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Gouranga Das Samrat
Gouranga Das Samrat

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IP & Networking Basics

#systemdesign #networking #network

One-liner: IP (Internet Protocol) is the addressing system of the internet — every device gets a unique address, and packets are routed between them.

📌 IP Addresses

IPv4

  • 32-bit address → 2³² = ~4.3 billion addresses (running out!)
  • Format: 192.168.1.1 (four 8-bit octets, 0–255)
  • Private ranges (not routable on internet):
    • 10.0.0.0/8
    • 172.16.0.0/12
    • 192.168.0.0/16

IPv6

  • 128-bit address → 2¹²⁸ = ~340 undecillion addresses
  • Format: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
  • Solves IPv4 exhaustion problem

🔢 Ports

A port is a logical channel on an IP address. One server can run many services on different ports.

Port Service
22 SSH
25 SMTP (email)
53 DNS
80 HTTP
443 HTTPS
3306 MySQL
5432 PostgreSQL
6379 Redis
27017 MongoDB

Ports 0–1023 = well-known (require root). Ports 1024–65535 = available.

📦 TCP vs UDP

TCP (Transmission Control Protocol)

  • Connection-oriented — 3-way handshake (SYN, SYN-ACK, ACK)
  • Reliable — guarantees delivery, ordering, error checking
  • Slower — overhead of acknowledgments
  • Use: HTTP, HTTPS, SSH, databases

UDP (User Datagram Protocol)

  • Connectionless — just fire and forget
  • Unreliable — no delivery guarantee, no ordering
  • Fast — no handshake overhead
  • Use: DNS, video streaming, gaming, VoIP 
TCP: SYN ──► SYN-ACK ◄── ACK (connection established, then data)
UDP: DATA ──► (no response needed, no connection)
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🏠 NAT (Network Address Translation)

Your router at home has ONE public IP. All your devices share it via NAT.

Device (192.168.1.5:1234) ──► Router ──► Internet (Public IP:5000)
                               NAT table: 192.168.1.5:1234 ↔ PublicIP:5000
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This is why IPv4 hasn't completely run out — NAT multiplies addresses.

🔗 OSI Model (7 Layers)

Layer Name Example
7 Application HTTP, DNS, SSH
6 Presentation TLS, encryption
5 Session Session management
4 Transport TCP, UDP
3 Network IP routing
2 Data Link Ethernet, MAC
1 Physical Cables, WiFi signals

For system design: mostly care about L3 (IP), L4 (TCP/UDP), L7 (HTTP).

🔑 Key Takeaways

  • Every server has an IP + port — that's how clients find it
  • TCP = reliable but slower; UDP = fast but unreliable
  • Load balancers can operate at L4 (TCP) or L7 (HTTP)

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