Introduction to Computer Networks

• The unit aims to provide an in-depth understanding of network and security issues and teach students to use available tools for detecting, responding to, and recovering from security incidents.

Introduction to Computer Networks

• Computer networks are defined as collections of autonomous computers interconnected by a single technology, enabling information exchange through various methods like copper wire, fiber optics, microwaves, infrared, and communication satellites.
• Networks vary in size and shape, often connecting to form larger networks, with the Internet being a prime example of a network of networks.
• The lecture will cover the uses of computer networks, their key components, classification, software, and reference models.

Uses of Computer Networks

• Interacting with others is a fundamental human need, nearly as vital as sustaining life, making communication highly important.
• Communication methods continually evolve, extending beyond face-to-face conversations with breakthroughs like the printing press and television enhancing communication.
• Early data networks were confined to exchanging character-based information; today's networks support diverse data types across various devices.

Business Applications

• Businesses utilize numerous computers for tasks like product design, brochure creation, and payroll management.
• Connecting these computers enables information distribution across the company, facilitating resource sharing regardless of physical location
• A company's information system is conceptualized as databases accessed remotely by employees via servers.
• Centrally housed servers maintained by system administrators store data, which employees access through client machines for tasks like constructing spreadsheets.
• In the client/server model, the client requests information, and the server responds, connected through a network.
• A prevalent example is a web application where the server dynamically generates web pages from a database based on client requests.
• Client-server models are suitable whether clients and servers are in the same building or geographically distant.
• The detailed client-server model involves processes on both client and server machines, with the client sending a message and awaiting a reply.

Home Applications

• Internet access enables home users to connect remotely for accessing information, communicating, and e-commerce.
• Remote access includes web surfing for both informational and recreational purposes, covering diverse topics.
• While much is accessed via the client-server model, peer-to-peer communication presents an alternative information access method.
• Peer-to-peer networks allow resource sharing without a dedicated server; each connected device can act as both client and server.
• In peer-to-peer networks, any member can communicate with others, lacking a strict client-server division.
• Peer-to-peer networks decentralize resources; instead of relying on dedicated servers, information resides on connected devices.
• P2P networks typically lack centralized user accounts, which complicates security and access policy enforcement, requiring individual configuration on each device.

Mobile Users

• Mobile computers are a fast-growing sector surpassing desktop sales, enabling users to perform tasks like emailing, streaming, gaming, and web browsing from anywhere.
• Connectivity to the Internet drives mobile usage, with wireless networks like cellular and 802.11 hotspots providing essential access.
• Wireless networks benefit transportation, military, and service industries by maintaining contact with bases.
• The convergence of phones and the Internet has led to smartphones, which offer both mobile phone and computer capabilities.
• Modern phones support fast data via 3G/4G networks, handling calls and internet use while automatically switching between networks for optimal service.
• Mobile phones use GPS for location-dependent services like maps, directions, and local searches.
• Mobile commerce (m-commerce) has emerged, using text messages for payment authorization.
• Sensor networks consist of wirelessly connected nodes gathering and relaying environmental data, integrated into items like cars to collect data on location, speed, and efficiency.

Social Issues

• Computer networks enable widespread content distribution, mirroring the impact of the printing press but introducing social, political, and ethical challenges.
• Online platforms allow individuals to share views, but issues like copyright, cookies, and spam can arise.

Networks

• A network comprises devices (nodes) connected by communication links, where nodes can be computers, printers, or any device capable of data exchange.
• Networks employ distributed processing by dividing tasks among multiple computers, where separate machines handle subsets of a process instead of one large machine managing all aspects.

The Elements of Computer Network

• Common networking devices are represented by icons in this graphically oriented subject.
• Devices originate messages and include computers and IP phones typically connected by LAN media.
• Intermediate devices direct and manage messages across the network, with common symbols representing switches, firewalls, and routers.
• Key networking symbols:
  • Switch for interconnecting local area networks.
  • Firewall for network security.
  • Router for directional message across networks.
  • Wireless Router for home networks.
  • Cloud for a group of networking devices.
  • Serial Link for WAN interconnection.
• Devices need interconnection, either wired or wireless. Wired connects with copper or fiber optics; wireless utilizes the atmosphere.
• Industry standard TCP/IP governs how networked devices communicate using rules and protocols.

Introduction to Network Security

• Enterprise networks are vulnerable to malicious activities and unintentional breaches with the expansion of internet, intranet, and extranet applications.
• Computer networks are sets of connected computers (nodes) sharing resources via cabling or wireless connections.
• The OSI model is used to understand network workings.

Open Systems Interconnection (OSI) Model

• The OSI model is defines a networking framework that uses a layered approach, used as a teaching tool, and logically divides network structure in 7 layers
• Lower layers handle electrical signals and data routing; higher layers manage requests, responses, data representation, and network protocols.
• The OSI model acts as a standard architecture for network systems.

Physical Layer (Layer 1)

• Defines the physical host to network connection and convert bits to physical signaling.
• Device drivers for communication hardware function at this layer.
• Hubs and repeaters are standard network devices and cable connectors.

Data Link Layer

• When obtaining data from the Physical layer, the Data Link layer checks for physical transmission errors and packages bits in data "frames".
• The Data Link layer also manages physical addressing schemes, such as MAC addresses for Ethernet networks, controlling access of any various network devices to the physical medium.
• The "Media Access Control" sub layer and the "Logical Link Control" sub layer make up the Data Link layer.

Network Layer

• The Network layer uses routing the above the Data Link Layer.
• When data arrives; examines source and destination addresses to determine if the destination is reached.
• Otherwise the network layer updates the destination before moving to lower layers.
• Logical addresses are maintained for routing and are mapped with physical ones.
• Address Resolution Protocol (ARP) is accomplished through IP networking.

Transport Layer

• Transfers data across network connections.
• TCP and UDP are transport layer 4 network protocol examples.
• Capabilities like error recovery, flow control, and re-transmission are supported by other transport protocols.

Session Layer

• Manages the order and flow of events of tearing down and initiating network connections at Layer 5.
• Supports multiple connection types dynamically.

Presentation Layer

• In the OSI model, it converts syntax, processes message data by conversion and encryption needed by the application layer, at Level 6

Application Layer

• Supplies network services to end-user applications.
• Protocols operate with user data
• HTTP packages data for sending and receiving web content.

Computer Security

• Computer security preserves data integrity, availability, and confidentiality in information systems.
• This definition introduces three key objectives that are at the heart of (goals of) computer security:
  • Confidentiality to private or confidential information is not made available or disclosed to unauthorized individuals.
  • Privacy assurances include personal data being collected, stored, and shared to who and why.
  • Integrity - Data and systems performing intended functions in specified and authorized manners unimpaired from free or deliberate unauthorized manipulation.
  • Availability - systems work promptly, and service is not denied to those authorized.
• The CIA triad model gives policies for information security within an organization. These include confidentiality, integrity and availability.
• Additional concepts are needed to complete the image, although the CIA Triad model is well established.

Additional Computer Security Definitions

• Authenticity: Property of being genuine, verified, and trusted; inspires confidence in validity which each input originated from.
• Accountability: Generates security which traces actions to an entity and enables nonrepudiation, deterrence, intrusion detection, and legal action.

Security Architecture for OSI

• ITU's X.800 recommendation defines OSI security architecture useful for providing security.
• Computer and communications vendors developed security features for their products and services related to structured definition and mechanisms due to it being developed as an international standard
• The OSI security architecture focuses on security attacks, mechanisms, and services.
  • Security attack - compromises the security through any action of owned information
  • Security Mechanism - a process that is designed to detect, prevent, or recover from a security attack
  • Security Service - enhance the security of the data processing systems and the information transfers of an organization.
  • Threat - A potential for violation of security circumstance, capability, action, or event that could cause harm.
  • Attack - Assault on system security, that is an intelligent act that is a deliberate attempt evade security services.

Security Attacks

• X.800 classifies security attacks as passive or active.
• Passive attacks aims learn or make use of information from the system but does not affect system resources
• Active Attacks - alter system resources or affect the operation.

Passive Attacks

• Consists of eavesdropping on communications to obtain underlying transmitted information that are difficult to detect.
• Release message of Contents can contain electronic mail, sensitive information, which allows to prevent learning the contents.
• Traffic analysis uses encryption contents where if captured cannot extract data, however pattern can be seen from location, identity and the observation of messages. This information can guess the nature of the communications.

Active Attacks

• Involve the creation of a false stream or modification of the data stream and can be subdivided into four categories.
• Masquerade - pretending to perform entity.
• Replay - passively capture results in a data unit.
• Modification of messages - Altering legitimate messages that delays the orders of things
• Denial of service facilities - prevents normal use or communication management which is difficult due to potential vulnerabilities.

Achieving Network Security

• ITU X.800 security architecture provides protocols to achieve methods in network security.
• Includes Encipherments which converts data into a secret form using symmetric/asymmetric keys.
• Digital Signatures are electronic versions used provide authentication of data/data origin integrity, and nonrepudiation services
• Access Control: Used for determine/enforce entity through identification/authentication rights, which may use privileges and firewalls.
• Authentication: These mechanisms provide identification of a principle by cryptographic and password techniques.
• Traffic Padding: Provides protection from traffic analysis - several networks include padding to protect the communication.
• Routing Control - allows one to select a route for data dynamically/statically, especially from malicious exploits.

Network Security Attacks

• Common Vulnerability involves both wireless and wired networks through "unauthorized access".
• Wireless networks are less secure due to easy access:
  • Sniffing - Steal packet data to gain valuable information
  • DOS (Denial of Service): flooding with medium spurious packets for legitimate users.
  • Spoofing - claiming identities to steal data for unauthorized hosts and launch man in the middle attacks.
  • Eavesdropping - Unauthorized interaction is disclosed/exchanged through network communications.
  • Logon Abuse - successful attacks uses user authentication and gets access/control mechanism and gains more privileged accesses and control.
  • Intrusion Attack - Attack targets gained access of unauthorizes to the network.
  • Hijacking Attacks - Attack tempts system access using someone else's existing connection.
  • Application Attacks - Exploit weaknesses of the application layer by injecting remote command execution structure into queries.