[arin-ppml] Global Uniqueness vs Global Reachability
farmer at umn.edu
Wed Jun 3 18:53:59 EDT 2009
I've mostly been sitting back and watching the discussion
ensuing from the Open Access to IPv6 Proposal.
In much of the discussion I've seen a tension between two
separate camps pushing the dominance of one of two
properties Global Uniqueness vs Global Reachability.
Maintaining a scalable routing table is essential for Global
Reachability, and given current technologies this is best
insured by maintaining a routing hierarchy. Multihoming
seems to be the key discriminator if you should have a spot in
that hierarchy or exist under another part of the hierarchy. This
is by and large the primary use that most people have for
Global Unique IP addresses, in this case IPv6 addresses.
However, there are several uses that Global Reachability is not
entirely necessary but Global Uniqueness is necessary or at
least highly desirable. I believe that the IPv6 address space is
more than large enough to meet both needs, that's not the
issue. I believe the issue is one of assumptions made by
some operators and most users too, that all Globally Unique
IPv6 addresses should be or need to be Globally Reachable.
Now ULA (RFC 4193) exists and can probably meet some of
these needs, but ULA is not quite the same as real Globally
Unique IPv6 addresses, the primary differences are the RIRs
and the Registries they provide, authoritative reverse DNS,
and explicit uniqueness vs. the statistical uniqueness of ULA.
So currently ARIN assignes from two pools of IPv6 addresses
one for IPv6 Allocations and IPv6 Assignments. There are
several other micro-allocation pools too, but I'll ignore those for
now. These two pools are split to allow for easy filter
assumptions to be made, one /32 or less and the other /48 or
less. Further, I believe most people assume these two pools
to be for Globally Reachable allocations and assignments.
What if we made the Global Reachability assumption explicit
and created a separate pool without an explicit assumption of
In this way we could create policies which reinforce the routing
hierarchy for the pools that explicitly have the Global
Reachability. While at the same time, we can provide the full
benefit of Global Uniqueness to those that don't necessarily
need that Global Reachability. Creating a separate pool for
this later purpose allows network operators to easily filter
blocks that don't necessarily require Global Reachability if they
There should be more that enough IPv6 address space to
allow this even if everyone had two /48s one from the Global
Reachability pools, either an allocation from a LIR or an
assignment direct from ARIN and a separate NON-Globally
Reachable assignment. (I know, I need a better name for it,
but right now it is the idea that is important).
This isn't fully fleshed out, but if people like the idea I'll work on
it. If we can really get an ID/Locator split going in the future the
distinction my be come a mute point, or maybe this new pool is
used for those that need IDs and the Global Reachability
Allocations become Locators. But for now I think this could
work as a way to make both camps happy.
What do you think?
David Farmer Email:farmer at umn.edu
Office of Information Technology
Networking & Telecomunication Services
University of Minnesota Phone: 612-626-0815
2218 University Ave SE Cell: 612-812-9952
Minneapolis, MN 55414-3029 FAX: 612-626-1818
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