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RE: IKEv2 and NAT traversal
On Mon, 17 Dec 2001, Stephen Kent wrote:
> As one of the folks who was involved in the address space size
> decisions in the late 70s and early 80s, I can confirm that the 32
> bit size was chosen because of register/word sizes in current
> machines, including IBM, DEC, and others...
I don't dispute that given the hardware of the time (which I worked with
extensively, although not in the context of IP), it was clearly imperative
to make fixed-width addresses a multiple of 8, strongly preferable to make
them a multiple of 16, and definitely desirable to make them a multiple of
32. And obvious considerations of both network bandwidth and processing
power meant that they shouldn't be longer than "necessary"...
This is rather different from the assertion that the registers of one
particular machine (especially the nonexistent 32-bit PDP) dictated the
choice, which is the claim I was responding to.
Interestingly enough, when Xerox designed XNS, not very much later, they
chose 48. (Which is why Ethernet addresses are 48 -- they were intended
to be identical to XNS addresses.) Would that have sufficed for IP? An
interesting although now academic question... It certainly wouldn't have
permitted some of the clever tricks the IPv6 folk have come up with for
using their enormous address space, but those can be seen as side issues
rather than necessities.
> needless to say, if we had to do it again ...
Well, we have... with, so far, uncertain success.
Henry Spencer
henry@spsystems.net
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