Wireless ad hoc networks are an emerging technology. These networks are composed of mobile nodes and may adopt different topologies depending on the nature of the environment. Nevertheless, they are vulnerable to network layer attacks that cannot be neutralized easily. In wired networks, firewalls improve the level of security by means of packet filtering techniques that determine what traffic is allowed, thereby reducing the impact of such attacks. In this work, we overview the requirements to adapt firewalls to wireless ad hoc networks and highlight the advantages of the use of filtering techniques based on Bloom filters.