Buying IP Bandwidth Across a Peering Exchange

[owen at delong.com (Owen DeLong)]

> On Nov 25, 2014, at 10:56 AM, Bill Woodcock <woody at pch.net> wrote:
> 
> 
> On Nov 25, 2014, at 10:47 AM, Colton Conor <colton.conor at gmail.com> wrote:
>> I know typically peering exchanges are made for peering traffic between
>> providers, but can you buy IP transit from a provider on an exchange? An
>> example, buy a 10G port on an exchange, peer 5Gbps of traffic with multiple
>> providers on the exchange, and buy 5Gbps of IP transit from others on the
>> exchange?
> 
> Some IXPs have a rule that explicitly disallows this, others encourage it, most donâ??t care.  I donâ??t know of any that have a mechanism to enforce a rule prohibiting it.
> 
> PCHâ??s guidance in the IXP formation process is to avoid creating rules which are, practically, unenforceable.  So we generally counsel IXPs against having a rule precluding transit across the switch fabric.  That said, a crossconnect is a _much better idea_.  
> 
>> Some might ask why not get a cross connect to the provider. It is cheaper
>> to buy an port on the exchange (which includes the cross connect to the
>> exchange) than buy multiple cross connects. Plus we are planning on getting
>> a wave to the exchange, and not having any physical routers or switches at
>> the datacenter where the exchange/wave terminates at. Is this possible?
> 
> Yes, itâ??s possible, but what you describe is a pretty fragile setup.  Lots of common points of failure between peering and transit; places where screwing one up would screw both up.  If all of this is really tangential to whatever youâ??re doing, and you donâ??t mind looking a little out-of-step with best practices, and you donâ??t mind it all being down at once, any time anything breaks, then it may be a reasonable economy.  If youâ??re planning on actually depending on it, you need to do better engineering, and either spend more money, or allocate your money more conservatively.
> 
> Doing everything the cheapest possible way, regardless of the fragility or complexity, is very short-sighted, and is unlikely to be an economy in the long run.
> 
>                                -Bill
> 
> 
> 
> 

Iâ??d say that dependsâ?¦

If itâ??s an equal cost choice, for example, between getting waves to multiple exchanges and peering with multiple providers at each exchange that way vs. putting a router at one exchange and getting cross-connects there, then I would argue that the former is actually more robust.

Owen