1. The OSI Model 🌐
The 7-layer framework you MUST memorize. "Please Do Not Throw Sausage Pizza Away"
| Layer | PDU | Function | Examples |
|---|---|---|---|
| 7. Application | Data | Network process to application | HTTP, DNS, SMTP |
| 6. Presentation | Data | Encryption, formatting | SSL, JPEG |
| 5. Session | Data | Interhost communication | NetBIOS |
| 4. Transport | Segment | End-to-end connection, reliability | TCP, UDP |
| 3. Network | Packet | Routing, logical addressing (IP) | IP, ICMP, Routers |
| 2. Data Link | Frame | Physical addressing (MAC) | Ethernet, Switches |
| 1. Physical | Bit | Media, signal, binary transmission | Cables, Hubs |
2. IP Addressing 🔢
IPv4: 32-bit address. Dotted decimal (192.168.1.1).
IPv6: 128-bit address. Hexadecimal.
Subnetting
Borrowing bits from host ID to create networks.
CIDR (Classless Inter-Domain Routing) uses /notation (e.g., /24 means 24 bits for network, 8 bits for host).
3. CIA Triad of Security 🔒
Confidentiality
Only authorized access. Tools: Encryption, MFA.
Integrity
Data is accurate/unaltered. Tools: Hashing, Checksums.
Availability
Data is accessible when needed. Tools: Redundancy, DDoS protection.
4. Cryptography 🗝️
- Symmetric: Same key for encryption and decryption. Fast. (AES, DES). Issue: Key exchange.
- Asymmetric (Public Key): Public key encrypts, Private key decrypts. Secure key exchange. (RSA, ECC). Slow.
- Hashing: One-way transformation. Unique fingerprint. (SHA-256, MD5). Used for passwords and integrity.