If you're really paranoid about DHCP availability on your network and are already using the 80/20 rule of having two DHCP servers, you might consider configuring a third DHCP server that mirrors the configuration of your 80 percent server. Once you've configured this server, however, keep it disconnected from the network as a hot backup DHCP server. Then if your main DHCP server goes down you can bring the backup one online to take its place. In this scenario you might ask, "Why keep the 20 percent server if you have a hot backup?" The reason is, what if your 80 percent server dies during the night and you're not around to flip the switch and connect your backup to the network? Unless you have sophisticated network management software that can handle this situation by bringing your spare 80 percent server online, some of your clients may be out of luck if they want to connect to the network before morning comes.