Erzeugung und Optimierung eindeutiger kürzester Pfade für ausfallsicheres IP Routing und Fast Reroute

Transcription

1 Institute of Computer Science Chair of Distributed Systems Prof. Dr.-Ing. P. Tran-Gia Erzeugung und Optimierung eindeutiger kürzester Pfade für ausfallsicheres IP Routing und Fast Reroute, Matthias Hartmann, Michael Menth, Christian Schwartz www3.informatik.uni-wuerzburg.de IP-FAST-RESILIENCE Workshop der ITG Fachgruppe 5.. Stuttgart,

2 Outline Intradomain IP Routing and IP Link Cost Optimization Multiple Shortest Paths Equal Cost Multi Path (ECMP) Single Shortest Path (SSP) and Tie-breakers Tie-breaker Problems Unique Shortest Paths (USP) Probability of USP Solutions Effective Creation and Optimization of USP USP Optimization for Fast Reroute

3 Intradomain Routing in IP Networks Exchange of topology information Calculation of routing table Shortest path principle 0 S D

4 IP Link Cost Optimization Traffic engineering by adjusting link costs Manual cost optimization impossible for larger networks Special tools are required Threshold accepting heuristic Different objective functions Maximum link utilization Penalized average link utilization 4

5 Link Cost Optimization Example Input Parameters (Topology, Traffic Matrix, Failure scenarios) Topology Traffic Matrix Failure Scenarios Optimization Process Optimized Link Costs Threshold Accepting Link Cost Matrix 5

6 Multiple Shortest Paths in IP Networks Flowbased splitting S Flow Flow Flow 3 S Tiebreaker decision 3 3 D Equal Cost Multi Path (ECMP) D Single Shortest Path (SSP) 6

7 Tie-breaker Decisions Different tie-breaker criteria, e.g. forwarding port numbers Tie-breaker criteria not standardized Used information can change Unpredictable path layout Risk of overload even for optimized routing Link utilization up to 00% higher than expected 7

8 Solution: Unique Shortest Paths (USP) S 4 D 3 Link costs are chosen such that no multiple shortest paths exist unique shortest paths Possible for failure-free case S and for a set of protected failure scenarios, e.g. single link failures S L 8

9 Influence of the Allowed Link Cost Range Range to chose link costs from is configurable (maximum range in OSPF: [, 6 ]) Possibilities of path layout depend on allowed link cost range Allowed link cost range may influence USP possibilities For different link cost ranges, networks, and failures Evaluation of 000 random link cost settings on USP property Estimation of the empirical USP probability 9

10 Probability of USP Solutions USP probability Dependency on the allowed link cost range Dependency on the network size Dependency on the failure scenarios 00% 80% 60% 40% 0% 0% S S L Maximum link cost k max TI (3,3) CO (,5) Maximum link costs k max CO 5 GE 60 S EX AT EB AB 56 SP 90 TI 3 Number of links & topologies S L 95 % 50 % % 0

11 Effective Creation and Optimization of USP Extension of the normal heuristic optimizer to create USP solutions Normal Optimization of USP solutions Primary objective: Maximum link utilization Secondardy objective: Penalized average link utilization Optimization with ECMP option to allow multiple paths But additive penalty for each splitting point in solution S S S 000% 500% 40% D D D

12 Maximum link utilization Ψ Algorithm success ratio Effective Creation and Optimization of USP Algorithm success ratio very high even for low USP probability Better optimization results with higher link costs 5 00 % 4 80 % 3 USP probability Best optimization result 60 % 40 % 0 % USP probability 0 0 % Maximum link costs k max

13 Maximum link utilization Average path length Quality of Optimized USP Solutions Similar quality as optimized SSP solutions Similar path lengths Holds for failure-free case and protected failure scenarios SSP USP CO GE EX AT EB AB SP TI 0.0 CO GE EX AT EB AB SP TI Topologies ordered by number of links Topologies ordered by number of links 3

14 Maximum link utilization Average path length Optimization of Fast Reroute USP optimization especially important for Fast Reroute (ECMP not possible, overload even higher due to local repair) USP optimization is possible but still more load and longer paths IP Reconvergence Notvia MPLS OneToOne CO GE EX AT EB AB SP TI 0.0 CO GE EX AT EB AB SP TI Topologies ordered by number of links Topologies ordered by number of links 4

15 Conclusion Multiple shortest paths can lead to problems especially for Fast Reroute USP is an efficient possibility to avoid these problems USP leads to predictable backup paths USP can be efficiently optimized also for Fast Reroute and results are of similar quality as optimized SSP 5

16 Thank you for your attention! 6

17 Kontaktinformationen Michael Menth Matthias Hartmann Phuoc Tran-Gia 7

18 BACKUP SLIDES 8

19 Increase in max. link utilization Severness of Tie-breaker Problems 00% 80% 60% 40% 0% 00% 80% 60% 40% 0% Failure-free S Single link failure S L 0% CO GE EX AT EB AB SP TI Topologies ordered by number of links 9

20 Fast Reroute and Multiple Shortest Paths Precalculation of backup paths based on link costs Immediate path change in case of failures (Tunneling) IP Reconvergence S A B C D Notvia S A B C D MPLS OneToOne S A B C D ECMP on backup paths not possible due to tunnel endpoints 0