On 13/11/2012 17:47, james woodyatt wrote:
On Nov 13, 2012, at 10:33 , Randy Turner <rtur...@amalfisystems.com> wrote:
I've been away from the list for awhile, and am trying to catch up -- is there a reference or quick
explanation as to why a "/64" assigned to a home network is considered to be potentially
"constrained" somehow ?
Once upon a time [RFC 3177], we believed that creating a numbering plan for
subscriber networks was intolerably difficult and expensive, so we thought it
would be a very good idea to make sure every new subscriber of any size would a
/48 delegation, which we all thought was big enough for all but the most
titanic of organizations. The idea was you'd get enough space up front that
you could take your numbering plan with you if you ever moved from one provider
to another. Space was thought to be too cheap to meter, and the benefit of
number plan stability across providers was thought to be beneficial.
Since then, we have discovered two things: A) service providers guard with
astonishing ferocity every last number they get from their registries even when
they are too cheap to meter, and B) the problem of number plan scaling is one
that only people without any money have any interest in seeing solved. Hence,
we have a new recommendation from IAB [RFC 6177], which capitulates on the
one-size-fits-all recommendation. It also says this in section 2:
However, this precludes the expectation that even home sites will
grow to support multiple subnets going forward. Hence, it is
strongly intended that even home sites be given multiple subnets
worth of space, by default. Hence, this document still recommends
giving home sites significantly more than a single /64, but does not
recommend that every home site be given a /48 either.
For my part, I have a hard time foreseeing how the expectation that residential
sites will always have more space to assign than a single /64 subnet is even
remotely reasonable. Far too many service providers are casting into
operational concrete topologies that assign only one subnet to each billable
subscriber gateway.
I don't hold out much hope that much of a market will ever exist for
residential networks with multiple subnets per subscriber. I also don't hold
out much hope for the kind of coordination between service providers that will
permit multihomed residential sites to work well.
That's why it looks to me like HOMENET will eventually converge on specifying
single /64 links behind a single residential gateway.
I think Homenet should not make the assumption that the different
networks are from a larger block like /5x but rather a collection /64's.
Think about the dual ISP connection case, the ISPa/xx allocated blocks
is quite likely to be disjoint from the ISPb/yy allocated blocks,
and xx != yy is quite possible.
Olafur
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