Structure, Hierarchy, and Standards of the Internet: ISPs, RFCs, and IPv4 Addressing
The Internet is not owned by any single president, government, or corporation. It is a hierarchical federation of thousands of privately owned commercial networks linked together through standardized agreements.
1. The 3-Tier Hierarchy of the Internet
The global Internet is organized into three hierarchical levels of Internet Service Providers (ISPs):
The 3-Tier Internet Hierarchy
🌐 Tier-1 ISPs (Global Backbone: Tata Communications, AT&T, Lumen)
Tier-2 Regional ISPs
National coverage (Reliance Jio, Bharti Airtel)
Tier-3 Local Access ISPs
City/Neighborhood cable broadband providers (Hathway, ACT)
- Tier-1 ISPs (The Global Backbone): Giant international telecom networks owning undersea trans-oceanic fiber cables. They connect to each other for free via Peering agreements without paying anyone for transit (e.g., Tata Communications, AT&T).
- Tier-2 ISPs (Regional/National): Large national networks (like Jio and Airtel in India) that lease transit capacity from Tier-1 backbones to reach foreign countries.
- Tier-3 ISPs (Local Access): The neighborhood broadband providers that sell home Wi-Fi and fiber connections directly to students and local shops.
- IXPs (Internet Exchange Points): Physical data center facilities where different ISPs meet to exchange local internet traffic directly without paying high international transit fees (e.g., NIXI - National Internet eXchange of India).
2. Standards of the Internet: RFCs
Internet protocols are defined through documents called RFCs (Request for Comments) published by the Internet Engineering Task Force (IETF):
- RFC 791: Internet Protocol (IPv4).
- RFC 793: Transmission Control Protocol (TCP).
- RFC 2616: Hypertext Transfer Protocol (HTTP/1.1).
3. IPv4 Addressing and Address Classes
An IPv4 Address is a 32-bit (4-byte) logical address written in dotted-decimal notation (e.g., 192.168.1.1):
The 5 IPv4 Address Classes
Class A (1 - 126)
Huge networks (8 bits Net ID, 24 bits Host ID). Default mask: `255.0.0.0`
Class B (128 - 191)
Medium networks (16 bits Net ID, 16 bits Host ID). Default mask: `255.255.0.0`
Class C (192 - 223)
Small LANs (24 bits Net ID, 8 bits Host ID = 254 PCs). Default mask: `255.255.255.0`
Class D (224 - 239)
Reserved for Multicasting (streaming video groups). No subnet mask!
Class E (240 - 255)
Reserved for experimental and research use
- Special Loopback IP:
127.0.0.1(127.x.x.x) is reserved for internal testing on your own computer (localhost).
💡 DAVV Exam Tip
Question (10 Marks): “Explain the hierarchy of the Internet. What are IPv4 address classes? Write the range and subnet mask for each class.”
- Draw the Tier-1, Tier-2, Tier-3 ISP pyramid.
- Write the table of all 5 IPv4 classes with their first octet range and default subnet masks.
- Mention the loopback address
127.0.0.1.