See also section 2.5.4 of RFC 4291: "All Global Unicast addresses other than those that start with binary 000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as described in Section 2.5.1."
So I'd say the answer is the IID MUST be 64 bits long, and MUST satisfy the properties of uniqueness discussed in 2.5.1 (and set the "u" bit accordingly). An IID in modified EUI-64 format satisfies these requirements, but in general IIDs are formed according to rules specified by the particular "IP over ..." RFC, e.g. RFC 4944. For example, an actual EUI-64 may be preferred for interfaces that have them. Finally, those with privacy concerns may elect methods for creating IIDs that mask the underlying hardware identifier; see RFC 3041. HTH, -K- On Fri, Jul 15, 2011 at 3:03 AM, Washam Fan <washam....@gmail.com> wrote: > Hi, > > I quoted this paragraph from RFC4291: > > For all unicast addresses, except those that start with the binary > value 000, Interface IDs are required to be 64 bits long and to be > constructed in Modified EUI-64 format. > > But I am not sure how to interpret the text in a correct way. > > If I assign an ordinary unicast address (except reserved anycast > addresses mentioned in RFC5453) to an interface and the address > doesn't start with 000, MUST the prefix be 64 bits? MUST the IID be > constructed in Modified EUI-64 format? > > We are providing WebUI for our customer to manually assign IPv6 > addresses, we want to do hygiene check before the actual move. > > Thanks in advance > washam > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > ipv6@ietf.org > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- >
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