The use of different network security components, such as firewalls and network intrusion detection systems (NIDSs), is the dominant method to monitor and guarantee the security policy in current corporate networks. To properly configure these components, it is necessary to use several sets of security rules. Nevertheless, the existence of anomalies between those rules, particularly in distributed multi-component scenarios, is very likely to degrade the network security policy. The discovery and removal of these anomalies is a serious and complex problem to solve. In this paper, we present a complete set of mechanisms for such a management.Keywords Network Security · Firewalls · Intrusion Detection Systems · Policy Anomalies IntroductionGenerally, once a security administrator has specified a security policy, he or she aims to enforce it in the information system to be protected. This enforcement consists in distributing the security rules expressed in this policy over different security components of the information system -such as firewalls, intrusion detection systems (IDSs), intrusion prevention systems (IPSs), proxies, etc. -both at application, system, and network level. This implies cohesion of the security functions supplied by these components. In other words, security rules deployed over the different components must be consistent, not redundant and, as far as possible, optimal.

The use of different network security components, such as firewalls and network intrusion detection systems (NIDSs), is the dominant method to survey and guarantee the security policy in current corporate networks. On the one hand, firewalls are traditional security components which provide means to filter traffic within corporate networks, as well as to police the incoming and outcoming interaction with the Internet. On the other hand, NIDSs are complementary security components used to enhance the visibility level of the network, pointing to malicious or anomalous traffic. To properly configure both firewalls and NIDSs, it is necessary to use several sets of filtering and alerting rules. Nevertheless, the existence of anomalies between those rules, particularly in distributed multi-component scenarios, is very likely to degrade the network security policy. The discovering and removal of these anomalies is a serious and complex problem to solve. In this paper, we present a set of algorithms for such a management.

We provide in this paper three algorithms that enable the sensor nodes of a Wireless Sensor Network (WSN) to determine their location in presence of neighbor sensors that may lie about their position. Our algorithms minimize the number of trusted nodes required by regular nodes to complete their process of localization. The algorithms always work for a given number of neighbors provided that the number of liars is below a certain threshold value, which is also determined.