NXDomain for AAAA at vtext.com

[Mark_Andrews at isc.org]

> I am trying to send mail to vtext.com (Verizon Cell Phone SMS).  My system 
> is running NetBSD/i386 1.6 with bind "8.3.3-REL-NOESW" and the Verizon DNS 
> servers claim "9.2.1".
> 
> My system is configured for IPv6 and sendmail does a lookup for the AAAA 
> record first.  Verizon's DNS servers respond with NXDomain.  Shouldn't they 
> respond with NoError and no answer records?  Sendmail then does a lookup 
> for the A record and seems to have cached the NXDomain reply.
> 
> The result is that I am unable to send an email to my new phone.
> 
> Is my DNS at fault or theirs?

	Theirs.  The server doesn't even meet the requirement of RFC 1034
	and RFC 1035.  The server is lying when it returns NXDOMAIN.

	Resolvers are perfectly entitled to take a NXDOMAIN and act
	on it.  Your lucky that sendmail even re-queried after
	getting the NXDOMAIN.  Named will cache NXDOMAIN for the
	current clock tick even with a TTL of zero or no SOA record.

> Results from a `dig smtp.css.vtext.com aaaa ; dig smtp.css.vtext.com a`
> 
> tcpdump on lo0:
> 
>    11:46:04.781297 10.1.1.33.59538 > 10.1.1.33.53:  2+ AAAA? 
> smtp.css.vtext.com. (36)
>    11:46:04.884862 10.1.1.33.53 > 10.1.1.33.59538:  2 NXDomain 0/0/0 (36)
>    11:46:04.906100 10.1.1.33.59537 > 10.1.1.33.53:  2+ A? 
> smtp.css.vtext.com. (36)
>    11:46:04.907856 10.1.1.33.53 > 10.1.1.33.59537:  2 NXDomain 0/0/0 (36)
> 
> tcpdump on ethernet:
> 
>    11:46:04.783478 208.176.108.1.59567 > 66.174.3.4.53:  20445 AAAA? 
> smtp.css.vtext.com. (36)
>    11:46:04.883994 66.174.3.4.53 > 208.176.108.1.59567:  20445 NXDomain- 
> 0/0/0 (36)
> 
> $dig @66.174.6.71 version.bind chaos txt

	66.174.6.71 is at a higher level in the DNS heirarchy.

	The broken load balancer is 66.174.3.4 (njbdcss.vtext.com).

> 
>    version.bind.           0S CHAOS TXT    "9.2.1"
> 
> Answers for various queries:
> 
>    vtext.com.              2D IN NS        NJBDNS2.vtext.com.
>    vtext.com.              2D IN NS        CAWCNS1.vtext.com.
>    vtext.com.              2D IN NS        CAWCNS2.vtext.com.
>    vtext.com.              2D IN NS        NJBDNS1.vtext.com.
> 
>    NJBDNS2.vtext.com.      2D IN A         66.174.3.72
>    CAWCNS1.vtext.com.      2D IN A         66.174.6.71
>    CAWCNS2.vtext.com.      2D IN A         66.174.6.72
>    NJBDNS1.vtext.com.      2D IN A         66.174.3.71
> 
>    vtext.com.              30M IN MX       100 smtp.css.vtext.com.
> 
>    smtp.css.vtext.com.     0S IN A         66.174.3.10
> 
> 
--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at isc.org