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

神明達哉 <jinmei@wide.ad.jp> Tue, 19 June 2018 18:51 UTC

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From: 神明達哉 <jinmei@wide.ad.jp>
Date: Tue, 19 Jun 2018 11:51:18 -0700
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To: Shumon Huque <shuque@gmail.com>
Cc: Florian Weimer <fw@deneb.enyo.de>, dnsop <dnsop@ietf.org>, Paul Vixie <paul@redbarn.org>
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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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At Mon, 18 Jun 2018 17:51:26 -0400,
Shumon Huque <shuque@gmail.com> wrote:

> Client applications delegate address sorting to name resolution functions
> like getaddrinfo() - correct?
>
> Doing some quick tests of getaddrinfo() just now on a recent *NIX machine,
> it appears to return addresses sorted roughly in accordance with RFC
> 6724, but rule 9 (longest prefix match) seems to be only applied to
> IPv6 addresses. For IPv4 addresses (using an upstream resolver
> that randomizes the response RRset), the order returned by getaddrinfo()
> is ever changing - I assume presented in the order received.

The very original implementation of BSD getaddrinfo() conformed to the
RFC, but FreeBSD seems to have changed the behavior a few years ago so
rule 9 wouldn't apply to IPv4 addresses:
https://github.com/freebsd/freebsd/commit/1390d13ae69089142f6c6465dbb24438f295edee
The commit log suggests the rrset round-robin was exactly the
motivation for the change (whether it was good or bad).

--
JINMEI, Tatuya

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