> Siva Veerepalli wrote:
> In "2.5.6 Local-Use IPv6 Unicast Addresses", the figure shows that
> the 54 bits following the first 10 bits of the link local address
> are set to 0. However, it is not explicitly stated anywhere that
> this is a requirement. If that is the intent, then shouldn't the LL
> prefix really be FE80::/64?

The answer to this question is both yes and no at the same time. With
the current use of link-locals, maybe. However, there is IMHO value in
keeping the prefix as a /10 for future use.

It easy to make a relation with site-local addresses (following the same
logic, the prefix should be a /48). There are drafts both on the table
and upcoming that propose using the extra bits for purposes that have
not been envisioned at the time of the original design.

> If that is not the intent, are the 54 bits following the first 10
> considered part of the prefix (subnet ID?), that can be any value
> (or) is it considered part of the interface ID (but that does not
> agree with b., above).

Neither one. At this point in time, there is no such thing as a subnet
ID for link-local addresses and the IID is 64bits long. I agree that
these 54 bits are in some kind of semantic void. I guess "unused" would
be a good term for now.

Michel.


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