Trying to understand DNSSEC and BIND versions better

Jeff Lightner jlightner at
Fri Jun 5 12:09:11 UTC 2009

BIND versions on RHEL (e.g. 9.3.4-6.0.3.P1.el5_2) have backported
patches from later BIND versions so it isn't exactly the same animal as
the EOL 9.3 which is why it isn't listed simply as 9.3

-----Original Message-----
From: bind-users-bounces at
[mailto:bind-users-bounces at] On Behalf Of Mark Andrews
Sent: Friday, June 05, 2009 12:23 AM
To: Chris Adams
Cc: comp-protocols-dns-bind at
Subject: Re: Trying to understand DNSSEC and BIND versions better 

In message <eYSdnVoGu5EsGrXXnZ2dnUVZ_vudnZ2d at posted.hiwaay2>, Chris
Adams write
> Since I read that the root is supposed to be signed by the end of the
> year, I am just trying to understand DNSSEC support and the various
> versions of BIND a little better here, so please don't throw too many
> rocks if I ask something stupid...
> I run the nameservers for an ISP.  For the recursive servers, what are
> the hazzards in enabling DNSSEC (once the root is signed, so no DLV
> necessary I guess)?

	Once the root is signed you will be able to validation answers
	where there is a unbroken chaing of trust.  DLV will still be
	useful for zones were the TLD isn't yet signed or there is
	another break in the chain of trust.

> I know the things that generally break with
> "regular" DNS, but I don't know that with DNSSEC (I know there have
> DLV troubles but that's it).

	Not having a clean EDNS path between the validator and
	authoritative server can result in validation failures.
	EDNS responses are bigger that plain DNS and may result in
	fagmented responses.  You need to ensure that any NAT's and
	firewalls are configured to handle fragments UDP responses
	up 4096 bytes with a modern BIND.  Any forwarders used
	should also support EDNS and preferably be performing
	validation as well.

	Failure to re-sign a zone will cause lookups to fail.
	Failure to update DS records on DNSKEY changes will cause
	lookups to fail.  Failure to update DLV records on DNSKEY
	changes will cause lookups to fail.

	"dig +cd +dnssec <query>" is your friend.  This will let
	you see what is failing to validate.

	"dig +cd +multi DNSKEY <zone>" will provide you with the
	keyids necessary to check the signatures.

	"dig +cd +multi DS <zone>" will provide you with the DS
	records so you can check the linkage between parent and
	child.  Look at the key id field.

	"dig +cd +multi DLV <zone>.<dlvroot>" will provide you with the
	records so you can check the linkage between parent and
	child.  Look at the key id field.

	If the zone is using NSEC3 then nsec3hash can be used to
	check workout in the NSEC3 records are sane.

	"date -u +%Y%m%d%H%M%S" returns the system date in a form
	that is easy to comare to the dates in the RRSIG records.

	A understand of how DNSSEC works is useful.

	Checking if you get a DNSKEY returned, without +cd, at each zone
	cut is useful for working out where to examine more closely.

	dig, date and a understanding of DNSSEC is all you should
	need to identify a configuration error.  If the keyid match
	and timestamps are good and associated NSEC/NSEC3 appear
	to be sane the you will most probably have found a
	implementation bug.

> Currently, my servers run BIND 9.3.4-10.P1 (as patched by Red Hat in
> RHEL; we typically stick with their security patched version, since
> that's what we pay them for).  What does that mean with .ORG for
> example, where NSEC3 is used?  Would we just not see NXDOMAIN
> as validated (and what happens to unvalidated responses)?  I've put in
> request to Red Hat to update to a version that supports NSEC3 but I
> don't know what their response will be yet.

	BIND 9.3 is already at EOL.

> For our authoritative servers, we'll need to set up a system to sign
> zones.  Is it expected that ISPs will sign every zone they serve, or
> just the domains we consider "important"?  What kind of problems might
> be expected here?
> In both cases, what kind of CPU and/or RAM overhead will large-scale
> of DNSSEC add?
> -- 
> Chris Adams <cmadams at>
> Systems and Network Administrator - HiWAAY Internet Services
> I don't speak for anybody but myself - that's enough trouble.
> _______________________________________________
> bind-users mailing list
> bind-users at
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at
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