Another v6 question

[pelle at hemmop.com (Per Carlson)]

Hi Owen.

> The downside is that it doesn't provide enough bits for certain kinds of auto-topology
> management that are being considered by CE vendors. I highly recommend /48 instead.

I've seen this claim (you need a /48) from your side several times,
but never seen any explanation why a /56 won't work.

Is there any requirement that sub-delegations must happen on 8-bit
boundaries? AFAICS there is at least nothing in the RFC. Wouldn't for
example a nibble boundary work equally well (splitting a /56 into 16
/60s, each containing 16 /64s)?

I don't challenge the claim, I'm just trying to understand the
rationale behind it.

-- 
Pelle

RFC1925, truth 11:
?Every old idea will be proposed again with a different name and
?a different presentation, regardless of whether it works.