login.authorize.net has A and CNAME records

Wed Apr 7 07:32:56 UTC 2021

> On 7 Apr 2021, at 17:20, Bjørn Mork <bjorn at mork.no> wrote:
> 
> Bjørn Mork <bjorn at mork.no> writes:
> 
>> Seth Mattinen <sethm at rollernet.us> writes:
>>> On 4/6/21 11:35 AM, Arne Jensen wrote:
>>>> login.authorize.net. is a CNAME, but does not have any A records itself.
>>> 
>>> 
>>> This one returns A records:
>> 
>> Looks like they host DNS on both cloudflare and akami, but zone contents
>> are different on the two platforms:
>> 
>> bjorn at miraculix:~$ for s in $(dig +short ns authorize.net|sort); do echo -n "$s: ";dig +short login.authorize.net @$s|xargs; done
>> a10-64.akam.net.: login.authorize.net.cdn.cloudflare.net.
>> a1-190.akam.net.: login.authorize.net.cdn.cloudflare.net.
>> a2-65.akam.net.: login.authorize.net.cdn.cloudflare.net.
>> a9-64.akam.net.: login.authorize.net.cdn.cloudflare.net.
>> ns0090.secondary.cloudflare.com.: 104.18.8.127 104.18.9.127
>> ns0210.secondary.cloudflare.com.: 104.18.9.127 104.18.8.127
> 
> Doh! I should know better.  Sorry, ignore that.  Don't ask for A records
> if you want to see CNAMEs..

It shouldn’t matter.  Only non-rfc-compliant servers allow A and CNAME
to co-exist at the same name.  That combination was prohibited by RFC
1034.

"The domain system provides such a feature using the canonical name
(CNAME) RR.  A CNAME RR identifies its owner name as an alias, and
specifies the corresponding canonical name in the RDATA section of the
RR.  If a CNAME RR is present at a node, no other data should be
present; this ensures that the data for a canonical name and its aliases
cannot be different.  This rule also insures that a cached CNAME can be
used without checking with an authoritative server for other RR types.”

Returning a signed CNAME is cryptographic proof that an A record does not
exist at the name with DNSSEC.

Mark

> Bjørn

-- 
Mark Andrews, ISC
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PHONE: +61 2 9871 4742              INTERNET: marka at isc.org