Logo

VPN & Types

 Secured tunnel (protected network) between different networks using the internet (public network)

Access VPN: Provide connectivity to remote mobile users and telecommuters Site to Site VPN: Large companies having branches in different locations to connect the network of one office to another in different locations. It can be Intranet or Extranet

SMTP

Send-to-End and Store-and-Forward methods. Default: port 25.
Protocol for Mail Transfer across servers.

Pasted image 20240809004242.png

OSI Model & TCP/IP

Note

Transport Layer is the heart of OSI

OSI - 7

Pasted image 20240809004254.png

ARP

Convert IP to MAC Pasted image 20240809004528.png

What happens when you enter google.com in the web browser?

  • Check the browser cache first if the content is fresh and present in cache display the same.
  • If not, the browser checks if the IP of the URL in cache (browser and OS) if not then request the OS to do a DNS lookup using UDP to get the corresponding IP address of the URL from the DNS server to establish a new TCP connection.
  • A new TCP connection is set between the browser and the server using three-way handshaking.
  • An HTTP request is sent to the server using the TCP connection.
  • The web servers running on the Servers handle the incoming HTTP request and send the HTTP response.
  • The browser process the HTTP response sent by the server and may close the TCP connection or reuse the same for future requests.
  • If the response data is cacheable then browsers cache the same.
  • Browser decodes the response and renders the content.

Router vs Gateway

Router: Directs the traffic in the network from source to destination in the form of packets. It operates at the [network layer]
Gateway: The gateways are also used to route and regulate the network traffic but, they can also send data between two dissimilar networks

  • While a router can only send data to similar networks.

Default PORTS

  • HTTP: 80
  • HTTPS: 443
  • SSL: 443 (commonly used with HTTPS)
  • SMTP: 25
  • POP3: 110
  • IMAP: 143
  • FTP: 21 (control), 20 (data)
  • SSH: 22
  • Telnet: 23
  • DNS: 53
  • DHCP:
    • 67 (server)
    • 68 (client)
  • RDP: 3389
  • MySQL: 3306
  • PostgreSQL: 5432
  • ICMP: 7

ICMP

  • Internet Control Message Protocol.
  • Network layer protocol used for error handling.
  • Used by network devices like routers for diagnosing the network connection issues and crucial for error reporting

© 2025 All rights reservedBuilt with DataHub Cloud

Built with LogoDataHub Cloud