Fast recovery in IP networks using Multiple Routing Configurations

1. Fast recovery in IP networks using Multiple Routing Configurations Amund Kvalbein Simula Research Laboratory

2. Motivation • Increasing use of the Internet for applications with stringent performance requirements • Telephony, videoconferencing, online games • ISPs must adhere to tough SLAs • The recovery mechanisms in the Internet are not designed for these requirements • Many (most) failures are short lived • Failures are advertised too widely! • This gives slow reaction and fosters instability GaTech networking seminar

3. Our approach • Failure reaction should be local • To avoid instability and overhead • Challenge: avoid loops • Failure reaction should be proactive • To reduce recovery times and packet loss • Challenge: minimize overhead GaTech networking seminar

4. Outline • Multiple Routing Configurations • The basic idea • Generating backup configurations • Forwarding • Evaluation • Load balancing improvement • Implementation issues • Wrap up GaTech networking seminar

5. Multiple Routing Configurations • Guaranteed protection against single link, node or SRLG failures • Same mechanism for both link and node failures • Generally difficult to distinguish at neighbor • A configuration is the graph and the weight function • Different weight setting in each configuration GaTech networking seminar

6. The general observation • An unused link can fail without consequences • So can a single-connected node • Several links and/or nodes can be protected in one logical topology • All nodes are still reachable • Build topologies so that all elements are protected • Few such topologies are needed to protect all elements! GaTech networking seminar

7. Isolated links and nodes • An isolated link has infinite weight • A restricted link has a high weight wr • wr is chosen so that the link is used only as a ”last resort” • A node is isolated when all attached links are either isolated or restricted Traffic never goes through an isolated link or an isolated node! GaTech networking seminar

8. Building backup configurations 6 1 7 4 2 5 0 3 C0 GaTech networking seminar

9. Building backup configurations 6 6 6 1 1 1 7 7 7 4 4 4 2 2 2 5 5 5 0 0 0 3 3 3 C1 C2 C3 GaTech networking seminar

10. Forwarding 6 6 1 1 7 7 4 4 2 2 5 5 0 0 3 3 GaTech networking seminar

11. How many configurations are needed? 32 64 128 512 16 GaTech networking seminar

12. How long are the backup paths? GaTech networking seminar

13. What about load distribution? GaTech networking seminar

14. Why bother to avoid overload?- it’s only for short while… • Motivation for fast rerouting • Do not loose packets • Increase stability • FRR should not make it worse for unaffected traffic GaTech networking seminar

15. Routing performance during FRR • Given TM estimate: What decides the load distribution? • Link weights in C0 • Structure of backup configurations • Link weights in backup configurations • Three step approach • Optimize link weights in C0 • Build backup configurations • Optimize link weights in backup configurations GaTech networking seminar

16. Building backup configurations • Optimize C0 independently • Identify the ”heaviest” nodes (most traffic) • Build configs with good connectivity for heavy nodes GaTech networking seminar

17. Optimizing link weights • Heavy optimization task • Dependencies between configurations • Local weight search heuristic • Based on well known Fortz/Thorup method • Optimize only for most severe link failures • Take advantage of configuration structure • A link failure only activates one or two backup configurations GaTech networking seminar

18. Evaluation – Max link load • Real and synthetic network topologies • Gravity model traffic demands GaTech networking seminar

19. Evaluation – Number of configurations GaTech networking seminar

20. Implementation issues • Representing backup configurations • IETF: Multi-Topology routing • Can calculate independent shortest path trees in each topology • Need ability to switch configuration in-flight • Marking packets • Same problem as in MT-routing • Reuse of ToS/DSCP bits has been proposed GaTech networking seminar

21. Summary • MRC guarantees protection against any single link or node failure • Modest state overhead • Small path length stretch for recovered traffic • Flexibility in how recovered traffic is routed • Realistic to implement GaTech networking seminar

22. Related work • Failure Insensitive Routing (FIR) • Relies on interface-specific routing tables to infer link failures • Not-via addresses • Calculates one ”configuration” for each protected element GaTech networking seminar

23. MRC extensions • Multi-failure protection • SRLG, uncorrelated failures • Can guarantee protection against two independent failures (at a cost) • Improved configuration construction • Eliminate isolated links • Use deflection in forwarding procedure • Use in TE context • Spread demands on several topologies • Lab implementation • Using Quagga routing software GaTech networking seminar