[ppml] Solicing comments: IPv4 to IPv6 Migration Incentive Address Space

William Herrin arin-contact at dirtside.com
Thu Jun 28 11:32:21 EDT 2007

On 6/27/07, John Paul Morrison <jmorrison at bogomips.com> wrote:
> I do not support this proposal as it essentially duplicates the IPv6
> address space already allocated to IPv4 users, documented in RFC 3056
> (6to4).


  First, thank you for privately discussing 6to4's functionality with
me. You were very helpful and informative.

  You are not alone in suggesting that 6to4 might suitably replace the
Migration Incentive Space proposal, however 6to4 has several issues
which would need to be addressed before it could be considered a valid
alternative. I'd like to find if there is a consensus on ppml as to
whether those issues should be addressed in 6to4. If they should, I'll
start working on such a proposal with the intent that it replace the
Migration Incentive Space proposal. If they should not, then I would
ask that 6to4 be considered irrelevant to and dropped from the

6to4 Problem #1: Implementation of 6to4 is an optional component of
the IPv6 protocol. Devices confronted with a 2002:: address may but
need not recognize that packets to such a destination should be
encapsulated in an IPv4 packet. The Migration Incentive Space proposal
is intended to rely on only those components of IPv6 which are

6to4 Problem #2: Its unclear whether the authors of RFC 3056 intended
that it be possilble for prefixes within 2002:: to be announced into
the global IPv6 BGP table so that all native IPv6 networks could reach
such hosts without IPv4 encapsulation. Indeed, some parts of the
document suggest that an available IPv6 route should NOT take priority
over encapsulation. For 6to4 to reasonably replace the Migration
Incentive Space, it would need to be clarified that ARIN encourages
IPv4 holders to announce an appropriately selected 2002:: route, that
remote IPv6 systems should give native IPv6 routes to 2002::
destinations priorirty over the encalsulated IPv4 route, and that ARIN
intends such blocks within 2002:: to have the same validity as any
other IPv6 block they assign or allocate.

6to4 Problem #3: Its unclear whether the authors of RFC 3056 intended
that prefixes within 2002:: continue to exist in IPv4's
post-exhaustion phase when IPv6 has become the dominant protocol. The
Migration Incentive Space is intended to be a permanant solution whose
addresses continue to see use after IPv4's end of life.

6to4 Problem #4: ARIN does not control the reverse DNS for 6to4
prefixes associated with the IPv4 blocks which ARIN manages. It is
presently managed by the NRO, an organization in which ARIN
participates (see https://6to4.nro.net/). The documentation for 6to4
reverse dns states that, "This password is not mandatory when the site
is accessed from inside your 6to4 source address. It is intended to
prevent an arbitrary access from locking out the domain if the address
is not static. (It is recognized that this places far less trust than
normal in the correctness of a 6to4 delegation)." For 6to4 to work as
a replacement for the Migration Incentive Space, reverse DNS for the
blocks under ARIN's authority would need to be operated with a degree
of security and access comperable to what ARIN applies to its normal
delegation of reverse DNS.

So, the question I put to you and to the others who have suggested
6to4 is this: Do we seek changes and clarifications to address these
four problems or do we drop 6to4 from consideration as an alternative
to the Migration Incentive Space proposal?

Bill Herrin

William D. Herrin                  herrin at dirtside.com  bill at herrin.us
3005 Crane Dr.                        Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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