On 2007-11-28 16:50, Tony Li wrote:
On Nov 25, 2007, at 12:24 PM, Brian E Carpenter wrote:
I really wish it could be like that, but I think all the history,
including pre-CIDR days and the modern PI heresy, shows that we simply
aren't going to achieve congruence between topology and address
structure. So yes, I guess I'm arguing that *if* we want a defined
hierarchy, it has to be orthogonal to address structure (which is why
I suggest borrowing some AFI bits to represent the hierarchy in the
maps).
Well, I think it's pretty clear that congruence isn't entirely
possible. If nothing else, addressing naturally forms a hierarchy,
whereas topology is an arbitrary graph. Perhaps I'm putting more into
'congruence' than you really meant.
Yes, clearly we need hierarchy so that we have abstraction. Yes, we
would clearly like to have things defined, as the alternative is worse.
;-) However, it's not at all clear to me that borrowing bits from the
AFI really changes anything conceptually. It's basically just more bits
that could have been part of the address prior.
It means you can change a prefix's place in the hierarchy without changing
the bits in the prefix - given the allergy of most user sites to
renumbering, that seems to be a plus point.
[rant about variable length addressing elided...]
[rant about how we could have added address extensions in 1994
elided...]
Brian
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