Advanced · 15 lessons

Networking

Computer networking connects servers, clients, and services across the internet. Understanding TCP/IP, ports, routing, firewalls, and DNS is essential for hosting engineers, sysadmins, and anyone troubleshooting connectivity issues.

Key Concepts

TCP/IP Model Ports (80, 443, 22) Firewalls NAT & Private IPs Subnetting VPN BGP Routing Latency & Bandwidth

Key Takeaways

✓ HTTP uses port 80, HTTPS uses 443, SSH uses 22, MySQL uses 3306.
✓ Firewalls control which ports and IPs can connect to your server.
✓ Private IPs (10.x, 192.168.x) are used inside data centers; public IPs face the internet.
✓ Latency matters — place servers close to your users or use a CDN.

Lessons in This Topic

TCP/IP & the OSI Model

How data travels across networks.

OSI has 7 layers; TCP/IP simplifies to 4: Link, Internet (IP), Transport (TCP/UDP), Application (HTTP/DNS). TCP guarantees delivery with handshakes; UDP is faster but unreliable. IP addresses route packets; MAC addresses work locally.

Ports, Protocols & Services

Which port does what service use.

Port 80=HTTP, 443=HTTPS, 22=SSH, 21=FTP, 25=SMTP, 53=DNS, 3306=MySQL, 5432=PostgreSQL, 6379=Redis, 27017=MongoDB. Only one service per port per IP. Use `netstat -tlnp` or `ss -tlnp` to see listening ports. Close unused ports in firewall.

Firewalls & Access Control

ufw, iptables, and security groups.

Firewalls filter traffic by IP, port, and protocol. Default deny: block everything, allow only needed ports. AWS security groups and cloud firewalls work similarly. Allow SSH only from your IP, not 0.0.0.0/0. Log dropped packets for analysis.

NAT, Private IPs & VPCs

How internal networks connect to the internet.

Private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are not routable on the public internet. NAT translates private IPs to public IP for outbound traffic. VPCs isolate cloud resources with custom subnets and routing tables.

CDN & Network Performance

Reduce latency with edge delivery.

CDN caches content at 200+ global edge locations. Users connect to nearest edge, not distant origin. Reduces latency from 500ms to 50ms. Also provides DDoS protection and SSL termination. Purge cache when deploying updates.