How the Internet Is Run

Introduction

Nobody owns the internet. It is tens of thousands of independent networks that agree to exchange traffic using common protocols. This last lesson zooms out to see how that works and who coordinates it.

Networks of networks

• Internet service providers (ISPs) connect homes and businesses. You pay yours for access.
• Large backbone or transit providers carry traffic across countries and continents. Smaller networks buy transit from bigger ones.
• Content companies and cloud providers run their own huge networks, and connect directly to ISPs so that popular content takes a short path.
• Internet exchange points (IXPs) are buildings where many networks plug into shared switches and swap traffic directly, usually cheaply. This is called peering, and it keeps local traffic local and costs low.

A packet usually crosses several networks, each acting on its own agreements and policies.

Autonomous systems and BGP

Each independently run network is an autonomous system (AS), identified by an AS number. Networks need to tell each other which IP addresses they can reach. They do this with the Border Gateway Protocol (BGP), which is the glue of the internet.

• Each network announces the address blocks it originates, and passes on routes it has learned.
• Routers build tables of the paths to each block, and choose among them using policies (cost, agreements, preferences), not simply the shortest path.
• BGP runs on trust. A wrong or malicious announcement can misdirect traffic, which is why route filtering and RPKI are important, as you saw in the last lesson.

Cables, data centres and satellites

• The great majority of intercontinental data travels through submarine fibre-optic cables laid on the seabed, owned by consortia and large companies. They can be damaged by ships' anchors, fishing and earthquakes, so diverse routes matter.
• On land, fibre crosses countries, with mobile networks, cable, DSL and fixed wireless on the last mile.
• Satellite internet reaches remote areas, with newer low-orbit systems offering better delay than older ones.
• Data centres house the servers and are linked to many networks.

Names and numbers: who coordinates?

Some things must be unique worldwide, so they need coordination:

• IANA (Internet Assigned Numbers Authority) manages the root of the DNS, IP address pools and protocol parameters.
• ICANN is the non-profit that coordinates these functions and sets policy for domain names. It accredits registrars, which sell domains to you.
• Regional Internet Registries (RIRs) give IP address blocks and AS numbers to organisations in five world regions.
• Registries run each top-level domain, such as .com or country domains.

Standards

Open standards make interoperation possible. The IETF (Internet Engineering Task Force) develops protocols such as TCP, TLS, HTTP and DNS through public documents called RFCs. The W3C and WHATWG standardise web technologies. Anyone can take part in the open processes.

IPv6

IPv4 offers about 4.3 billion addresses, and they ran out. IPv6 uses 128-bit addresses, giving a practically unlimited number, written in hexadecimal like 2001:db8::1. It removes the need for NAT and simplifies some features. Both run side by side today, and adoption keeps growing, but progress is gradual because each network upgrades on its own schedule.

Governance, law and openness

• Countries apply laws to the networks and services inside their borders: privacy, content rules, security and surveillance. These differ greatly.
• Some governments block or throttle access. People use encryption and other tools, and the legal status of such tools varies by place.
• Net neutrality, the principle that providers should treat traffic equally, is debated and regulated differently around the world.
• The multi-stakeholder model, with governments, companies, technical groups and civil society, is how many internet policy decisions are made.

Why this matters to you

Understanding the structure helps you reason about outages (a cable cut, a BGP leak, an expired certificate or a DNS failure), speed (distance and peering), security and privacy (who can see your traffic) and careers in networking, cloud and security.

Try it yourself

Look up the AS number of your internet provider with a public lookup tool, and find the name of the nearest internet exchange point to you. Draw a rough path a request might take from your home to a website on another continent.

Summary

• The internet is thousands of autonomous networks, linked by ISPs, transit and peering at exchange points.
• BGP spreads reachability information between networks, and runs on trust, so it needs protection.
• IANA, ICANN, the registries and the IETF coordinate names, numbers and standards, while laws and policies vary by country.