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Proposed change in 6bone pTLA 3FFE usage

6bone Folk,

At the Minneapolis IETF I proposed changing the pTLA 3FFE:/16 usage to
allow future growth as the 6bone becomes used more for production. The
current usage specifices an 8-bit pTLA (prefix 3FFE:xx00::/24). This only
provides for 256 pTLAs, of which 55 are currently in use.

In addition, if 6bone prequalification for Sub-TLAs becomes a common
operational mode, we will need more pTLAs. 

The proposal I made in Minneapolis was for split usage of the pTLA space,
with the lower half of the space left for the current 8-bit pTLAs
(3FFE:0000::/24 thru 3FFE:7F00::/24, for a total of 128 8-bit pTLAs), and
the upper half for 13-bit pTLAs (3FFE:8000::/29 thru 3FFE:FFF8:/29 for a
total of 4096 13-bit pTLAs). As I remember, there was positive support for
this with the exception comment being the difficulty in specifying the
reverse path for the DNS given the 29 bit boundary.

One suggestion for this was to use a 12-bit pTLA (thus a /28 prefix) to
keep to a 4-bit boundary. My suggestion would be to use a full 16-bit pTLA
(thus a /32) as the remaining 16-bit NLA space, up to the site's 80-bit
space, is big enough for 6bone use. Also, we don't have to assign any more
pTLAs than we collectively deem reasonable.

Another (offline) suggestion was to use the /29 as a forcing factor to have
folks adopt the newer DNS bit specification method (I'm unfamiliar with
this and when it might appear).

Another question about this proposal is, do we leave the first half /24
usage as is, or make those folk renumber eventually to the bigger space?
Maybe this doesn't matter at the start, but I'd like opinions on this.

Your comments to the list please.