Subject: [manet] AODV RERR and precursor list - RFC 3561

From: Bracha Hod <[email-masked]>
Date: Tue, 21 Dec 2004 11:17:07 +0200

Hi,

According to RFC 3561:

1) In the route discovery phase, every node that get RREQ creates or updated the reverse path to the RREQ originator.
2) The precursor list is updated only during the RREP generating and forwarding.
3) The neighboring node(s) that should receive the RERR are all those that belong to a precursor list of at least one of the unreachable
   destination(s) in the newly created RERR.  

Based on those facts, consider the following case:

0<--->1 <---> 2 <---> 3 <--->4

All the route tables are empty, then node 2 initiates RREQ to find a route to 0.
Nodes 3 and 4 get the RREQ and create a route to 2.
The RREP that is forwarded from 0 via 1 to 2, does not have any effect of nodes 3 and 4. 
Since node 4 has route to 2, it uses it to transmit data.  
Then, if the link between 2 and 3 is broken, node 3 does not have any node in the precursor list of its route entry, since no RREP was generated or forwarded by it.
Consequently, when it gets data from node 4 and no local repair is done, or the local repair is failed, it does not send any RERR since the precursor list is empty. 

This situation causes packet dropping, without any notification.                         
Do you have any solution to that case?

Thanks,

Bracha Hod
The Hebrew University of Jerusalem 
Israel

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