Why Secondary ADS Server Doing All DHCP Work?

[dgagne316]

We are a Cisco campus area net site with two Windows Servers 2003 running ADS and dishing out IPs on two subnets. The designated Primary is supposed to dish out most IPs with Secondary used as overflow. Problem is the Secondary is doing most of the DHCP work. Both servers are not busy (users not migrated to ADS yet). We use ip helper-address with Primary & Secondary listed in correct order for each subnet. Not sure where to sniff yet or what might be the issue. Any help is appreciated. Thanks.

Denny G

http://www.placer.ca.gov/admin/infotech.htm

 

[ADB100]

The order of IP Helpers is not relevent, the Cisco router forwards the packets (after modifying them) at the same time. The chances are the secondary one was up offering IP addresses when the networks were initially built. Clients will contact thier DHCP server at half the lease period to renew so the broadcast element is not relevent at this point.
Try doing a manual release on a client and then a renew. Even then the client will respond to the first reply it receives anyway. Are both your servers on the same Subnet or are they physically located different distances (from an IP perspective as well as a distance - WAN etc)?

HTH

Andy

 

[dgagne316]

Thanks, Andy. These are new servers. Each are on diff. subnets and not across a WAN from each other though they serve clients across a WAN. My PC (on CAN) did rel/ren and got the Secondary DHCP server each time. Our two previous (Win2K) servers used to be on same subnet, but are no longer on wire and assoc. ip helpers on router's VLAN sub-interfaces are gone. We don't think it's a routing or switch forwarding issue, but wonder if it may be a client (Win2K Pro & WinXP Pro) config issue or a server collaboration issue regarding Active Directory Service registration. -dg

Denny G

http://www.placer.ca.gov/admin/infotech.htm

 

[ADB100]

Unless you are clustering the DHCP servers then they simply don't communicate with each other regarding DHCP; hence the scopes can't be overlapping. If you disable a scope on the 'secondary' server does the 'primary' one lease an ip address sucessfully?

The next thing is to put a sniffer on and capture the DHCP release/renew process and look at the timing of the packets. I suspect it is just the 'secondary' one responding quicker.

Andy