Re: [v6ops] Vicious circle [ULA precedence [Thoughts about wider operational input]]

[David Farmer <[e-mail]>]

On Mon, May 2, 2022 at 7:32 AM Mark Smith <[e-mail]> wrote:

>
>
> On Mon, 2 May 2022, 13:51 David Farmer, <farmer=[e-mail]>
> wrote:
>
>> ...
>> I believe RFC 6724 is correct, ULAs that are not known to be local,
>>
>
> If a host is given a ULA as a candidate DA, then it is to be considered
> local and reachable, because per RFC4193, ULA addresses are not to appear
> in global DNS.
>

So IFF, the ULA addresses are not learned from DNS, and I'm not sure that
is a safe assumption. For example, RFC 5220 section 2.2.2 seems to imply
ULAs within the DNS, which is one of the referenced sections in the first
paragraph of 10.6.

Further, as noted in RFC 5220 section 2.1.4, again one of the referenced
sections in the first paragraph of 10.6;

If the ULA is used for internal communication, packets with the ULA need to
be filtered at the Router.


That being the router at the Internet boundary for the local network. Your
statement also assumes such filtering is present, and again that doesn't
seem to be a safe assumption.

So, IFF ULAs are not in the DNS, and ULAs are filtered at the Internet
boundary for the local network, can a host assume a ULA given as a
candidate DA, is in fact local and not a remote ULA address.

And at least in my personal experience and the problems as stated in RFC
5220, seems to indicate those conditions are not reliably the case. Put
another way, the assumption that a ULA given as a candidate DA is in fact a
local ULA, and not a remote ULA, is probably only true for well-run and
well-configured networks.  And I for one would like IPv6 to operate as
robustly as possible and work even when a network is misconfigured in some
way(s).

Remember, RFC 6724 was intended to deal with issues that caused traffic to
be black-holed when IPv6 was enabled, and as a result, many people were
simply disabling IPv6, so let's be careful not to go back to those days.

should be considered remote and GUA IPv6 and IPv4(both GUA and RFC 1918)
>> should be considered more reliable than any possibly/probably remote ULA
>> prefix. Where RFC 6724 failed, is not to require the known to be local ULAs
>> to be added to the table, so ULA will function as intended.
>>
>> Thanks
>>
>
Thanks.

-- 
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