Christopher Morrow wrote:
2 way flow means something on your home host or home gateway. It means very little at internet scale... since, in many cases, you -> server and server -> you are not sharing many of the same links / routers / etc.
Subject suggests it's retail ISP to homes, which are unlikely to be multihomed.
It probably depends on where you want to do such limiting, right? "At peering/transit edge" - save your core, dont' carry traffic you "know" you will throw away anyway. "At the customer edge" - scaling of state management could be problematic && you'll carry this 'bad' traffic across your network.
Limiting is not by edges but by ISPs. In transit ISPs, there are numerous flows generated by customers of other ISPs that customer wise rate limiting does not scale. In access ISPs, revenue increases proportional to the number of customers that you can prepare rate limiting devices proportional to the number of customers to make customer wise rate limiting scale. Masataka Ohta