Fast IP Rerouting Using Multiple Routing Configurations
V. Santhosh Kumar, Venkatesh Shankar, Monisha S Reddy · 2012
As the Internet takes an increasingly central role in our communications infrastructure. The slow convergence of routing protocols after a network failure becomes a growing problem. To assure fast recovery from link and node failures in IP networks, we present a new recovery scheme called Multiple Routing Configurations (MRC). Our proposed scheme guarantees recovery in all single failure scenarios, using a single mechanism to handle both link and node failures, and without knowing the root cause of the failure. MRC is strictly connectionless, and assumes only destination based hop by hop forwarding. MRC is based on keeping additional routing information in the routers, and allows packet forwarding to continue on an alternative output link immediately after the detection of a failure. It can be implemented with only minor changes to existing solutions. In this paper we presented MRC, and analyze its performance with respect to scalability, backup path lengths, and load distribution after a failure. We also show how an estimate of the traffic demands in the network can be used to improve the distribution of the recovered traffic, and thus reduce the chances of congestion when MRC is used. IN recent years the Internet has been transformed from a special purpose network to a ubiquitous platform for a wide range of everyday communication services. The demands on Internet reliability and availability have increased accordingly. A disruption of a link in central parts of a network has the potential to affect hundreds of thousands of phone conversations or TCP connections, with obvious adverse effects. The ability to recover from failures has always been a central design goal in the Internet . IP networks are intrinsically robust, since IGP routing protocols like OSPF are designed to update the forwarding information based on the changed topology after a failure. This re-convergence assumes full distribution of the new link state to all routers in the network domain. When the new state information is distributed, each router individually calculates new valid routing tables. This network-wide IP re-convergence is a time consuming process, and a link or node failure is typically followed by a period of routing instability. During this period, packets may be dropped due to invalid routes. This phenomenon has been studied in both IGP and BGP context , and has an ad-verse effect on real-time applications . Events leading to a re-convergence have been shown to occur frequently . Much effort has been devoted to optimizing the different steps of the convergence of IP routing, i.e., detection, dissemination of information and shortest path calculation, but the convergence time is still too large for applications with real time demands . A key problem is that since most network failures are short lived , too rapid triggering of the re-convergence process can cause route appalling and increased network instability . The IGP convergence process is slow because it is reactive and global. It reacts to a failure after it has happened, and it involves all the routers in the domain. In this paper we present a new scheme for handling link and node failures in IP networks. Multiple Routing Configurations (MRC) is a proactive and local process, and a link or node failure is typically followed by a period of routing instability. During this period, packets may be dropped due to invalid routes. This phenomenon has been studied in both IGP and BGP context , and has an adverse effect on real-time applications . Events leading to a re-convergence have been shown to occur frequently . Much effort has been devoted to optimizing the different steps of the convergence of IP routing, i.e., detection, dissemination of information and shortest path calculation, but the convergence time is still too large for applications with real time demands . A key problem is that since most network failures are short lived , too rapid triggering of the re-convergence process can cause route mapping and increased network instability . The IGP convergence process is slow because it is reactive and global. It reacts to a failure after it has happened, and it involves all the routers in the domain. In this paper we present a new scheme for handling link and node failures in IP networks. Multiple Routing Configurations(MRC) is a proactive and local, the main idea of MRC is to use the network graph and the associated link weights to produce a small set of backup network configurations. The link weights in these backup configurations are manipulated so that for each link and node failure, and regardless of whether it is a link or node failure, the node that detects the failure can safely forward the incoming packets to-wards the destination on an alternate link. MRC assumes that the network uses shortest path routing and destination based hop-by-hop forwarding. The shifting of traffic to links bypassing the failure can lead to congestion and packet loss in parts of the network. This limits the time that the proactive recovery scheme can be used to forward traffic before the global routing protocol is informed about the failure, and hence reduces the chance that a transient failure can be handled without a full global routing re-convergence. Ideally, a proactive recovery scheme should not only guarantee connectivity after a failure, but also do so in a manner that does not cause an unacceptable load distribution. This requirement has been noted as being one of the principal challenges for pre-calculated IP recovery schemes. With MRC, the link weights are set individually in each backup configuration. This gives great flexibility with respect to how the recovered traffic is routed. The backup conjurations used after a failure is selected based on the failure instance, and thus we can choose link weights in the backup configurations that are well suited for only a subset of failure instances.