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Strange IP conflict with DHCP

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7 replies

by alavery2004

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DHCP running on Server 2003
Client running XP Pro
My client is running DHCP. Randomly when he boots up and connects to the network, my exchange box (Server 2003) gets an ip address conflict error. I know it is this laptop as it gives the MAC address. If I check his laptop, he has an IP from the DHCP scope. The exchange box address is 10.0.0.3 and the DHCP scope is 10.0.1.x. He gets an address in the correct scope. I can ping the exchange box on the correct address 10.0.0.3 straight away and by the DNS hostname, although users cannot connect to their mailboxes until I reboot the server. The laptop has only one network card. Is it possible for the card (Realtek RTL1839/810x) to try to use the 10.0.0.3 address first and then when that is not available, it uses DHCP? If so, how do I stop this and get it to use DHCP straight away and not try to use 10.0.0.3?

7 replies

by bfilmfan

Create a DHCP exclusion in the scope for 10.0.0.3.

The DHCP server will attempt to hand out each system the same IP address it last posessed, unless another client has it.

by alavery2004

This exclusion is already in place. That and the fact that it is only this laptop that it happens on, in a network of >150 seats, makes me think that it is some sort of setting on the laptop. The DHCP setup is as follows: There are two DHCP servers, both with an address pool of 10.0.0.1 - 10.0.2.254. Exclusions on one server are 10.0.0.1 - 10.0.0.255 and 10.0.2.0 - 10.0.2.254, while on the other server exclusions are 10.0.0.1 - 10.0.0.255 and 10.0.1.0 - 10.0.1.254. Available addresses on the primary DHCP server are 10.0.1.0 - 10.0.1.254 and on the secondary are 10.0.2.0 - 10.0.2.254.

by cg it

you said both have this address pool 10.0.0.1 - 10.0.2.254 they both can't have the same address pool, both be authorized to provide clients on the subnet with IP addresses.

by sgt_shultz

this does not compute to poor sgt's aging brain.
i would try setting up the laptop at a static ip address that i thought would work, just for a test. once i had that working, i'd configure the dhcp server to 'pre-assign' that ip address to the mac address of the laptop. who else is using dhcp on this network, i wonder, and how is it working for them? what is in the event log on the laptop i wonder

by curlergirl

Is this user taking his laptop somewhere else inbetween and possibly connecting to a network with an IP address range of 10.0.0.1-10.0.0.254? If that's the case, the conflict may be caused by the fact that when he boots up, his laptop will try to renew the lease for the 10.0.0.x address, and then when it receives a NACK from the server, it tries for a new lease and gets a new IP addy in the correct subnet.

Hope this helps!

by hozcanhan

You seem to have experience to overcome simple problems. An intelligent guess might be this : When a Windows 2000 client configured for
automatic addressing boots, it attempts to
obtain an address from a DHCP server. If that
attempt fails, the client attempts to ping the
default gateway defined in its current lease.
The client continues to use the existing lease
if the ping succeeds, and then checks for a
DHCP server every five minutes for a new
lease. If the ping fails, the client assumes that
DHCP services are not available on the network
and automatically assigns itself a nonconflicting
IP address in the private address range . This address it gets conflicts with an address already issued by the DHCP server . Stop it by disabling automatic addressing of the 2000 client. Good luck !

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