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In AODV protocol an intermediate node can send a Route Reply if it has an active route to the destination, the destination sequence number in the node's existing route table entry for the destination is valid and greater than or equal to the Destination Sequence Number of the RREQ (comparison using signed 32-bit arithmetic), and the "destination only" ('D') flag is NOT set. (Reference: Section 6.6.2 of RFC 3561 https://tools.ietf.org/html/rfc3561)

Consider the simple MANET network where the RREP of AODV is sent by an intermediate node instead of the destination node during route discovery (associated experiment configuration is attached herewith).

Figure:1

Here Node 1 communicates with Node 5 and Node 2 communicates with Node 4 using AODV protocol.  The Route Table is created or updated only when RREQ, RREP, or RRER messages are received by the corresponding nodes.

Application 1:

1. Node 1 has to communicate with the destination Node to which there is no Route established previously hence the Node 1 sends a Route Request broadcast message RREQ as shown in Figure 2 with its own sequence number to the neighboring nodes, here Node 2.

Before broadcasting the RREQ, the originating node buffers the RREQ ID and the Originator IP address (its own address) of the RREQ for PATH_DISCOVERY_TIME.  In this way, when the node receives the packet again from its neighbors, it will not reprocess and re-forward the packet. 

Wireless_Node_1:

Figure:2

2. Node 2 receives the RREQ message from Node 1.Since Node 2 is not the destination Node, it makes note of the reverse route to reach Node 1 in its Route table as shown in TABLE and it changes the Hop Count value to 1 in RREQ and broadcasts the message to its neighbor nodes Node 1 and Node 3 as shown in Figure 

Wireless_Node_2:

Figure:3

3. Node 1 receiving the RREQ from Node 2 identifies that it is the same RREQ sent by its own Node hence it does not broadcast it to other Nodes. Similarly, Node 3 creates its Route Table as shown in the table below noting the reverse route to reach the source Node and changes the Hop count in the RREQ message, and broadcasts it to its neighboring Nodes, Node 4 and Node 2

Wireless_Node_3:

Figure:4

4. Node 2 receiving the RREQ from Node 3 identifies that it is the same RREQ sent by its own Node hence it does not broadcast it to other Nodes. Similarly, Node 4 receives and creates its Route Table as shown in TABLE noting the reverse route to reach the source Node and changes the Hop count in the RREQ message and broadcasts it to its neighboring Nodes, Node 5 as shown in Figure 

Wireless_Node_4:

Figure:5

5. Node 5 receives RREQ from Node 4. Node 5 identifies that its IP Address is the same as the Destination IP Address field in RREQ. The Destination Node when generating an RREP message copies the Destination IP Address and the Originator Sequence Number from the RREQ message into the corresponding fields in the RREP message. Hence Node 5 sends its RREP to the Next Hop Node 4 as shown in Figure  and creates its Route Table as shown in Table 

Wireless_Node_5:

Figure:6

6. When a node receives an RREP message, it searches for a route to the previous hop. If needed, a route is created for the previous hop. Node 4 receives RREP and updates its Route Table with the reverse route to reach Node 5 notes the Destination Seq No and forwards the RREP to Next Hop Node 3

Wireless_Node_4:

Figure:7

7. Node 3 receives the RREP and updates its Route Table with the reverse route to reach Node 5, notes the Destination Seq No, and forwards the RREP to the Next Hop Node 2

Wireless_Node_3:

Figure:8

8. Node 2 receives the RREP and updates its Route Table with the reverse route to reach Node 5, notes the Destination Seq No, and forwards the RREP to the Next Hop Node 1

Wireless_Node_2:

Figure:9

9. Originator Node 1 receives the RREP from the Next Hop Node 2 and creates the entries in the Route Table and starts the data transmission through the Route thus established

Wireless_Node_1:

Application 2:

Application 2 is run after the start of Application 1.Application 2 here was started after 5sec from the start of Application 1. Here Node 2 has to transmit data to Node 4. The intermediate Node between Node 2 and Node 4 is Node 3 which has a route to Node 4 since it is the Next Hop. The Route discovery for Application 2 is as follows

1. Node 2 sends an RREQ broadcast message to the neighbour nodes Node 1 and Node 3 as shown in Figure 10 and updates its Route Table as shown

Wireless_Node_2:

Figure:10

2. Node 3 receives the RREQ from Node 2 and refers to its Route Table for a route to reach the destination Node 5.Since the Route Table has an active route, Node 3 sends an RREP to Node 2 on behalf of Node 4 without a valid Destination Seq No and by incrementing the Hop Count to 1.If the RREQ has the 'G' flag set, and the intermediate node returns an RREP to the originating node, it MUST also unicast a gratuitous RREP to the destination node. The Node 3 updates its Route Table as follows

Wireless_Node_3:

Figure:11

3. Node 2 receives the RREP from Node 3 and updates its Route Table with the route thus obtained. The Node 2 starts its data transmission as shown in Figure 11

Wireless_Node_2:

Figure:12

Related article:

Understanding AODV route discovery procedure using route table logs

Obtain logs for AODV route table updates in NetSim : NetSim Support Portal (tetcos.com)