> On Feb 23, 2024, at 01:09, Dave Cohen <craetdave@gmail.com> wrote:
> Prior to roughly 2016-17, most IXs in the US that we worked with were in a single site

The vast majority of IXPs are still in a single site, but all the ones with normal switch-fabric extension policies are on a growth path to multiple sites, provided the markets they’re in are of sufficient size to support it.  Both of those things have been the case for more than thirty years.

> …that site was often not a third-party facility, often a private R&E oriented datacenter.

Can you explain in more words what you’re saying here?  IXPs spring up in all kinds of sites…  Many of them are in closets of buildings which happen to have multiple ISPs already present because all of the ISPs already have customers in the building.  Some of them are in datacenters, and some of those are “neutral” datacenters, while others are owned or operated by one of the participating networks, and others are governmental or academic.  There’s a very wide diversity of IXP siting arrangements, and often individual IXPs are spread across several different kinds of sites; that’s always been the case.

Over time, existing IXPs, as they grow, tend to spread across more sites; but also, new IXPs form, which almost always form in a single location before growing to multiple sites.  IXPs that _start_ organically in multiple sites simultaneously certainly aren’t common.

                                -Bill