Computer Network Notes

📥 assignment

📥 assignment 1

📥 UNIT 4

📥 UNIT 3

📥 UNIT 1

Computer Networks

Introduction

A computer network is a collection of computers and other devices connected together to share resources and communicate. Networks are essential for modern computing environments.

1. Network Architecture

OSI Model Layers:

• Physical Layer
• Data Link Layer
• Network Layer
• Transport Layer
• Session Layer
• Presentation Layer
• Application Layer

2. Network Protocols

• TCP/IP Protocol Suite
• HTTP/HTTPS
• FTP
• DNS
• SMTP
• POP3

3. Key Concepts

• IP Addressing and Subnetting
• Routing and Switching
• Network Devices (Router, Switch, Gateway)
• Wireless Networks
• Network Security
• VPN and Firewalls

Comprehensive Computer Networks Guide

1. OSI Model - Seven Layers

Layer 1: Physical Layer

• Physical transmission of raw bits
• Physical media: copper cables, fiber optics, wireless
• Hardware components: hubs, repeaters
• Signals: analog, digital, modulation techniques
• Examples: Ethernet cables, WiFi radio waves

Layer 2: Data Link Layer

• Frame-based communication
• MAC (Media Access Control) addressing
• Switches operate here
• Protocols: Ethernet, PPP, HDLC
• Error detection: CRC (Cyclic Redundancy Check)
• ARP (Address Resolution Protocol)

Layer 3: Network Layer

• Routing and logical addressing
• IP (Internet Protocol) operation
• Routers operate here
• IPv4 and IPv6
• ICMP (ping), IGMP (multicast)
• Routing protocols: OSPF, BGP, RIP

Layer 4: Transport Layer

• End-to-end communication
• TCP (Transmission Control Protocol): Reliable, connection-oriented
• UDP (User Datagram Protocol): Unreliable, connectionless
• Ports and sockets
• Flow control and congestion control
• Error checking

Layer 5: Session Layer

• Session establishment, maintenance, termination
• Dialog control
• Token management
• NetBIOS, SOCKS, NFS
• Session recovery

Layer 6: Presentation Layer

• Data translation and encryption
• Character set conversion
• Compression and decompression
• SSL/TLS for encryption
• Image formatting (JPEG, PNG)
• Audio/video codecs

Layer 7: Application Layer

• User applications and services
• HTTP, HTTPS, FTP, SMTP, POP3, DNS, Telnet
• User interfaces
• Email, web browsing, file transfer
• Protocols specific to applications

2. TCP/IP Protocol Suite

IP Protocol (Layer 3)

• IPv4: 32-bit addressing (4.2 billion addresses)
• IPv6: 128-bit addressing (340 undecillion addresses)
• Connectionless, unreliable delivery
• Routing to destination networks
• TTL (Time To Live) for loop prevention

TCP Protocol (Layer 4)

• Reliable, connection-oriented
• Three-way handshake (SYN, SYN-ACK, ACK)
• Flow control with sliding windows
• Congestion control
• Ordered delivery of segments
• Error checking and retransmission

UDP Protocol (Layer 4)

• Connectionless, unreliable
• Low overhead, fast
• Uses: DNS, DHCP, VoIP, video streaming
• No flow control or congestion control

ICMP (Internet Control Message Protocol)

• Error reporting
• Ping functionality (echo requests)
• Traceroute
• Router solicitation

IGMP (Internet Group Management Protocol)

• Multicast group management
• Used for video conferencing and streaming

3. IP Addressing and Subnetting

IPv4 Addressing

• Format: 4 octets (e.g., 192.168.1.1)
• Classes: A, B, C (and deprecated D, E)
• Public vs Private addresses
• Special addresses: Loopback (127.0.0.1), Broadcast

IPv6 Addressing

• 128-bit address (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334)
• Improved routing and multicasting
• Built-in security (IPSec)
• Better auto-configuration

Subnetting

• Dividing networks into smaller subnets
• Subnet mask: Identifies network and host portions
• CIDR notation (/24, /16, etc.)
• Calculating subnets: Address space, broadcasts, usable hosts
• Supernetting: Combining networks

DHCP (Dynamic Host Configuration Protocol)

• Automatic IP address assignment
• Lease-based allocation
• Reduces manual configuration
• Server, relay agent, client model

NAT (Network Address Translation)

• Translating private to public IP addresses
• Port mapping
• Security benefit: hides internal network
• Types: Static NAT, Dynamic NAT, PAT (Port Address Translation)

4. Routing and Switching

Routing Fundamentals

• Forwarding packets based on destination IP
• Routing table: Destination, gateway, metric, interface
• Longest prefix match algorithm
• Static vs Dynamic routing

Dynamic Routing Protocols

Distance-Vector (RIP, EIGRP):

• Routing decisions based on hop count
• Simpler but less efficient
• Slower convergence time

Link-State (OSPF, IS-IS):

• Complete network topology knowledge
• Dijkstra's algorithm
• Faster convergence
• Better for large networks

Path-Vector (BGP):

• Internet-scale routing
• AS-Path selection
• Scalable but complex

Switching Fundamentals

• Layer 2 forwarding using MAC addresses
• Learning MAC addresses: MAC table, aging
• VLAN (Virtual LAN): Logical network segmentation
• Spanning Tree Protocol (STP): Preventing loops
• Switch types: Unmanaged, managed, smart

VLAN

• Logical network segmentation
• Improved security and performance
• Trunk links between switches
• Inter-VLAN routing

5. Network Devices

Router

• Layer 3 device
• Connects different networks
• Makes routing decisions
• NAT and firewall capabilities
• Connects to ISP for Internet access

Switch

• Layer 2 device
• Connects devices on same network
• MAC learning and forwarding
• Full-duplex communication
• Port speed: Fast Ethernet (100 Mbps), Gigabit (1000 Mbps)

Gateway

• Network access point
• Protocol translation
• May operate at multiple layers
• Default gateway for network

Firewall

• Network security device
• Stateless vs Stateful filtering
• Rule-based access control
• Proxy firewall for deep inspection
• Next-generation firewalls (NGF)

Load Balancer

• Distributes traffic across servers
• Health checking
• Session persistence
• Improves reliability and performance

6. DNS (Domain Name System)

DNS Functionality

• Translates domain names to IP addresses
• Hierarchical system
• Root, TLD, authoritative servers
• Recursive and iterative queries

DNS Records

• A: IPv4 address mapping
• AAAA: IPv6 address mapping
• CNAME: Canonical name (alias)
• MX: Mail exchange servers
• TXT: Text records
• NS: Nameserver records
• SOA: Start of Authority
• PTR: Reverse DNS mapping

DNS Resolution Process

1. Query goes to recursive resolver
2. Resolver queries root nameserver
3. Root responds with TLD nameserver
4. TLD responds with authoritative server
5. Authoritative server returns IP address

DNSSEC

• Cryptographic security
• Prevents DNS spoofing
• Digital signatures for records

7. Email Protocols

SMTP (Simple Mail Transfer Protocol)

• Sending emails from client to server
• Port 25, 465 (SSL), 587 (TLS)
• Commands: EHLO, MAIL, RCPT, DATA
• Authentication and encryption

POP3 (Post Office Protocol)

• Retrieving emails from server
• Typically downloads to client device
• Port 110, 995 (SSL)
• Stateless protocol

IMAP (Internet Message Access Protocol)

• More advanced email retrieval
• Keeps emails on server
• Folder management
• Synchronization across devices
• Port 143, 993 (SSL)

8. Wireless Networks

WiFi Standards

• 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.11ax (WiFi 6)
• Frequency bands: 2.4 GHz, 5 GHz, 6 GHz
• Channels and interference
• Speed improvements: 54 Mbps → 11 Gbps (WiFi 6)

WiFi Security

• WEP: Deprecated, insecure
• WPA: TKIP encryption
• WPA2: AES encryption, currently standard
• WPA3: Latest, improved security features
• Pre-shared key (PSK) vs Enterprise authentication

Cellular Networks

• 3G, 4G LTE, 5G
• Mobile broadband
• Cell towers and handoff
• Frequency bands allocation

Bluetooth

• Short-range wireless
• Personal Area Network (PAN)
• Versions: Bluetooth Classic, Bluetooth Low Energy (BLE)
• Pairing and bonding

9. Network Security

Common Threats

• Eavesdropping: Intercepting communications
• Man-in-the-Middle (MITM): Intercepting and altering data
• DoS/DDoS: Overwhelming server with requests
• Malware: Viruses, worms, trojans
• Social engineering: Tricking users

Cryptography Basics

• Symmetric encryption: Same key for encrypt/decrypt
• Asymmetric encryption: Public/private key pair
• Hash functions: MD5, SHA-1, SHA-256
• Digital signatures: Authentication and integrity

SSL/TLS

• Secure communication over internet
• Handshake process: Authentication, key exchange
• Certificates: Issued by Certificate Authorities (CA)
• HTTPS: HTTP over TLS
• TLS 1.3: Latest version

Firewalls

• Packet filtering: Rule-based filtering
• Stateful inspection: Tracking connections
• Application-level gateways: Deep packet inspection
• Zone-based firewalls

VPN (Virtual Private Network)

• Encrypted tunnel over public network
• Remote access security
• Site-to-site connections
• Protocols: PPTP, L2TP, IPSec, SSL/TLS
• VPN types: Access VPN, Intranet VPN, Extranet VPN

Intrusion Detection/Prevention (IDS/IPS)

• Monitoring for malicious activity
• Signature-based detection
• Anomaly-based detection
• Network-based vs Host-based

10. Network Management

SNMP (Simple Network Management Protocol)

• Monitoring and managing network devices
• Agents send information to manager
• MIBs (Management Information Base)
• Traps for alerts
• Versions: SNMPv1 (insecure), SNMPv3 (secure)

Network Monitoring

• Traffic analysis
• Bandwidth monitoring
• Device health checks
• Performance metrics: Latency, packet loss, jitter

Syslog

• Centralized logging
• Message severity levels
• Remote log collection
• Security analysis

11. Quality of Service (QoS)

QoS Parameters

• Bandwidth: Data transfer rate
• Latency: Delay in transmission
• Jitter: Variation in delay
• Packet loss: Dropped packets
• Priority: Importance of data

QoS Mechanisms

• Traffic shaping: Controlling data rate
• Prioritization: Marking traffic priority
• Congestion management
• Link efficiency

12. Network Design

LAN (Local Area Network)

• Limited geographic area
• High speed (100 Mbps - 10 Gbps)
• Low latency
• Ethernet technology

WAN (Wide Area Network)

• Large geographic area
• Lower speed
• Higher latency
• Leased lines, MPLS, Frame Relay

MAN (Metropolitan Area Network)

• City-scale network
• Between LAN and WAN
• WiFi mesh networks

Network Topology

• Star: Central hub
• Bus: Shared medium
• Ring: Circular connections
• Mesh: Multiple connections
• Hybrid: Combinations

13. Troubleshooting Tools

Ping

• Tests reachability
• ICMP echo request/reply
• Measures round-trip time
• Command: ping www.example.com

Traceroute/Tracert

• Shows path to destination
• Hop-by-hop analysis
• Identifies latency issues
• Command: tracert www.example.com

Ipconfig/Ifconfig

• Shows IP configuration
• DNS servers, gateways
• MAC addresses

Netstat

• Network statistics
• Active connections
• Listening ports
• Protocol statistics

Nslookup/Dig

• DNS resolution testing
• Query DNS records
• Troubleshoot DNS issues

14. Learning Path for Computer Networks

1. Understand OSI model layers
2. Learn TCP/IP fundamentals
3. Study IP addressing and subnetting
4. Master routing concepts
5. Explore switching and VLANs
6. Learn DNS and email protocols
7. Understand wireless technologies
8. Study network security
9. Learn management protocols (SNMP)
10. Practice troubleshooting

15. Certifications

• CompTIA Network+
• Cisco CCNA (Certified Cisco Network Associate)
• CCNP (Cisco Certified Network Professional)
• Juniper JNCIA, JNCIS

16. Career Paths

Network Administrator

• Configure and manage networks
• User support
• Basic troubleshooting

Network Engineer

• Design and optimize networks
• Complex troubleshooting
• Project implementation

Network Architect

• Strategic network design
• Enterprise solutions
• Technology selection

For more information and detailed explanations on Computer Network concepts, refer to the study materials above.