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Subject: Re: [OMPI devel] [OMPI svn] svn:open-mpi r17307
From: Adrian Knoth (adi_at_[hidden])
Date: 2008-01-30 12:56:45


On Wed, Jan 30, 2008 at 03:38:00PM +0100, Bogdan Costescu wrote:

> The results is that, with the default Linux kernel settings, there is
> no way to tell which way a connection will take in a multi-rail TCP/IP
> setup. Even more, when the ARP cache expires and a new ARP request is
> made, the answer (MAC address) from the target/destination could be
> different, so that from that moment on the connection could switch to
> a different media. I've tested this recently with the RHEL5 kernels
> with one gigabit and one Myri-10G connection, seeing a TCP stream
> switching randomly between the gigabit and the Myri-10G connection.

That's weird. I've never seen this, but according to the various ARP
settings in the Linux kernel, I could imagine such a scenario.

IPv6 doesn't use ARP, but neighbourhood discovery. It's completely
different, and I hope it behaves "link local". It's a whole protocol
("ICMPv6"), so things might be better.

JFTR: http://www-uxsup.csx.cam.ac.uk/courses/ipv6_basics/x84.html

-- 
Cluster and Metacomputing Working Group
Friedrich-Schiller-Universität Jena, Germany
private: http://adi.thur.de