Sua configuração deve se parecer mais com isso:
subnet 1.2.3.0 netmask 255.255.255.0 {
range 1.2.3.128 1.2.3.254
next-server 1.2.3.199;
filename "pxelinux.0";
option routers 1.2.3.1;
option subnet-mask 255.255.255.0;
option domain-name "host.edu";
option domain-name-servers 1.2.8.;
option broadcast-address 1.2.3.255;
default-lease-time -1;
max-lease-time -1;
host node-1 {
hardware ethernet 00:00:00:01:01:5d;
fixed-address 1.2.3.12;
option host-name "node-1";
}
}