Peering

A peering point is a physical location where multiple ISPs exchange Internet
traffic with their peers in so-called peering arrangements. Most peering
points are located in colocation centres, where the different network
operators 'co-locate' their Points of Presence.

History of peering

In the early days of the Internet, a backbone network existed in the form of
first the ARPANET and later the NSFNET. All other networks connected with
one another via the backbone, and routing information was conveyed between
the backbone and the other networks via the Exterior Gateway Protocol (EGP).

With the decommissioning of the NSFNET Internet backbone network on April
30, 1995, the Internet now consists entirely of the various commercial ISPs
and private networks, as connected at their peering points.

The Border gateway protocol (BGP) was designed to allow the different
networks to exchange routing information, allowing them to route packets
from network to network without needing any central authority to coordinate
the operation of the Internet.

A neutral peering point or Internet exchange is a peering point that is
independent of any single provider, and provides a commercially neutral
venue for peering.

Not all peering happens at neutral peering points: private peering between
large providers is very common, as is a customer-provider relationship,
particularly at the bottom tiers of the Internet business. The latter is not
a true peering relationship.

Peering agreements

Peering has three elements: the physical interconnection of the networks,
technical liaison between the networks to allow exchange of routes, and the
commercial and contractual peering agreements.

Providers with large traffic volumes can peer without charge with other
large providers, often known as Tier 1 carriers.