RREQs

RREQs, or Route Request messages, are control messages used in reactive routing protocols to discover routes in networks with dynamic topologies, such as mobile ad hoc networks. When a source node needs a path to a destination, it broadcasts an RREQ. The message is propagated hop by hop or flooded through the network until the destination is reached or an intermediate node with a valid route to the destination issues a Route Reply (RREP) back to the source, establishing a path.

RREQs typically carry fields that support loop-free, up-to-date route discovery. Common fields include the source address, source sequence number, destination address, destination sequence number, a broadcast identifier, and a hop count. The hop count starts at zero and is incremented at each forwarding hop. Each node records the most recent RREQ from a given source to suppress duplicates, and the broadcast ID, together with the source address, uniquely identifies each RREQ to prevent processing the same request multiple times.

Handling duplicates and controlling overhead are important aspects of RREQ-based discovery. Duplicate suppression, time-to-live or hop limits, and route caching help mitigate broadcast storms and reduce unnecessary transmissions. The RREQ mechanism is used in protocols such as AODV and other on-demand routing schemes; upon receipt, a node may reply with an RREP if it has a fresh route to the destination or if it is the destination itself. Together with RREPs, RREQs enable dynamic, on-demand path construction in networks where routes are not maintained proactively. Security considerations, such as spoofing or tampering with control messages, can also affect the reliability of RREQ-based routing.