DNS name compression with BIND9

Mark Andrews Mark_Andrews at isc.org
Fri May 26 00:55:52 UTC 2006

> pascalpoirier at gmail.com wrote:
> >Hi there,
> >
> >I am working on a testsuite for DNS server. I would like to know if
> >there is something to do to remove the name compression used by BIND9.
> >
> Just stick to using names that have nothing in common with each other, 
> so that label compression is not possible. For your (in)convenience 
> there are plenty of TLDs from which to choose.
> Seriously, how valid can it be to test anything in DNS with 
> label-compression disabled? Label compression is pervasive in day-to-day 
> DNS. It would be like trying to do automotive crash-testing with 
> vehicles that include no glass, rubber or plastic in their construction. 
> Sure you could test like that, but would the results have any value?
>                                                    - Kevin

	It's useful if you want to test that the resolver can also
	handle uncompressed responses.  There is atleast one firewall
	that assumes that the first record in the answer section
	to a query will be a compression pointer to octet 12 of the

	The is not true with DNAME.

	Being able to disable compression is a easy way to find
	implementation bugs like this.

	See lib/dns/compress.c / lib/dns/include/dns/compress.h for
	the code which handles compression.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org

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