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1 Algorithms for computing Maximally Redundant Trees for IP/LDP Fast-Reroute draft-enyedi-rtgwg-mrt-frr-algorithm-01 Alia Atlas (Juniper Networks) Gabor Enyedi, Andras Csaszar (Ericsson) IETF 83, Paris, France

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2 Agenda Briefly about the algorithm Problem Avoid using a node Non-2-connected networks

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3 Agenda Briefly about the algorithm Problem Avoid using a node Non-2-connected networks

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4 ADAG and partial order Root A B C E H S G D

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5 ADAG and partial order Root A B C E H S G D Almost DAG (ADAG) A<**
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6 ADAG and partial order S<

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7 ADAG and partial order S>>A –Blue path: increasing [S,Root] and [Root, A] –Red path: decreasing [A, S] Root A B C E H S G D

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8 ADAG and partial order S and C are not ordered –Blue path: [S, E] and [C, E] –Red path: [A, S] and [A, C] Root A B C E H S G D

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9 Agenda Briefly about the algorithm Problem Avoid using a node Non-2-connected networks

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10 Three trees We have tree trees –SPT –Two MRTs There is no connection between SPT and MRTs Impossible to find a redundant pair for SPT Example: S C BA D Dest Shortest path No redundant pair for that!

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11 Agenda Briefly about the algorithm Problem Avoid using a node Non-2-connected networks

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12 Total order Partial order can compare any X only with S –We need to compare any two nodes Make a total order as well –If A<**
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13 A possible total order Numbers are written next to nodes Root A B C E H S G D

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14 Possible cases If dst>>src, failed node F Root A B C E H S G D If S<

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15 Possible cases If dst<

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16 Possible cases If dst and src are not ordered –There are four sub-paths Root A B C E H S G D If F>>src, it may be on the first part of the RED path If F<

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17 Agenda Briefly about the algorithm Problem Avoid using a node Non-2-connected networks

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18 Non-2-connected problem In this case we don’t have a single order –Neither a partial order –Nor a total order Convert the GADAG into an ADAG! A B X C D Non-root blockLocal root block

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19 Non-2-connected problem In this case we don’t have a single order –Neither a partial order –Nor a total order Convert the GADAG into an ADAG! A B X1 C D Non-root block X2 Local root block

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20 Thank you!

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