So in this series we're going to look at the value of peering. While it's not directly related to BGP configuration or BGP best practices it's actually very important for network operators and end sites who are considering traffic engineering and multihoming requirements to consider some of the issues and items that we bring up in the next few minutes. The internet is made up of networks and network operators of all shapes and sizes some of local coverage and they're generally access providers others can provide regional or per country coverage and other operators are global in scale and these network operators interconnect their businesses you don't interconnect with every other isp the rover 58,000 distinct autonomous networks at the time we made this recording and that just won't scale the interconnect according to practical and business or operational needs some network operators provide transit to others and they interconnect other ISP networks and they're just over 7800 autonomous networks which are providing translate today if we look at the diagram we have categorized ISPs we have the access providers which are providing access to the end-user we have the regional ISP which is covering several countries or regional networks and then we have the tier ones which are providing global connectivity and the interconnect with each other depending on business or operational needs on the left of the diagram I have an arrow with dollar symbols in it this is indicating the flow of money the end-user pays the access is p4 Internet access the access is P will by transit from the regional ISP and the regional ISP will by transit from the tier 1 the tier 1 by definition no transit from anyone notice the position of the internet exchange point we have mentioned exchange point throughout this series the internet exchange point is very much for connecting the access providers to each other so they don't have to use transit via the regional or Tier one provider simply for local traffic internet exchange points are very common and very popular around the globe we're now going to look at the definitions of peering and transit we've seen these at the start of this series transit means carrying traffic across a network usually for a fee for example an access provider connects to a regional provider peering means exchanging routing information and traffic the technical activity of peering the business activity of peering is done for no fee sometimes it's called settlement free peering for example a regional provider connects to another regional provider a private interconnect is where two network operators connect the networks over a private link today this is called private network interconnect or P&I it can be appearing arrangement for example a private peering where there's no charge for traffic and the operators share the cost of the link between each other's networks it can be a transit arrangement where one ISP will charge the other for traffic and one ISP usually the customer will pay for the physical link between the two networks the diagram shows a private interconnect a public interconnect is where several network operators meet in a common neutral location and interconnect their networks. Usually this is as a peering arrangement between their networks. The diagram shows a typical public interconnect where there's an exchange point with its Ethernet switch connecting the six ISPs shown.

© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.

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