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Subject: Re: [OMPI users] How are IP addresses determined?
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2011-02-17 14:24:05

On Feb 17, 2011, at 12:37 PM, Barnet Wagman wrote:

>> The short version is that open MPI does not support NAT. There was some research work a long time ago investigating supporting firewalls and NAT, but I don't think it was ever completed / published.
> That makes sense. Do you know how open MPI gets the ip addresses it
> uses? And where in the src this is done? Sounds like I won't be able to
> run open mpi from a system without a direct connection to the net, but
> I'd like to look at the relevant code any way.

We just query the local OS for all of its available/up ethernet interfaces. The relevant code is in opal/util/if.c, but I warn you -- this is pretty gnarly code because the different flavors of OS do these kinds of things just *slightly* different from each other. Ugh! It's effectively a portable, API way of getting the same information that you get from ifconfig(1).

But just to be clear: your OS isn't going to have any idea what the IP address is on the other side of NAT -- that's kind of the point of NAT.

Jeff Squyres
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