FEC0::/10 has about 38 usable bits there. That's enough for "unique enough". No need for even that. Let's assume /16 - /40 -- 24 bits would be enough too. By birthday paradox, even in that case, collisions should only be probable if you communicate thousands of different sites simultaneously and there are referrals and third party interconnections.
I don't think that you can, or should put the new globally-unique, provider independent address space inside the FECO::/10 allocation. As far as I know, we still plan to allow the FECO::/10 prefix to be used for disconnected sites, and perhaps other "moderate" usage.
Margaret -------------------------------------------------------------------- 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] --------------------------------------------------------------------
