An originating node often expects to have bidirectional
communications with a destination node. In such cases, it is not
sufficient for the originating node to have a route to the
destination node; the destination must also have a route back to the
originating node. In order for this to happen as efficiently as
possible, any generation of a RREP by an intermediate node (as in
section 6.6) for delivery to the originating node SHOULD be
accompanied by some action that notifies the destination about a
route back to the originating node. The originating node selects
this mode of operation in the intermediate nodes by setting the 'G'
flag. See section 6.6.3 for details about actions taken by the
intermediate node in response to a RREQ with the 'G' flag set.