* Verified with ISC DHCPd 4.3.5 running under Debian Stretch and Windows 2008R2 DNS
* Adapted from
  - https://unix.stackexchange.com/questions/270097/isc-dhcp-with-active-directory-secure-dynamic-dns-updates/271815#271815
  - https://blog.michael.kuron-germany.de/2011/02/isc-dhcpd-dynamic-dns-updates-against-secure-microsoft-dns/

NOTE: Verify DHCPd is working and handing out IPs before starting this process.
 
1. Install heimdal and ntp

    apt-get install heimdal-clients ntp

 2. Configure ntp to sync clock with DC 

 3. Generate keytab file (see https://pastebin.com/7KBafRVp) from domain controller

 4. Test the kerberos connection on DHCPd side

    kinit -k -t ‘<keytab_file>’ ‘<user_principal@REALM>’
    klist

 5. Create script on DHCPd server (see https://pastebin.com/taNfvCSt)

 6. Test DDNS through manual creation of RR

    dns-krbnsupdate.sh add  <host_ip> -h <host_name> -d

 7. Verify creation of DDNS entry on DNS server

 8. Delete test DDNS entry manually

    dns-krbnsupdate.sh delete <host_ip> -d

 9. Modify /etc/dhcp/dhcpd.conf file and apply hooks either at the global or pool-level (see https://pastebin.com/vXjERNuS)

10. Perform a DHCP request/renew

11. Check /var/log/syslog for Dynamic DNS entries.