Editing Peering (section)

==How peering works==
The Internet is a collection of separate and distinct networks referred to as [[Autonomous System (Internet)|autonomous systems]], each one consisting of a set of globally unique [[IP address]]es and a unique global BGP [[routing]] policy.

The interconnection relationships between Autonomous Systems are of exactly two types:

* Peering - Two networks exchange traffic between their users freely, and for mutual benefit.
* [[Internet transit|Transit]] – One network pays another network for access to the Internet.

Therefore, in order for a network to reach any specific other network on the Internet, it must either:

* Sell transit service to that network or a chain of resellers ending at that network (making them a 'customer'),
* Peer with that network or with a network which sells transit service to that network, or
* Buy transit service from any other network (which is then responsible for providing interconnection to the rest of the Internet).

The Internet is based on the principle of ''global'' or ''end-to-end reachability'', which means that any Internet user can transparently exchange traffic with any other Internet user. Therefore, a network is connected to the Internet if and only if it buys transit, or peers with every other network which also does not purchase transit (which together constitute a "default free zone" or "DFZ").

Public peering is done at [[Internet exchange point]]s (IXPs), while private peering can be done with direct links between networks.<ref>{{cite book | url=https://books.google.com/books?id=vXZODwAAQBAJ&dq=tier+1+peering&pg=PA156 | title=Information Network Engineering | date=20 July 2015 | publisher=株式会社 オーム社 | isbn=978-4-274-99991-8 }}</ref><ref name="Springer">{{cite book | url=https://books.google.com/books?id=MgDQDwAAQBAJ&dq=tier+1+peering&pg=PA88 | title=Internet Computing: Principles of Distributed Systems and Emerging Internet-Based Technologies | isbn=978-3-030-34957-8 | last1=Sunyaev | first1=Ali | date=12 February 2020 | publisher=Springer }}</ref>