Use two DHCP servers in one LAN

Question

How do I configure Windows XP to choose between one of as two DHCP servers in one (same) LAN?

Solution 1

If you've got two (2) DHCP server computers in the same layer 2 broadcast domain, clients are going to be (mostly) randomly assigned addresses by either server computer. The one that answer's the client's DHCPDISCOVER reuqest first is going to end up assigning the address to the client.

I'm not sure this is a great idea. You're adding what is, essentially, a non-deterministic element to your network. If you want redundancy in DHCP, consider using a program to monitor the "health" of the primary DHCP server and, in the event of failure, bring up the secondary DHCP server.

Solution 2

Please see the existing question that directly answers this issue

Split your DHCP scope among multiple servers?

These are not client side changes

Solution 3

I don't think it is really recommended to have two DHCP servers on one lan...

If it is for redundancy one option is to use cluster services so that the dhcp files are stored and referenced by which ever server is running the dhcp service.

another solution would be to put you separate lans in vlans or similar so that only the client that are on that lan with each dhcp service will receive the correct dhcp request

hope that helps

Solution 4

I am not aware of any way to specify a DHCP server from a network client. My question to you would be - why would you want to? In an AD, you can have multiple redundant DHCP servers, and you can configure them to manage the same scope without overlapping addresses. You can also configure reservations and several other things. If you need to have different DNS or WINS servers for some reason, the machines that require the exceptions can have manually configured DNS or WINS entries but still use DHCP.

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Comments

[Saurabh Barjatiya]

Just curious. Why do you have two DHCP servers in same LAN?

[squillman]

You would want two servers for redundancy, for example. If one goes down the other will still be around to hand out addresses while you get the other one back up.

[Ernie]

If you have two servers for redundancy, why would you want XP to choose only one to use? :)

[squillman]

WINS <> DHCP. WINS is for name resolution, not IP address assignment.

[aeroshock]

AD does not handle DHCP like this. In fact, AD has nothing (intrinsically) to do with DHCP. They authorize themselves every minute, but there is no DHCP redundancy in AD. Are you thinking of clustered DHCP servers?

[Jes]

There are many ways to implement DHCP. However, if you run DHCP on an AD server, it has to be authorized to distribute addresses. You can have several servers with the DHCP role installed, and they can all be configured for the same scope. This is redundant but not clustered. However, when you configure this, you also have to configure non-overlapping exclusion ranges. You put the full range on both servers, then exclude a range from one server and a different range on the other (about 80/20 split). They won't distribute duplicate IP's, but they will allow a renewal in the exclusion range.

[Florian Haider]

if you want some clients use 1 gateway and others to use another gateway, having 2 DHCP servers with "client utilities" is not the way to accomplish this...

[Philip]

+1, This is the correct way to setup two DHCP server on the same network (unless you're running a DHCP server that coordinates redundancy, ISC's DHCPd supports failover now). Configure the same scope with different exclusions on each, or two different scopes (either way works); also they should be split 80/20 or 50/50 (most use the former, I've seen the latter work just as well though).

[kasperd]

Reliably determining whether a service is up or down is a hard problem. The non-determinism introduced by running two DHCP servers is not too bad, since each client is going to keep using whatever DHCP server it happened to be using at first for as long as that DHCP server keeps responding to the client. One just has to ensure the configuration of the two DHCP servers is not directly in conflict with each other.