Den Dribbles

OSI Layers

June 24, 2019

A quick and dirty on the seven layers of the OSI Model.

OSI Layers in Network Traffic

Layer 1: Physical

Represents the bit-level transmission between network nodes over the connection medium.

Data: Bits across the wire (1s and 0s) as pulse of electricity or light.

Layer 2: Data Link

Data Link Layer handles communications between adjacents network nodes via physical addressing (MAC).

Data: Frames.

Layer 3: Network

Handles routing messages (packets) via the best route to reach its destination based on IP address.

Data: Packets.

Layer 4: Transport

Defines how data will be sent providing validation and security.

Data: Segments.

Layer 5-7: Application, Presentation, Session

Layers 5-7 are typically managed by the application itself, providing the interface for the user to communicate.

Data: Data.

Data in a TCP/IP Example

  • Data Link Layer (2): Frame = Frame Header + Frame Data
  • Network Layer (3): Packet = IP Header + IP Data
  • Transport Layer (4): Segment = TCP Header + Application Data
  • Application Layer (5-7): Data = App Header + User Data

When dealing with subnetting, network masks etc, note that you are working in the Network Layer (layer 3).

A personal blog on all things of interest. Written by Dennis O'Keeffe, Follow me on Twitter