While having 2 DHCP servers on a same network is possible, I would say that the most probable cause of the address conflict is simply that the IP address 172.22.3.125 was configured statically on some device.
It is difficult to prevent these situations from occuring. Any user having its own PDA, laptop or computer can configure its IP address statically and possibly create an address conflct. That is why both DHCP client and DHCP server try to ascertain whether the IP address being assigned is currently free. The DHCP server does it by pinging the IP address before assigning it, and the client performs an ARP query on this IP address after it has been assigned to it. Both these methods, especially the ARP method used on the client, should be able to detect the conflicts.
There are certain mechanisms on Catalyst switches that can prevent users from attaching illegal DHCP servers to the network, or using statically configured addresses instead of acquiring the IP configuration via DHCP. Illegal DHCP servers can be prevented using the DHCP Snooping feature while the clients' address verification can be performed using the IP Source Guard. However, deploying these mechanisms requires a degree of planning.
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