MAC address filter Linux DHCP

/etc/dhcpd.conf
-----------------

ddns-update-style interim;

allow booting;
allow bootp;

authoritative;

ignore client-updates;
set vendorclass = option vendor-class-identifier;
 

# VDI Vcenter IPs
class "private-hosts" {
        match if substring(hardware,1,4) = 00:50:56:84;
}

subnet 192.168.100.0 netmask 255.255.255.0 {
     option routers             192.168.100.1;
     option domain-name-servers 192.168.100.1;
     option domain-name         "example.com";
     option subnet-mask         255.255.255.0;
     filename                   "/pxelinux.0";
     default-lease-time         2419200;
     max-lease-time             2419200;
     option ntp-servers         192.168.100.1;
     pool {
                range dynamic-bootp     192.168.100.200 192.168.100.255;
                deny members of "private-hosts";
        }
}

group {

    host test.example.com {

        hardware ethernet 00:23:7D:DE:97:E4;

        fixed-address 192.168.100.2;

        option host-name "test.example.com";

        option routers 192.168.100.1;

        filename "/pxelinux.0";

        next-server 156.132.110.119;

    }

}

------------------
Additional info:

http://petuu.org/?e=22