This configuration is desired when there are two DHCP servers on the network, and IP helper addresses are configured for each server. However, only one server receives most of the DHCP address requests.
In order to verify that only one server receives most of the requests, it is necessary to perform a sniffer trace on the ports connected to DHCP servers.
If there are multiple DHCP servers, load balancing is not possible because the DHCP client PC-broadcasts a DHCP discover packet sourced from 0.0.0.0 and destined for 255.255.255.255. By default, the router blocks all of the broadcasts packets.
Refer to Understanding and Troubleshooting DHCP in Catalyst Switch or Enterprise Networks and Configuring the Catalyst Switched Port Analyzer (SPAN) Feature for additional information.