Networking notes

OSI Model

7 layers that standartize networks

Not used anymore - tcp / ip is used


  • Physical - cable
  • Data link - mac address
  • Network - ip address, routing
  • Transport - TCP / UDP
  • Session - start / stop sessions
  • Presentation - format data, encryption
  • Application - SMTP (email)

TCP/IP model

Created to standartize computer networking

  • Application - application protocols (http, smtp, ftp) - DATA

  • Transport - TCP/UDP protocols - SEGMENT

  • Network - IP - PACKET

  • Data link - ETHERNET - FRAME

  • Physical - Cable



  • Used when good and reliable connection is needed (for example to download files)

  • Two computers ack the connection before it takes place. Three way handshake

    Syn -> Syn Ack -> Ack Received

  • Tcp assigns numbers to data that being sent

  • Receiver calculates checksum and sends to sender

  • Tcp will re-send data if it wasn’t delivered


  • It doesn’t establish a session

  • Fire and forget protocol

  • Udp is faster

  • Live realtime connections - voice call, video calls, gaming

Mac Address

Unique address assigned to network interface card

DNS - domain name system

DNS translates domain name into ip address

  • Check local cache first
  • If it’s not found in local cache - dns resolver
  • If it’s not found in dns resolver - root server
  • Top level domain server


HTTP - data transferred not encrypted

HTTPS - data transferred encrypted

  • a client tries to access an https site

  • a site returns a certificate with public key

  • a client verifies certificate in the certificate authority

  • a client create a new secret key and signs it with the public key in the certificate

  • all communication is encrypted with this private key

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