Internet Structure and Governance

Context: FIT1047_MOC · the Internet as a network of networks — how independent networks interconnect and who sets the rules · extends routing to the inter-network scale

Quick Revision

• 🎯 Objective: the Internet = interconnected Autonomous Systems (mostly ISPs) that exchange traffic via border routers running BGP ➔ decentralised, no single owner.
• ⚡ Key Constraint: distinguish interior routing (inside one AS: RIP/OSPF/EIGRP, admin’s choice) from exterior routing (between ASes: BGP only) — and peering (free, mutual) from transit (paid, smaller→larger ISP).

📝 Core

• Network of networks ➔ no central Internet; each participating network is owned/run by an organisation (ISP LANs, backbones), interconnected.
• ISP (Internet Service Provider) ➔ operates a network and sells access to end users (via 4G) or dedicated links; an ISP’s network is usually one Autonomous System.
• Autonomous System (AS) ➔ a collection of IP networks + routers under one organisation with a unique AS Number (ASN); the Internet is a network of ASes.
• Border routers ➔ connect one AS to another; enforce traffic policy (which networks’ traffic to accept) and speak BGP (Border Gateway Protocol) — the single exterior routing protocol.
• Interior vs exterior ➔ inside an AS, admins pick any interior protocol (RIP, OSPF, EIGRP); between ASes, only BGP — see Network Layer (Routing and Routing Tables).
• ASN allocation ➔ ASNs (and IP ranges) are handed out by a Regional Internet Registry (RIR) — e.g. APNIC for Asia-Pacific.

🔀 How ISPs interconnect

• Tiers ➔ Tier-1 = huge global WANs; Tier-2/3 are smaller and buy upward. Smaller ISP routes via a larger ISP.
• Transit ➔ a smaller AS pays a transit provider (higher-tier ISP) for access to its infrastructure and the broader Internet. Tier-1s charge smaller ISPs to carry their traffic.
• Peering ➔ two ISPs agree to accept each other’s traffic without charge (usually when similar size / similar traffic); bilateral or multilateral via an IXP.
• IXP (Internet Exchange Point) ➔ shared hardware (racks of high-speed switches + fibre) where many ISPs physically interconnect; often owned by a consortium of ISPs.

🏛️ Governance — no single organisation governs the Internet

• ISOC (Internet Society) ➔ umbrella for IAB (Architecture Board), IETF (Engineering Task Force — the standards/RFCs), IESG (steering), IRTF (research).
• ICANN ➔ Internet Corporation for Assigned Names and Numbers — manages IP addresses and host names (DNS root).
• IGF ➔ Internet Governance Forum — annual multi-stakeholder meetings.
• ITU ➔ International Telecommunication Union — mostly hardware standards (e.g. DSL).

⚠️ Common Mistakes

• 💡 BGP is exterior-only ➔ RIP/OSPF/EIGRP route inside an AS; BGP routes between ASes. Naming an interior protocol for inter-AS routing loses the mark.
• 💡 Peering ≠ transit ➔ peering is settlement-free and mutual; transit is a paid customer→provider relationship. Similar-sized ISPs peer; small ISPs buy transit.
• 💡 “Who owns the Internet?” ➔ no one — ASes are individually owned; standards come from many bodies (ISOC/IETF, ICANN, ITU…), not a single governor.

🧠 Active Recall

Why do two Tier-1 ISPs peer for free while a small ISP pays for transit?

Answer

• Short answer: peering is worthwhile when both parties exchange roughly equal traffic, so settlement-free swapping benefits both; a small ISP sends/receives far less and depends on the larger network, so it buys transit to reach the rest of the Internet.
• Why: Reciprocity vs dependence ➔ peers connect as equals at an IXP (no charge); transit is an asymmetric customer→provider link (paid), reflecting who needs whom.