Windows DHCP - Non Split Scopes

Hi all,

What happens when there are two DHCP servers on a domain both authorised to to serve a scope in DHCP (same IP Range)?  Will clients always choose one server or will it be randomly split between both?

(FYI I have set up split scopes on two other Windows Servers (2008 R2) but cannot do in this instance as all the leases are currently on a 2003 Server.)


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when a client broadcasts messages on the physical subnet to discover available DHCP servers...  the IP will be assigned by the server that first responds to the DHCPDISCOVER from the clients...

unless you have some special routing rules....


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The client broadcasts a DHCP Request packet, both servers send their DHCP Offer, and the client answers with a DHCP Acknowledge on the request it received first.

The reason why you would configure a split scope in such cases is this: if the scope isn't splited, assume both DHCP-servers can assign the - range.
Client 1 requests DHCP
=> Server 1 offers
=> Server 2 offers
Client accepts offer from Server 1.
Everything fine :)
Client 2 requests DHCP
=> Server 1 offers (as is already acknowledged by client 1)
=> Server 2 offers (as this server didn't receive an acknowledgement)
Client accepts offer from Server 2 (as it did come before the server 1 offer).
Now there are two clients with, which WILL give you problems.

So set up a split scope by mutually excluding ranges, and avoid problems.
Brian PiercePhotographerCommented:
If the client does no have an IP then the client will essentially get its IP from whichever server responds first with a DHCP offer.

If the client already hads and IP and is trying to renew its lease it will contact the DHCP server from which the original lease was obtained to have it renewed.
techmissAuthor Commented:

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