RE: Question about RFC6724

It is not an simple errata because it was done on purpose.

>From one point of view, RFC 6724 is very clear that the longest match should happen for IPv4 too.
Look section 3.2 and section 6 of RFC 6724.

But from another point of view
look to appendix B:
"      Changed the definition of CommonPrefixLen() to only compare bits
       up to the source address's prefix length.  The previous
       definition used the entire source address, rather than only its
       prefix.  As a result, when a source and destination addresses had
       the same prefix, common bits in the interface ID would previously
       result in overriding DNS load balancing [RFC1794] by forcing the
       destination address with the most bits in common to be always
       chosen.  The updated definition allows DNS load balancing to
       continue to be used as a tie breaker."
And look to section 2.2 (Common Prefix Length):
"up to the length of S's prefix (i.e., the portion of the address not including the interface ID)"

It looks like Windows implementation is right and fully compliant with RFC 6724 in this respect.
64 border is hardcoded into RFC 6724 on purpose.

Are you going to kill DNS load balancing again? (for IPv6 as well as for IPv4)

Ed/
-----Original Message-----
From: ipv6 [mailto:ipv6-bounces@ietf.org] On Behalf Of Philip Homburg
Sent: Wednesday, May 4, 2022 10:27 AM
To: ipv6@ietf.org
Subject: Re: Question about RFC6724 

>10.1.0.10 printer.mynet.example.com
>192.168.178.99 printer.mynet.example.com
>
>then getaddrinfo() returns this, on a Windows host whose IPv4 address 
>is 192.168.178.20:
>
>(<AddressFamily.AF_INET: 2>, 0, 0, '', ('10.1.0.10', 0))
>(<AddressFamily.AF_INET: 2>, 0, 0, '', ('192.168.178.99', 0))

Thanks for the example.

After careful reading of RFC 6724, I think you are right.

We should update the description of CommonPrefixLen, such that for IPv4-mapped it considers the length of IPv4 prefix.

I thought the reason it mentions 64, is that it is hard to use the real prefix length. For example, in a system that receives addresses using IA_NA and where there are no onlink prefixes, how does one determine "the portion of the address not including the interface ID".

However, that is an IPv6 problem. For IPv4 it should be clear what the prefix length is.

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