Validating packet origin using external route information

URPF is a widely used technology for filtering source IP spoofed packets by using route information. With uRPF filtering, a router automatically updates filtering rules based on its route information and does not require manual changes by operators. However, uRPF, specifically when it is in strict mode, has a drawback in that it may incorrectly detect packets as spoofed when a route is asymmetric, i.e., the routes from and to the sender are different from each other. This is due to uRPF using the internal (receiving router´s own) route information. In this paper, we present a method for filtering using external route information. Here, external means that the route information of sender routers is included. Generally, however, the route information of sender routers is not available. Thus, we use publicly available route information, which is provided by research projects, and infer the route information of sender routers.