On Tue, 2012-01-03 at 15:45 -0800, Owen DeLong wrote:
Technically, link local is fe80::/10, though many implementations erroneously treat it as fe80::/64. In most cases, since the 54 bits between fe80 and the IID are almost always 0, this error has no impact.
Yes, well, I'm a bit confused about that. Maybe I haven't read the trail of overlapping, obsoleting and conflicting RFCs carefully enough. RFC 4862 (section 5.3) says that the interface ID can run all the way up to the end of the link-local prefix. Since this is defined as a /10, an interface ID can be up to 118 bits long. In RFC 4862 the prefix length is not actually given; instead it says "the well-known link-local prefix FE80::0 [RFC4291] (of appropriate length)". RFC 4862 also says that the whole thing must be consistent with RFC 4291. RFC 4291 (section 2.5.6), defines the first ten bits as 1111111010, then the next 54 bits as zero - BUT does not specify a prefix length. Those implementations that use /64 can thus be forgiven, I think. So - are those 54 bits reserved and zero, or can an interface ID be anything up to 118 bits long? I'd be interested in a definitive answer, if there is one. Regards, K. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Karl Auer (kauer@biplane.com.au) http://www.biplane.com.au/kauer GPG fingerprint: AE1D 4868 6420 AD9A A698 5251 1699 7B78 4EEE 6017 Old fingerprint: DA41 51B1 1481 16E1 F7E2 B2E9 3007 14ED 5736 F687