Hi Jinmei, I was confused by the same inconsistency couple of years ago and a thread resulting from my question failed to clarify the choice. I guess it is something we have to live with. You can look at this thread.
http://www.atm.tut.fi/list-archive/ipng/msg10039.html Cheers Suresh JINMEI Tatuya / 神明達哉 wrote: > I believe this was discussed and clarified before, but I could not > find any pointer, so let me ask here... > > It's regarding the "magic number" of 0xFFFE used in the modified > EUI-64 format for the interface identifier of an IPv6 address. > > According to draft-ietf-ipv6-addr-arch-v4-04.txt (or already-published > RFCs), we insert 0xFFFE in the middle of the interface identifier in > order to convert an 48-bit MAC address to the modified EUI-64 format: > > [EUI64] defines a method to create a IEEE EUI-64 identifier from an > IEEE 48bit MAC identifier. This is to insert two octets, with > hexadecimal values of 0xFF and 0xFE, in the middle of the 48 bit MAC > (between the company_id and vendor supplied id). > (in APPENDIX A) > > However, according to [EUI64], we use 0xFFFF (not 0xFFFE) "to create > an EUI-64 identifier from a 48bit MAC identifier" for network devices > (i.e., MAC-48): > > To support encapsulation of EUI-48 and MAC-48 values within small > subsets of the EUI-64 values, the first four digits of the > manufacturer's extension identifier shall not be FFFF16 or > FFFE16. Thus, the 64-bit values of the following form are > never-assigned EUI-64 values: > > ccccccFFFEeeeeee(16) (an EUI-48 extension) > > ccccccFFFFeeeeee(16) (a MAC-48 extension) <==== this one > (from http://standards.ieee.org/regauth/oui/tutorials/EUI64.html) > > My question is whether there was any special reason why the IPv6 > addr-arch document specified 0xFFFE. > > I googled and found a web page saying this is "an error": > > Confusingly IPv6 -- one of the most prominent standards that uses > EUI-64 -- applies these rules inconsistenly. Due to an error in the > appendix to the specification of IPv6 addressing, it is currently > standard practice in IPv6 to extend MAC-48 addresses (such as IEEE 802 > MAC address) to EUI-64 using 'FF-FE' rather than 'FF-FF'; it remains > to be seen how this inconsistency will be resolved in the future. > (http://www.kingj.com/articles/MAC_address) > > Is this true, or was there any particular reason for the "confusing" > choice? > > I appreciate any clarification in advance, > > JINMEI, Tatuya > Communication Platform Lab. > Corporate R&D Center, Toshiba Corp. > [EMAIL PROTECTED] > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > [email protected] > Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
