IS IS Reducing Failure Detection

Introduction

The amount of time an ISIS router takes to detect a failure can be tuned with some best practices, which relate to BFD, dampening, hello parameters or point to point timers.

Reducing Failure Detection

  • The sooner networks can detect failure, the sooner they can react and propagate alternate routing information.
  • Below are some of the features that help with detection:
    • BFD
    • IP Event Dampening
    • Hello Parameters
    • Point to Point Network type.

BFD

  • Bidirectoin Forwarding Detection is an independent protocol that sends hellos on the physical interface.
  • It has the publisher subscriber model, where ISIS subscribes to BFD events.
  • Depending on the hardware platform, BFD can detect a failure in 100s of msec.

IP Event Dampening

  • Prevents flapping interfaces from destabilizing the network of constant convergence.
  • Using exponential delay, interface state is suppressed until interface is stable.

Hello Parameters

  • Option should be used when BFD is not supported on an interface.
  • Lowering the hello timers, increasing the bandwidth and CPU requirements.

Point to Point Network Type

  • Eliminates the need to have a DIS or DR.
  • No need to elect a new DIS.
  • No need to flood CSNP for database synchronization.

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