Packet-Dropping and False-Recommendation Attacks on Trust-Based Gateway Selection in an Integrated Internet-MANET: An NS-3 Study

In an integrated Internet-MANET a mobile node reaches the Internet through a gateway, and the choice of gateway decides which relay nodes carry its traffic. If some of these relays accept packets and then discard them, the choice of the nearest gateway is no longer the safest one. This paper studies a trust-based gateway selection in the ns-3 simulator. A watchdog based on overheard transmissions supplies evidence, the Beta expectation turns it into trust, and a source switches to another gateway when the relays on its route to the current one are not trusted. Two gateways serve a 30-node AODV network in which 0, 10, 20 and 30 per cent of the nodes drop every packet they should relay; every setting was run ten times. Compared with selecting the nearest gateway, trust-aware selection lowered the share of selections whose route contained a dropping relay from 5.9 to 3.6 per cent at 30 per cent dropping nodes and raised the packet delivery ratio from 0.922 to 0.936, at the price of about seven additional gateway switches per flow. The trust values themselves were reliable only while the opinions of other nodes were honest: when the dropping nodes also sent false opinions, mean and median aggregation condemned 55 and 43 per cent of the honest nodes at 10 per cent attackers, whereas weighting the opinions by the trust of their sender removed the effect. The results show that a trust-aware gateway choice gives a small but consistent gain in an attack-prone network, and that the treatment of recommenders decides whether the trust values can be used at all.