# Network Security Introduction ## What is Network Security Network security is the practice of protecting a computer network and its data from unauthorized access, misuse, malfunction, modification, destruction, or improper disclosure. It involves implementing policies, procedures, and technologies that defend against a wide range of threats including external attacks from hackers, internal threats from malicious or negligent employees, malware, data breaches, and service disruptions. Network security is not a single technology but a layered approach combining multiple defenses. ## Why Network Security is Important Networks carry sensitive and valuable information including financial data, personal information, trade secrets, government information, and communications between people and organizations. The consequences of security failures can be severe. A data breach may expose millions of customers' personal data, leading to financial losses, regulatory fines, and reputational damage. A ransomware attack may encrypt all of an organization's data, halting operations until a ransom is paid. A denial of service attack may take a website or online service offline, costing the organization revenue and customer trust. Nation-state attackers may target critical infrastructure such as power grids and water treatment facilities. ## Security Goals - CIA Triad Network security aims to maintain three fundamental properties known as the CIA triad. Confidentiality ensures that information is accessible only to those authorized to access it. Unauthorized parties should not be able to read sensitive data. Integrity ensures that data has not been altered in an unauthorized manner. Data received should be identical to data sent, with no modifications by attackers in transit. Availability ensures that network services and data are accessible when needed by authorized users. Attacks that disrupt service undermine availability. ## Defense in Depth Effective network security uses a defense in depth approach, layering multiple security controls so that if one control fails, others remain to prevent damage. Perimeter security includes firewalls and intrusion prevention systems at the network boundary. Network segmentation divides the network into zones with different security levels. Endpoint security protects individual devices. Application security addresses vulnerabilities in software. Data security protects stored data through encryption and access controls. User authentication and authorization control who can access what. Security monitoring detects suspicious activity. ## Security Threats Network threats come from multiple directions. External attackers attempt to penetrate networks from the internet to steal data, install malware, or disrupt services. Insider threats from employees with malicious intent or simply careless behavior are responsible for a significant proportion of security incidents. Malware including viruses, worms, ransomware, and spyware is delivered through email attachments, malicious websites, and compromised software. Social engineering attacks manipulate people into revealing credentials or taking actions that compromise security.