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Delwin Thermitus
03/27/2022
Cyber Security
The OSI Model
-
The Open System Interconnection model is a model for layered communications and
computer network protocol design
...
7 Layers of the OSI Model
1
...
(Physical Structure)
(Coax, Fiber, Wireless, Hubs, Repeaters)
2
...
(Frames) (Ethernet, PPP, Switch, Bridge
...
Network – Defines network addresses in a way that routes can be determined
systemically
...
Transport – transfers data between end users (This is where TCP & UDP live) (End-ToEnd connections)
5
...
It’s also referred to as ‘Port Layer’
...
) (API’s, Sockets,
WinSock
...
Presentation – Formats the data (e
...
, encryption
...
)
7
...
(Programs that fallout the scope of
the OSI Model
...
) (HTTP, FTP, IRC, SSH, DNS
...
- Guide to understand the flow of data across a network
...
o Reference for the location of protocols
...
- Upper Layer (Host)
o Application
o Presentation
o Sessions
- Lower Layers (Network)
o Transport
o Network
o Data Link
o Physical
-
Common Mnemonics
o (A)ll (P)eople (S)eem (T)o (N)eed (D)ata (P)rocessing
...
Physical – Layer 1
- Physical and Electric components
...
o 1’s & 0’s
...
- Not really about protocols
...
Data Link – Layer 2
- The ‘Switching’ layer
o Logical Link Controls (LLC)
...
o Media Access Control (MAC)
...
- PDU Frames
o Organizes bits into frames
- Protocols
o ARP, Spanning tree protocol token ring, Frame Relay, IEEE(The Institute of Electrical
& Electrical Engineers
...
)
Network – Layer 3
- The ‘routing’ layer
o Path determination
o IP Addresses
o IP Fragments
- PDU : Packets
o Packets can be fragmented for specific bandwidth constraints between routers
...
- Hardware
o Routers
Transport – Layer 4
- Protocols
o TCP (Transmission Control Protocol
...
o UDP (User Datagram Protocol
...
- The ‘post office’ layer
o Port numbers
...
o End-to-end service
...
o Flow control
...
- PDU: Segments/ Datagrams
o TCP Segments
...
o Syncs multiple transport layer connections and send them to ports
...
o Encodes/ translates data
...
o Compresses data
...
- Protocols:
o SSL, TLS, MIME
...
Application – Layer 7
- End – User layer
o Human – Computer Interaction
...
o Or create what will be sent
- Where apps access Network Services
- Protocols
o HTTP/S, DNS, SMTP, Email, FTP, Telnet, SSH
- Software
o Browsers, Email clients, User Apps