Secure communications is essential in many areas such as disaster management and battlefield communications. To detect and prevent attacks in such applications, most existing protocols adopt a cryptography-based approach, trust-based approach (reputation of nodes), or incentive-based approach. However, such protocols still have drawbacks, such as expensive overhead, difficulty in maintaining secure key and session management, or leaving routes unsecured against Byzantine attacks. In this paper, we introduce a monitoring-based method in the link state routing protocol to secure the packets' route against Byzantine attacks. The goal of our proposed scheme is to guarantee communication among connected benign nodes in the network. Specifically, each node monitors the action of neighboring nodes and compares the optimal packet route against the packet route history. Nodes in the network create a packet history field which is used to record all activities of an intermediate node when receiving and forwarding packets. Our scheme provides mutual monitoring in which nodes in the network can validate the packet history field of other nodes and report malicious activities. Also, our scheme uses a statistical method to know if a node is dropping packets intentionally by analyzing the packet dropping behavior of each node. The proposed scheme provides protection against colluding attacks and other Byzantine attacks. The proposed monitoring-based method achieves an average of 89% to 96% packet delivery ratio when 11% to 21% active malicious links are excluded from the network.