Question on the topology of Internet Exchange Points

Thu Feb 14 23:27:26 UTC 2008

On Feb 14, 2008, at 3:44 PM, Andy Davidson wrote:
> On 14 Feb 2008, at 17:02, Kai Chen wrote:
>
>> A typical Internet Exchange Point (IXP) consists of one or more  
>> network switches, to which each of the participating ISPs connect.  
>> We call it the exchange-based topology. My question is if some  
>> current IXPs use directly-connected topology, in which ISPs just  
>> connect to each other by direct link, not through a network  
>> switch?? If so, what's the percentage of this directly-connected  
>> case?
>
> ISPs use a "direct link" (PNI) all the time to peer, and they don't  
> need to be a member/customer of an internet exchange point to do  
> so.  In fact, the network you want to peer with might not be  
> available at your local IXP even though they're in your local  
> carrier hotel - then it becomes pretty much the only way to peer.
>
> In London, the LINX offer switched *and* unswitched connectivity  
> between members - you can rent fibers from them in order to perform  
> PNI with other members.  That the exchange offer this is unusual,  
> and it's offered as an additional service, in order to smooth the  
> process of organising interconnection between member organisations. [www.linx.net 
> ]

LINX doesn't rent fibers.  It's a one-time (NRC) fee for 8 pairs,  
which are patched to any other member on the service for free for  
life.  (Although I don't know if they promise to keep it free forever,  
but it's been free for many years with no mention of it changing.)

> We (LONAP) don't offer PNI services, and only offer the conventional  
> switch ports, which members normally want so that they can get  
> access to our peering lan and swap some traffic. [www.lonap.net]   
> All exchanges offer this connectivity model.  We offer private CUG  
> and member-to-member private VLANs, which is similar, but still  
> passes through the switch fabric.

I believe Exchange Point offers a PNI-like service over their network.

But in general, an "Internet eXchange Provider" offers a shared  
switch.  Anything else is really just a meet-me room.  For instance, I  
wouldn't call Suite 1515 (formerly NYCC) an "IXP".

-- 
TTFN,
patrick