Bob Hinden wrote: >There is a clear tradeoff between a longer ID (to allow for better random >numbers or MAC addresses) and the size of the subnet field. > >Before revising the draft, I would prefer to hear from more people on these >tradeoffs.
Although I was one of those that suggested a technique that would generate /56 prefixes, I see great value in arranging for /48 prefixes where possible, for uniformity with RFC3177. For randomly-generated addresses (both centrally allocated and individually allocated), an 8-bit format prefix and 40 bits of randomness seems like a good tradeoff. 40 bits seems to be about the amount of entropy we're aiming at, and a handful of bits either way makes no difference. An 8-bit format prefix is not too wasteful of address space. The case for which I suggested /56 prefixes was generating a prefix from a MAC-48. In that case, with 46 effective bits of identifier to fit into the prefix, we clearly can't get a /48. It seems like a valuable technique, but would have to be an exception to the /48 rule. Of course, any site needing more than eight bits of subnet ID is likely to have many MAC-48s to play with if they have any at all. -zefram -- Andrew Main (Zefram) <[EMAIL PROTECTED]> -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
