Brian,
> Well, I miswrote slightly - the fact is that an implementation has to
> first check if the address is any of the non-global-unicast cases, and that
> involves doing a sequence of matches which involve the bits
> Formerly Known as the Format Prefix (not just 3 of them of course).
The key here is that implementations need to check for a list of
prefixes that they special case. None of them (at the present time)
are just the first 3 bits. So they shouldn't check the format prefix
per se.
Having a format prefix doesn't actually help in the overall scheme. If
at some point someone wants to reserve a swath of address space for
some special/experimental purpose (e.g., 8+8, etc.), that can be done
by simply reserving a specific prefix that is big enough to meet the
need. Moreover, that prefix may be quite a bit smaller than a /3,
which is what an FP is.
So, IMO, actually removing the FP from the document is a reasonable
approach. If there is no FP, implementations won't make the mistake of
looking at just those bits and doing the wrong thing.
[Note: whether the current text is adequately clear on all this is
something I haven't checked. My comments are on the rational for not
having an FP.]
Thomas
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