Google DNS --- Figuring out which DNS Cluster you are using

Bjørn Mork bjorn at
Thu Aug 24 11:41:10 UTC 2017

Stephane Bortzmeyer <bortzmeyer at> writes:

> On Thu, Aug 24, 2017 at 10:53:58AM +1000,
>  Mark Andrews <marka at> wrote 
>  a message of 39 lines which said:
>> If Google was being sensible the servers would just return the
>> information along with the answer.  They all support EDNS.
> I fully agree with you that NSID (RFC 5001) is great and Google should
> really deploy it.

+1 for NSID! Should be mandatory for anycast DNS, IMHO.  I don't
understand why Google haven't enabled it.

> However:
>> e.g. dig +nsid @
> I assume that Google wants also to be debuggable by people who work on
> inferior operating systems, and have no dig. Hence this trick. For
> instance, has both NSID and a special name,
> (see RFC 7108).

As you state, there is no problem providing both.  Or an infinite number
of special names if they like.  But NSID provides something none of the
special names can.  Quoting the justification in the intro of RFC5001:

   Given that a DNS query is an idempotent operation with no retained
   state, it would appear that the only completely reliable way to
   obtain the identity of the name server that responded to a particular
   query is to have that name server include identifying information in
   the response itself.

Sometimes it just isn't enough to know which server answered the
previous or next requests.


More information about the NANOG mailing list