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

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 3 B A H 1 2

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

15. Possible cases If dst<<src, failed node F
Otherwise: it may be on the BLUE path 8 7 E G 6 D
Root C S 4 5 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
Root 4 C S 5 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 1 A H 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!