Question on the topology of Internet Exchange Points

Sat Feb 16 15:30:36 UTC 2008

On Feb 15, 2008, at 8:04 AM, Greg VILLAIN wrote:
>
> 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.

"HAVE to" is such a strong phrase.

First, who said the switch is a SPoF?  And since when is a PNI not a  
SPoF?  If the peer is that big, you should peer in more than one  
place.  For instance, LINX has two LANs, or you can use PAIX and  
Equinix.  Connecting to a "big peer" in a single location, whether  
over PNI or shared switch, creates a SPoF.  Peering in multiple  
locations removes the SPoF, regardless of the method.

> 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.

Using shared for small peers and direct for big peers is a time  
honored practice on the Internet.  But you can justify this in  
finance, not just engineering.  A fiber x-conn costs less than an IX  
port (usually).  Any peer big enough to take up a significant fraction  
of the IX port probably justifies the CapEx for a dedicated router port.

Does this make things more reliable?  Many would argue it does.  I  
would argue that large IXes have amazing uptime these days.  The MAEs  
& GigaSwitches are long gone, public IXes are no longer guaranteed to  
give you problems.

> 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.

Do you mean "save money on transit" when you say "make you spare money  
on transit"?  Just want to make sure we are on the same page.

That is not an assumption, it is a provable - or disprovable! - fact.   
If you run the numbers and the IX saves you money, well, it saves you  
money.  If it does not, it does not.  Where does the word "assumption"  
come in?

That doesn't mean they are not also additional vectors.  But Item #1  
does not conflict with Item #2.

-- 
TTFN,
patrick