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Subject: Re: [OMPI devel] [OMPI svn] svn:open-mpi r17307
From: George Bosilca (bosilca_at_[hidden])
Date: 2008-01-30 12:05:50

What is the real issue behind this whole discussion ? With one or
multiple IP addresses by interface the connection step will work. Now
I can see a benefit of having multiple socket over the same link (and
it's already implemented in Open MPI), but I don't see the interest of
using multiple IP in this case.


On Jan 30, 2008, at 9:37 AM, Jeff Squyres wrote:

> Is one possible solution to have Open MPI mark in the packet where the
> incoming connection is coming from?
> On Jan 30, 2008, at 9:20 AM, Tim Mattox wrote:
>> Hello,
>> On Jan 30, 2008 3:17 AM, Adrian Knoth <adi_at_[hidden]>
>> wrote:
>> [snip]
>>> As mentioned earlier: it's very common to have multiple addresses
>>> per
>>> interface, and it's the kernel who assigns the source address, so
>>> there's nothing one could say about an incoming connection. Only
>>> that it
>>> could be any of all exported addresses. Any.
>> This is only partially correct. Yes, by default the Linux kernel
>> will
>> fill in the IP header with any of the IP addresses associated with
>> the machine, regardless of which NIC the packet will be sent on.
>> It was a never ending debate on the Linux Kernel Mailing list as to
>> what was the right way to do things... are IP addresses "owned" by
>> the machine, or are they "owned" by the NIC? The kernel defaults
>> to the former definition (which is contrary to pretty much every
>> other OS on the planet... but the relevant RFCs left both
>> interpretations
>> open). Anyway, there are ways to configure the networking stack of
>> the Linux kernel to get the other behavior, so that a packet will be
>> guaranteed to have one of the IP addresses associated with the NIC
>> that it uses for egress.
>> See Documentation/networking/ip-sysctl.txt in your Linux Kernel
>> sources
>> for a description of these relevant options:
>> arp_filter, arp_announce, arp_ignore
>> which are accessed on a live system here:
>> /proc/sys/net/ipv4/conf/all/
>> I guess if I put in the time, I could create a FAQ entry about it,
>> and what values to use... though I am not familiar with any
>> equivalent IPv6 settings (or if any exist).
>> --
>> Tim Mattox, Ph.D. -
>> tmattox_at_[hidden] || timattox_at_[hidden]
>> I'm a bright...
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]
> --
> Jeff Squyres
> Cisco Systems
> _______________________________________________
> devel mailing list
> devel_at_[hidden]

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