Question on the topology of Internet Exchange Points

Fri Feb 15 13:04:48 UTC 2008

On Feb 14, 2008, at 7:06 PM, Paul Vixie wrote:

>
> kch670 at eecs.northwestern.edu ("Kai Chen") writes:
>
>> A typical Internet Exchange Point (IXP) consists of one or more  
>> network
>> switches <http://en.wikipedia.org/wiki/Network_switch>, 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?
>
> when i last worked at PAIX, the private interconnects wildly  
> outnumbered
> the switch connection.  the model seemed to be, use the switch to  
> reach all
> of the other participants, but whenever you had a hot neighbor, get  
> a PNI.
>
> in other words there appeared to be no "exchange-based topology",  
> more like
> a "hybrid exchange and PNI topology."
> -- 
> Paul Vixie

Obvious as it is, if one of your peerings on an IX gets big in terms  
of in/out volumes, you HAVE to secure it by PNI.
You need a way to prevent the IX's equipments from being a SPoFs  
between you and that peer.
I'm not saying one should convert every single IX peering into a PNI,  
as I feel both are pretty much required: your smallest peers shall be  
secured on as many IXes as possible, your biggest ones via PNI. IX  
peering is mandatory to keep internet routing diversity up to par -  
and enable small ASes to grow.
Also, it is a wrong assumption to state that IX will make you spare  
money on transit, from my perspective they should be seen as securing  
multiple narrower paths to the internet.

Greg VILLAIN
Independant Network & Telco Architecture Consultant