a script for converting domain names to DHCP Option 119 (Domain Search Option)

dhcp_option119.py

#!/usr/bin/env python3
"""Command generator for setting DHCP Option 119

This script converts the specified domain names to DHCP Option 119
(Domain Search Option) and prints commands for various DHCP servers.

USAGE:
  ./dhcp_option119.py DOMAIN ...

EXAMPLE:
  ./dhcp_option119.py apple.com google.com
"""

from __future__ import print_function
import sys

hexlist = []
for domain in sys.argv[1:]:
    for part in domain.split('.'):
        hexlist.append('%02x' % len(part))
        hexlist.extend(['%02x' % ord(char) for char in str.lower(part)])
    hexlist.append('00')

print("""
MikroTik RouterOS
-----------------
/ip dhcp-server option
add code=119 name=domain-search value=0x""", ''.join(hexlist), sep='')

print("""
Cisco IOS
---------
ip dhcp pool POOL_NAME
   option 119 hex """, ''.join([(".%s" % (x) if i and not i % 2 else x)
                                for i, x in enumerate(hexlist)]), sep='')

print("""
Windows DHCP Server
-------------------
netsh dhcp server V4 set optionvalue 119 BYTE """, ' '.join(hexlist), sep='')

print("""
Juniper SRX
------------
set access address-assignment pool POOL_NAME family inet \
dhcp-attributes option 119 hex-string """, ''.join(hexlist), sep='')

print("""
ZyXEL Keenetic
--------------
ip dhcp pool POOL_NAME option 119 hex """, ''.join(hexlist), sep='')

Thanks, this worked nicely.

wow! very useful, thank you

Nice one! 😉

Thanks, very useful! 👍

The spec requires DNS name compression to be used, see https://gist.github.com/grawity/7828db5ec8ab363dafb981f77a0aa02e for an implementation. (For internal search lists with a lot of subdomains under the same domain, it can make the option a lot shorter – e.g. if you want to list {foo,bar,baz,quux}.example.com, the list is compressed from 69 down to just 36 bytes.)

thanks this was perfect for using with my windows dhcp server