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Date: Tue, 19 Dec 1995 14:45:03 -0500
From: "Garrett A. Wollman" <wollman@lcs.mit.edu>
Message-Id: <9512191945.AA15941@halloran-eldar.lcs.mit.edu>
To: Peter Berger <peterb@telerama.lm.com>
Cc: Terry Lambert <terry@lambert.org>,
        "Garrett A. Wollman" <wollman@lcs.mit.edu>,
        freebsd-questions@freefall.freebsd.org
Subject: Re: 2 (or more) LAN interface on SAME subnet ?
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References: <199512191750.KAA14777@phaeton.artisoft.com>
	<Pine.BSI.3.91.951219141540.835A-100000@ivory.lm.com>
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<<On Tue, 19 Dec 1995 14:19:19 -0500 (EST), Peter Berger <peterb@telerama.lm.com> said:

> -------------
> 147.72.1.2  |		147.72.56.1--------------147.72.56.1     -----------
> (netblazer) |----------------------|FreeBSD     |================|..56.2   |
> -------------			   --------------		 ---(pc)----
> 		^ppp link			    ^ethernet

> Both tun0 and ep0 have the same IP address (147.72.56.1).  I haven't 
> noticed any problems just yet.  Are you saying that this is somehow 
> invalid, and need difference networks on each interface?

This is invalid, but as a special case we include hackery to make it
work most of the time.  It only works for you because the second link
is a point-to-point interface, so the kernel installs a host route to
the destination.

If your situation were:

                147.72.56.nnn/24           147.72.56.nnn/24
               ==================|FreeBSD|==================

Then it wouldn't work, because the kernel would be unable to figure
out which interface to use.

-GAWollman

--
Garrett A. Wollman   | Shashish is simple, it's discreet, it's brief. ... 
wollman@lcs.mit.edu  | Shashish is the bonding of hearts in spite of distance.
Opinions not those of| It is a bond more powerful than absence.  We like people
MIT, LCS, ANA, or NSA| who like Shashish.  - Claude McKenzie + Florent Vollant