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RE: 240/4 unreservation (was RE: Last Call: <draft-weil-shared-transition-space-request-03.txt> (IANA Reserved IPv4 Prefix for Shared Transition Space) to Informational RFC)

2011-09-26 13:15:52
From: ietf-bounces(_at_)ietf(_dot_)org<mailto:ietf-bounces(_at_)ietf(_dot_)org> 
[mailto:ietf-bounces(_at_)ietf(_dot_)org] On Behalf Of Keith Moore
Sent: Friday, September 23, 2011 10:04 PM

The problem is in the zillions of systems in the field that have assumptions 
about 240/4 wired into them, most of which either have no automatic upgrade 
mechanism, aren't set up to use it, or aren't being maintained.
<snip>
Honestly I'd guess that if vendors started changing their code today, it would 
be 10 years before 240/4 could be widely used in the field.


WEG] See that's the point, I think we keep looking at this from a "boil the 
ocean" perspective. The question is not, "could we use 240/4 as more global 
unicast space?" as the ship sailed on that years ago when IETF apparently 
decided it was too hard to change and nothing should be done.
The question is, "if the space were unreserved, are there valid use cases where 
networks within a given administrative control might be able to make use of it?"
This idea of limited use puts the impetus on the network/operator itself to 
identify a use case and force their vendors to confirm support for the space, 
but it makes it more likely that for that definition of "widely used" it would 
be successful. But if IETF/IANA removes the reservation, this means means that 
people can go in and check in the update to the 3 lines of BSD kernel code 
(based on a private reply I received on the matter) necessary to remove the 
block, vendors can stop putting that logic into new devices, etc, thus making 
it more attractive to attempt to use the space from that point forward.
I don't expect this to be a perfect solution for legacy IPv4-only devices, but 
I do expect that it could have some use, especially when compared with other 
alternatives.

Cameron's example is a case in point - you have a mobile provider who for the 
most part tells the vendors exactly what features their user devices need to 
support and they are built to spec, plus a closed network with NAT at the edges 
that is currently squatting on public space. This means that a large amount (or 
possibly all) of the devices that would need to support use of this space are 
within their administrative control, and they would be responsible for updating 
the code to a version that won't reject 240/4, and they could contain it within 
their environment by keeping it inside of the NAT border.

Wes George

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