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| Layer | Name | Function | Protocols/Devices |
|---|---|---|---|
| 7 | Application | User interface | HTTP, FTP, SMTP, DNS |
| 6 | Presentation | Data format, encryption | SSL/TLS, JPEG, ASCII |
| 5 | Session | Connection management | NetBIOS, RPC |
| 4 | Transport | End-to-end delivery | TCP, UDP |
| 3 | Network | Logical addressing, routing | IP, ICMP, Routers |
| 2 | Data Link | Physical addressing, framing | Ethernet, MAC, Switches |
| 1 | Physical | Bits on wire | Cables, hubs, signals |
| Class | First Octet | Default Mask | Private Range |
|---|---|---|---|
| A | 1-126 | 255.0.0.0 (/8) | 10.0.0.0 - 10.255.255.255 |
| B | 128-191 | 255.255.0.0 (/16) | 172.16.0.0 - 172.31.255.255 |
| C | 192-223 | 255.255.255.0 (/24) | 192.168.0.0 - 192.168.255.255 |
/24 = 255.255.255.0 (256 IPs)
Each additional bit halves the addresses: /25=128, /26=64, /27=32