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RE: ND-proxy applicability and loop-prevention



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Ole Troan wrote:

> > I'd sure be interested in hearing what others in the WG think
> > on this issue.
> 
> I agree with Erik.
> 
> I see two alternatives:
> 
>  1. ND proxy. Limited to single router, proxy from uplink to
>     downlink. No need for loop detection.
> 
>  2. Multilink subnet routing. Handles arbitrary topologies. Must
>     handle loops.
> 
> publishing a specification for ND proxy with support for a restricted
> topology (multiple routers) without handling loops is just
> irresponsible.

The same applies to the current MLD proxy document (MAGMA WG).

I heared a report of some person who setup ecmh on 4 different
routers which then collapsed as it didn't prevent a routing loop.

One easy way to do this would be define a special multicast group,
to which all routers will listen, thus parse and forward these
packets to their uplinks. The packet would contain the primary
identification of that host and the uplink over which the packet
gets sent, one could include a 'trace' of where the packet passed
to aid in further diagnosis. When a router gets a packet containing
it's own ID it can use the link field contained in the packet to
see where it sent the packet too and then simply disable that link
from being used for forwarding packets too, notifying the admin
in some way or another. This at least prevents the loop from
happening for too long and thus minimizes damage.

This could then also be used in traceroute scenarios later on.
Though mtrace is probably more suited for that situation.

Greets,
 Jeroen

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