How to replace DHCP server from domainA with DHCP from domainB?

Question

Hello fellow Administrators,
We have one remote site with one subnet. There's domainA domain controller and about 100 domainA's client computers in that subnet. We're about to send 100 domainB's client computers there as well.
There's also domainA's DHCP server running on the same subnet. DHCP scope options include domainA's domain name, gw and domainA's DNS server addresses.
DomainA and DomainB belongs to separate forests and there's two-way trust between them. DomainA DNS has stubzone for DomainB and DomainB has stubzone for domainA. That's how
clients can resolve hostnames of other domain.
All domainA's clients in remote site will be replaced gradually with domainB's client computers, but this can take a long time.
I want to note, that I cannot create second subnet for domainB at the moment.
At some point, we need to deploy DHCP server to domainB's member server in the remote site. What are the steps I should take to replace existing domainA's DHCP server with domainB's DHCP server while still allowing clients from domainA and domainB to successfully
find domain controller of their own domain and being able to resolve hostnames from both domains?

Answer 1

When the devices on your network first request an IP address or reach the end of their leases (or you force them to check their lease is still valid) they will simply
broadcast a request for a DHCP server, and will accept an offer from the first DHCP server
to reply. 
Multiple DHCP servers PT 1: Spanning multiple subnets.
If you have several VLANs or physical network segments that are separated into different subnets, and you want to provide a DHCP service to devices in all those subnets then there are two ways of doing this.
If the router / layer 3 switch separating them can act as a BOOTP/DHCP relay agent, then you can continue to keep all your DHCP server(s) in one or two central parts of your network and configure your DHCP server(s) to support multiple ranges of addresses.
In order to support this, your router or layer 3 switch must support the BOOTP relay agent specification covered in section
4 of RFC 1542.
If your router does not support RFC 1542 BOOTP relay agents, or if some of your network segments are geographically dispersed over slow links, then you will need to place one or more DHCP server in each subnet. This ‘local’ DHCP server will only serve its own
local segment’s requirements, and there is no interaction between it and other DHCP servers. If this is what you want then you can simply configure each DHCP server as a standalone server, with the details of the address pool for its own subnet, and not worry
about any other DHCP servers on other parts of the network. This is the most basic example of having more than one DHCP server on the same network.
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