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Understanding High Availability of IP and MPLS Networks

Chapter Description

This chapter describes major sources of network failures and provides an overview of techniques that are commonly used to improve availability of IP/MPLS networks. In particular, this chapter outlines mechanisms for reducing network downtime due to control-plane failures.

Scope of the Book

From the discussions in this chapter so far, you know that the design of carrier-class IP/MPLS networks involves reducing both unplanned and planned outages by using a variety of fault-tolerance techniques, including node-level hardware redundancy, control-plane software redun-dancy, MPLS-layer redundant LSPs, OAM mechanisms, and in-service software upgrades. In short, the reliability and availability of an IP/MPLS network encompasses a broad set of functional areas.

The main purpose of this book is to describe IP/MPLS control-plane fault-tolerance mecha-nisms that enable you to reduce downtime and improve network availability (by reducing unplanned IP/MPLS control-plane failures). Specifically, this book intends to cover three aspects of the control plane, as follows:

  • IP/MPLS forwarding-plane NSF mechanisms that allow a router to continue to forward traffic while its control plane recovers from a failure

  • IP/MPLS control-plane restart mechanisms that enable IP/MPLS control-plane components to restart and recover state without disrupting the forwarding plane

  • Use of the previous two mechanisms to reduce downtime in the converged IP/MPLS backbone when using MPLS applications such as traffic engineering (TE), Layer 2 VPNs (L2VPNs), and Layer 3 VPNs (L3VPNs).

In the remainder of this book, it is assumed that the control-plane software executes as a single image containing inseparable nonrestartable components. A detailed discussion of process-level modularity and restartability is beyond the scope of this book.

Although for completeness sake fault-tolerance mechanisms such as MPLS FRR, MPLS OAM, and in-service software upgrades are briefly mentioned in a later chapter, a detailed discussion of these mechanisms is also beyond the scope of this book.

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