Multihomed DHCP Server issue

[gdp100]

Our network has six VLANS on our network that we are handing out IP Addresses for. We have two DHCP servers with 3 NIC cards each. We will say the six VLANS are vlan10, vlan11, vlan12, vlan13, vlan14, and vlan15.
Vlan10’s IP address range is 10.1.1.20 – 254 with a subnet mask of 255.255.255.0 and default gateway 10.1.1.1.
Vlan11’s IP address range is 10.2.2.20 - 254 with a subnet mask of 255.255.255.0 and a default gateway 10.2.2.1.
Vlan12’s is 10.3.3.20-254, vlan13 is 10.4.4.20-254, vlan14 is 10.5.5.20-254, and vlan15 is 10.6.6.20-254. All are class C and default gateway ends with.1.
All DHCP server interfaces for each segment end with a .5. The three interfaces on server1 are 10.1.1.5, 10.2.2.5 and 10.3.3.5. The three interfaces on server2 are 10.4.4.5, 10.5.5.5 and 10.6.6.5.
IP addresses are being handed out on all segments as should be, except that when a person with a computer on vlan10 moves to vlan11, the server1 still hands the pc the IP address for vlan10. And as you can see it is the vlan11 interface that is handing out the vlan10 address.

Windows IP Configuration

Host Name . . . . . . . . . . . . : tech1
Primary Dns Suffix . . . . . . . : tech.net
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : tech.net

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel(R) PRO/100 VE Network Connection
Physical Address. . . . . . . . . : 00-0C-F1-AC-9C-0F
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 10.1.1.22
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.1.1.1
DHCP Server . . . . . . . . . . . : 10.2.2.5
DNS Servers . . . . . . . . . . . : 10.1.1.10

Primary WINS Server . . . . . . . : 10.1.1.6
Secondary WINS Server . . . . . . : 10.5.5.6
Lease Obtained. . . . . . . . . . : Tuesday, October 04, 2005 12:04:39 PM
Lease Expires . . . . . . . . . . : Tuesday, October 04, 2005 8:04:39 PM
But if someone on vlan10 moves to vlan13 which is on the other server, server2, he gets the IP address for vlan13.
Also we have forwarding turned off on our router for DHCP request.
Any ideals how to fix this would be greatly appreciated.

 

[Serbtastic]

What OS are the DHCP servers using?

 

[gdp100]

The servers are running Windows Server 2000 with all SP and patches installed. The are member servers and not domain controllers.

 

[itsp1965]

How are VLANS 10,11,12 communicating with each other; are you using the DHCP server as a router also?

 

[gdp100]

We have a core switch/router in our LAN which handles all routing and VLANS.

 

[Serbtastic]

According to the Windows 2000 DHCP help file, leases are retained in the DHCP server database approximately one day after expiration. When a scope is created, the default lease duration is set to 8 days. So your client would have to be off the network for 9 days in order to pull a new IP from the correct scope.

The answer lies in either shortening your lease time, or delete the lease after taking the client off the old VLAN and before putting it back on the new VLAN.