[mrngm]

Ideally, participants in an internet exchange purely exchange routing information, usually using the Border Gateway Protocol (BGP). This implies that devices connected to an internet exchange are routers. These devices receive routes for other autonomous systems (AS), and (selectively) publish their routes to other parties on the internet exchange.

(Internet exchanges typically offer a route server, such that every participant of the IX can easily publish routes for other participants, and simultaneously receive published routes of all other participants.)

The _effect_ of exchanging routing information is that IX-local participants know where to send traffic destined for certain IP ranges from other participants.

An autonomous system internally "knows" where each of their routers are located, and all these routers are typically connected with each other. When several routers of an AS are connected on different IXes, this means they can take informed decisions on where to send traffic destined for other ASes. It could be that AS 64496 is only present in IX-A, while AS 64510 is only present at IX-B. Suppose AS 64499 is connected to both IX-A and IX-B, traffic sourced from AS 64499 (e.g. endusers or "eyeballs") and destined for either 64496 or 64510 knows, through internally exchanged routes, where to send that traffic.

Scale this to even more autonomous systems and IXes in different geographic reasons, and you'll find it becomes a network of networks, or: the internet.

[Hikikomori]

>Ideally, participants in an internet exchange purely exchange routing information

I would hope they exchange Internet traffic as well.

[mrngm]

That really depends on local policy. It could be that an AS x present on multiple IXes (assuming another peer AS y is present on the same IXes) prefers sending traffic for AS y on IX t, while AS y prefers sending traffic for AS x on IX v.

Of course, the goal is to transport traffic in many directions, but in essence only routing information is explicitly exchanged.