OSI 7-layer model

OSI

Open Systems Interconnection Reference Model

• Describes the broad overview (not the details) of how data traverses our networks
• NOT the OSI protocol suite
  • but we can apply to many different protocols & it works perfectly with the TCP/IP protocols we use today
• There are unique protocols at every layer of the OSI layer

• When we’re talking with other ppl we can refer to the issues to specific layers so they know exactly what we’re talking about
• As data is passed down the OSI model, it’s encapsulated into more and more components
• Anything below the point that you are communicating with is abstracted away

Networking Stack

All People Seem To Need Data Processing Please Do Not Throw Sausage Pizza Away

• diagram
  • Host layer
    • how the data is chopped & reassembled for transport
    • how the data is formatted for both sides of the network connection
  • Media layer
    • how data is moved between point A and B (in the same local network or across the internet)
• The software that does each of these functions(layers) → networking stack
  • your phone, laptop, wifi, the server has a network stack
• A layer X device means that it has the capabilities of layer X AND below

Layer 7: Application

• The layer we see on our screen
• common operations that operate here
  • HTTP, FTP, DNS, POP3

Layer 6: Presentation

• Putting all data we can read & understand
  • character encoding
  • application encryption
• often combined with the application layer
• Layer 5 - Session
• Layer 4 - Transport
• Layer 3 - Network
• Layer 2 - Data Link
• Layer 1 - Physical

Diagram

OSI model to real world

Layers
7: Application	Your eyes
6: Presentation	Application Encryption (SSL/TLS)
5: Session	Control protocols, tunneling protocols
4: Transport	TCP segment, UDP datagram
3: Network	IP address, router, packet
2: Data Link	MAC address, Frame, Switch, Extended Unique Identifier (EUI-48, EUI-64)
1: Physical	Cables, fiber, and the signal itself

Wireshark

• lets u capture the data in your network
• 3 screens
  • 1st - frame by frame breakdown
  • 2nd - more detail in the single frame
  • 3rd - hexadecimal & ASCII breakdown of the data