Algorithms for computing Maximally Redundant Trees for IPLDP

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 1

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

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

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

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 5

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 6

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 7

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 8

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

Three trees • We have 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 S Dest 1 10 No redundant pair for that! 1 B A 1 10

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

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 12

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

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

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

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

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

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 B X Local root block D 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 C X 1 Non-root block B Local root block X 2 D 19

Thank you! 20