sample isc dhcp config

default-lease-time 600;
max-lease-time 7200;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.4.255;
option routers 192.168.4.1;
option domain-name-servers 192.168.4.1;
option domain-name "localhost.localdomain";

subnet 192.168.4.0 netmask 255.255.255.0 {
range 192.168.4.10 192.168.4.254;
}

host somehost1 {
        hardware ethernet aa:aa:aa:aa:aa:99;
        fixed-address 192.168.4.99;
}