Maybe it is time to consider layer 3 internet exchanges

Internet exchanges have presented as shared layer 2 networks for thirty years. I will show the mechanisms that silently blackhole exchange traffic or forward it to the wrong port: missing or incorrect neighbour entries, and unknown unicast flooding. In each case BGP stays established to the route servers and nothing reports a fault.

A large exchange stated in writing that it gives no guarantee traffic sent to a peering LAN goes to, and only to, the port of the network it was meant for, and that it knows of no exchange that does. I do not know how many members expect that answer.

The rest of the industry has spent years dismantling large layer 2 domains in favour of routed ones. Perhaps it is time for internet exchanges to forward at layer 3, rather than running a layer 2 forwarding domain with a route server making routing decisions.

Running at layer 3 gives participants complete isolation between ports, the same model that already applies to every other upstream connection that networks buy.