RFC 6724

Florian Weimer fweimer@redhat.com
Tue Nov 13 10:51:00 GMT 2018

* Phillip Hellewell:

> I tracked down the reason for the difference to the prefix policy
> table.  Linux adheres to the older RFC 3484, whereas Windows uses RFC
> 6724.  I was surprised to see Windows ahead of Linux in adhering to
> IPv6 standards.  But the strangest part about all this is that, the
> older standard actually gives more appropriate results in this case,
> since IPv6 ought to be preferred over IPv4 when choosing between
> equally valid and useful addresses.

It's not so strange at all.  The address selection criteria have always
been fairly arbitrary.

> That's why in conjunction with my suggestion to update to the RFC 6724
> policy, I also brought up the idea of adding the rules for private
> IPv4 prefixes so that IPv6 ULA will be preferred over them.  To be
> honest, unless those rules are included I would prefer glibc be left
> alone, because in my opinion the slight improvements are not worth it
> unless that drawback is addressed.

I'm more interested in arguments for preferring some IPv4 addresses over
IPv6 address in the destination selection algorithm, and IPv6 over IPv4
in other cases.

>> To be honest, I don't see any other way to get full RFC 6724 support
>> because the RFC requires various things for which I do not see direct
>> kernel support.
> I'm not sure what exactly you are referring to in RFC 6724 that the
> kernel doesn't support, but I was just focused on updating the
> precedence rules.  I'm assuming those could be updated to include nine
> rules from RFC 6724 rather than five rules from RFC 3484.

I'm not sure if the kernel has a concept of a home address.  That seems
to be something that would be maintained by higher-level tools such as
NetworkManager or systemd.


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