EDNS compliance of servers for the Alexa Top 1M

Mark Andrews marka at isc.org
Tue May 31 06:56:19 UTC 2016


If you are a Alexa Top 1M entry or host the DNS for a Alexa Top 1M
entry you should be paying attention.

I'm focusing here on unknown EDNS option handling as ISC is about
to release a version of named which will exercise these errors in
your nameservers.  BIND 9.11.0 will ship with EDNS COOKIE enabled
by default (RFC 7873) which will appear to be a unknown EDNS option
to servers that do not understand it.

RFC 6891 states that unknown EDNS options should be ignored but that is
not always the case.

These answers are all for servers that nominally support EDNS.

You can test your servers via https://ednscomp.isc.org

Mark

232270 ednsopt=noopt

	Servers that only respond with a EDNS response if something
	else is in the EDNS query (DO=1, a known EDNS option e.g.
	ECS or NSID present).

220083 ednsopt=timeout

	The firewall is dropping queries with EDNS options present.
	
	THIS WILL CAUSE INTERMITTENT LOOKUP FAILURES.

	This stupidity needs to be fixed along with dropping queries
	due to unknown EDNS versions, unknown EDNS/DNS flags and
	unknown query types.

 64945 ednsopt=formerr,echoed,nosoa

	Failed to ignore the EDNS option.  This results in EDNS
	being disabled for the server and additional queries being
	made.  If it is serving a signed zone this may result in
	PERMANENT lookup failures if all the available servers for
	the zone exibit this error.

 30917 ednsopt=echoed

	This is a benign failure for DNS COOKIES but could result
	in errors for other options.

  2142 ednsopt=noopt,nosoa

	This is similar to ednsopt=noopt but no SOA record was
	returned which may result in answers being treated as
	NOERROR,NODATA when they shouldn't be.

  1490 ednsopt=nosoa

	No SOA record was returned which may result in answers being
	treated as NOERROR,NODATA when they shouldn't be.

   774 ednsopt=badvers,nosoa

	BADVERS is supposed to be for EDNS version negotiation.
	Named will treat the server as not supporting EDNS.  This
	results in additional queries being made.  If it is serving
	a signed zone this may result in PERMANENT lookup failures
	if all the available servers for the zone exibit this error.

   106 ednsopt=echoed,nosoa

	No SOA record was returned which may result in answers being
	treated as NOERROR,NODATA when they shouldn't be.  The
	echoed EDNS option is benign for DNS COOKIES but could
	result in errors for other options.

    93 ednsopt=servfail,noopt,nosoa

	Possible a false positive due to the plain DNS query timing
	out or the server returning SERVFAIL.  If the later this is
	unrecoverable and will result in lookup failures.

    69 ednsopt=badversion

	Absolutely bizarre response as the EDNS version was non 0.
	Probably a proxy which is not EDNS version aware.

    68 ednsopt=status,nosoa

	Unknown RCODE returned.

    54 ednsopt=badversion,echoed

	Absolutely bizarre response as the EDNS version was non 0.
	Probably a proxy which is not EDNS version aware.


    20 ednsopt=refused,nosoa

	Possible a false positive due to the plain DNS query timing
	out or the server returning REFUSED.  If the later this is
	unrecoverable and will result in lookup failures.

    14 ednsopt=status,noopt,nosoa

	Unknown RCODE returned.

    14 ednsopt=formerr,nosoa

	This is similar to ednsopt=formerr,echoed,nosoa above.

    13 ednsopt=nxdomain

	Possible a false positive due to the plain DNS query timing
	out or the server returning NXDOMAIN.  If the later this
	is unrecoverable and will result in lookup failures.

     9 ednsopt=servfail,nosoa

	This is similar to ednsopt=servfail,echoed,nosoa above.

     6 ednsopt=formerr,echoed

	This is similar to ednsopt=formerr,echoed,nosoa above.

     3 ednsopt=nxdomain,echoed,nosoa

     2 ednsopt=nxdomain,noopt

     1 ednsopt=refused,noopt,nosoa

     1 ednsopt=formerr,badversion,echoed,nosoa

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


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