> this is kinda the problem though: multicast resource usage on intermediate routers scales according to the number of sessions going through those routers. The more sessions, the more state that the routers need to maintain. I don’t see it that way. If there are 100,000 sessions going on that is 100,000 in a subset of all core routers. A BGP router has 100,000 in every core router. Just to compare. So with multicast routing, you have an opportunity to have less state. But we are only talking about one dimension of scaling. > This is fundamentally different from unicast where it doesn't matter to the router how many sessions or data flows are passing through it. State is state, doesn’t matter how it is created. > We tried session based routing years ago. It was an interesting idea at the time but it didn't work at scale. > > Nick And with overlays you can reduce the state even more at the expense of 'non-perfect replication”. What is the definition of “non-perfect replication”. When a device has to replicate packets that may traverse over the same outgoing interface. What is the definition of “perfect replication”. When a device, typically a high-speed router, replicates packets where it is guaranteed that packet doesn’t go multiple times over that interface. And total perfection, the packet doesn’t traverse over its internal backplane more than once. Dino
