OSI Model Flashcards
What’s the OSI Model?
Open Systems Interconnection Reference Model
Layer 7
Application Layer
Layer 1
Physical Layer
Layer 6
Presentation Layer
Layer 2
Data Link Layer
Layer 5
Session Layer
Layer 3
Network Layer
Layer 4
Transport Layer
What relation does the OSI Model have with the OSI Protocol Suite?
The OSI model was based around the protocols in the OSI Protocol Suite; however, most of them didn’t catch on. Nowadays we mainly use the TCP/IP protocol.
What’s a good mnemonic for memorizing the 7 Layers of the OSI model?
All
People
Seem
To
Need
Data
Processing
Physical Layer
Layer 1
- physics of the network (no protocols)
- Signaling, cabling, fiber, connectors
- “physical layer problem”
- Fix cabling, punch-downs, connectors
- Run loopback tests, test/replace cables, swap adapter cards
Data Link Layer
Layer 2
- The basic network language
- the foundation of communication at the data link layer
- Data Link Control (DLC) protocols
-MAC (Media Access Control) address on Ethernet, also referred to as Layer 2 addresses because they correlate back to DLC protocols
- The “Switching” layer
- Frame, MAC Address, Extended Unique Identifier (EUI-48, EUI-64), Switch
Network Layer
Layer 3
- The “routing” layer
- layer associated with Internet Protocol (IP) addresses
- Fragments frames to traverse different types of networks
- e.g., Ethernet -> WAN -> Ethernet, this occurs at Layer 3
- Router, Packet
Transport Layer
Layer 4
- The “post office” layer (how and where)
- Transmission Control Protocol (TCP) segment and User Datagram Protocol (UDP) datagram
- port numbers
- e.g., accessing a large webpage where it can’t be sent via a single frame and is split into multiple pieces and put back together on the other side
Session Layer
Layer 5
- Communication management between devices
- Start, Stop, Restart between endpoints
- Control protocols, tunneling protocols
Presentation Layer
Layer 6
- Character Encoding
- Application Encryption (SSL/TLS)
- Often Combined with the Application Layer (Layer 7) b/c functionality is so closely associated with the ability to use these applications
Application Layer
Layer 7
- The Layer we see
- HTTP, FTP, DNS, POP3
Packet Capture Application
- Wireshark
- Summary View, w/ ea. Line showing a frame going across the network
- detail view, each part of the communication broken up into the OSI layers for a frame
- 5,6,7 layer info grouped together
- Hexadecimal representation of the data
ex. Google Mail describe via OSI Model
- Layer 7: https://www.mail.google.com
- Layer 6: SSL encryption
- Layer 5: Link the presentation to the transport
- Layer 4: TCP encapsulation, Port 443
- Layer 3: IP encapsulation, Ethernet frames
- Layer 2: Ethernet
- Layer 1: Physical electrical signals
PDU
- Protocol Data Unit
- getting data from one part of the network to the other relies on PDUs
- or Transmission Units
- a different group of data at different OSI layers
- Ethernet operates on a frame of data
- it doesn’t care what’s inside, sends everything within the ethernet frame across (encapsulation)
- IP operates on a packet of data
- inside is TCP data, or UDP data, or some other type but IP doesn’t care
- TCP header or UDP header
- TCP segment
- UDP datagram
Encapsulation and Decapsulation
