BFD Working Group                                               W. Cheng
Internet-Draft                                                   R. Wang
Updates: 5880 (if approved)                                 China Mobile
Intended status: Standards Track                                  X. Min
Expires: March 13, May 6, 2021                                           A. Liu                                           ZTE Corp.
                                                               R. Rahman
                                                           Cisco Systems
                                                           R. Boddireddy
                                                        Juniper Networks
                                                       September 9,
                                                        November 2, 2020

                     Unaffiliated BFD Echo Function
                  draft-ietf-bfd-unaffiliated-echo-00
                  draft-ietf-bfd-unaffiliated-echo-01

Abstract

   Bidirectional Forwarding Detection (BFD) is a fault detection
   protocol that can quickly determine a communication failure between
   two forwarding engines.  This document proposes a use of the BFD echo Echo
   function where the local system supports BFD but the neighboring
   system does not support BFD.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 13, May 6, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Unaffiliated BFD Echo Behavior  Updates to RFC 5880 . . . . . . . . . . . . . . . . . . . . .   3
   3.  Discussion  Unaffiliated BFD Echo Procedures  . . . . . . . . . . . . . .   6
   4.  Unaffilicated BFD Echo Applicability  . . . . . . . . . . . .   4
   4.   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.   8
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5   9

1.  Introduction

   To minimize the impact of device device/link 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 [RFC5880] is a low-overhead, short-duration method to detect
   faults on the communication path between adjacent forwarding engines.
   The faults can be on interface, data link, and even forwarding engine faults.
   engine.  It is a single, unified mechanism to monitor any media and
   protocol layers in real time.

   BFD defines asynchronous Asynchronous mode to satisfy various deployment
   scenarios, and also supports echo Echo function to reduce the device
   requirement for BFD.  When the echo Echo function is activated, the local
   system sends a BFD echo packet Echo packets and the remote system loops back the
   packet
   received Echo packets through the forwarding path.  If several
   consecutive echo BFD Echo packets are not received, received by the local system,
   then the BFD session is declared to be Down.

   When using BFD echo 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.

      o Full BFD procotol protocol capability with affiliated echo Echo function: this
      scenario requires both the local device and the neighboring device
      to support full BFD protocol.

      2.

      o Only BFD echo Echo function without full BFD procotol protocol capability:
      this scenario requires only the local device to support sending
      and demultiplexing BFD Control packets.

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

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

   This document describes the use of the Unaffiliated BFD Echo function
   over IPv4 and IPv6 for single IP hop.

2.  Updates to RFC 5880

   The Unaffiliated BFD Echo function described in this document reuses
   the BFD echo Echo function as described in [RFC5880] and [RFC5881], but
   independent of
   does not require BFD asynchronous 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. mode.  When using unaffiliated the Unaffiliated
   BFD echo Echo function, just only the local device works on system has the BFD protocol and
   enabled, the BFD peer doesn't, which only loopback remote system just loops back the received BFD echo Echo
   packets as usual regular data packets without enabling BFD protocol.

   Section 6.2.2 of [BBF-TR-146] describes one use case of packets.

   With that said, this document updates [RFC5880] with respect to its
   descriptions on the
   unaffiliated BFD echo function, and at least one more use case is
   known Echo function as follows.

   o [RFC5880] states in the field BFD deployment.

2.  Unaffiliated BFD Echo Behavior

   With 4th paragraph of Section 3.2:

      An adjunct to both modes is the more and more application Echo function.  When the Echo
      function is active, a stream of BFD detection, there Echo packets is transmitted in
      such a way as to have the other system loop them back through its
      forwarding path.  If a number of packets of the echoed data stream
      are some
   scenarios not received, the BFD echo function session is deployed.  And due declared to be down.  The Echo
      function may be used with either Asynchronous or Demand mode.
      Since the
   different capabilities Echo function is handling the task of detection, the devices deploying BFD echo function,
   it's required to apply unaffiliated BFD echo to
      rate of periodic transmission of Control packets may be reduced
      (in the devices that
   couldn't afford case of Asynchronous mode) or eliminated completely (in
      the overhead case of Demand mode).

   * This paragraph is now updated to:

      An adjunct or complement to both modes is the full Echo function.  When
      the Echo function is active, a stream of BFD protocol capablity, Echo packets is
      transmitted in such a way as to have the servers running virtual machines other system loop them
      back through its forwarding path.  If a number of packets of the
      echoed data stream are not received, the session is declared to be
      down.  The Echo function may be used with either Asynchronous or some Internet
      Demand mode.  Since the Echo function is handling the task of Things
   (IoT) devices.  Unaffiliated BFD echo can
      detection, the rate of periodic transmission of Control packets
      may be reduced (in the case of Asynchronous mode) or eliminated
      completely (in the case of Demand mode).  The Echo function may
      also be used independently, with neither Asynchronous nor Demand
      mode.

   o [RFC5880] states in the 3rd and 9th paragraphs of Section 6.1:

      Once the BFD session is Up, a system can choose to start the Echo
      function if it desires and the other system signals that it will
      allow it.  The rate of transmission of Control packets is
      typically kept low when the Echo function is active.

      If the session goes Down, the transmission of Echo packets (if
      any) ceases, and the transmission of Control packets goes back to
      the slow rate.

   * The two devices paragraphs are connected now updated to:

      When a system is running with Asynchronous mode, once the BFD
      session is Up, it can choose to start the Echo function if it
      desires and only the other system signals that it will allow it.  The
      rate of transmission of Control packets is typically kept low when
      the Echo function is active.

      In Asynchronous mode, if the session goes Down, the transmission
      of Echo packets (if any) ceases, and the transmission of Control
      packets goes back to the slow rate.

   o [RFC5880] states in the 2nd paragraph of Section 6.4:

      When a system is using the Echo function, it is advantageous to
      choose a sedate reception rate for Control packets, since liveness
      detection is being handled by the Echo packets.  This can be
      controlled by manipulating the Required Min RX Interval field (see
      section 6.8.3).

   * This paragraph is now updated to:

      When a system is using the Echo function with Asynchronous mode,
      it is advantageous to choose a sedate reception rate for Control
      packets, since liveness detection is being handled by the Echo
      packets.  This can be controlled by manipulating the Required Min
      RX Interval field (see section 6.8.3).

   o [RFC5880] states in the 2nd paragraph of Section 6.8:

      When a system is said to have "the Echo function active" it means
      that the system is sending BFD Echo packets, implying that the
      session is Up and the other system has signaled its willingness to
      loop back Echo packets.

   * This paragraph is now updated to:

      When a system in Asynchronous or Demand mode is said to have "the
      Echo function active" it means that the system is sending BFD Echo
      packets, implying that the session is Up and the other system has
      signaled its willingness to loop back Echo packets.

   o [RFC5880] states in the 7th paragraph of Section 6.8.3:

      When the Echo function is active, a system SHOULD set
      bfd.RequiredMinRxInterval to a value of not less than one second
      (1,000,000 microseconds).  This is intended to keep received BFD
      Control traffic at a negligible level, since the actual detection
      function is being performed using BFD Echo packets.

   * This paragraph is now updated to:

      When the Echo function is active with Asynchronous mode, a system
      SHOULD set bfd.RequiredMinRxInterval to a value of not less than
      one second (1,000,000 microseconds).  This is intended to keep
      received BFD Control traffic at a negligible level, since the
      actual detection function is being performed using BFD Echo
      packets.

   o [RFC5880] states in the 1st and 2nd paragraphs of them supports Section 6.8.9:

      BFD Echo packets MUST NOT be transmitted when bfd.SessionState is
      not Up.  BFD Echo packets MUST NOT be transmitted unless the last
      BFD Control packet received from the remote system contains a
      nonzero value in Required Min Echo RX Interval.

      BFD Echo packets MAY be transmitted when bfd.SessionState is Up.
      The interval between transmitted BFD Echo packets MUST NOT be less
      than the value advertised by the remote system in Required Min
      Echo RX Interval, except as follows:

         A 25% jitter MAY be applied to the rate of transmission, such
         that the actual interval MAY be between 75% and 100% of the
         advertised value.  A single BFD Echo packet MAY be transmitted
         between normally scheduled Echo transmission intervals.

   * The two paragraphs are now updated to:

      When a system is using the Echo function with either Asynchronous
      or Demand mode, BFD protocol capability.
   A Echo packets MUST NOT be transmitted when
      bfd.SessionState is not Up, and BFD echo session can Echo packets MUST NOT be established at
      transmitted unless the device that supports
   BFD, and last BFD Control packet received from the device will send
      remote system contains a nonzero value in Required Min Echo RX
      Interval.

      When a system is using the Echo function with either Asynchronous
      or Demand mode, BFD echo Echo packets with MAY be transmitted when
      bfd.SessionState is Up, and the IP
   address destined for itself, whereas interval between transmitted BFD
      Echo packets MUST NOT be less than the other peer device just
   loopback value advertised by the received BFD echo packets.

   After receiving a BFD echo packet,
      remote system in Required Min Echo RX Interval, except as follows:

         A 25% jitter MAY be applied to the device rate of transmission, such
         that does not support
   BFD protocol immediately loops back the actual interval MAY be between 75% and 100% of the
         advertised value.  A single BFD Echo packet by normal IP
   forwarding, implementing quick link failure detection. MAY be transmitted
         between normally scheduled Echo transmission intervals.

3.  Unaffiliated BFD Echo Procedures

   As shown in Figure 1, device A supports BFD, whereas device B does
   not support BFD.  To rapidly detect any IP forwarding faults between
   device A and device B, a BFD Echo session MUST be created at device
   A, and the BFD Echo session is RECOMMENDED to follow the BFD state
   machine defined in Section 6.2 of [RFC5880], except that the received
   state is not sent but echoed from the remote system.  In this case,
   although BFD Echo packets are transmitted with destination UDP port
   3785 as defined in [RFC5881], the BFD Echo packets sent by device A
   are BFD Control packets too, the looped BFD Echo packets back from
   device B would drive BFD state change at device A, substituting the
   BFD Control packets sent from the BFD peer.

   Once a BFD Echo session is created at device A, it starts sending BFD
   Echo packets, which SHOULD include a BFD Echo session demultiplexing
   field, such as BFD Your Discriminator defined in [RFC5880] (BFD My
   Discriminator can be set to 0 to avoid confusion), except that device
   A can use IP source address or UDP source port to demultiplex BFD
   Echo session, or there is only one BFD Echo session running at device
   A.  Device A would send BFD Echo packets with IP destination address
   destined for itself, such as the IP link between device A
   and address of interface 1 of device B, a
   A.  All BFD echo Echo packets for the session can MUST be sent with a Time to
   Live (TTL) or Hop Limit value of 255.

   Considering the BFD peer wouldn't advertise Required Min Echo RX
   Interval as defined in [RFC5880], the transmit interval for sending
   BFD Echo packets MUST be provisioned and created at device A, how to make sure
   the BFD peer is willing and device A starts sending able to loop back BFD echo packets, which should
   include a Echo packets sent
   with the provisioned transmit interval is outside the scope of this
   document.  Considering the BFD echo session demultiplexing field, such peer wouldn't advertise Detect Mult as BFD
   discriminator
   defined in [RFC5880]. [RFC5880], the Detect Mult for calculating the Detection
   Time MUST be provisioned at device A, the Detection Time in device A
   is equal to the provisioned Detect Mult multiplied by the provisioned
   transmit interval.

   After receiving the BFD echo Echo packets sent from device A, the one-hop-
   away BFD peer device B immediately loops them back them, by normal IP
   forwarding, this allows device A to rapidly detect a connectivity
   loss to device B.

   Device A                                   Device B
                      BFD echo 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

4.  Unaffilicated BFD Echo Applicability

   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 capability,
   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.

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

4.

5.  Security Considerations

   Unicast Reverse Path Forwarding (uRPF), as specified in [RFC3704] and
   [RFC8704], is a security feature that prevents the IP address
   spoofing attacks which is commonly used in DoS, DDoS. uRPF has two
   modes called strict mode and loose mode. uRPF strict mode means that
   the router will perform checks for all incoming packets on a certain
   interface: whether the router has a matching entry for the source IP
   in the routing table and whether the router uses the same interface
   to reach this source IP as where the router received this packet on.
   Note that the use of BFD echo Echo function would prevent the use of uRPF
   in strict mode.

5.

6.  IANA Considerations

   This document has no IANA action requested.

6.  Acknowledgements

   TBD.

7.  Acknowledgements

   The authors would like to acknowledge Ketan Talaulikar, Greg Mirsky
   and Santosh Pallagatti for their careful review and very helpful
   comments.

8.  Contributors

   Liu Aihua
   ZTE
   Email: liu.aihua@zte.com.cn

   Qian Xin
   ZTE
   Email: qian.xin2@zte.com.cn

   Zhao Yanhua
   ZTE
   Email: zhao.yanhua3@zte.com.cn

9.  References

7.1.

9.1.  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.

9.2.  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>.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
              2004, <https://www.rfc-editor.org/info/rfc3704>.

   [RFC8704]  Sriram, K., Montgomery, D., and J. Haas, "Enhanced
              Feasible-Path Unicast Reverse Path Forwarding", BCP 84,
              RFC 8704, DOI 10.17487/RFC8704, February 2020,
              <https://www.rfc-editor.org/info/rfc8704>.

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 Corp.
   Nanjing
   CN

   Email: xiao.min2@zte.com.cn

   Aihua Liu
   ZTE Corp.
   Shenzhen
   CN

   Email: liu.aihua@zte.com.cn
   Reshad Rahman
   Cisco Systems
   Kanata
   CA

   Email: rrahman@cisco.com

   Raj Chetan Boddireddy
   Juniper Networks

   Email: rchetan@juniper.net