192.168.1.0/24なら以下のようにする
ddns-update-style interim;
ignore client-updates;
subnet 192.168.1.0 netmask 255.255.255.0 {
# --- default gateway
option routers 192.168.1.1;
option subnet-mask 255.255.255.0;
option domain-name "domain.org";
option domain-name-servers 192.168.1.78;
option time-offset -18000; # Eastern Standard Time
range dynamic-bootp 192.168.1.128 192.168.1.254;
default-lease-time 21600;
max-lease-time 43200;
}
dhcpd -f -d