docker-dhcp-server/isc-dhcp/config/dhcpd.conf

#Dynamic DNS security settings
key "key-internal" {
        algorithm HMAC-MD5;
        secret "DNS_TSIG_KEY_INTERNAL_SECRET";
};

zone DHCP_DYN_IPS_DOMAIN {
    primary DHCP_DNS_MASTER;
    key "key-internal";
}

zone DHCP_SITE_DOMAIN {
    primary DHCP_DNS_MASTER;
    key "key-internal";
}

zone DHCP_REV_DOMAIN {
    primary DHCP_DNS_MASTER;
    key "key-internal";
}


# Custom routes classes
option classless-routes code 121 = array of unsigned integer 8;
option classless-routes-win code 249 = array of unsigned integer 8;

# Leases settings
default-lease-time 600;
max-lease-time 7200;

# Dynamic DNS update
ddns-updates on;
ddns-update-style interim;
update-static-leases on;
#allow client-updates;

# Misc settings
use-host-decl-names on;
authoritative;
log-facility local7;

subnet DHCP_SUBNET netmask DHCP_NETMASK {

  # Dynamic DNS update
  ddns-domainname "DHCP_DYN_IPS_DOMAIN";
  update-conflict-detection false;

  # IP settings
  range DHCP_IP_FIRST DHCP_IP_LAST;
  option subnet-mask DHCP_NETMASK;
  option broadcast-address DHCP_BROADCAST;
  option routers DHCP_ROUTERS;

  # DNS settings
  option domain-name "DHCP_SITE_DOMAIN";
  option domain-search "DHCP_SITE_DOMAIN", "DHCP_DOMAIN", "DHCP_DYN_IPS_DOMAIN";
  option domain-name-servers DHCP_DNS_SERVER;

  # Push custom routes to clients
  #option classless-routes 24, 10,15,42, 10.15.12,2;
  #option classless-routes-win 24, 10,15,42, 10.15.12,2;

  # Netboot settings
  next-server DHCP_TFTP_SERVER;
  #option root-path "10.15.100.1:/pxeroot/ubuntu";
  if exists user-class and ( option user-class = "iPXE-rthoni" ) {
    option domain-search "DHCP_SITE_DOMAIN";
    filename "http://netboot/boot.ipxe";
  }
  else {
    filename "ipxe-rthoni.kpxe";
  }

  # Static IP hosts
  group {
    include "/etc/dhcp/config/static_ips.conf";
    ddns-domainname "DHCP_SITE_DOMAIN";
    option host-name = host-decl-name;
    ddns-hostname = config-option host-name;
  }

  # Force a default hostname if not present
  if option dhcp-message-type = 3 and not exists host-name and config-option host-name = null {
    option host-name = concat("dyn-", binary-to-ascii(10, 8, "-", leased-address));
    ddns-hostname = config-option host-name;
  }
}