Re: IPv6 Link Local Addresses

[Kerry Lynn <[e-mail]>]

On Tue, Jun 11, 2019 at 9:05 AM Alexandre Petrescu <
[e-mail]> wrote:

>
>
> Le 10/06/2019 à 18:44, Bob Hinden a écrit :
> > Hi,
> >
> > RFC4291 defines Link Local Address as:
> >
> >   2.5.6.  Link-Local IPv6 Unicast Addresses
> >
> >     Link-Local addresses are for use on a single link.  Link-Local
> >     addresses have the following format:
> >
> >     |   10     |
> >     |  bits    |         54 bits         |          64 bits           |
> >     +----------+-------------------------+----------------------------+
> >     |1111111010|           0             |       interface ID         |
> >     +----------+-------------------------+----------------------------+
> >
> >     Link-Local addresses are designed to be used for addressing on a
> >     single link for purposes such as automatic address configuration,
> >     neighbor discovery, or when no routers are present.
> >
> >     Routers must not forward any packets with Link-Local source or
> >     destination addresses to other links.
> >
> > This means that link local addresses have a 10 bit prefix (1111111010)
> followed by 54 bits of zeros.  That is it, nothing more.   Address with
> different prefixes or with a 1111111010 prefix followed by non-zero 54 bits
> are not link local addresses.
> >
> > This is not ambiguous.
>
> Bob,
>
> The RFC4291 link local addresses have a 10 bit prefix and 54bits of
> zero.  That is fe80::/64.
>
> The IANA allocation of IPv6 link-local addresses is fe80::/10.
>
>  > fe80::/10    Link-Scoped Unicast     [RFC3513][RFC4291]
>
> In that sense, the IANA definition and the RFC4291 differ with respect
> to the definition of link-local addresses.
>
> fe80::/10 and fe80::/64 are not the same thing.
>
> Alex
>
>
Bob et al.

Would a correct router implementation base its "must not forward" decision
on the most-significant 10 bits or most significant 64 bits?

Kerry