6to4 clarification needed

[Pekka Savola]

On Tue, 12 Jun 2001, John Comeau wrote:
> I've read all I could find on the web regarding 6to4, and am somewhat
> confused. Since the IPV4 address of the target router is embedded in the IPV6
> address, shouldn't my IPV6 stack be smart enough to follow ipv4 routing for
> all 6to4 traffic? So, my relay router would only need to be used for inbound
> traffic and for non-6to4 IPV6 outbound traffic?
>
> I was thinking of hacking the sit.c source to make it treat 6to4 traffic in
> this manner. Or has someone already done this for linux? Is the freebsd stf
> device what I'm looking for?

This is exactly what's happening; if the destination address is a 6to4
address, a tunnel is created automatically (in sit.c in Linux 2.4).

FreeBSD stf does the same thing.

> Of course I could, as some 6to4 descriptions say, route all my IPV6 traffic to
> the relay router, but isn't that somehow defeating the beauty of the 6to4
> mechanism, being able to use all my available links to route the traffic? Not
> to mention, if another host on my network starts using 6to4, it doesn't make
> much sense having to talk to him via the 6bone when he's reachable on my LAN.

The tunneling is done before routing table is considered, so adding
2000::/3 to point to your relay router will not route _6to4_ traffic
there.

You can observe the behaviour by running tcpdump when pinging 6to4
addresses.

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords