Local Loop

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 <simeon@localloop.co.za>
# Tue Sep 23 10:03:35 SAST 2008
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 :-)