The OSI model

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  • Layer 1 – Physical: The layer that responsible for the layout of cables and devices
  • Layer 2 – Data Link: This is where the Media Access Control (MAC) addresses reside. The data link layer is used to transfer data between between nodes on a portion of a network to the physical layer.
  • Layer 3 – Network: Do you want your packets routed? Well this is the layer where this data in the form of packets is routed across network segments.
  • Layer 4 – Transport: The home of TCP/UDP. The transport layer ensures that the packets are transported reliably and without errors.
  • Layer 5 – Session: The session layer is used to establish sessions between networked devices.
  • Layer 6 – Presentation: Data translator for network devices.
  • Layer 7 – Application: This is where the protocols that hosts use to communicate on a network live. Here’s some Application layer protocols that you would have heard of: Domain Name System (DNS), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Server Message Block (SMB), Network File System (NFS) and Telnet.
Some of the protocols used

The OSI model is more of a general networking model and it most definitely has it’s purpose, but it has largely been replaced by the TCP/IP model AKA the Internet protocol suite. The Internet protocol suite is comprised of 4 layers which include the following:

  • Application layer – SNMP, HTTP/HTTPS, BGP, SMTP, NTP, SSH, Telnet, TLS/SSL, FTP, RDP, BitTorrent, Websocket
  • Transport layer – TCP, UDP
  • Internet Layer – IP (IPv4, IPv6), ICMP, IPsec
  • Link Layer – ARP, Ethernet, WiFi, MAC, PPP