# A lia Atlas (Juniper Networks) Gabor Enyedi , Andras Csaszar (Ericsson) IETF 83, Paris, France - PowerPoint PPT Presentation

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Algorithms for computing Maximally Redundant Trees for IP/LDP Fast-Reroute draft-enyedi-rtgwg-mrt-frr-algorithm-01. A lia Atlas (Juniper Networks) Gabor Enyedi , Andras Csaszar (Ericsson) IETF 83, Paris, France. Agenda. Briefly about the algorithm Problem Avoid using a node

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

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## 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

### Agenda

• Problem

• Avoid using a node

• Non-2-connected networks

### Agenda

• Problem

• Avoid using a node

• Non-2-connected networks

E

G

D

Root

C

S

B

A

H

• 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

• S<<E

• Blue path: increasing [S, E]

• Red path: decreasing [Root, S] and [E, Root]

E

G

D

Root

C

S

B

A

H

• S>>A

• Blue path: increasing [S,Root] and [Root, A]

• Red path: decreasing [A, S]

E

G

D

Root

C

S

B

A

H

• 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

### Agenda

• Problem

• Avoid using a node

• Non-2-connected networks

### 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

### Agenda

• Problem

• Avoid using a node

• Non-2-connected networks

### 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

### 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

### 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

### 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

### 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

### Agenda

• Problem

• Avoid using a node

• Non-2-connected networks

### Non-2-connected problem

• In this case we don’t have a single order

• Neither a partial order

• Nor a total order

C

A

Non-root block

X

Local root block

D

B

### Non-2-connected problem

• In this case we don’t have a single order

• Neither a partial order

• Nor a total order

C

A

X1

Non-root block

Local root block

X2

D

B

Thank you!