IP helper not working with mobile ports?

[matthewit]

Hello all, I've got an odd issue that I'm hoping you might be able to help me sort out. The problem is with clients not being able to pull DHCP addresses from a Windows 2k8 DHCP server when plugged into a mobile port. The client is able to pull an IP address just fine from a Windows 2k3 DHCP server however. The client is also able to pull a DHCP address from a Windows 2k8 DHCP server if statically assigned to an appropriate vlan.

The hardware configuration were working with is Windows XP and 7 clients connected to a 6648 switch with port mobility enabled on their associated ports. The 6648 switch is connected to a OS7700 backbone using 802.1q. The backbone is then connected by to the VMware ESX host running the windows 2k8 DHCP server.

The DHCP helper is setup only on the OS7700 as show below. I only see the IP Helper stats "Tx Server" increment when a workstation has been statically assigned to an appropriate VLAN. Packet captures from a mobile port client to the Windows 2k8 DHCP server do show a DHCP discover packet come through but with no relay agent info attached. When statically assigned to a vlan the relay agent information is included in the packet and the DHCP DORA process completes just fine.

vlan 3 dhcp generic
vlan 7 ip [Workstation1].0 255.255.254.0
vlan 8 ip [workstation2].0 255.255.254.0
!
!============= UDP Relay Services =============================================
!
ip helper address x.x.x.x