The Internet is an interconnection of networks, each controlled by separate entities. Those entities are generally called Internet Service Providers (ISP), and the networks they control are grouped by Autonomous Systems (or AS) RFC1930.
In order to have connectivity to the "global Internet", an AS of an ISP must be connected to an AS of at least one other ISP which already has "global Internet" connectivity. This is called "buying transit", as the process usually involves an economic transaction. Autonomous Systems are interconnected via the BGP protocol RFC4271. All Internet Service Providers must buy transit, with the exception of a small number of very large ISPs (called "Tier 1" ISPs), who get global Internet connectivity simply by being interconnected with each other. In this model, all Internet traffic flowing between smaller ISPs (also called "Tier 2" ISPs) has to pass through their upstream providers' networks.
Some of the Tier 2 ISPs decide to interconnect their AS directly, in order to reduce the amount of different networks (the number of 'hops') the traffic has to traverse, and at the same time save some transit costs. This practice is called "peering".
Internet eXchange Points
Whilst peering reduces upstream costs, providing physical connection between two ISP's networks is not for free, and this must be considered when calculating the savings by having a direct interconnection. There are many thousands of ISP networks all over the world. It would not be cost effective, scaleable or manageable to interconnect with all of them individually.
Internet Exchange Points (IXPs) provide a partial solution to this. An IXP is a single physical network infrastructure (typically an Ethernet local area network) to which many ISPs can connect. Any ISP that is connected to the IXP can exchange traffic with any of the other ISPs connected to the IXP, using a single physical connection to the IXP, thus overcoming the scaleability problem of individual interconnections. Such peering practice is called "public peering" (as opposed to "private peering", where two ISPs have a direct physical interconnection as described above), and IXPs are often referred to as "peering points" or "public peering points".
By enabling traffic to take a shorter path to many ISP networks, an IXP can improve the efficiency of the Internet, resulting in a better service for the end user. Furthermore, since many networks have more than one connection to the Internet, it is not unusual to find several routes to the same network available at an IXP, thus providing a certain amount of redundancy.
IXPs are not, generally, involved in the peering agreements between connected ISPs; whom an ISP peers with, and the conditions of that peering, are a matter for the two ISPs involved. IXPs do however have requirements that an ISP must meet to connect to the IXP; also, since the physical network infrastructure is shared by all the connected ISPs, and activities of one ISP can potentially affect the other connected ISPs, all IXPs have rules for proper use of the IXP.
This document aims to put in writing some technical practices which are widely accepted in the IXP world, concerning the setup and maintenance of an Exchange Point infrastructure and the rules that ISPs who connect to an IXP should follow. It is important to stress that this document is not a standard, nor a set of strict guidelines to follow; it is merely a set of recommendations deriving from the experience of a number of already established IXPs, for the use of other IXPs or of people wanting to start an IXP. In addition, this document focuses on the technical best practices related to Internet Exchange Points; commercial and political issues will not be discussed.