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Date: Wed, 14 Nov 2012 10:48:56 +0100
From: Daniel Hartmeier <daniel@benzedrine.cx>
To: Sean Chittenden <sean@chittenden.org>
Subject: Re: 0.0.0.0/8 oddities...
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On Tue, Nov 13, 2012 at 11:06:04PM -0800, Sean Chittenden wrote:

> Where does it say that it shouldn't be used? Which RFC & ?? There are plenty of RFCs and I haven't exhaustively read things, so I reserve the right to be wrong & corrected, but I haven't seen anything that says, "do not use 0.0.0.0/8."  0.0.0.0/32, yes, that's a reserved and special IP address, but the remainder of the /8? It's a stretch to argue that it can't be used.

RFC1122 Section 3.2.1.3 (which RFC5735 references directly)

            (a)  { 0, 0 }

                 This host on this network.  MUST NOT be sent, except as
                 a source address as part of an initialization procedure
                 by which the host learns its own IP address.

                 See also Section 3.3.6 for a non-standard use of {0,0}.

            (b)  { 0, <Host-number> }

                 Specified host on this network.  It MUST NOT be sent,
                 except as a source address as part of an initialization
                 procedure by which the host learns its full IP address.

So a sender MUST NOT use 0.0/16 or 0/8 as destination, ever...

Daniel