Making BIND zone files readable

Simeon Miteff — Tue, 23 Sep 2008 09:11:50 +0000

Update: Added MIT License

The zone configuration format for BIND has a number of short-cuts that make writing DNS zone files easy, but also make them hard to read. Here is an example:
$TTL 3D @ SOA server1.example.com. hostmaster.example.com. (1 8H 2H 4W 1D) NS server1 NS server2 MX 10 server1 MX 20 server2 server1 A 127.0.0.1 server2 A 127.0.0.2 www CNAME server1

Python to the rescue. The dnspython module has support for parsing BIND zones, and rendering them without the shortcuts:

#!/usr/bin/python
# bindnorm.py - "normalise" a bind zone file by expanding relative names.
# Simeon Miteff 
# Tue Sep 23 10:03:35 SAST 2008
#
#Copyright (c) 2008 Simeon Miteff
#
#Permission is hereby granted, free of charge, to any person obtaining a copy
#of this software and associated documentation files (the "Software"), to 
#deal in the Software without restriction, including without limitation the 
#rights to use, copy, modify, merge, publish, distribute, sublicense, and/or 
#sell copies of the Software, and to permit persons to whom the Software is 
#furnished to do so, subject to the following conditions:
#
#The above copyright notice and this permission notice shall be included in 
#all copies or substantial portions of the Software.
# 
#THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
#IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
#FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 
#THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
#LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
#FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS 
#IN THE SOFTWARE.
 
import dns.zone
import sys
 
if len(sys.argv)<2:
	sys.stderr.write("Usage: %s [zone fqdn]\n" % sys.argv[0])
	sys.stderr.write("Example: %s example.com < db.example.com > norm.db.example.com\n" % sys.argv[0])
	sys.exit(1)
 
zone = dns.zone.from_text(sys.stdin.read(), sys.argv[1], relativize=False, check_origin=False)
zone.to_file(sys.stdout, relativize=False)

To use it, you’ll need to install dnspython first. Fortunately, on Debian or Ubuntu, it’s just an apt-get install python-dnspython away. Running this little script with the example zone above as input yields:
example.com. 259200 IN SOA server1.example.com. hostmaster.example.com. 1 28800 7200 2419200 86400 example.com. 259200 IN NS server1.example.com. example.com. 259200 IN NS server2.example.com. example.com. 259200 IN MX 10 server1.example.com. example.com. 259200 IN MX 20 server2.example.com. server1.example.com. 259200 IN A 127.0.0.1 server2.example.com. 259200 IN A 127.0.0.2 www.example.com. 259200 IN CNAME server1.example.com.

This format is less canonical, but at least each line is context-free. Now you can proceed to grep the output to your heart’s desire :-)

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Making BIND zone files readable