The goal of a Network is to allow data sharing among hosts.
The OSI model is a definition of a networking system which ensures data-sharing among hosts is attained.
7 Layers
They are usually represented in reverse order (Application -> Physical).
- Physical: Transporting bits
- Data exists in form of bits 1-0
- What transports this data from a to b
- Ex: Cables, Wifi, Repeaters, Hubs are layer 1 tech
- Data Link: Hop-to-hop
- Interacts with layer 1, puts bit in the wire and retrieves bits from the wire
- whatever connects to the wire is considered a layer 2 item
- Ex: NIC Network Interface Card / Wi-Fi access cards
- MAC addressing schemes: 48 bit represented as 6 octet hex digits:
94-65-9C-3B-8A-E5(windows like)94:65:9C:3B:8A:E5(linux like)9465.9C3B.8AE5(cisco routers and switches like)
- Every NIC has a unique MAC address
- Switches belong to layer 2
- Communication between two remote hosts require multiple hop between many routers, each hop is achieved by layer 2
- Each router has one NIC per port
- Network: End-to-End
- Makes sure that each hop in layer 2 end up forming a complete end-to-end communication between two remote hosts
- This is done through IP addresses, 32 bits represented as 4 octets.
- Ex: Routers, Hosts, anything with an IP address is considered layer 3 tech
- Transport
- Session
- Presentation
- Application