The last time I got a tour of the SIX, there were switches on two different floors in the Westin building. This is more for capacity than redundancy. The origi

The last time I got a tour of the SIX, there were switches on two different floors in the Westin building. This is more for capacity than redundancy. The original location is literally a janitor's closet in a hallway and it's so tight that exhaust fans are built into the door. The second location was in proper four-post racks in a small room. It is possible they have ports on both switches for redundancy but more likely both are on the newer location. The SIX is also built into other buildings and they could connect to more than one, but there is typically only 200G backhaul to the other sites. https://www.seattleix.net/topology https://www.seattleix.net/topology 2x100G to an IX are usually connected as separate ports, each with their own assigned IP ont he IX subnet. BGP multipath can enable load balancing across both ports. Otherwise you might have some peers configured on one port and others on the second. These days I like to have all peers on both ports and use BGP multipath. If both ports are connected to a single switch on the IX side and the same router on the customer side then LACP can be used to combine them into a single 200G port with one IP. This is a less common configuration unless you are doing more than two ports (4x100G as 2x 2x100G lags for example). There is another consideration: what happens if there is an icmp or arp flood on the IX? It's not supposed to happen but sometimes it does, even on the most major and well-run exchanges. In that case you might want to have all of your IX ports on one of your routers, keeping the other one "clean", just in case your control plane policing doesn't mitigate it. Different networks place different priority on IX ports. In most cases it's ok if it's down for a short time (traffic will just shift to paid transit) so redundancy is not essential. In other cases it may be too much traffic to reroute so you care more about IX reliability and redundancy.