How a Broken Device Can Exhaust Your DHCP Server's IP Pool

An unusual way for your DHCP server to run out of dynamic IPs

I discovered a bizarre failure mode where a misconfigured device answered ICMP pings for every IP address on our network. Because the ISC DHCP server checks if an IP is free before assigning it, this 'screaming' machine tricked the server into thinking the entire dynamic pool was exhausted. Tracking down the culprit required tracing ARP tables, but luckily the device used its real MAC address, allowing us to identify and remove it quickly.

"Today's new and exciting failure mode for a DHCP server handing out leases to dynamic clients: have something on your network that answers pings for absolutely every IP address."