North American Network Operators Group

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Re: Question on the topology of Internet Exchange Points

  • From: Patrick W. Gilmore
  • Date: Sat Feb 16 10:35:19 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.