it keeps relaying the ip addresses.

by maxwell edison

Sometimes a third party solution makes sense. There's a product called, "JOIN DHCP", that will accommodate your requirements.

"....Multiple logical networks can exist on a single physical network segment in order to accommodate growth or to provide creative administration. JOIN supports this model by permitting secondary addressing; ranges of IP addresses on the router's secondary networks can be allocated just like any other IP address range...."

You can read all the features and download an evaluation copy at the following site:

http://www.join.com/dhcp.html

(REMOVE SPACES from the pasted URL.)

Best of luck and have a GREAT 2002!

Maxwell

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