On Thu, 28 Jun 2007 17:46:53 -0400 Valdis.Kletnieks@vt.edu wrote:
On Thu, 28 Jun 2007 13:08:52 PDT, Bora Akyol said:
At a very low, hardware centric level, IPv6 would be a lot easier to implement if
1) The addresses were 64 bits instead of 128 bits. 2) The extension headers architecture was completely revamped to be more hardware friendly.
Wow, a blast from the past. The *current* IPv6 design was selected to a good extent because it was *easier* to do in hardware than some of the other contenders. You think 64 versus 128 is tough - think about the ASIC fun and games to support *variable length* addresses (not necessarily even a multiple of 4 bytes, in some of the proposals. Could be 7, could be 11, check the address length field for details. Yee. Hah).
I'm not going to revist all of the design issues; as I said, at this point IPv6 is what is is. On that point, you're mostly right; there were indeed a class of CLNP-derived solutions that were rejected. That said, some of us -- including me -- wanted to use the two high-order bits of the address to select among {64,128,192,256}-bit addresses. Settling on 128 bits was a compromise between that group and advocates of a 64-bit fixed-length address. History since then persuades me that sticking with 64 bits would have been a very bad mistake. --Steve Bellovin, http://www.cs.columbia.edu/~smb