RE: Automatic tunnels

["Christian Huitema" <huitema@windows.microsoft.com>]

> > (...) [configured tunnels] don't follow the natural
> > Internet topology and thus often result in rather poor
> > transmission times
> 
> and a bit further:
> 
> > Automatic tunnels like 6to4 (...) have the advantage of being
> > potentially "very short": the transmission between two transition
> > hosts follows the IPv4 topology,
> 
> What do you mean by "following or not the IPv4 topology" ?
> 
> From the IPv4 forwarding point of view, I can't figure out such
> a difference between configured or 6to4 tunnels.

Traffic between two 6to4 routers will follow exactly the same path as
IPv4 traffic between these two routers. If the network topology changes,
the path will automatically follow the new routing state. This is a big
difference to traffic over overlay networks like the 6Bone, in which
packets hop from tunnel to tunnel; the tunnel layout is typically meant
to reflect the nominal network topology, but it will not change if
events affect the routing. A practical consequence is that a ping
between two 6to4 addresses often shows a much shorter delay than a ping
between two tunneled hosts.

-- Christian Huitema