Networking and Remote Management Basics - Linux Class 13

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Common Networking Commands

  • ifconfig: Displays network interface configuration (Linux).
  • ping <ip>: Tests connectivity to a specific IP address.
  • hostname: Shows the system's hostname.
  • nslookup <ip>: Resolves an IP to a hostname.
  • nslookup <hostname>: Resolves a hostname to an IP address.
  • traceroute: Tracks the path network packets take to a destination.
  • netstat: Displays network statistics (connections, ports, etc.).
  • Edit DNS entries: Modify /etc/resolv.conf (e.g., nameserver 8.8.8.8).

Enable/Disable Network Interface

  • Enable: ip link set <port> up (e.g., ip link set eth0 up).
  • Disable: ip link set <port> down (e.g., ip link set eth0 down).

Remote Management Tools

  • Windows to Linux:
    • PuTTY, MobaXterm, SuperPuTTY (uses SSH, Telnet, etc.).
  • Linux to Linux:
  • Windows to Windows:
    • RDP (Remote Desktop Protocol).

Common Port Numbers

  • SSH: 22
  • Telnet: 23
  • HTTP: 80
  • HTTPS: 443
  • FTP: 21
  • SFTP: 22

What is a Port Number and Its Impact on Connectivity?

A port number is a 16-bit number (0-65535) that identifies specific services or applications on a device within a network. It works with an IP address to route traffic to the correct process.

  • Examples:
    • Port 80: HTTP (web browsing).
    • Port 443: HTTPS (secure web browsing).
  • Impact: If a port is blocked (e.g., by a firewall) or not open on the target machine, connectivity fails. The port must match the service (e.g., SSH won’t work on port 80).

File Transfer Between Machines

  • Within Linux:
    • cp file1 target_dir: Copy a file.
    • cp -r dir1 target_dir: Copy a directory recursively.
  • Linux to Linux:
  • Windows to Linux:
    • WinSCP: GUI tool using SFTP (port 22).
  • Windows to Windows:
    • Copy-paste via RDP (Ctrl+C, Ctrl+V).

Answers to Key Questions

1. Passwordless Login to Remote Host Using SSH

Steps:

  1. Generate SSH key pair: ssh-keygen (press Enter for defaults).
  2. Copy public key to remote host: ssh-copy-id username@ipaddress (e.g., ssh-copy-id [email protected]).
  3. Test: ssh username@ipaddress—no password required.

2. HTTP and HTTPS

  • HTTP: HyperText Transfer Protocol, unencrypted, uses port 80 for web pages.
  • HTTPS: HTTP Secure, encrypted with SSL/TLS, uses port 443.
  • Difference: HTTPS ensures privacy and security with encryption; HTTP does not.

3. What is an API?

An API (Application Programming Interface) is a set of rules and tools allowing software applications to communicate. It acts as a middleman for data exchange (e.g., a weather app fetching data from a server).

4. Different Types of APIs

  • REST: Lightweight, stateless, uses HTTP methods.
  • SOAP: Structured, protocol-based, uses XML.
  • GraphQL: Query-based, flexible data retrieval.
  • RPC: Remote Procedure Call, executes functions remotely.

5. HTTP Methods

  • GET: Retrieve data from a server.
  • POST: Send data to a server (e.g., form submission).
  • PUT: Update existing data on a server.
  • DELETE: Remove data from a server.
  • PATCH: Partially update data on a server.

6. HTTPS Status Codes

  • 200: OK (success).
  • 201: Created (resource created successfully).
  • 400: Bad Request (client error).
  • 401: Unauthorized (authentication required).
  • 403: Forbidden (access denied).
  • 404: Not Found (resource missing).
  • 500: Internal Server Error (server issue).

7. Postman Tool

Postman is a tool for testing APIs. It allows you to:

  • Send HTTP requests (GET, POST, etc.).
  • Test responses (status codes, data).
  • Automate API testing with scripts.
  • Save and organize API requests.