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Subject: [OMPI devel] RFC: IPv6 support
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-09-16 23:53:18

WHAT: change the IPv6 configuration option to enable IPv6 if and only
if specifically requested

WHY: IPv6 support is only marginally maintained, and is currently
broken yet again. The current default setting is causing user systems
to break if (a) their kernel has support for IPv6, but (b) the system
administrator has not actually configured the interfaces to use IPv6.

TIMEOUT: end of Sept

SCOPE: OMPI trunk + 1.3.4

There appears to have been an unfortunate change in the way OMPI
supports IPv6. Early on, we had collectively agreed to disable IPv6
support unless specifically instructed to build it. This was decided
because IPv6 support was shaky, at best, and used by only a small
portion of the community. Given the lack of committed resources to
maintain it, we felt at that time that enabling it by default would
cause an inordinate amount of trouble.

Unfortunately, at some point someone changed this default behavior. We
now enable IPv6 support by default if the system has the required
header files. This test is inadequate as it in no way determines that
the support is active. The current result of this test is to not only
cause all the IPv6-related code to compile, but to actually require
that every TCP interface provide an IPv6 socket.

This latter requirement causes OMPI to abort on any system where the
header files exist, but the system admin has not configured every TCP
interface to have an IPv6 address...a situation which is proving
fairly common.

The proposed change will heal the current breakage, and can be
reversed at some future time if adequate IPv6 maintenance commitment
exists. In the meantime, it will allow me to quit the continual litany
of telling users to manually --disable-ipv6, and allow OMPI to run out-
of-the-box again.