In MANET, providing authentication and security to location-based routing is a big task. To overcome this problem, in this paper, we proposed a defense against Sybil attacks and authentication for anonymous location-based routing in MANET. Each random forwarder has a table of RSS values estimated from the previous message exchanges across a zone to detect the Sybil attack. The difference in RSS values of two neighboring nodes is estimated based on which the node’s arrival angle into the zone is detected. Depending on the arrival angle, the nodes can be categorized as safety zone and caution zone. The messages exchanged between the RFs and senders can be protected by means of group signature. Finally, misrouting packet drop attack is detected and eliminated by using ant colony optimization technique. By simulation results, we show the proposed technique reduces the packet drop due to attacks, thereby increasing the delivery ratio.