From: Scott Ramsby (sramsby_at_cs.washington.edu)
Date: Tue Feb 03 2004 - 12:45:32 PST
I see how we can eliminate the use of the neighbor discovery packets now
that we have all this other stuff we're broadcasting. However, I'm
failing to see how we could hit that problem you mentioned. I assumed
that if we didn't have a route to a node we could just broadcast the
packet and hope that someone else knows a route. This is more
inefficient, but is more reliable, and this error case shouldn't happen
often anyway. So, is the correct thing to do on handling a packet
forward for which we have no route to broadcast it or just drop it?
Scott
Janet Davis wrote:
>Hi all,
>
>Abhinav and I just discovered an important interoperability issue with
>neighbor discovery and link state routing.
>
>The scenario is this:
>
>* For neighbor discovery, node 1 sends a ping with a special message and
>TTL=1, and expects to receive a ping with the same message back.
>
>* Node 2 receives this ping, discovers it has no route to node 1, and
>consequently does not send a reply.
>
>* As a result, node 1 never recognizes node 2 as its neighbor, and since
>we only use bidirectional links in our Dijkstra computation, node 2 never
>does compute a route to node 1.
>
>For interoperability, we all need to agree on one method of recognizing
>your neighbors. The most efficient approach is to use the 'from' argument
>of the onReceive method -- it's guaranteed that this is the address of one
>of your neighbors, regardless of the packet contents.
>
>Note that if you use this method, you can eliminate the special neighbor
>discovery ping packets entirely! (Why?)
>
>So, for this assignment you should decide who your neighbors are based on
>the 'from' argument of the onReceive method, not on the contents of
>neighbor discovery ping packets.
>
>Cheers,
>Janet
>
>
>
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