...
- one of the subnetworks used is not specified
- classes are specified incorrectly
- pool vacant addresses exhaustion
- failover problems
2.1 One of the subnetworks used is not specified
Subnetworks containing addresses of listened interfaces and a DHCP-relay (if used) should be specified in the file /etc/dhcp/dhcpd.conf. Even if addresses from these subnetworks are not allocated by the server, for example:
subnet 192.168.1.0 netmask 255.255.255.0 {}
2.2 Pool vacant addresses exhaustion
One of the common causes is a case when a server runs out of vacant addresses. To check it, use a guide: ISC DHCP server pool range usage monitoring
...