Why don't ISPs peer with everyone?

Mon Jun 6 23:35:11 UTC 2011

> >
> > Hello,
> >
> > 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
> > would only save EVERYONE money if they did this, no? Only issue I
> > see is with possibly hijacked / malicious AS owners, but that's not
> > very common to do without being caught.
> 
> The answer to _every_ question that  starts of "why don't they..." is
> "money".
> 
> Who pays for the circuits to establish a 'peering connection' with an
> ISP half-the world away?   How much does traffic does "Joes Bait Shop
> and ISP" in Painted Privvy, Nebraska have with a community ISP in
> Honshu, JP?"
> 
> 
There are a lot of considerations.  How many peering sessions can your
hardware support?  How many peering locations are you going to need?
What will the internal network to tie all those together look like. Will
you now need to upgrade your core? 

Will adding a new peer place another peering agreement at risk by
changing the traffic balance?

So even if the peering itself is "free", the infrastructure required to
support large scale peering at multiple locations can be quite
expensive.  Are you going to want to haul traffic from New Jersey to
California to hand it to a peer who hauls the traffic all the way back
to New Jersey again?  Does your router in Kansas City want to hand the
traffic to the peer in New York or in Seattle? For a small regional
network, peering can be easy.  For a large network that spans a
continent, it can be pretty hard.