If DHCP fails to start and throws an error “No subnet declaration for ethx”, subnet declaration for the interface to which DHCP listens is missing in the configuration.
Declare the same subnet as the DHCP listening interface.
For example, if DHCP is listening on the eth0 interface 192.168.1.1, then declare a subnet for 192.168.1.0.
NOTE:If you decide not to manage this subnet by this DHCP server, leave the subnet declaration empty i.e, do not create any pools within this subnet.
If you have multiple network interfaces on different subnets, the DHCP service will listen to only eth0 by default. Besides defining the subnet in the DNS/DHCP console, you can edit the /etc/sysconfig/dhcpd file and modify the DHCPD_INTERFACE="eth0" parameter to DHCP_INTERFACE="eth0 eth1".