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DHCP in multi-domain environment

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8 replies

by mynt_boro 1 view

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Hello everybody,

I have 2 domain in my local network, each domain have a DNS and DHCP (authorized), let call them domain A and domain B.

Some computers in domain A get IP address from DHCP of domain B and some computers in domain B get IP address from DHCP of domain A, although all the DHCP is authorized.

Could somebody show me how to make the client computer get the IP address from the DHCP server of the registered domain only.

Thanks in advance.
TheMy

8 replies

by p.j.hutchison

DHCP works on subnets, so you will need to reconfigure the switch or router where the PC is connected to use a different subnet and then it will get the IP address you want from DHCP.

by mynt_boro

Hello,

My 2 domains trust each others so I cannot specify 2 different subnet (cause if I do so, the client computer cannot communicate with each other).

I try to figure out how to make client computer just receive the IP address from the authorized DHCP within the domain. "Authorized" DHCP is a way to prevent rouge IP address in a domain environment, but I have no luck with it, please help.

Thanks,
TheMy

by cg it

unless your using advanced features of DHCP.

There can be only 1 DHCP server on a subnet or else there is a conflict and this warning box pops up notifing you of the fact. unless you have DHCP relay agent running to get to another subnet, clients should only go to the DHCP server on their subnet.

If you have 2 domains on the same subnet, then you can have 1 DHCP server handing out addressing in ranges for each domain. You then have to specify in DHCP which client gets what range.

by mynt_boro

Hello,

How to specify in DHCP which client gets what range ?

Thanks in advance.
TheMy

by p.j.hutchison

Tother alternative is:

a) Turn off dynamic DHCP allocation and put a reservation for each of the clients in the DHCP console by specifying its phsyical MAC address and IP to allocate to that client.
The the clients will get the IP it requires.

Otherwise the only other way is to use VLANs and enable forwarding between the subnets so that they can talk to one another on the router. TCP/IP is routable over subnets (only netbeui cannot route, but you can install a WINS server to get around Netbios type calls using short names).

by mynt_boro

Hello all,

THanks for your help with this issue, after 2 days trying to figure out (and have no luck), I decided to use 1 DHCP and 1 DNS server for 2 domain.

It works fine now.

Thanks,
TheMy

by churdoo

You simply cannot have multiple DHCP servers on a single "collision domain," period. Authorized DHCP servers is a Microsoft thing, but it does not mean what you think it means. To do what you wanted to do, you would have had to separate the domains physically by separate switches with a router in between the switches, or logically with VLAN's, and you would have had to assign different subnets to each segment or VLAN. You could have achieved your goals this way because you could have used secondary DNS servers for name resolution and routing between the subnets and/or VLANs.

The way you did it is fine too. 1 DHCP server. fine. You don't have the logical separation of domains that you originally wanted, but as long as you set up DNS properly and each workstation can find the AD information for it's domain via DNS, then all is well.

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