One-Pager — Networks & Security (P1 Rank 1)

• LAN / MAN / WAN — local / city / wide area
• Topologies: Bus (backbone), Star (hub/switch center), Ring, Mesh (n(n−1)/2 links full), Tree
• Hub = Layer 1 broadcast; Switch = Layer 2 MAC; Router = Layer 3 IP; Gateway = protocol conversion
• OSI: 7 layers — Physical→Data Link→Network→Transport→Session→Presentation→Application
• TCP/IP: Network Access → Internet → Transport → Application
• TCP reliable connection-oriented; UDP fast connectionless
• DNS name→IP; DHCP auto IP; HTTP 80; HTTPS 443; FTP 20/21; SMTP mail send
• Private IP: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
• CIA: Confidentiality, Integrity, Availability
• Firewall filters traffic; VPN secure tunnel; Phishing fake identity; DoS flood service
• Symmetric one key; Asymmetric public/private; hash → integrity (not encryption)

Practice: practice/topic-mcqs/01-networks-security.md