Unit V Computer Network and Communication & Security Essentials | Cse111 Orientation Of Computing | B.tech CSE

Computer Network and Communication & Security Essentials

1. Network Types (Wired and Wireless)

Wired Networks

Ethernet (Wired LAN)
- Overview: Ethernet is the most common wired LAN technology. It uses twisted pair cables (Cat5, Cat6) or fiber optic cables to transmit data.
- Protocols: Uses the IEEE 802.3 standard for transmission.
- Types:
  - 10BASE-T (10 Mbps): Legacy standard.
  - 100BASE-TX (100 Mbps): Fast Ethernet.
  - 1000BASE-T (1 Gbps): Gigabit Ethernet.
  - 10GBASE-T (10 Gbps): 10 Gigabit Ethernet.
- Example: A home router connected to several computers via Ethernet cables.
- Advantages:
  - High reliability and stability.
  - No interference from external factors (e.g., radio frequency interference).
- Disadvantages:
  - Requires installation of cables, which can be cumbersome.
  - Fixed location (no mobility).
Fiber Optic Networks
- Overview: Fiber optic cables transmit data using light signals. These cables offer significantly higher bandwidth and lower latency compared to traditional copper cables.
- Protocols: Fiber networks use ITU-T G.65x for fiber optics and IEEE 802.3ae for 10-Gigabit Ethernet.
- Example: Google Fiber for high-speed internet connections.
- Types:
  - Single-mode fiber (SMF): Uses a single light path for data, suitable for long-distance transmission (e.g., cross-country connections).
  - Multi-mode fiber (MMF): Uses multiple paths for data transmission, typically used within buildings or short-range.
- Advantages:
  - Very high data transmission rates (up to 100 Gbps and beyond).
  - Low latency and resistance to electromagnetic interference.
- Disadvantages:
  - Expensive installation.
  - Fragile cables and requires precision in installation.
Coaxial Cable Networks
- Overview: Coaxial cables transmit data via copper wire and are used for internet connections, TV signals, and local networks.
- Protocols: DOCSIS (Data Over Cable Service Interface Specification) for broadband data over coaxial.
- Example: Broadband internet using cable providers like Comcast or Spectrum.
- Advantages:
  - Widely available and affordable.
  - Better shielding from interference than twisted-pair cables.
- Disadvantages:
  - Lower bandwidth than fiber optic.
  - Limited range compared to fiber optics.

Wireless Networks

Wi-Fi (Wireless Fidelity)
- Overview: Wi-Fi uses radio frequency (RF) to enable devices to connect wirelessly to a network. The most common standards are IEEE 802.11.
- Types:
  - 802.11a/b/g/n/ac/ax (Wi-Fi 6): From early Wi-Fi standards (802.11b) to the current Wi-Fi 6 (802.11ax) offering improved speed and performance.
  - Wi-Fi 6 (802.11ax): The latest standard, providing speeds up to 9.6 Gbps and improved capacity and efficiency in crowded environments.
- Example: A typical home Wi-Fi router using 802.11ac for high-speed internet access.
- Advantages:
  - Mobility, allowing devices to move freely within the coverage area.
  - Easy to set up and scale.
- Disadvantages:
  - Security vulnerabilities (e.g., WEP and WPA2).
  - Interference from other devices (microwaves, cordless phones).
Bluetooth
- Overview: Bluetooth is a short-range wireless communication technology used for connecting devices like headphones, keyboards, and mice.
- Protocols: IEEE 802.15.1.
- Example: Wireless Bluetooth headsets for hands-free communication.
- Types:
  - Bluetooth Classic: Older version, supports up to 3 Mbps.
  - Bluetooth Low Energy (BLE): Designed for low power consumption, widely used in IoT devices.
- Advantages:
  - Low power consumption.
  - Seamless device connectivity.
- Disadvantages:
  - Limited range (usually up to 100 meters).
  - Lower data transfer speeds compared to Wi-Fi.
Cellular Networks (4G, 5G)
- Overview: Cellular networks (4G and 5G) are used for mobile data communication. These technologies rely on radio frequencies to connect users to the internet.
- Protocols:
  - 4G LTE (Long-Term Evolution) for faster mobile data transfer.
  - 5G for ultra-fast data speeds and low latency.
- Example: Smartphones using 5G for high-speed internet access.
- Advantages:
  - High mobility (always connected when moving).
  - Wide coverage (global, provided by mobile carriers).
- Disadvantages:
  - Expensive data plans.
  - Slower than fiber for large data transfers.

2. Network Topologies

Bus Topology
- Description: All devices are connected to a single cable, or backbone. Data sent by a device is broadcast to all other devices.
- Example: Early Ethernet networks used bus topology.
- Advantages: Simple and cost-effective for small networks.
- Disadvantages: A failure in the main cable brings down the entire network.
Star Topology
- Description: All devices are connected to a central device (typically a hub or switch).
- Example: Modern office networks with a switch connecting all devices.
- Advantages:
  - Easy to manage and extend.
  - Failure in one device doesn’t affect others.
- Disadvantages:
  - Central device failure brings down the entire network.
Ring Topology
- Description: Devices are connected in a circular fashion. Data flows in one direction, passing through each device until it reaches the intended recipient.
- Example: Used in legacy Token Ring networks.
- Advantages:
  - Data flow is predictable.
  - Equal access for all devices.
- Disadvantages:
  - A break in the loop causes a failure in the entire network.
Mesh Topology
- Description: Every device is connected to every other device. Provides multiple paths for data to travel.
- Example: Large-scale enterprise networks use mesh for high redundancy.
- Advantages:
  - High fault tolerance.
  - Multiple paths reduce congestion.
- Disadvantages:
  - Expensive to implement due to the number of cables needed.
Hybrid Topology
- Description: A combination of two or more topologies (e.g., star-bus or star-ring).
- Example: Large organizations may use a star topology within departments and a bus topology to connect those departments.
- Advantages: Flexible, scalable.
- Disadvantages: More complex to design and manage.

3. Network Communication Devices

1. Router

Function: Routes data between different networks, typically between a local area network (LAN) and a wide area network (WAN), like the internet.
Example: A router provided by an ISP for internet access at home.
Protocols:
- Routing Protocols: OSPF (Open Shortest Path First), BGP (Border Gateway Protocol).
- NAT (Network Address Translation): Allows multiple devices to share a single public IP address.

2. Switch

Function: Connects multiple devices within the same network and forwards data based on MAC addresses.
Example: A 24-port switch in a company office network.
Protocols:
- Ethernet (802.3) for data transfer.
Difference from Hub: Unlike a hub, a switch does not broadcast data to all connected devices. It sends data only to the intended device, improving efficiency.

3. Modem

Function: Converts digital signals from a computer into analog signals for transmission over a phone line or cable.
Example: Cable modem that connects to a home broadband internet connection.
Types:
- DSL Modem: Used for internet access over telephone lines.
- Cable Modem: Used for broadband access over coaxial cables.

4. Hub

Function: A basic networking device that broadcasts data to all connected devices.
Example: Older networks used hubs before the advent of switches.
Disadvantages: Data is sent to all devices, leading to network congestion and collisions.

5. Access Point (AP)

Function: Provides wireless access to a wired network. Extends the wireless coverage of a network.
Example: A wireless access point in a coffee shop to provide free Wi-Fi to customers.
Protocols: Uses WPA2 or WPA3 for encryption and security.

4. Setting IP Addresses

An IP address (Internet Protocol address) is a unique string of numbers assigned to each device connected to a network. It identifies the device on the network and allows communication between devices.

Setting an IP address involves configuring the device's network interface card (NIC) with a static or dynamic IP address. There are two types of IP addressing:

Static IP address: A fixed IP address assigned manually to a device. It doesn’t change unless manually reconfigured. It's used for devices that need constant access (e.g., servers, printers).
Dynamic IP address: Assigned automatically by a DHCP (Dynamic Host Configuration Protocol) server when the device joins the network. It can change over time, as the DHCP server allocates different addresses to devices as needed.

Configuring an IP address on a device typically involves:

Accessing network settings (either through the operating system or router).
Manually entering the static IP or enabling DHCP to obtain an address automatically.
Configuring subnet masks and gateways if using static IP.

6. Sharing Files and Folders

File sharing allows users on a network to access files and folders stored on another computer. This can be done in several ways:

Network Sharing: In a Windows environment, files and folders can be shared over the network by right-clicking on the folder, selecting 'Properties,' and configuring sharing settings. The shared folder is made accessible to other computers on the same network, which can then view or modify the content based on permissions.
SMB (Server Message Block): Commonly used for sharing files in Windows environments. It allows for shared access to files and printers over a network.
NFS (Network File System): A protocol used mainly in UNIX/Linux systems for sharing files.

Steps to share a folder on Windows:

Right-click the folder you want to share.
Choose 'Properties' and go to the 'Sharing' tab.
Enable 'Share this folder' and adjust permissions for read/write access.
Other users on the same network can now access the shared folder.

7. Remote Login

Remote login allows a user to access a computer from a distant location over a network. This is typically done through command-line interfaces or graphical interfaces.

SSH (Secure Shell): A protocol used to securely log into another computer over a network. SSH encrypts all communication between the client and the server to protect data integrity. It is mainly used for managing servers and performing administrative tasks remotely.
RDP (Remote Desktop Protocol): A protocol that provides a graphical interface to connect to another computer over a network. It is commonly used in Windows environments to log in remotely.
VNC (Virtual Network Computing): Allows graphical desktop sharing. It's platform-independent and used for remote control of another computer.

To remote login via SSH:

Install an SSH client (like PuTTY) on the client machine.
Ensure the remote server has an SSH server installed and running.
Use the SSH client to connect to the server by specifying the IP address or hostname of the server, along with the login credentials.

8. SSH (Secure Shell)

SSH is a cryptographic network protocol used for securely accessing a device over an unsecured network. It's used mainly for:

Logging into remote servers or devices.
Running commands on remote machines.
Securely transferring files (using SFTP or SCP).

Key features of SSH:

Encryption: Encrypts all traffic between the client and server, preventing eavesdropping and man-in-the-middle attacks.
Authentication: Supports password-based or public key-based authentication, adding layers of security.
Port Forwarding: Allows secure forwarding of network ports over SSH, making it useful for bypassing firewalls or creating secure tunnels.

Basic SSH Command:

ssh username@hostname_or_IP

9. Wireless Security (HTTP vs HTTPS)

Wireless security primarily concerns protecting the confidentiality and integrity of data transmitted over wireless networks. The difference between HTTP and HTTPS is crucial when considering web security:

HTTP (Hypertext Transfer Protocol): The standard protocol for transferring web pages over the internet. However, it does not encrypt data between the client and the server, making it susceptible to eavesdropping, tampering, and man-in-the-middle attacks.
HTTPS (Hypertext Transfer Protocol Secure): An extension of HTTP but with added security. It encrypts the data using SSL/TLS (Secure Sockets Layer/Transport Layer Security), ensuring that the communication between the browser and the server is secure. HTTPS is essential for protecting sensitive information, such as login credentials, credit card numbers, etc.

Wireless Network Security:

Ensure that your router is configured with strong WPA2 or WPA3 encryption.
Disable WPS (Wi-Fi Protected Setup) and use a strong, unique password for your wireless network.
Always use HTTPS for secure communication over the internet.

10. Client-Server Model

The client-server model is a network architecture where clients (users or devices) request services or resources from a server. Servers are typically more powerful machines that provide services to multiple clients.

Components:

Client: A device or software that makes requests for resources (e.g., web browsers, email clients).
Server: A machine or application that provides resources or services to clients (e.g., web servers, database servers).

Example: A user using a web browser (client) to access a website hosted on a web server. The server processes the request and returns the requested web page.

Key features:

Centralized resources: Servers often host resources like files, applications, or databases.
Scalability: New clients can easily join the network, and servers can be scaled to accommodate more clients.

11. Types of Servers

Different types of servers perform specific roles in a network or an organization:

Proxy Server: A server that acts as an intermediary between a client and another server. It is used to filter requests, provide caching, and hide client details. Proxies can improve security, performance, and anonymity.
Application Server: A server that hosts applications and serves them to client devices. It provides an environment for running business logic and data processing, often used in multi-tier application architectures (e.g., web applications).
Web Server: A server that serves web pages to clients using the HTTP/HTTPS protocols. It processes client requests (e.g., from web browsers) and returns HTML files, images, or data.
File Server: A server responsible for storing and managing files and making them available to users on a network. It provides centralized storage and access control for shared files.
Database Server: A server that stores and manages databases. Clients can query the database to retrieve, insert, update, or delete data. Common examples include MySQL, SQL Server, and Oracle databases.
Synchronization Server: A server that ensures data consistency across multiple devices or locations. For example, a synchronization server can keep data in sync between mobile devices and a central database, ensuring that all devices have the latest information.
Log Server: A server that collects, stores, and analyzes log files generated by other servers or applications. It is used for troubleshooting, monitoring performance, and ensuring security compliance.

12. Security Essentials

1. Basic Security Threats

Malware:
- Viruses: Self-replicating programs that attach themselves to other programs (e.g., ILOVEYOU virus).
- Worms: Malware that spreads without user intervention (e.g., Conficker worm).
- Trojan Horses: Malware disguised as legitimate software (e.g., Zeus Trojan for banking fraud).
- Ransomware: Encrypts user data and demands payment for decryption (e.g., WannaCry ransomware attack).
Phishing:
- Description: Fraudulent attempt to acquire sensitive information by pretending to be a trustworthy entity, typically via email.
- Example: An email from a bank asking users to click a link to verify their account details (a fake website designed to steal credentials).
Social Engineering:
- Description: Manipulating individuals into divulging confidential information through deception.
- Example: An attacker calls pretending to be IT support and convinces an employee to reveal their password.
Password Cracking:
- Techniques:
  - Brute Force: Trying every possible combination of characters until the correct one is found.
  - Dictionary Attack: Using a precompiled list of common passwords.
  - Rainbow Tables: Precomputed hash values for cracking passwords efficiently.

2. Password Management

Password Complexity:
- Strong passwords should have at least 12 characters, using a combination of uppercase, lowercase, numbers, and special symbols (e.g., W1nter@2024!).
- Password policies should enforce complexity and regular changes (every 60-90 days).
Changing Default Passwords:
- Default passwords (e.g., admin/admin) are common and can be easily guessed or found in manuals. Always change them after setup.

3. Open Wi-Fi vs. Secure Wi-Fi

Open Wi-Fi:
- Unprotected network, usually found in public spaces.
- Risks: Vulnerable to Man-in-the-Middle attacks, data interception.
Secure Wi-Fi (WPA2/WPA3):
- WPA2 and WPA3 protocols encrypt data transmitted over the network, preventing unauthorized access.
- WPA3: Offers stronger security than WPA2, including protection against offline dictionary attacks.

4. Multi-Factor Authentication (MFA)

Description: MFA requires two or more forms of identification:
- Something you know (Password).
- Something you have (Smartphone, hardware token).
- Something you are (Biometrics).
- Example: Logging into a banking app using both your password and a fingerprint scan.

5. Admin vs. User vs. Guest Accounts

Admin Accounts: Full control of the system, can install software and change system settings.
User Accounts: Limited control, only allows users to perform everyday tasks (e.g., web browsing, file access).
Guest Accounts: Temporary accounts with the least privileges, typically used by visitors who don’t need access to sensitive data.