A second belated response...
> Just throwing some ideas and questions... the draft
>
> draft-ietf-ipngwg-default-addr-select-00.txt
>
> uses at one stage CommonPrefixLen(SA, D) as a comparison value to
> select between candidate source addresses (prefixes). This is simple
> common bits counted from left ("most significant end"), right?
Yes.
> In our code we use following ComparisonValue(SA, D), returns
>
> prefixlength, if the common bits covers the prefix,
> and
> (common bits - prefixlength), when match is less (e.g. this value is
> always negative)
>
> This prefers the longest prefix that matches fully. If none matches,
> it prefers the prefix with least differing bits in the "routing
> part".
>
> "My version" differs only when none of the prefixes match fully. For
> example, if D=xxxyyy... (x = 4bit unit)
>
> SA= xxxzzzz/32 CommonPrefixLen=12 ComparisonValue= -20
> SB= xxz/12 CommonPrefixlen=8 ComparisonValue= -4
>
> CommonPrefix would select SA, ComparisonValue would select SB.
If I understand this correctly, it sounds like your implementation maintains
a prefix length associated with each unicast address that is assigned to an
interface. This is why you can speak about SA having a 32 bit prefix length.
This is not universal among IPv6 implementations. There is no specification
that requires or uses such a prefix length. So I don't want to put anything
in the src/dst address selection spec that relies on such a prefix length.
Restricting our attention to implementations that do maintain such a prefix
length associated with unicast addresses, I still don't understand your
motivation. For autoconfigured addresses, wouldn't this prefix length always
be 64? And then if I understand your rule correctly, in most cases it would
prefer exactly the wrong source address - it would prefer the one that has
fewest bits in common with the destination.
Thanks,
Rich
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