A network of networks
There is no single owner of the Internet.
The Internet is made of many independently operated networks. A home or campus network connects to an access provider; that provider can exchange traffic with other providers or reach them through transit networks.
Routers move packets between networks one hop at a time. Networks share reachability information so routers can choose useful next hops, but no single router needs a complete map of every path.
Between independently operated networks, Border Gateway Protocol (BGP) commonly exchanges routes. An announcement describes reachability, not a guarantee of successful delivery or the fastest path. Routes, forwarding and policy must also permit traffic.
Peering exchanges agreed traffic and routes; it does not normally provide full Internet transit. A direct interconnection does not guarantee better performance: policy, congestion and capacity still matter.
The Web is one service that uses the Internet. The return path can differ from the forward path. One organization may provide access, transit and peering: these are roles, not fixed identities.
Build the model
Four roles along the way
Local network
Connects nearby devices and sends off-network traffic to a router.
Access provider
Connects a customer network to destinations beyond its local link.
Transit provider
Carries traffic between networks that do not connect directly.
Interconnection
Lets independent networks exchange traffic and reachability information.
Mini experiment
Follow an interconnection
Compare three simplified relationships, assuming usable routes and forwarding. An organization can perform more than one role.
Knowledge check