Why don't ISPs peer with everyone?

John Kristoff jtk at cymru.com
Mon Jun 6 23:45:35 UTC 2011

On Mon, 06 Jun 2011 18:19:37 -0400
rucasbrown at hushmail.com wrote:

> I wouldn't consider myself a network engineer, nor do I have any 
> formal training, but why don't ISPs peer with every other ISP? It 

It depends on the ISP, but there are a variety of reasons for not
wanting to peer with any potential peer or in this case "every other
ISP".  Also let's distinguish between paid-peering and settlement-free
peering.  I think we can agree that if there were only paid-peering,
then a complete mesh would be not only technologically impractical, but
also economically as well.

Plug the terms "economics", "internet" and "peering" into your favorite
search engine and you should come up with some relevant reading

> Only issue I 
> see is with possibly hijacked / malicious AS owners, but that's not 
> very common to do without being caught.

Can you explain why this is a bigger issue in your scenario?

> All the whole "don't peer with this guy" only makes your customers 
> have worse latencies and paths to other people, making the Internet 
> less healthy.

Certainly most ISPs care about that to some degree, but to get to the
heart of the matter, consider the mindset of any profit-motivated ISP,
especially where one is "larger" in some sense of the word than the
other who wants to peer.  If I'm the larger ISP, and you're the smaller
ISP coming to me to peer settlement-free, why should I peer with you?
So our customers can get better performance to each other?  Why don't
your customers just connect to me instead?  What do I lose if we don't
peer?  If you're small, probably not too much.


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