FSM health status support in BFD
draft-bfd-fsm-health-status-00

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Author Palpandi Perumal 
Last updated 2020-10-13
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Network Working Group                         Palpandi Perumal
Internet Draft                                Pluribus Networks
Updates: 5880 (if approved)                                   
Intended status: Proposed Standard 
Expires: April 14, 2021                       October 13, 2020

              FSM health status support in BFD
               draft-bfd-fsm-health-status-00

Abstract

Bidirectional Forwarding Detection operates in different modes.
When BFD runs in asynchronous mode requires hello packet needs
to be transmitted and received on regular intervals. In software
based BFD application, hello packets processing path may be
heavy weight which may involve many processing levels to reach
BFD application. On a scaled system, processing delay may not
be constant at all the time and this processing delay does appear
at any point between software path entry point and BFD application.
This delay needs to be identified and suppressed otherwise system
may end up on false link failure detection. This internet draft
deals on this particular case.

Since introducing new Diagnostic bit, it requires to update RFC5880.

Status of this Memo

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   This Internet-Draft will expire on April 14, 2021

Palpandi Perumal         Expires April 14, 2021            [Page 1]
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Internet-Draft           BFD FSM health status        October 13, 2020

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  FSM Diagnostic bit  . . . . . . . . . . . . . . . . . . . . .   2
   3.  Setting up tolerance point on FSM health status . . . . . . .   3
     3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Conventions used in this document . . . . . . . . . . . . . .   4
   5.  Echo BFD  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1. Introduction

The Bidirectional Forwarding Detection describes how to calculate
the FSM timer(Detection timeout). It is calculated basically by
multiplying negotiated transmit interval and detection multiplier.
On a complex software architecture, reaching to BFD application may
involve many queue processing, may require shared critical common
resources and also may involve IP/UDP header processing in kernel
or customised IP stack. Theoretically on a steady system, this software
path should not be delayed. On some critical occasions, this path
may not be in steady state and may introduces some delays. This
latency will be added as variant in the software path. To monitor
this variant, proposing a new diag bit (FSM health status) in the BFD
packet.

2. FSM Diagnostic bit

Currently Bidirectional Forwarding Detection has 8 diagnostic bits
totally to find out the last state change in the local system.
Introducing a new diagnostic bit called FSM health status.
Basically FSM timer value will be set as detection timeout
(multiplication of negotiated transmit interval and detection
multiplier). On asynchronous mode,  FSM timer will be reseted once
the BFD application receives the packet. If there is no packet
received till the detection timeout, BFD will decide this as link
failure and will notify to all routing protocols. Sometime keep alive
packet would have reached to the peer system and from there,
reaching to the BFD application would have been delayed by some
critical events in the software path. This bit will be set when
the FSM timer reaches to certain threshold level upon not receiving
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