NOVEL ALGORITHMS FOR IP FAST REROUTE (DRAFT)

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14Not-Via and a possible way to eliminate or at least to mitigate them.The most important drawback of Not-Via is based on that this technique usesIP addresses for indicating failed resource, making operators to face serious addressmanagement challenges. Furthermore, Not-Via needs numerous shortest path treecomputations, generating signicant additional complexity. Finally, Not-Via needstreating some special cases making the algorithm hard to trace for debugging ordevelopment purposes.THESIS 4: [C5][C6] I have shown that utilizing the concept of maximally redundanttrees for backup paths, the computational and management complexity of Not-via canbe reduced to a level that is on par with the complexity of traditional shortest pathrouting.THESIS 4.1: I have redened the backup path computing method of Not-via, sothat detours are organized over maximally redundant trees. I called the new IPFRRmethod as Lightweight Not-via.Instead of computing numerous shortest paths for backup paths, Lightweight Notviacomputes a pair of maximally redundant trees for all the nodes of the network asa root. Since I have not modied the computing of the default paths, if there is nofailure the shortest paths are used. If a failure shows up, Lightweight Not-via usestunnels to transport the packet to the next-next hop, as the original technique does,but now, packets on detour are forwarded along one of maximally redundant treesrooted at the next-next hop.THESIS 4.2: I have shown that Lightweight Not-via uses only three IP addressesper node at most.Remark: Lightweight Not-Via does not need additional IP addresses at all in mostof current IP networks.Since there are only maximally redundant trees rooted at a node, a default addressis needed for shortest path routing and two additional for selecting the propermaximally redundant tree. In contrast, three IP addresses is the absolute minimumof the original Not-via, reachable only in point-to-point networks with ring topology.Furthermore, the the number of additional IP addresses needed by the originalNot-via scales quadratic with the nodes in LANs.Moreover, since each node has only a constant number of IP addresses, in mostof current IP networks no additional address is needed at all. In these networks eachinterface has its own IP address, and the router itself has another loopback address.The loopback addresses can be used as default addresses and two interface addressesfor detours. Since rerouting needs networks to be 2-node-connected, at least twointerfaces per node is common.THESIS 4.3: I have shown that Lightweight Not-via asymptotically eliminates theadditional complexity penalty that stems from the need to compute backup paths for
IP Fast ReRoute.Computing the next hops on maximally redundant trees rooted at each nodeneeds only O(e) time. Additionally, since default paths are the shortest ones, usingDijkstra's algorithm is also needed. Thus, the overall complexity of computing thepaths of Lightweight Not-via is O(e + n log n + e) = O(n log n + e), which equals thecomplexity of the mere Dijkstra's algorithm.THESIS 4.4: By means of extensive measurements conducted on an IP Fast ReRouteprototype with real trac traces, I have shown that the extra management and computationalburden of the original Not-via is higher than that of the Lightweight Not-viaby at least one order of magnitude.I used the full-edged Not-via and Lightweight Not-via prototype network deployedat Department of Telecommunications and Media Informatics at BudapestUniversity of Technology and Economics. I injected articial Link State Advertisements(LSAs) of various real-life network topologies into the Link State Database ofthe routers and I measured the computational complexity and the number of addressesneeded.15
Page 2 and 3: 21 IntroductionIP has come a long w
Page 4 and 5: 4Figure 1: Loop in a network with i
Page 6 and 7: 6Figure 3: A pair of node-redundant
Page 8 and 9: 8almost fullling DAG properties. Mo
Page 10 and 11: 10Algorithm 2 Finding the edges (h
Page 13: THESIS 3.4: I dened heuristics to c
Page 17: 17Publication of new results[J] Jou

NOVEL ALGORITHMS FOR IP FAST REROUTE (DRAFT)

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