A lia Atlas (Juniper Networks) Gabor Enyedi , Andras Csaszar (Ericsson) IETF 83, Paris, France

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

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

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

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

5. ADAG and partial order • Almost DAG (ADAG) • A<<B if there is a path from A to B • Root is both the shortest and the greatest E G D Root C S B A H

6. ADAG and partial order • S<<E • Blue path: increasing [S, E] • Red path: decreasing [Root, S] and [E, Root] E G D Root C S B A H

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

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] E G D Root C S B A H

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

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: Shortest path 1 C D 10 1 Dest S No redundant pair for that! 1 10 1 B A 1

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

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<<B, let A<B • If A and B are not ordered select either A<B or B<A • This can be done with a topological oder after converting the ADAG into a DAG • Results: • If A<B, either A<<B or A and B are not ordered

13. A possible total order • Numbers are written next to nodes 8 7 E G 6 D Root C S 4 5 0 3 B A H 1 2

14. Possible cases • If dst>>src, failed node F If S<<F<E, it may be on the BLUEpath 8 7 E G 6 D Root C S 4 5 0 3 B Otherwise: it may be on the REDpath A H 1 2

15. Possible cases • If dst<<src, failed node F Otherwise: it may be on the BLUEpath 8 7 E G 6 D Root C S 4 5 0 3 If A<F<<S, it may be on the RED path B A H 1 2

16. Possible cases • If dst and src are not ordered • There are four sub-paths If F>>src, it may be on the first part of the RED path If F and src are not ordered, and F>dest, it may be on the second part of the RED path 7 8 E G 6 D 4 Root C S 5 0 3 F and src are not ordered, and F<dest, it may be on the second part of BLUE path B If F<<src, it may be on the first part of the BLUE path A H 1 2

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

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! C A Non-root block X Local root block D B

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! C A X1 Non-root block Local root block X2 D B

20. Thank you!