ipv6 source address selection

[Arifumi Matsumoto]

Hi,

I agree with Ole.
The longest matching rule was already there in RFC 3484.

2013/10/20 Ole Troan <otroan at employees.org>:
> Mikael,
>
>> I'm trying to influence my source address selection. First I thought I'd figure out how it works by default.
>>
>> I have a /48. Let's call it 2001:db8:1::/48
>>
>> I created three /64s on the same LAN with A-bit set so clients would do SLAAC within these:
>>
>> 2001:db8:1:0000:/64
>> 2001:db8:1:1000:/64
>> 2001:db8:1:2000:/64
>>
>> Then I set up loopback addresses on my router:
>>
>> 2001:db8:1:0001:1/128
>> 2001:db8:1:1001:1/128
>> 2001:db8:1:2001:1/128
>>
>> Then I tried pinging each loopback address from a host which has 2 addresses out of each /64. It now picked a source address within the same /56. I consistently both on a Ubuntu 13.04 and OSX 10.8.5 machine get the same behaviour.
>>
>> So above means that pinging 2001:db8:1:1fff::1 it would use the :1000: address, and pinging :2fff::1 would use the :2000::/64 address.
>>
>> If I ping outside my /48 it will consistently use the last created address (I tried adding a 4th lan, 8000, and it then uses that one), which I perfectly understand.
>>
>> When I ping :5000: and so on, it will sometimes use the :0000: address and not the :8000: that is used for the rest of global traffic.
>>
>> I have nothing /56 or /48 magic in routing table or "ip addrlabel list", but it still seems to be something special when it comes to the same /48 as the machine has addresses in.
>>
>> Any help understanding what is going on is appreciated.
>
> wouldn't this be RFC6724:
>
> Rule 8: Use longest matching prefix.
>    If CommonPrefixLen(SA, D) > CommonPrefixLen(SB, D), then prefer SA.
>    Similarly, if CommonPrefixLen(SB, D) > CommonPrefixLen(SA, D), then
>    prefer SB.
>
> cheers,
> Ole