This blog post by Owen summarizes well how the Border Gateway Protocol (BGP) in its current version 4 (BGP4), which runs the Internet since 1994 and makes it redundant, can be considered superseding the "Tier-1" level on the Internet:

BGP and the System of Trust that Runs the Internet

by Owen Lystrup, 18 JUN 2015

https://blog.opendns.com/2015/06/18/bgp-and-the-system-of-trust-that-runs-the-internet-pt-1/

This is part one of a two-part series on BGP.

(my own US license plates)

The number of smart devices connecting to the Internet are reaching an unprecedented level. Estimates are predicting as many as 75 billion devices will come online by 2020, which means Internet traffic routing is going to get a lot more complex.

What most Internet users don’t know, but many are beginning to discover, is the entire framework that holds the Internet together can be quite fragile. In fact the system in charge of correctly routing Internet traffic is largely built on a collective trust, or as The Washington Post recently described it, an ‘honor code’ of the Internet.

The fact is we all rely on core protocols of the Internet like BGP (border gateway protocol) and DNS (domain name services) every day. They are a foundation of the Internet. Even companies that provide content on the Internet but don’t need BGP services directly, still rely on the service to get that content to their customers.

This two-part series will cover BGP, what it is, how it works, and what global moving parts are involved. Part two of this series, publishing next week, will cover the technical and security issues surrounding BGP, and why they often have a drastic effect on a global scale.

The Buried Superhighway
There is good reason behind portraying the Internet as a superhighway. Internet requests have a starting point (usually a device or computer) and a destination (like a website or app service). But the superhighway analogy is also apt because the Internet–despite its illusionary feeling of magic behind a box–is largely a physical thing, consisting of cables that run for hundreds of thousands of miles, many of them underground.

Pictured is a map of the submarine routes Internet cables take around the globe. They are literally physical cables that surface out of the ocean to connect all the countries of the world to one another. The other half of what makes the magic of the Internet work, are the various standards and protocols involved–the documented, collective agreement on how the Internet and its protocols should function, and the provider companies who pledge to make them work the way they should. The resulting covenants between Internet providers, are what keep the entire wheel of the Internet churning. And BGP plays a major role.

A common description of DNS (domain name services) is “the address book” of the internet. DNS looks up and resolves domains, like google(.)com, to their correct IP addresses, which are the actual desired destinations. If DNS is the address book that finds the destination, BGP is the system of freeway signs that show which routes can get there.

Just like roads and freeways, some routes are quick and direct, and some routes send traffic on misdirected tangents. BGP is the complex, interweaving system that gets Internet traffic where it needs to go, hopefully as efficiently as possible.

Peering: Good Neighbors Make Faster Internet
Andree Toonk, founder of BGPMon and manager of network engineering at OpenDNS, explained in an interview that the problems and outages the world has seen recently that involved BGP start with how the networking relationships between providers and businesses work.

The Internet as it is today consists largely of two types of relationships between businesses and ISPs, Toonk said. The first and more straightforward type of relationship is between providers and customers. In this scenario, customers–smaller regional ISPs and businesses like DropBox and OpenDNS–pay large providers–like AT&T and Level 3–to provide connectivity service for their users and customers. This type of relationship is formal, and can be costly depending on the providers and the details involved.

Peering is the second type of relationship, Toonk says, and it brings a few unique benefits. If a small local ISP wants to connect its customers to Facebook, for example, and doesn’t want to pay the large ISP acting as the middleman, the smaller ISP can connect using a peering relationship. Getting to Facebook is much easier done when there is a direct connection, and it will usually have less latency. And, Toonk says, one of the great benefits in a peering relationship is usually much more cost effective.

These peering relationships are typically established at an Internet exchange (IX). They are pretty much exactly what they sound like, a central location where a large number of ISPs, businesses, and content providers connect to one another physically. Exchanges exist all over the globe, and they allow a more direct way of connecting end users to the Internet and its bounty of sites and services.

These relationships are at the core of how companies and Internet providers connect to one another globally. But, as Toonk explained, they can also be the source for huge routing and security issues. That is because the relationships keeping the Internet functioning, especially peering relationships, are where the “honor code” mentioned earlier comes into play.

Stay tuned for part two, which will explain how the honor code works, how BGP is becoming a new target for hackers, its involvement in some of the largest Internet outages ever seen, and the steps the industry is taking to correct the issues.