Re: Question about RFC6724

I'm pretty sure for Linux it's just bitwise comparison all the way down.
addrconf.c's "/* Rule 8: Use longest matching prefix */":

    https://github.com/torvalds/linux/blob/master/net/ipv6/addrconf.c#L1622

calls ipv6_addr_diff(), which I think is:

    https://github.com/torvalds/linux/blob/master/include/net/ipv6.h#L761

or the diff64 variant, depending.

On Sun, May 1, 2022 at 9:33 PM Brian E Carpenter <
brian.e.carpenter@gmail.com> wrote:

> Hi,
>
> Excuse my ignorance, but I have a question about RFC6724. The rules depend
> on longest prefix matching and therefore on the definition of
> CommonPrefixLen(S, D).
>
> The way it's defined doesn't work for ::ffff:0:0/96, as far as I can see:
>
> >
> > 2.2.  Common Prefix Length
> >
> >    We define the common prefix length CommonPrefixLen(S, D) of a source
> >    address S and a destination address D as the length of the longest
> >    prefix (looking at the most significant, or leftmost, bits) that the
> >    two addresses have in common, up to the length of S's prefix (i.e.,
> >    the portion of the address not including the interface ID).  For
> >    example, CommonPrefixLen(fe80::1, fe80::2) is 64.
>
> The "interface ID" is simply a non-concept for IPv4-mapped IPv6 addresses.
> So what do implementations do? What is the common prefix length of
> ::ffff:10.1.0.10 and :ffff:10.1.0.1, in terms of the RFC6724 rules?
>
>       Brian
>
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