teredo.ipv6.microsoft.com off?

Brian E Carpenter brian.e.carpenter at gmail.com
Thu Jul 18 22:09:51 CEST 2013

On 18/07/2013 22:40, Tim Chown wrote:
> On 18 Jul 2013, at 11:29, Phil Mayers <p.mayers at imperial.ac.uk> wrote:
>> On 17/07/13 21:09, Brian E Carpenter wrote:
>>> On 17/07/2013 19:13, Ignatios Souvatzis wrote:
>>> ...
>>>> Let me ask one thing... a couple of years ago, when I read the
>>>> specification of Teredo, I was quite impressed by the details (If
>>>> you accept the premise that you have to work around being jailed
>>>> behind an IPv4 NAT) put into the protocol. One detail was that it
>>>> is supposed to be lowest priority and so go automatically away
>>>> (from the client end) as soon as some configued IPv6 is available
>>>> on the link.
>>>> Isn't that how it's implemented?
>>> Yes, but the result is that the host tries to use Teredo preferentially
>>> even if the IPv4 path is better; and if the Teredo path is broken
>> That is the opposite of how it's supposed to work. Teredo addresses should be de-pref'd below everything else, and would thus only be used for connection to IPv6-only hosts if the host lacked other IPv6 connectivity.
>> As someone else has pointed out, maybe it gets used for IPv6 literals, but not hostnames - the RFC 3484 table on windows ensures this.
> Indeed; that's how it *should* be.

Wait... I had the impression that iff there was no other IPv6 connectivity,
Teredo was used in older Windows because of the generic "prefer IPv6" rule.
The default RFC 3484 table covers 6to4 but not Teredo.

Recent Windows deprefs Teredo of course.


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