A destination node, after receiving the first Route Request packet, replies to the source node through the reverse path the Route Request packet had traversed.Nodes can also learn about the neighboring routes traversed by data packets if operated in the promiscuous mode (the mode of operation in which a node can receive the packets that are neither broadcast nor addressed to itself).
Consider a source node that does not have a route to the destination.
It has only two major phases, which are Route Discovery and Route Maintenance.
Route Reply would only be generated if the message has reached the intended destination node (route record which is initially contained in Route Request would be inserted into the Route Reply).
To avoid using source routing, DSR optionally defines a flow id option that allows packets to be forwarded on a hop-by-hop basis.
This protocol is truly based on source routing whereby all the routing information is maintained (continually updated) at mobile nodes.