6to4 status (again)

Mike Jones mike at mikejones.in
Thu Feb 28 00:56:58 CET 2013

On 27 February 2013 22:07, Max Tulyev <maxtul at netassist.ua> wrote:
> On 27.02.13 23:57, Dmitry Anipko wrote:
>>>> I see a lot of BitTorrent traffic from Win7/WinXP preferring
>>>> 6to4<->teredo.
>> My understanding is that some peer to peer apps are explicitly using
>> Teredo, because it gives them some amount of NAT traversal "for free".
> Yes, it's possible from Teredo side. But why 6to4 which can't be behind a
> NAT?

I could be missing something, but basically because the OS has given
them an IPv6 address* and they are dual stacked programs that want to
speak to other v6 peers.

Performance to peers you're pushing through the relays might be lower
than if you spoke directly, but I imagine that 'spare' bandwidth just
shifts around the swarm and the next effect is probably zero.

The main people who are impacted by this are torrent users who get
better connectivity, and some ISPs providing a free public service
getting their bandwidth bill increased. I believe most of the people
writing torrent clients are torrent users rather than ISPs.

- Mike

*the decision to use teredo was deliberate as it has to be explicitly
requested per-application. I put that down to either 'we want to reach
v6-only peers' or 'Free hole punching'.

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