Subject: draft-ietf-dnsext-ipv6-addresses-00.txt

From: [email-masked] (Andreas Gustafsson)
Date: Fri, 28 Sep 2001 14:03:10 -0700 (PDT)

draft-ietf-dnsext-ipv6-addresses-00.txt states:

    The hexadecimal text representation of IPv6 addresses appears to be
    capable of expressing all of the delegation schemes that we expect to
    be used in the DNS reverse tree, since we do not ever expect to see
    delegation in the least significant possible hexadecimal label.  That
    is, we do not ever expect to see an IPv6 address architecture that
    advocates address delegation in the least significant four bits of an
    IPv6 address.

As I tried to point out at the London meeting, there is absolutely
nothing special about the least significant label.  If someone wants
to delegate the reverse mapping of single IPv6 addresses to separate
zones each containing a single PTR record at its apex, they can.

The reason why RFC2317 makes the least significant octet a special
case when delegating IPv4 subnets is not that the general method of
multiple delegations doesn't work for the last octet -- it does.  It's
just that in the IPv4 case, delegations within the last octet are
common, and using the multiple delegation scheme for a /25 network
would mean that the leaf network owner would have to set up as many as
128 separate zones each containing a single PTR.  The RFC2317 CNAME
hack is merely a way to combine these into a single zone for the
convenience of the leaf network owner.

In IPv6, the corresponding /125 networks are so rare, and the
corresponding multiplicity of zones (8 rather than 128) so small,
that there is no need to make the last nibble a special case --
single-PTR zones will serve this purpose just fine.

Therefore, I suggest replacing the quoted paragraph by the following:

    Delegation of reverse mappings for networks whose prefix length is
    not a multiple of four bits can be expressed in the RFC1886 scheme
    by creating multiple delegations of consecutive hexadecimal
    labels.

-- 
Andreas Gustafsson, [email-masked]

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