Question on the topology of Internet Exchange Points

Thu Feb 14 20:44:40 UTC 2008

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 
]

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.

Best wishes
Andy 