Institute of Computer ScienceDepartment of Distributed Systems

Prof. Dr.-Ing. P. Tran-Gia

Loop-Free Alternates and Not-Via Addresses:A Proper Combination for IP Fast Reroute?

Rüdiger Martin, Michael Menth, Matthias Hartmann

University of Wuerzburg

Germany

Amund Kvalbein, Tarik Cicic

Simula Research Laboratories

Norway

IETF 70, Vancouver, CanadaRTGAREA Meeting

2Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Overview

Qualitative comparison: loop-free alternates (LFAs) vs. not-via addresses

LFAs Taxonomy Appropriate usage for different protection levels

Combined usage of LFAs and not-vias Availability of LFAs for different protection purposes Paths prolongation Decapsulation load from tunneled not-via traffic

Conclusion

3Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

LFAs and Not-Vias: Qualitative Comparison

LFAs Not-Vias

Tunneling + -

Backup path length + (?) o (?)

Computational routing complexity

o o

Failure coverage < 100% 100%

Compatibility with loop-free re-convergence schemes

o +

Protection of multicast traffic

- +

Adaptability to SRLGs - +

4Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Combined Use of LFAs and Not-Vias

Not-vias Coverage of 100% single failures More elegant and powerful

LFAs Readily available in today‘s routers No tunneling

– MTU issues– Performance issues on old hardware– Operators just don‘t like it

Idea to achieve 100% failure coverage Use LFAs where possible Use not-vias where needed

5Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Classification of Neighbors wrt a Destination

Neighbor nodes of router can be classified into Nodes protecting link and node failures

1. ECAs2. Downstream LFAs3. Non-downstream LFAs

Nodes protecting only link failures4. ECAs5. Downstream LFAs6. Non-downstream LFAs

Nodes leading to loops when traffic is sent to (7)

All neighbors

General LFAs

Downstream LFAs

Equal-cost alternate

LFC

DSC

ECA

7

2

3

5

6

41

NPC

NPC

NPC

6Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

LFAs and Not-Vias: Combination Options

Protection levels(i) Protection against all single link failures

(1), (4), (2), (5), (3), (6), and not-via

All neighbors

General LFAs

Downstream LFAs

Equal-cost alternate

LFC

DSC

ECA

7

2

3

5

6

41

NPC

NPC

NPC

7Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

LFAs and Not-Vias: Combination Options

Protection levels(i) Protection against all single link failures

(1), (4), (2), (5), (3), (6), and not-via

(ii) Protection against all single link and all single node failures (1), (2), (3), and not-via; (4), (5), and not-via for last link

All neighbors

General LFAs

Downstream LFAs

Equal-cost alternate

LFC

DSC

ECA

7

2

3

5

6

41

NPC

NPC

NPC

8Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

LFAs and Not-Vias: Combination Options

Protection levels(i) Protection against all single link failures

(1), (4), (2), (5), (3), (6), and not-via

(ii) Protection against all single link and all single node failures (1), (2), (3), and not-via; (4), (5), and not-via for last link

(iii) Protection against all single link and all single node failures with loop avoidance in the presence of multi-failures (1), (2), and not-via; (4), (5), and not-via for last link

All neighbors

General LFAs

Downstream LFAs

Equal-cost alternate

LFC

DSC

ECA

7

2

3

5

6

41

NPC

NPC

NPC

9Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Applicability of LFAs and Not-Vias

GEANT: resilience requriement (i): only link protection

0-80% not-vias required All ECAs link- & node- protecting No other dwnstrm LFAs

1

2

6

415

3

13

1214

8

10 917

1118

16

0

7

5

10Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Applicability of LFAs and Not-Vias

GEANT: resilience requriement (ii): link and node protection

1

2

6

415

3

13

1214

8

10 917

1118

16

0

7

5

• 20-100% not-vias required

11Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Applicability of LFAs and Not-Vias

GEANT: resilience requriement (iii): link, node protection, loop avoidance for multi-flrs

• 20-100% not-vias required

1

2

6

415

3

13

1214

8

10 917

1118

16

0

7

5

12Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Path Prolongation

GEANT

(protection of only link failures)(protection of link & node flrs, loop avdnce for mltflrs)

1

2

6

415

3

13

1214

8

10 917

1118

16

0

7

5

13Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Decapsulated Traffic from Not-Via Tunnels

GEANT

14Michael Menth

Loop-Free Alternates and Not-Via Addresses: Proper Combination for IP Fast Reroute?

Conclusion

Classification of LFAs Combined usage of LFA and not-via to achieve 100% failure coverage

Applicability of LFA types depends on desired protection level Availability of applicable LFA types to protect a dest depends on

– Topology and position of node in the network

– Desired protection level Backup path length

– Longer with IPFRR than with IP reconvergence

– Small difference between combined usage and not-vias only Decapsulated traffic with combined usage and not-vias

– Less in many cases

– Maximum about the same Same link utilization for both mechanisms (not shown)

LFAs attractive as a short-term solution