Why is ISC DHCP server ignoring the fixed-address statement?
The configuration below works only if the DHCP server uses multiple interfaces, for example eth1.10 and eth1.11 in the case of VLANs. If there is only one interface, then the subnet statements should be enclosed in a shared-network block.
According to the documentation:
The shared-network statement is used to inform the DHCP server that some IP subnets actually share the same physical network. Any subnets in a shared network should be declared within a shared-network statement.