OSI Model: Difference between revisions
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== OSI Layer Overview == | == OSI Layer Overview == | ||
The OSI model goes from Layer 1 (bottom) to Layer 7 (top). Each layer | The OSI model goes from Layer 1 (bottom) to Layer 7 (top). Each layer depends on the functionality of the ones above and below it. Knowing what happens at each layer helps in analyzing protocols, spotting weaknesses, and understanding where specific tools operate. | ||
{| class="wikitable" | {| class="wikitable" | ||
! Layer !! Number !! What it does !! | ! Layer !! Number !! What it does !! Common Examples | ||
|- | |- | ||
| Application || 7 || | | Application || 7 || Interfaces with user applications and defines network services || HTTP, HTTPS, DNS, FTP, SMTP, IMAP, SSH, Telnet | ||
|- | |- | ||
| Presentation || 6 || Translates and | | Presentation || 6 || Translates, encrypts, and compresses data for the application layer || TLS/SSL, ASCII, JPEG, MPEG, GZIP, Base64 | ||
|- | |- | ||
| Session || 5 || | | Session || 5 || Manages and maintains sessions between systems || NetBIOS, RPC, SMB, PPTP, SOCKS | ||
|- | |- | ||
| Transport || 4 || | | Transport || 4 || Provides reliable or fast delivery of data streams || TCP, UDP, SCTP, QUIC | ||
|- | |- | ||
| Network || 3 || | | Network || 3 || Handles routing and logical addressing across networks || IP, ICMP, IGMP, IPsec, BGP, OSPF | ||
|- | |- | ||
| Data Link || 2 || | | Data Link || 2 || Transfers frames between directly connected devices using MAC addressing || Ethernet, ARP, PPP, VLAN (802.1Q), LLDP | ||
|- | |- | ||
| Physical || 1 || Moves | | Physical || 1 || Moves electrical or optical signals across physical media || Ethernet (cabling), Wi-Fi (802.11), fiber optics, hubs, radio signals | ||
|} | |} | ||
== Easy Breakdown by Layer == | == Easy Breakdown by Layer == | ||
Each layer in the OSI model has a specific role. Together, they describe how data moves across a network — from your device to another system, step by step. | |||
=== Layer 1 – Physical === | === Layer 1 – Physical === | ||
Moves raw | |||
Involves | Moves raw bits (0s and 1s) over cables or air. | ||
Involves physical elements like Ethernet cables, fiber optics, and Wi-Fi signals. | |||
Example: When you plug in a network cable or connect to Wi-Fi, Layer 1 is active. | |||
=== Layer 2 – Data Link === | === Layer 2 – Data Link === | ||
Uses: MAC | Connects devices on the same local network. | ||
Uses MAC addresses to make sure data reaches the right device. | |||
Example: Your router sends a frame to your laptop using its MAC address. | |||
=== Layer 3 – Network === | === Layer 3 – Network === | ||
Routes data between networks. | |||
Uses IP addresses to find the best path for packets. | |||
Example: Sending a ping to a website shows Layer 3 in action. | |||
=== Layer 4 – Transport === | === Layer 4 – Transport === | ||
TCP | Ensures complete delivery of data. | ||
Splits information into segments and reassembles them correctly. | |||
Example: TCP guarantees a webpage loads fully, UDP is used for faster but less reliable connections like video calls. | |||
=== Layer 5 – Session === | === Layer 5 – Session === | ||
Keeps | |||
Manages the start, duration, and end of communication sessions. | |||
Keeps track of active connections between systems. | |||
Example: Maintaining a stable connection while using SSH or video conferencing. | |||
=== Layer 6 – Presentation === | === Layer 6 – Presentation === | ||
Handles | Makes data readable and secure. | ||
Handles file formats, encryption, and compression. | |||
Example: TLS secures your connection when using HTTPS, and JPEG ensures images display correctly. | |||
=== Layer 7 – Application === | === Layer 7 – Application === | ||
Connects software to the network. | |||
Defines how user-facing programs communicate over the network. Often includes a graphical user interface (GUI) for interacting with network services. | |||
Example: Opening a website in a browser (HTTP), sending an email from an app (SMTP), or resolving a domain name using DNS. | |||
== What You Can Do with It == | == What You Can Do with It == | ||
Latest revision as of 17:59, 7 June 2025
OSI Model[edit | edit source]
The OSI model explains how data travels through a network. It splits this process into **seven layers**. Each layer has its own job — from moving raw bits to showing a website.
Understanding the OSI model helps break down complex systems, and shows where tools, attacks, or failures happen.
OSI Layer Overview[edit | edit source]
The OSI model goes from Layer 1 (bottom) to Layer 7 (top). Each layer depends on the functionality of the ones above and below it. Knowing what happens at each layer helps in analyzing protocols, spotting weaknesses, and understanding where specific tools operate.
| Layer | Number | What it does | Common Examples |
|---|---|---|---|
| Application | 7 | Interfaces with user applications and defines network services | HTTP, HTTPS, DNS, FTP, SMTP, IMAP, SSH, Telnet |
| Presentation | 6 | Translates, encrypts, and compresses data for the application layer | TLS/SSL, ASCII, JPEG, MPEG, GZIP, Base64 |
| Session | 5 | Manages and maintains sessions between systems | NetBIOS, RPC, SMB, PPTP, SOCKS |
| Transport | 4 | Provides reliable or fast delivery of data streams | TCP, UDP, SCTP, QUIC |
| Network | 3 | Handles routing and logical addressing across networks | IP, ICMP, IGMP, IPsec, BGP, OSPF |
| Data Link | 2 | Transfers frames between directly connected devices using MAC addressing | Ethernet, ARP, PPP, VLAN (802.1Q), LLDP |
| Physical | 1 | Moves electrical or optical signals across physical media | Ethernet (cabling), Wi-Fi (802.11), fiber optics, hubs, radio signals |
Easy Breakdown by Layer[edit | edit source]
Each layer in the OSI model has a specific role. Together, they describe how data moves across a network — from your device to another system, step by step.
Layer 1 – Physical[edit | edit source]
Moves raw bits (0s and 1s) over cables or air.
Involves physical elements like Ethernet cables, fiber optics, and Wi-Fi signals.
Example: When you plug in a network cable or connect to Wi-Fi, Layer 1 is active.
Layer 2 – Data Link[edit | edit source]
Connects devices on the same local network.
Uses MAC addresses to make sure data reaches the right device.
Example: Your router sends a frame to your laptop using its MAC address.
Layer 3 – Network[edit | edit source]
Routes data between networks.
Uses IP addresses to find the best path for packets.
Example: Sending a ping to a website shows Layer 3 in action.
Layer 4 – Transport[edit | edit source]
Ensures complete delivery of data.
Splits information into segments and reassembles them correctly.
Example: TCP guarantees a webpage loads fully, UDP is used for faster but less reliable connections like video calls.
Layer 5 – Session[edit | edit source]
Manages the start, duration, and end of communication sessions.
Keeps track of active connections between systems.
Example: Maintaining a stable connection while using SSH or video conferencing.
Layer 6 – Presentation[edit | edit source]
Makes data readable and secure.
Handles file formats, encryption, and compression.
Example: TLS secures your connection when using HTTPS, and JPEG ensures images display correctly.
Layer 7 – Application[edit | edit source]
Connects software to the network.
Defines how user-facing programs communicate over the network. Often includes a graphical user interface (GUI) for interacting with network services.
Example: Opening a website in a browser (HTTP), sending an email from an app (SMTP), or resolving a domain name using DNS.
What You Can Do with It[edit | edit source]
Understanding the OSI layers helps you:
- Know where a tool or attack operates
- Analyze traffic at the right level
- Identify weak points or misconfigurations
- Work smarter with packet captures, scans, or payloads
Protocols by Layer[edit | edit source]
| Layer | Number | Function Summary | Common Protocols |
|---|---|---|---|
| Application | 7 | Interfaces with apps like browsers and mail | HTTP, FTP, DNS, SMTP |
| Presentation | 6 | Formats, encrypts, and compresses data | TLS/SSL, Base64, JPEG |
| Session | 5 | Manages connections and sessions | NetBIOS, PPTP, SMB |
| Transport | 4 | Ensures reliable or fast delivery | TCP, UDP |
| Network | 3 | Routes packets between networks | IP, ICMP, IPsec |
| Data Link | 2 | Sends frames on the local network | Ethernet, ARP |
| Physical | 1 | Transfers raw bits via cables or air | Wi-Fi (802.11), Ethernet (cabling) |