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BFD Working Group                                               W. Cheng
Internet-Draft                                                   R. Wang
Intended status: Informational                              China Mobile
Expires: September 8, 2020                                        X. Min
                                                                  A. Liu
                                                                     ZTE
                                                           March 7, 2020


                     Unaffiliated BFD Echo Function
                   draft-cw-bfd-unaffiliated-echo-00

Abstract

   Bidirectional Forwarding Detection (BFD) is a fault detection
   protocol that can quickly determine a communication failure between
   devices and notify upper-layer applications [RFC5880].  BFD has
   asynchronous detecting mode and demand detection mode to satisfy
   different scenarios, also supports echo function as an adjunct to
   both modes to reduce the device requirement for BFD.

   Unaffiliated BFD echo function described in this document reuses the
   BFD echo function as described in [RFC5880] and [RFC5881], but
   independent of BFD asynchronous mode or BFD demand mode, that means
   it doesn't need BFD protocol capability of state machine, but only
   BFD echo function to a deployed device supporting BFD detection.
   When using unaffiliated BFD echo function, just the local device
   works on BFD protocol and the BFD peer doesn't, which only loopback
   the received BFD echo packets as usual data packets without enabling
   BFD protocol.

   Section 6.2.2 of [BBF-TR-146] describes one use case of the
   unaffiliated BFD echo function, and at least one more use case is
   known in the field BFD deployment.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any




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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 8, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Unaffiliated BFD Echo Behavior  . . . . . . . . . . . . . . .   3
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   To minimize the impact of device faults on services and improve
   network availability, a network device must be able to quickly detect
   faults in communication with adjacent devices.  Measures can then be
   taken to promptly rectify the faults to ensure service continuity.

   BFD is a low-overhead, short-duration method to detect faults on the
   path between adjacent forwarding engines.  The faults can be
   interface, data link, and even forwarding engine faults.  It is a
   single, unified mechanism to monitor any media and protocol layers in
   real time.

   BFD has asynchronous detecting mode and demand detection mode to
   satisfy different scenarios, also supports echo function to reduce



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   the device requirement for BFD.  When the echo function is activated,
   the local system sends a BFD control packet and the remote system
   loops back the packet through the forwarding path.  If several
   consecutive echo packets are not received, the session is declared to
   be Down.

   When using BFD echo function, it is not clear whether the devices
   using echo function need to support the full BFD procotol, including
   maintaining the state machine of BFD session as described in
   [RFC5880] and [RFC5881].  According to different understanding, there
   are two typical scenarios as below:

      1.  Full BFD procotol capability with affiliated echo function:
      this scenario requires all the devices to support BFD protocol.

      2.  Only BFD echo function without full BFD procotol capability:
      this scenario requires only the local device to support sending
      BFD packets.

   The two typical scenarios are both reasonable and useful, and the
   latter is referred to as unaffiliated BFD echo function in this
   document.

   Unaffiliated BFD echo function described in this document reuses the
   BFD echo function as described in [RFC5880] and [RFC5881], but
   independent of BFD asynchronous mode or BFD demand mode, that means
   it doesn't need BFD protocol capability of state machine, but only
   BFD echo function to a deployed device supporting BFD detection.
   When using unaffiliated BFD echo function, just the local device
   works on BFD protocol and the BFD peer doesn't, which only loopback
   the received BFD echo packets as usual data packets without enabling
   BFD protocol.

   Section 6.2.2 of [BBF-TR-146] describes one use case of the
   unaffiliated BFD echo function, and at least one more use case is
   known in the field BFD deployment.

2.  Unaffiliated BFD Echo Behavior

   With the more and more application of BFD detection, there are some
   scenarios the BFD echo function is deployed.  And due to the
   different capabilities of the devices deploying BFD echo function,
   it's required to apply unaffiliated BFD echo to the devices that
   couldn't afford the overhead of the full BFD protocol capablity, such
   as the servers running virtual machines or some Internet of Things
   (IoT) devices.  Unaffiliated BFD echo can be used when two devices
   are connected and only one of them supports BFD protocol capability.
   A BFD echo session can be established at the device that supports



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   BFD, and the device will send the BFD echo packets with the IP
   address destined for itself, whereas the other peer device just
   loopback the received BFD echo packets.

   After receiving a BFD echo packet, the device that does not support
   BFD protocol immediately loops back the packet by normal IP
   forwarding, implementing quick link failure detection.  As shown in
   Figure 1, device A supports BFD, whereas device B does not support
   BFD.  To rapidly detect any faults with the IP link between device A
   and device B, a BFD echo session can be provisioned and created at
   device A, and device A starts sending BFD echo packets, which should
   include a BFD echo session demultiplexing field, such as BFD
   discriminator defined in [RFC5880].  After receiving the BFD echo
   packets sent from device A, device B immediately loops back them,
   implementing rapid link fault detection.


   Device A                                   Device B
                      BFD echo session
   BFD Enabled                                BFD Echo packets loopback
   +--------+                                 +---------+
   |   A    |---------------------------------|   B     |
   |        |Inf 1                       Inf 1|         |
   +--------+10.1.1.1/24           10.1.1.2/24+---------+
   BFD is supported.                 BFD is not supported.


            Figure 1: Unaffiliated BFD Echo deployment scenario

3.  Discussion

   Unaffiliated BFD echo function is reasonable and useful.  Firstly,
   unaffiliated BFD echo can use BFD protocol capability in the local
   BFD-supported device, while using IP forwarding capability in the
   peer non-BFD-supported device, so unaffiliated BFD echo can support
   fast detecting and manage BFD sessions very effectively.  Secondly,
   it is scalable when using unaffiliated BFD echo to adapt to different
   capabilities of devices.

4.  Security Considerations

   TBD.

5.  IANA Considerations

   This document has no IANA action requested.





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6.  Acknowledgements

   TBD.

7.  References

7.1.  Normative References

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <https://www.rfc-editor.org/info/rfc5881>.

7.2.  Informative References

   [BBF-TR-146]
              Broadband Forum, "BBF Technical Report - Subscriber
              Sessions Issue 1", 2013, <https://www.broadband-
              forum.org/technical/download/TR-146.pdf>.

Authors' Addresses

   Weiqiang Cheng
   China Mobile
   Beijing
   CN

   Email: chengweiqiang@chinamobile.com


   Ruixue Wang
   China Mobile
   Beijing
   CN

   Email: wangruixue@chinamobile.com


   Xiao Min
   ZTE
   Nanjing
   CN

   Email: xiao.min2@zte.com.cn



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   Aihua Liu
   ZTE
   Shenzhen
   CN

   Email: liu.aihua@zte.com.cn













































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