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Re: Alternatives to source address rewriting (was RE: Preserving established communications (was RE: about draft-nordmark-multi6-noid-00)

On 4 nov 2003, at 13:00, Erik Nordmark wrote:

But the host will never know better than the routing system because it
is operating on aggregated information.

The host??? No, hosts only know about individual correspondent addresses, they don't aggregate under normal circumstances.

What the host might know better than the routing system is that the
last N packets sent using a given source and destination didn't result
in packets being returned from the peer, thus something might be
broken.

Thus for the host to tell the routing system "please try sending this packet
over a different path than the default one" might be useful. But that is quite
different than having the routing system blindly honor the source address
for routing lookups.

So when we finally find that unused field in the IPv6 header (should have stuck to v4, there we can steal identification if DF is set which it nearly always is) we can use this field to say "I didn't care much for the connectivity provided by your previous routing decisions, please try something else". This field would be an index for finding the preferred route among the ones available. So if the packets don't make it using the best route (as determined by the router), the host increases the value of the field and the second best route is selected.

Hm, one way to do this would be to manipulate the hop limit field. Under normal circumstances, the hop limit a router sees in packets from hosts in the local network should be very consistent. The host could raise or lower the initial value for the hop limit to get the router to change its behavior.