In link state routing networks, every node has to construct a topological map through the generation and exchange of routing information. Nevertheless, if a node misbehaves then the connectivity in the network is compromised. The proactive Optimized Link State Routing (OLSR) protocol has been designed exclusively for Mobile Ad Hoc Networks (MANETs). The core of the protocol is the selection of Multipoint Relays (MPRs) as an improved flooding mechanism for distributing link state information. This mechanism limits the size and number of control traffic messages. As for several other routing protocols for MANETs, OLSR does not include security measures in its original design. Besides, OLSR has been extended to address a number of problems in MANETs. For example, Hierarchical OLSR (HOLSR) has been proposed to address scalability and Multipath OLSR (MP-OLSR) to address fault tolerance. However, these OLSR extensions can be affected either by inheriting or adding new security threats. In this chapter, we present a review of security issues and countermeasures in link state routing protocols for MANETs.
