Hi Jonathan,OK, understood. I was looking in an IPv6 book which stated link local prefix as FE80::/64. RFC 4291 Section 2.5.6 also shows it as effectively FE80::/64. But I agree the language in RFC 4862 is consistent with hc-11.
Robert Robert Cragie (Pacific Gas & Electric) Gridmerge Ltd. 89 Greenfield Crescent, Wakefield, WF4 4WA, UK +44 1924 910888 +1 415 513 0064 http://www.gridmerge.com <http://www.gridmerge.com/> On 02/09/2010 2:15 PM, Jonathan Hui wrote:
Hi Robert, On Sep 2, 2010, at 2:21 AM, Robert Cragie wrote:It's a minor point and the text is not specifically wrong in hc-11 but the following change would make things 100% consistent, in my view. The link-local prefix is by definition FE80::/64. So the following: 10: 16 bits. The first 112 bits of the address are elided. The value of the first 64 bits is the link-local prefix padded with zeros. The following 64 bits are 0000:00ff: fe00:XXXX, where XXXX are the 16 bits carried in-line. would look better as: 10: 16 bits. The first 112 bits of the address are elided. The value of the first 64 bits is the link-local prefix. The following 64 bits are 0000:00ff:fe00:XXXX, where XXXX are the 16 bits carried in-line. as the 'padded with zeros' seems to be a hangover from the previous text when it expanded it to a 112-bit prefix.As defined in Section 2.4 of RFC4291, the link-local prefix is only 10 bits long: Address type Binary prefix IPv6 notation Section ------------ ------------- ------------- ------- Unspecified 00...0 (128 bits) ::/128 2.5.2 Loopback 00...1 (128 bits) ::1/128 2.5.3 Multicast 11111111 FF00::/8 2.7 Link-Local unicast 1111111010 FE80::/10 2.5.6 RFC4862 has similar wording in forming a link-local address: 1. The left-most 'prefix length' bits of the address are those of the link-local prefix. 2. The bits in the address to the right of the link-local prefix are set to all zeroes. 3. If the length of the interface identifier is N bits, the right- most N bits of the address are replaced by the interface identifier. So the 'padded with zeros' text isn't a mistake, the well-known link-local prefix needs to be "expanded" from 10 to 64 bits. -- Jonathan Hui
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