Waste will kill ipv6 too

valdis.kletnieks at vt.edu valdis.kletnieks at vt.edu
Fri Dec 29 01:56:18 CST 2017


On Thu, 28 Dec 2017 14:14:06 -0500, bzs at theworld.com said:

> My wild guess is if we'd just waited a little bit longer to formalize
> IPng we'd've more seriously considered variable length addressing with
> a byte indicating how many octets in the address even if only 2
> lengths were immediately implemented (4 and 16.)

Actually, that got heaved over the side fairly early in the IPng discussion,
because nobody  who was building silicon last century wanted to
deal with arbitrary-length addresses.  The IPv4 header had source and
destination addresses on 4-byte boundaries for good reasons which
still held true when we did the IPv6 headers.

And "even if only 2 lengths were implemented" is a non-starter, because
whenever you decide that 7 should be allowed too, you *still* have to do
a forklift upgrade on all the stuff that's got 4/16 baked into the silicon.  Variable
length was only going to work if it was in there from the start - otherwise
you never get the first user of 8-byte or 20-byte to interoperate (in other
words, the same exact problem we have right now getting legacy IPv4 to
talk to anybody who isn't also doing IPv4).
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