Re: [DNSOP] BCP on rrset ordering for round-robin? Also head's up on bind 9.12 bug (sorting rrsets by default)

Florian Weimer <fweimer@redhat.com> Mon, 18 June 2018 08:22 UTC

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To: Erik Nygren <erik+ietf@nygren.org>, dnsop WG <dnsop@ietf.org>
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From: Florian Weimer <fweimer@redhat.com>
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Date: Mon, 18 Jun 2018 10:22:37 +0200
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Subject: Re: [DNSOP] BCP on rrset ordering for round-robin? Also head's up on bind 9.12 bug (sorting rrsets by default)
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On 06/15/2018 05:45 PM, Erik Nygren wrote:
> I suspect starting assumptions are roughly in the range of:
> 
> * Recursive (and stub?) resolvers (SHOULD/MUST?) do some form of 
> round-robin in RRset responses.
> 
> * There are a variety of ways to implement round-robin (randomize, 
> permute, etc).
> 
> * Server operators need to be aware that round-robin may be a part of a 
> load balancing scheme (especially if capacity is far greater than 
> average demand) but should not be relied on exclusively.  (Perhaps with 
> examples of why...)
> 
> Am I missing something in-terms of an existing BCP to this effect?

Unless all addresses happen to have identical shared prefix length with 
the client address (that is, count-leading-zeros(client-address XOR 
server-address) is the same), RFC 6724 Rule 9 requires that clients do 
*not* perform random server selection.

I think this was a mistake in RFC 3484, and it is still wrong.  But I 
think procedurally, you cannot change this in a BCP.

Thanks,
Florian