Network Security- Basic concepts and definition

Network security consists of the provisions made in an underlying computer network infrastructure, policies adopted by the network administrator to protect the network and the network-accessible resources from unauthorized access and the effectiveness (or lack) of these measures combined together.

How different is it from computer security?
Securing network infrastructure is like securing possible entry points of attacks on a country by deploying appropriate defense. Computer security is more like providing means of self-defense to each individual citizen of the country. The former is better and practical to protect the civilians from getting exposed to the attacks. The preventive measures attempt to secure the access to individual computers--the network itself--thereby protecting the computers and other shared resources such as printers, network-attached storage connected by the network. Attacks could be stopped at their entry points before they spread. As opposed to this, in computer security the measures taken are focused on securing individual computer hosts. A computer host whose security is compromised is likely to infect other hosts connected to a potentially unsecured network. A computer host's security is vulnerable to users with higher access privileges to those host .

Ingredients
Network security starts from authenticating any user. Once authenticated, firewall enforces access policies such as what services are allowed to be accessed by the network users. Though effective to prevent unauthorized access, this component fails to check potentially harmful contents such as computer worms being transmitted over the network. An intrusion prevention system (IPS)[1] helps detect and prevent such malware. IPS also monitors for suspicious network traffic for contents, volume and anomalies to protect the network from attacks such as denial of service. Communication between two hosts using the network could be encrypted to maintain privacy. Individual events occurring on the network could be tracked for audit purposes and for a later high level analysis.
Honeypots, essentially decoy network-accessible resources, could be deployed in a network as surveillance and early-warning tools. Techniques used by the attackers that attempt to compromise these decoy resources are studied during and after an attack to keep an eye on new exploitation techniques. Such analysis could be used to further tighten security of the actual network being protected by the honeypot.

Books about Network Security
Self-Defending Networks: The Next Generation of Network Security, Duane DeCapite, Cisco Press, Sep. 8, 2006. ISBN
Security Threat Mitigation and Response: Understanding CS-MARS, Dale Tesch/Greg Abelar, Cisco Press, Sep. 26, 2006. ISBN
Deploying Zone-Based Firewalls, Ivan Pepelnjak, Cisco Press, Oct. 5, 2006. ISBN
Network Security: PRIVATE Communication in a PUBLIC World, Charlie Kaufman Radia Perlman Mike Speciner, Prentice-Hall, 2002. ISBN .

External links
Cisco IT Case Studies about Security and VPN
Debate: The data or the source - which is the real threat to network security? - Video
SANS Institute network security resources
Network security dictionary and articles