Two-stage IP-address lookup in distributed routers

IP-address lookup is the primary processing function of Internet routers. While a wide range of algorithms have been developed to perform lookups, very few of them have the distributed architecture of current and future routers in consideration. To support rapidly increasing high data rates, packet processing in commercial routers today are divided into an ingress and an egress part, with the lookup performed at the ingress. In the lookup, the egress line card, the outgoing interface and the nexthop address of a given packet are determined. In this paper, we propose an alternative scheme to perform the lookup by dividing the task, which is named two-stage lookup scheme. In the lookup, the ingress determines the egress only, then it is up to the egress to determine the outgoing interface and the nexthop address. Based on our analysis and experimental study, we conclude that the proposed scheme has several advantages in both hardware lookup technologies and software lookup algorithms. In particular, it provides significantly more efficient high-speed packet lookup.