Network security consists of the provisions and policies adopted by a network administrator to prevent and monitor unauthorized access, misuse, modification, or denial of a computer network and network-accessible resources. Network security involves the authorization of access to data in a network, which is controlled by the network administrator. Users choose or are assigned an ID and password or other authenticating information that allows them access to information and programs within their authority. Network security covers a variety of computer networks, both public and private, that are used in everyday jobs conducting transactions and communications among businesses, government agencies and individuals. Networks can be private, such as within a company, and others which might be open to public access. Network security is involved in organizations, enterprises, and other types of institutions. It does as its title explains: It secures the network, as well as protecting and overseeing operations being done. The most common and simple way of protecting a network resource is by assigning it a unique name and a corresponding password.
Network security concepts 
Network security starts with authenticating, commonly with a username and a password. Since this requires just one detail authenticating the user name —i.e. the password— this is sometimes termed one-factor authentication. With two-factor authentication, something the user 'has' is also used (e.g. a security token or 'dongle', an ATM card, or a mobile phone); and with three-factor authentication, something the user 'is' is also used (e.g. a fingerprint or retinal scan).
Once authenticated, a 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 may fail to check potentially harmful content such as computer worms or Trojans being transmitted over the network. Anti-virus software or an intrusion prevention system (IPS) help detect and inhibit the action of such malware. An anomaly-based intrusion detection system may also monitor the network and traffic for unexpected (i.e. suspicious) content or behavior and other anomalies to protect resources, e.g. from denial of service attacks or an employee accessing files at strange times. Individual events occurring on the network may be logged for audit purposes and for later high-level analysis.
Communication between two hosts using a network may be encrypted to maintain privacy.
Honeypots, essentially decoy network-accessible resources, may be deployed in a network as surveillance and early-warning tools, as the honeypots are not normally accessed for legitimate purposes. 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 may be used to further tighten security of the actual network being protected by the honeypot.
Security management 
Security management for networks is different for all kinds of situations. A home or small office may only require basic security while large businesses may require high-maintenance and advanced software and hardware to prevent malicious attacks from hacking and spamming.
Homes & Small Businesses 
- A basic firewall or a unified threat management system.
- For Windows users, basic Antivirus software. An anti-spyware program would also be a good idea. There are many other types of antivirus or anti-spyware programs available.
- When using a wireless connection, use a robust password. Also try to use the strongest security supported by your wireless devices, such as WPA2 with AES. TKIP may be more widely supported by your devices and should only be considered in cases where they are NOT compliant with AES.
- If using Wireless: Change the default SSID network name, also disable SSID Broadcast; as this function is unnecessary for home use. (Security experts consider this to be easily bypassed with modern technology and some knowledge of how wireless traffic is detected by software).
- Enable MAC Address filtering to keep track of all home network MAC devices connecting to your router. (This is not a security feature per se; However it can be used to limit and strictly monitor your DHCP address pool for unwanted intruders if not just by exclusion, but by AP association.)
- Assign STATIC IP addresses to network devices. (This is not a security feature per se; However it may be used, in conjunction with other features, to make your AP less desirable to would-be intruders.)
- Disable ICMP ping on router.
- Review router or firewall logs to help identify abnormal network connections or traffic to the Internet.
- Use passwords for all accounts.
- For Windows users, Have multiple accounts per family member and use non-administrative accounts for day-to-day activities.
- Raise awareness about information security to children.
Medium businesses 
- A fairly strong firewall or Unified Threat Management System
- Strong Antivirus software and Internet Security Software.
- For authentication, use strong passwords and change them on a bi-weekly/monthly basis.
- When using a wireless connection, use a robust password.
- Raise awareness about physical security to employees.
- Use an optional network analyzer or network monitor.
- An enlightened administrator or manager.
- Use a VPN, or Virtual Private Network, to communicate between a main office and satellite offices using the Internet as a connectivity medium. A VPN offers a solution to the expense of leasing a data line while providing a secure network for the offices to communicate. A VPN provides the business with a way to communicate between two in a way mimics a private leased line. Although the Internet is used, it is private because the link is encrypted and convenient to use. A medium sized business needing a secure way to connect several offices will find this a good choice.
- Clear employee guidelines should be implemented for using the Internet, including access to non-work related websites, sending and receiving information.
- Individual accounts to log on and access company intranet and Internet with monitoring for accountability.
- Have a back-up policy to recover data in the event of a hardware failure or a security breach that changes, damages or deletes data.
- Disable Messenger.
- Assign several employees to monitor a group like CERT which studies Internet security vulnerabilities and develops training to help improve security.
Large businesses 
- A strong firewall and proxy, or network Guard, to keep unwanted people out.
- A strong Antivirus software package and Internet Security Software package.
- For authentication, use strong passwords and change it on a weekly/bi-weekly basis.
- When using a wireless connection, use a robust password.
- Exercise physical security precautions to employees.
- Prepare a network analyzer or network monitor and use it when needed.
- Implement physical security management like closed circuit television for entry areas and restricted zones.
- Security fencing to mark the company's perimeter.
- Fire extinguishers for fire-sensitive areas like server rooms and security rooms.
- Security guards can help to maximize physical security.
- An adjustable firewall and proxy to allow authorized users access from the outside and inside.
- Strong Antivirus software and Internet Security Software packages.
- Wireless connections that lead to firewalls.
- Children's Internet Protection Act compliance. (Only schools in the USA)
- Supervision of network to guarantee updates and changes based on popular site usage.
- Constant supervision by teachers, librarians, and administrators to guarantee protection against attacks by both internet and sneakernet sources.
- An enforceable and easy to understand acceptable use policy which differentiates between school owned and personally owned devices
- FERPA compliance for institutes of higher education network
Large government 
- A strong firewall and proxy to keep unwanted people out.
- Strong antivirus software and Internet Security Software suites.
- Strong encryption.
- Whitelist authorized wireless connection, block all else.
- All network hardware is in secure zones.
- All hosts should be on a private network that is invisible from the outside.
- Host web servers in a DMZ, or a firewall from the outside and from the inside.
- Security fencing to mark perimeter and set wireless range to this.
- Inventory controls of government owned mobile .
Types of Attacks 
Networks are subject to attacks from malicious sources. Attacks can be from two categories: "Passive" when a network intruder intercepts data traveling through the network, and "Active" in which an intruder initiates commands to disrupt the network's normal operation.
Types of attacks include:
See also 
- Cloud computing security
- Cyber security standards
- Data Loss Prevention
- Information Leak Prevention
- Metasploit Project
- Mobile security
- Network Security Toolkit
- TCP Gender Changer
- TCP sequence prediction attack
- Timeline of hacker history
- Wireless LAN Security
- Simmonds, A; Sandilands, P; van Ekert, L (2004). "An Ontology for Network Security Attacks". Lecture Notes in Computer Science. Lecture Notes in Computer Science 3285: 317–323. doi:10.1007/978-3-540-30176-9_41. ISBN 978-3-540-23659-7.
- A Role-Based Trusted Network Provides Pervasive Security and Compliance - interview with Jayshree Ullal, senior VP of Cisco
- Dave Dittrich, Network monitoring/Intrusion Detection Systems (IDS), University of Washington.
- "''Honeypots, Honeynets''". Honeypots.net. 2007-05-26. Retrieved 2011-12-09.
- "The six dumbest ways to secure a wireless LAN | ZDNet". Blogs.zdnet.com. Retrieved 2011-12-09.
- Julian Fredin, Social software development program Wi-Tech
- "Introduction to Network Security". Interhack.net. Retrieved 2011-12-09.
- "Welcome to CERT". Cert.org. 2011-10-17. Retrieved 2011-12-09.
- Wright, Joe; Jim Harmening (2009) "15" Computer and Information Security Handbook Morgan Kaufmann Publications Elsevier Inc p. 257
Further reading 
- Cisco. (2011). What is network security?. Retrieved from cisco.com
- Security of the Internet (The Froehlich/Kent Encyclopedia of Telecommunications vol. 15. Marcel Dekker, New York, 1997, pp. 231-255.)
- Introduction to Network Security, Matt Curtin.
- Security Monitoring with Cisco Security MARS, Gary Halleen/Greg Kellogg, Cisco Press, Jul. 6, 2007.
- Self-Defending Networks: The Next Generation of Network Security, Duane DeCapite, Cisco Press, Sep. 8, 2006.
- Security Threat Mitigation and Response: Understanding CS-MARS, Dale Tesch/Greg Abelar, Cisco Press, Sep. 26, 2006.
- Securing Your Business with Cisco ASA and PIX Firewalls, Greg Abelar, Cisco Press, May 27, 2005.
- Deploying Zone-Based Firewalls, Ivan Pepelnjak, Cisco Press, Oct. 5, 2006.
- Network Security: PRIVATE Communication in a PUBLIC World, Charlie Kaufman | Radia Perlman | Mike Speciner, Prentice-Hall, 2002. ISBN .
- Network Infrastructure Security, Angus Wong and Alan Yeung, Springer, 2009.