Computer Networks
CN Part-1
- What is a Computer Network?
- Goals and Applications of Computer Networking
- Computer Network Components
- Types of Computer Networks
- Network Topology
- Difference between Client Server and Peer to Peer Network
- Layered Architecture in Computer Networks
- Protocol Hierarchy in Computer Networks
- Interfaces and Services in Computer Networks
- Connection Oriented and Connectionless Services
- Service Primitives
- OSI Model
- TCP/IP Model
- Difference between OSI Model and TCP/IP Model
- Encapsulation and Decapsulation in Computer Networks
- Queueing Models in Computer Network
CN Part-2
- Physical Layer in Computer Networks
- Transmission Media in Computer Networks
- Analog and Digital Signals
- Data Rate and Bandwidth
- Encoding Techniques
- Multiplexing in Computer Networks
- Transmission Modes in Computer Networks
- Data Link Layer
- Framing in Data Link Layer
- Flow Control in Data Link Layer
- Error Control in Data Link Layer
- Error Detection and Correction in Computer Networks
- Stop and Wait Protocol
- Sliding Window Protocol
- SDLC(Synchronous Data Link Control) Protocol
- High-Level Data Link Control (HDLC) Protocol
- Point-to-Point Protocol (PPP)
CN Part-3
- MAC Sublayer and MAC Addressing
- Channel Allocation Methods
- ALOHA Protocol (Pure and Slotted ALOHA)
- CSMA/CD and CSMA/CA in Computer Networks
- Ethernet (IEEE 802.3)
- Wireless LANs (IEEE 802.11, Wi-Fi, and Bluetooth Basics)
- Network Layer and Design Issues
- IPv4 and IPv6 Protocols
- Addressing: IP Address, Subnetting, and Supernetting
- Routing Algorithms: Static vs Dynamic, Distance Vector, and Link State
- Routing Protocols: RIP, OSPF, and BGP
- Packet Switching and IP Fragmentation
- Network Layer Protocols: ICMP, ARP, RARP, DHCP, and NAT
CN Part-4
- Transport Layer and Functions
- Process-to-Process Delivery, Ports, and Sockets
- TCP Segment and Three-Way Handshake Connection Establishment
- UDP (User Datagram Protocol): Format and Features
- Flow Control and Error Control in Transport Layer
- Congestion Control: Leaky Bucket, Token Bucket, and TCP Congestion Control
CN Part-5
- Application Layer Architecture and Principles
- Domain Name System (DNS)
- Email Protocols: SMTP, POP3, and IMAP
- File and Web Protocols: FTP, HTTP, and HTTPS
- Remote Access Protocols: Telnet and SSH
- World Wide Web (WWW) and Web Architecture
- Network Security Basics: SSL, TLS, and Cryptography Fundamentals
Remote Access Protocols: Telnet and SSH in Computer Networks
Remote Access Protocols kya hote hain?
Remote Access Protocols ek administrator ya user ko kisi door sthit remote server, router, ya switch par Command Line Interface (CLI) session open karke commands execute karne ki suvidha dete hain.
Imagine kijiye aap Delhi mein baithe hain aur aapko California ke data center mein sthit Linux server par software install karna hai ya router configure karna hai. Aap Telnet ya SSH ke zariye remote login karte hain.
1. Telnet (Teletype Network)
Telnet 1969 mein develop hua ek puraana remote terminal protocol hai (RFC 854).
Yeh TCP Port 23 par kaam karta hai.
Critical Security Flaw (Telnet ka Khatra!):
Telnet 100% Plaintext (Unencrypted) communication use karta hai. Jab aap Telnet par login karte hain, toh aapka username aur password character-by-character unencrypted cable par travel karta hai. Agar koi hacker Wi-Fi par Wireshark ya packet sniffer run kar raha ho, toh wo aapka password screen par as-it-is dekh sakta hai!Is security risk ki wajah se modern production networks aur internet par Telnet completely banned aur obsolete ho chuka hai.
2. SSH (Secure Shell)
SSH (Secure Shell) ko Telnet ki security flaws ko replace karne ke liye 1995 mein Tatu Ylönen ne design kiya tha (RFC 4251).
Yeh TCP Port 22 par kaam karta hai aur remote server administration ka de facto global industry standard hai.
SSH strong Cryptographic Encryption use karta hai, jisse transmission ke dauran network par sirf unreadable ciphertext dikhta hai.
Key Security Features of SSH:
-> Strong Encryption: Symmetric encryption (AES, ChaCha20) ke zariye session data encrypt hota hai.
-> Public-Key Authentication: Password ke bajaye SSH Key Pairs (Private Key on client, Public Key on server) use karke passwordless secure login support karta hai.
-> Data Integrity: HMAC (Hash-based Message Authentication Code) use karta hai taaki transmission mein packet tampering na ho sake.
-> Port Forwarding & Tunneling: SSH ke andar doosre insecure protocols (jaise database traffic ya VNC) ko securely tunnel kiya ja sakta hai (SSH Tunneling).
Telnet vs SSH Comparison (Exam High-Yield!)
| Feature | Telnet | SSH (Secure Shell) |
|---|---|---|
| Default Port | TCP Port 23 | TCP Port 22 |
| Security & Encryption | No encryption (Plaintext). Highly vulnerable to sniffing. | End-to-End Cryptographic Encryption (AES). Fully secure. |
| Authentication Method | Plaintext Username & Password only. | Public Key / Private Key Pairs, Passwords, Kerberos. |
| Overhead | Low bandwidth & CPU overhead. | Moderate CPU overhead due to cryptographic handshake. |
| Current Status | Obsolete / Deprecated in production. | Current industry standard for server & cloud administration. |
Summary Table
| Protocol | Summary |
|---|---|
| Telnet | Port 23 plaintext CLI access. Insecure and strictly avoided today. |
| SSH | Port 22 encrypted shell access with public key authentication and tunneling capabilities. |