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I read all the posts on this site on IXP's and my question remains. Any clarity that anyone can bring to this topic would be much appreciated.

I have trying to get a better mental big-picture of how the internet works I stumbled across the Wikipedia article about Tier 1 networks that really helped build my picture. This lead to Wikipedia'ing about interconnect agreements and especially internet exchange points which helped to greatly clarify the mechanisms of the internet. I found www.internetexchangemap.com which helped with a physical picture.

I was then curious which tier 1 networks participate in my local IX, the Milwaukee Internet Exchange, but to my surprise I did not recognize any of the networks listed - no Verizon, AT&T, Sprint, Time Warner, although Verizon, AT&T, and Sprint are listed as Tier 1 Networks on Wikipedia. I also checked the Chicago Exchange Point and found the same. I looked up most of the companies that are listed; some were very small ISP’s. But if it is not these major ISP's (Verizon, AT&T, Sprint, Time Warner) that converge at Internet Exchange Points, then I feel there may still be a little infrastructure involved that I do not understand, like a hand off between these major ISP's and some more obscure major networks that don't deal with consumers. If not at these major IXP’s, then how does an AT&T end user request make it to a web server on a Verizon network?

A related question: I'm also wondering what the Milwaukee Internet Exchange means in their FAQ when they discuss how you can go there and "connect" (www.mkeix.net/faq/).

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To start, the reference you are using is incomplete. Here is another one, that is also incomplete (lists none in Milwaukee and only one in the Chicago area). Both are missing one of the largest IXPs in Chicago.

But more importantly, these are only the points where one network will peer with another network. This doesn't account for the breadth or scope of a single provider's network. For example, clearly AT&T has a presence in your area, but they may choose not to peer with anyone there. They may peer in Chicago and carry all the traffic across their network to that point (or one somewhere else).

Further, private organizations are not required to disclose their presence at any location. They may choose not to do so for any number of reasons.

Finally, most lists do not account for networks that may have been absorbed by a larger network but are still listed under an older name. One example you will often still see listed in places is UUNET although this network is now part of Verizon (which you can also find listed in places as MCI or MCI Worldcom as well).

  • So, my understanding is complete, it's just that you can't always find out which networks peer in what locations? Got it. Thanks a lot! – Filonowst Nov 13 '15 at 17:15
  • Also there is no rule that peering has to happen via an exchange point. Exchange points are a cost saving measure for making having lots of low traffic peering relationships more viable but the big tier 1 providers are usually uninterested in low traffic peering relationships anyway. – Peter Green Dec 13 '15 at 15:20
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I have trying to get a better mental big-picture of how the internet works I stumbled across the Wikipedia article about Tier 1 networks that really helped build my picture. This lead to Wikipedia'ing about interconnect agreements and especially internet exchange points which helped to greatly clarify the mechanisms of the internet. I found www.internetexchangemap.com which helped with a physical picture.

Exchange points are not the be-all and end all of peering. They are a mechanism to allow the costs of a physical connection to be shared among multiple peering relationships, the downside being that you have to pay for the exchange points switching infrastructure and organisational overhead. So low traffic peering relationships tend to go via exchange points while high traffic ones tend to go via dedicated private links.

When a provider buys "transit" (that is the service of providing connectivty to anywhere on the internet) then again that connection is almost certain to go over a private link.

There seems to be a big difference in attitude here between the US and Europe. The big access providers in the US tend to be very monopolistic and have the attitude that peering with "little guys" is giving away for free something that they could be charging for. In many cases those big access providers are also teir 1 transit providers.

On the other hand in Europe there is more competition among ISPs and the individual access providers are generally smaller and have to buy transit to reach large parts of the internet. The result is that there is more incentive for the access providers to peer directly with the content providers and internet exchanges flourish.

how does an AT&T end user request make it to a web server on a Verizon network?

Given that AT&T and Verizon are both teir 1 ISPs it will almost certainly pass over a private peering link between them. That link may well not be especially local though (you can often get hints as to the geographic route from the hostnames in traceroute).

A related question: I'm also wondering what the Milwaukee Internet Exchange means in their FAQ when they discuss how you can go there and "connect" (www.mkeix.net/faq/).

They don't explicitly list minimum requirements on that page but in practice they would almost certainly expect you to have your own IP space and AS number before allowing you to connect. I expect they would also at the very least consider it strange if you applied to connect to the exchange without first acquiring transit connectivity to the Internet in general

Note that connecting to an exchange doesn't necessarily let you interconnect with everyone on that exchange. The actual peering relationships are still at the discretion of the individual member.

The lack of requirements and fees listed on that page suggests they are a fairly minor internet exchange. Most of the big ones will have a lot more formalities and reccuring fees.

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