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

Sept GaTech networking seminar2 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

Sept GaTech networking seminar3 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

Sept GaTech networking seminar4 Outline Multiple Routing Configurations –The basic idea –Generating backup configurations –Forwarding Evaluation Load balancing improvement Implementation issues Wrap up

Sept GaTech networking seminar5 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

Sept GaTech networking seminar6 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!

Sept GaTech networking seminar7 Isolated links and nodes An isolated link has infinite weight A restricted link has a high weight w r –w r 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!

Sept GaTech networking seminar8 Building backup configurations C0C0

Sept GaTech networking seminar C1C1 C2C2 C3C3 Building backup configurations

Sept GaTech networking seminar10 Forwarding

Sept GaTech networking seminar11 How many configurations are needed?

Sept GaTech networking seminar12 How long are the backup paths?

Sept GaTech networking seminar13 What about load distribution?

Sept GaTech networking seminar14 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

Sept GaTech networking seminar15 Routing performance during FRR Given TM estimate: What decides the load distribution? –Link weights in C 0 –Structure of backup configurations –Link weights in backup configurations Three step approach –Optimize link weights in C 0 –Build backup configurations –Optimize link weights in backup configurations

Sept GaTech networking seminar16 Building backup configurations Optimize C 0 independently Identify the ”heaviest” nodes (most traffic) Build configs with good connectivity for heavy nodes

Sept GaTech networking seminar17 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

Sept GaTech networking seminar18 Evaluation – Max link load Real and synthetic network topologies Gravity model traffic demands NetworkFailure free MRC n=5 MRC n=10 OSPF Geant Cost Sprint US (POP) German Telecom

Sept GaTech networking seminar19 Evaluation – Number of configurations

Sept GaTech networking seminar20 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

Sept GaTech networking seminar21 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

Sept GaTech networking seminar22 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

Sept GaTech networking seminar23 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