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.
OSI Model & TCP/IP
NoteTransport Layer is the heart of OSI
OSI - 7
ARP
Convert IP to MAC
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