> [RFC4862] requires that subnets operating stateless address > autoconfiguration use 64 bit prefixes,
Actually, not true! Stateless address autoconfiguration supports different prefix lengths just fine. That was a deliberate design decision, even after we switched to 64-bit Interface IDs. E.g (from 4862): A link-local address is formed by combining the well-known link-local prefix FE80::0 [RFC4291] (of appropriate length) with an interface identifier as follows: 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. If the sum of the link-local prefix length and N is larger than 128, autoconfiguration fails and manual configuration is required. The length of the interface identifier is defined in a separate link- type-specific document, which should also be consistent with the address architecture [RFC4291] (see Section 2). These documents will carefully define the length so that link-local addresses can be autoconfigured on the link. and so on. > and [RFC4291] requires that interface identifiers conform to > modified EUI-64 format. That is where the effective requirement is hard coded in. Thomas -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------