Compression / Pointers on returned queries

Mark Andrews Mark_Andrews at
Thu Jun 5 03:17:57 UTC 2008

> > -----Original Message-----
> > From: Mark_Andrews at [mailto:Mark_Andrews at]
> > Sent: Wednesday, June 04, 2008 9:57 PM
> > To: Brian Feeny
> > Cc: bind-users at
> > Subject: Re: Compression / Pointers on returned queries
> > 
> > 
> > 	Why do you care?  As long as you get the answer in a single
> > 	packet it makes little to no difference.  Also why are you
> > 	asking recurive queries?  If you want to test authoritative
> > 	servers then you should be making non-recursive queries.
> > 	The server should also be configured not to accept recursive
> > 	queries from anywhere.
> Because a response of >512 bytes causes pain because of firewalls/etc that
> may drop the packets by default.
> So the goal would be a <512 byte response, which is what happens when the
> compression is used.

	A nameserver is broken if it emits a response which is
	greater than 512 bytes without EDNS being in effect.  A
	correctly functioning nameserver will drop additional records
	that do not fit to bring the response size to 512 or less
	bytes.  It will also set "tc" if it has to drop part of the
	authority or answer sections causing the client to retry
	with TCP.

	It appears that the nameserver is broken.  There is nothing
	a client can do to change the nameservers behaviour.  I suggest
	that you get on the phone and complain.

> I re-did the query without recursion, but it's a similar result, I think it
> shaved 30 bytes or so, but I am still
> Over 512 bytes.  

	It will change once the second CNAME times out.  Whether that
	bring it under 512 or not remains to be seen.  I don't intend
	to try and work it out.


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

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