G 120008 edges are links and business rela9onships 4

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Unformatted text preview: nce & Engineering 19 10/29/13 Topic •  More on shortest path routes –  Allow mul9ple shortest paths F G A Use ABCE and E ABE from Aà༎E D B H C 67 Mul9path Rou9ng •  Allow mul9ple rou9ng paths from node to des9na9on be used at once –  Topology has them for redundancy –  Using them can improve performance •  Ques9ons: –  How do we find mul9ple paths? –  How do we send traffic along them? 68 20 10/29/13 Equal- Cost Mul9path Routes •  One form of mul9path rou9ng •  Extends shortest path model –  Keep set if there are 9es G •  Consider Aà༎E –  ABE = 4 + 4 = 8 –  ABCE = 4 + 2 + 2 = 8 –  ABCDE = 4 + 2 + 1 + 1 = 8 –  Use them all! F 2 4 E 3 10 3 1 4 A 4 B H 2 D 1 2 3 C 69 Source “Trees” •  With ECMP, source/sink “tree” is a directed acyclic graph (DAG) –  Each node has set of next hops –  S9ll a compact representa9on Tree DAG 70 21 10/29/13 Source “Trees” (2) F •  Find the source “tree” for E –  Procedure is Dijkstra, simply G remember set of next hops –  Compile forwarding table similarly, may have set of next hops A •  Straighxorward to extend DV too 2 4 3 3 E 10 1 4 4 B H –  Just remember set of neighbors 2 D 1 2 3 C 71 Source “Trees” (3) Source Tree for E E’s Forwarding Table F 2 4 G E 3 10 3 1 4 A 4 B H New for ECMP D 2 1 2 3 Node A B C D E F G H Next hops B, C, D B, C, D C, D D -F F C, D C 72 22 10/29/13 ECMP Forwarding •  Could randomly pick a next hop for each packet based on des9na9on –  Balances load, but adds jiler •  Instead, try to send packets from a given source/des9na9on pair on the same path –  Source/des9na9on pair is called a flow –  Hash flow iden9fier to next hop –  No jiler within flow, but less balanced 73 ECMP Forwarding (2) Mul9path rou...
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This document was uploaded on 04/04/2014.

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