Internet is composed of numbers of independent autonomous systems. BGP is used to disseminate reachability information and establishing path between autonomous systems. Each autonomous system is allowed to select a single route to a destination and then export the selected route to its neighbors. The selection of single best route imposes restrictions on the use of alternative paths during interdomain link failure and thus, incurred packet loss. Packet loss still occurs even when multiple paths exist between source and destination but these paths have not been utilized. To minimize the packet loss, when multiple paths exist, multipath routing techniques are introduced. Multipath routing techniques ensure the use of alternative paths on link failure. It computes set of paths which can be used when primary path is not available and it also provides a way to transit domains to have control over the traffic flow. This can be achieved by little modification to current BGP. This paper highlights different multipath routing techniques and also discusses the overhead incurred by each of them.
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