TIL How to remember the OSI Model
POSTED ON:
TAGS: network certifications
You can remember using this mnemonic:
"Please do not throw Sausage Pizza, Asshole."
Layers:
Layer 1 - Physical
Layer 2 - Datalink
Layer 3 - Network
Layer 4 - Transfer
Layer 5 - Session
Layer 6 - Presentation
Layer 7 - Application
"Bitcoin for Professional Souls-players"
Bits
Frames
Packets
Sessions
Some random things to remember: #
Layer 1 - Hubs, Repeaters and ethernet wires
Layer 2 - Switches, and Bridges
Layer 3 - Routers (Switches can also be Level 3)
Differences
Layer 1 - Physical Link
- Repeaters copies the data over. It's a 2-port device.
- Hubs are just multiport repeaters.
Layer 2 - Data Link
- Bridges is like a repeater, but can filter MAC Addresses. It's also a 2-port device.
- Switches is like a multiport Bridge, but has buffer/effient tools. Like it doesn't forward damaged packets, and forwards to the correct port. It divides the collision domain, but keeps the broadcast domain.
A 24-port unmanaged switch creates 24 collision domains, but 1 broadcast domain. (unmanaged means Layer 2)
Layer 3 - Network
- Routers is like a switch, but uses IP addresses. It divides into broadcast domains.
Switches can also be a Layer 3. It would be called a 'managed' switch, and would provide routing/break apart broadcast domains.
Encapsulation
Data is encapsulated going up, and de-capsulated going down.
Your browser sends data, and it gets encapsulated... all the way down to Layer 1, where it gets sent over the wire.
Anything above Layer 3 relies on knowing the packet type. Firewalls, for example. or ACL to block things. They need to be done on a higher level.
Collision Domain vs Broadcast Domains #
Collision domain is a domain where:
- packet collision can occur.
- traffic flows forward and backwards
Broadcast Domain is a domain where:
- A logical division of a network
- All ports on a router are in distinct broadcast domains
Routers kill broadcasts. They don't bring them anywhere.
Via
https://www.guru99.com/collision-broadcast-domain.html
Related TILs
Tagged: network