[dns-operations] Using all the addresses of every name server? (Was: ANY efforts at taking additional responses more compact?

Florian Weimer fweimer at redhat.com
Mon Sep 12 07:47:50 UTC 2016

On 09/11/2016 09:09 PM, Stephane Bortzmeyer wrote:
> On Wed, Sep 07, 2016 at 05:33:48PM +0900,
>  Paul Vixie <paul at redbarn.org> wrote
>  a message of 30 lines which said:
>> but the non-unrolling behaviour is reasonable and it is compliant
> Really? I read RFC 1035, section 4.2.1, and specially 7.2, as saying
> that a resolver must (not RFC 2119 MUST, RFC 1035 was written before)
> try all IP addresses of an authoritative name server. RFC 1034,
> section 5.3.3 is even clearer "The strategy is to cycle around all of
> the addresses for all of the servers with a timeout between each
> transmission.  In practice it is important to use all addresses of a
> multihomed host [...]"

It's a bad idea.  A few resolvers implement this, but it leads to a 
problem: If there is a query which leads to an unexpected response from 
the upstream servers, the query will be *sent* to all of them.  This can 
lead to service availability problems.


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