I would like to talk about defeating DDOS and scenarios how we can actually use it. Let’s get started ! I’m going to talk about two methods: 1) before you forward any packet, check if you know the return path. If you know, forward the packet, if you don’t – drop it. There are two ways of implementation: strict and loose. First one accepts packets only when the return path is through the interface which is the ingress one. The second one accept any packet if the router has the return path via any interface. As you can see you can’t use this solution for transit or multihomed networks. It should be rather singlehomed, stub network. During DDOS attackers spoof a source IP and the solution will work (packets will be dropped) only for those with invalid source IP addresses. If the source IP is a valid, the packet will be forwarded. 2) edge router checks if the source IP is the one, which is allocated for particular ISP client – this is the best, easiest for single homed