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[DNSOP] interop problems with getaddrinfo() address selection

Tony Finch <dot@dotat.at> Tue, 04 December 2007 21:44 UTC

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Date: Tue, 04 Dec 2007 21:44:51 +0000
From: Tony Finch <dot@dotat.at>
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Cc: Ian Jackson <ian@davenant.greenend.org.uk>
Subject: [DNSOP] interop problems with getaddrinfo() address selection
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Rule 9 of RFC 3484 specifies that the IP addresses (v4 and v6) returned by
getaddrinfo() should be sorted according to the size of their common
prefix with the local host's chosen source IP address. This defeats DNS
round robin load balancing which has led to some severe operational
problems. DNS round robin needs to be documented in an RFC, and RFC 3484
should be updated with rule 9 deleted or substantially modified for
compatibility with DNS round robin.

Ian Jackson has written a thorough description of the problem from the
perspective of a proposal that Debian's version of glibc should have the
troublesome sorting behaviour removed:

http://lists.debian.org/debian-ctte/2007/11/msg00029.html

FreeBSD's getaddrinfo() only implements Rule 9 if the kernel's address
selection policy is configured, which is not done by default so DNS round
robin is passed through.

Tony.
-- 
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