Networking: TELNET, SSH, TLS, ARP, DNS

  TELNET, SSH, TLS, ARP, DNS 

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📘 1. TELNET

Full Form: Telecommunication Network
Layer: Application Layer

🔹 What it does:

• Remote login protocol

• Access another computer and run commands

🔹 Features:

• Username + password required

• Gives command-line access to remote system

❌ Problem:

• Sends data (username & password) in plain text

• Easily intercepted (very insecure)

📌 Conclusion:

• Not used in secure networks anymore

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📘 2. SSH

Full Form: Secure Shell
Layer: Application Layer

🔹 What it does:

• Secure remote login

• Execute commands on remote machine

🔹 Features:

• Encrypts username & password

• Supports key-based authentication (more secure)

• Used in:

  • Linux servers

  • Routers & switches

  • Cloud systems

🔐 Key Difference:

• SSH = Secure

• TELNET = Insecure

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📘 3. TLS

Full Form: Transport Layer Security

🔹 What it does:

• Encrypts communication between two devices

• Provides:

  • Encryption

  • Integrity (no data change)

  • Authentication

🔹 Layer:

• Works between Transport & Application layer

• Practically considered Application Layer

🔹 Why needed:

Without TLS:

• Passwords, messages, card info → plain text

• Hackers can read data

🔹 Where used:

1. HTTPS websites

2. Mobile apps (API communication)

3. Email security (SMTP, IMAP, POP3 with TLS)

🔹 How it works (simple):

1. Client requests secure connection

2. Server sends certificate

3. Verify certificate

4. Create shared key

5. Start encrypted communication

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📘 4. ARP

Full Form: Address Resolution Protocol
Layer: Network / Data Link

🔹 What it does:

• Converts IP address → MAC address

• Required for communication inside LAN

🔹 Why needed:

• IP = logical address

• MAC = physical address

• Data transmission needs MAC

🔹 How it works:

1. Check ARP cache

2. If not found → Broadcast request

   • “Who has this IP?”

3. Target replies with MAC

4. Store in ARP table

🔹 Important:

• Uses broadcasting

• Works only in local network

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📘 5. DNS

Full Form: Domain Name System
Layer: Application Layer

🔹 What it does:

• Converts Domain name → IP address

• Example:

  • google.com → 8.8.8.8

🔹 Why needed:

• Humans remember names, not numbers

🔹 Features:

• Hierarchical system (servers, zones)

• Uses caching for faster response

🔹 Components:

• Domain

• Subdomain

• DNS servers

🔹 Example:

• mail.google.com → subdomain

• google.com → domain

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🔥 Quick Comparison (Exam Shortcut)

Protocol	Purpose	Security	Layer
TELNET	Remote login	❌ No encryption	Application
SSH	Secure remote login	✅ Encrypted	Application
TLS	Secure data transmission	✅ Encrypted	App/Transport
ARP	IP → MAC mapping	❌ No encryption	Network/Data Link
DNS	Domain → IP	❌ (basic)	Application

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🎯 Super Important MCQ Points

• TELNET → plain text (insecure)

• SSH → encrypted remote login

• TLS → used in HTTPS

• ARP → IP → MAC conversion

• DNS → Domain → IP conversion

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