Configuring DHCPD to use option 66, in a specific subnet

Question

I am trying to configure DHCP to use option 66 to provide a TFTP server to Sunray thin clients. The clients in a specific subnet must use a specific TFTP server so that they are served configuration specific to their subnet. Can I place the option in a subnet block as follows

 subnet 192.168.1.128 netmask 255.255.255.128 {

    # don't let clients modify their own A records
    ignore client-updates;

    # options
    option subnet-mask 255.255.255.128;
    option broadcast-address 192.168.1.255;

    option domain-name "domain.com";
    option domain-name-servers 192.168.3.55, 192.168.3.56;
    option routers 192.168.1.129;
    option 66 ip 192.168.16.21;

    option ntp-servers 192.168.3.57;
    option interface-mtu 1500;
    ddns-domainname "dhcp.domain.com.";
    ddns-rev-domainname "dhcp.in-addr.arpa.";
    pool {
            failover peer "dhcp-failover";
            range 192.168.1.140 192.168.1.249;
    }

}

Solution

In isc-dhcp-server I create the option globally and then use it at the host level. You should be able to use vendor-option-space at the subnet level as well.

option space SunRay;
option SunRay.FWSrvr code 31 = ip-address;      
option SunRay.FWSrvr 10.99.90.160;
option SunRay.AuthSrvr code 21 = ip-address;
option SunRay.AuthSrvr 10.99.90.160;
option SunRay.AltAuth code 35 = array of ip-address;
option SunRay.AltAuth 10.99.90.161, 10.99.90.160;

host 10.96.0.11 {
    vendor-option-space SunRay;
    hardware ethernet 00:ff:ff:ff:ff:ff;
    fixed-address 10.96.0.11;
}