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MPLS Working Group                                             G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                            June 4, 2019
Expires: December 6, 2019


     BFD for Multipoint Networks over Point-to-Multi-Point MPLS LSP
                     draft-mirsky-mpls-p2mp-bfd-07

Abstract

   This document describes procedures for using Bidirectional Forwarding
   Detection (BFD) for multipoint networks to detect data plane failures
   in Multiprotocol Label Switching (MPLS) point-to-multipoint (p2mp)
   Label Switched Paths (LSPs).  It also describes the applicability of
   LSP Ping, as in-band, and the control plane, as out-band, solutions
   to bootstrap a BFD session in this environment.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on December 6, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Multipoint BFD Encapsulation  . . . . . . . . . . . . . . . .   3
     3.1.  IP Encapsulation of Multipoint BFD  . . . . . . . . . . .   3
     3.2.  Non-IP Encapsulation of Multipoint BFD  . . . . . . . . .   4
   4.  Bootstrapping Multipoint BFD  . . . . . . . . . . . . . . . .   4
     4.1.  LSP Ping  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Control Plane . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Multipoint BFD over MPLS LSP Associated Channel Type  . .   6
     6.2.  Source MEP ID IP Address Type . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   [RFC8562] defines a method of using Bidirectional Detection (BFD)
   [RFC5880] to monitor and detect unicast failures between the sender
   (head) and one or more receivers (tails) in multipoint or multicast
   networks.  This document describes procedures for using such mode of
   BFD protocol to detect data plane failures in Multiprotocol Label
   Switching (MPLS) point-to-multipoint (p2mp) Label Switched Paths
   (LSPs).  The document also describes the applicability of out-band
   solutions to bootstrap a BFD session in this environment.

2.  Conventions used in this document

2.1.  Terminology

   MPLS: Multiprotocol Label Switching

   LSP: Label Switched Path

   BFD: Bidirectional Forwarding Detection

   p2mp: Point-to-Multipoint




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   FEC: Forwarding Equivalence Class

   G-ACh: Generic Associated Channel

   ACH: Associated Channel Header

   GAL: G-ACh Label

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Multipoint BFD Encapsulation

   [RFC8562] uses BFD in the Demand mode from the very start of a point-
   to-multipoint (p2mp) BFD session.  Because the head doesn't receive
   any BFD control packet from a tail, the head of the p2mp BFD session
   transmits all BFD control packets with the value of Your
   Discriminator field set to zero.  As a result, a tail cannot
   demultiplex BFD sessions using Your Discriminator, as defined in
   [RFC5880].  [RFC8562] requires that to demultiplex BFD sessions, the
   tail uses the source IP address, My Discriminator, and the identity
   of the multipoint tree from which the BFD control packet was
   received.  The p2mp MPLS LSP label MAY provide the identification of
   the multipoint tree in case of inclusive p-tree or upstream assigned
   label in case of aggregate p-tree.  If the BFD control packet is
   encapsulated in IP/UDP, then the source IP address MUST be used to
   demultiplex the received BFD control packet as described in
   Section 3.1.  The non-IP encapsulation case is described in
   Section 3.2.

3.1.  IP Encapsulation of Multipoint BFD

   [RFC8562] defines IP/UDP encapsulation for multipoint BFD over p2mp
   MPLS LSP:

      UDP destination port MUST be set to 3784;

      destination IP address MUST be from the 127/8 range for IPv4 and
      from the 0:0:0:0:0:FFFF:7F00/104 range for IPv6;

   This specification further clarifies that:





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      if multiple alternative paths for the given p2mp LSP Forwarding
      Equivalence Class (FEC) exist, the MultipointHead SHOULD use
      Entropy Label [RFC6790] used for LSP Ping [RFC8029] to exercise
      that particular alternative path;

      or the MultipointHead MAY use the UDP port number as discovered by
      LSP Ping traceroute [RFC8029] as the source UDP port number to
      possibly exercise that particular alternate path.

3.2.  Non-IP Encapsulation of Multipoint BFD

   In some environments, the overhead of extra IP/UDP encapsulations may
   be considered as overburden and make using more compact G-ACh
   encapsulation attractive.  Also, the validation of the IP/UDP
   encapsulation of BFD control packet of p2mp BFD session may fail
   because of a problem not related to neither MPLS label stack nor to
   BFD.  Avoiding unnecessary encapsulation of p2mp BFD over MPLS LSP
   improves the accuracy of correlation of the detected failure and
   defect in MPLS LSP.  Non-IP encapsulation for multipoint BFD over
   p2mp MPLS LSP MUST use Generic Associated Channel (G-ACh) Label (GAL)
   (see [RFC5586]) at the bottom of the label stack followed by
   Associated Channel Header (ACH).  The Channel Type field in ACH MUST
   be set to TBA1 value Section 6.1.  To provide the identity of the
   MultipointHead for the particular multipoint BFD session this
   document defines the new Source MEP ID IP Address type (TBA2) in
   Section 6.2.  If the Length value is 4, then the Value field contains
   an IPv4 address.  If the Length value is 16, then the Value field
   contains an IPv6 address.  Any other value of the Length field MUST
   be considered as an error, and the BFD control packet MUST be
   discarded.

4.  Bootstrapping Multipoint BFD

4.1.  LSP Ping

   LSP Ping is the part of on-demand OAM toolset to detect and localize
   defects in the data plane, and verify the control plane against the
   data plane by ensuring that the LSP is mapped to the same FEC, at the
   egress, as the ingress.

   LSP Ping, as defined in [RFC6425], MAY be used to bootstrap
   MultipointTail.  If the LSP Ping used, it MUST include the Target FEC
   TLV and the BFD Discriminator TLV defined in [RFC5884].  The Target
   FEC TLV MUST use sub-TLVs defined in Section 3.1 [RFC6425].  It is
   RECOMMENDED setting the value of Reply Mode field to "Do not reply"
   [RFC8029] for the LSP Ping to bootstrap MultipointTail of the p2mp
   BFD session.  A MaultipointTail that receives the LSP Ping that
   includes the BFD Discriminator TLV:



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   o  MUST validate the LSP Ping;

   o  MUST associate the received BFD Discriminator value with the p2mp
      LSP;

   o  MUST create p2mp BFD session and set bfd.SessionType =
      MultipointTail as described in [RFC8562];

   o  MUST use the source IP address of LSP Ping, the value of BFD
      Discriminator from the BFD Discriminator TLV, and the identity of
      the p2mp LSP to properly demultiplex BFD sessions.

   Besides bootstrapping a BFD session over a p2mp LSP, LSP Ping SHOULD
   be used to verify the control plane against the data plane
   periodically by checking that the p2mp LSP is mapped to the same FEC
   at the MultipointHead and all active MultipointTails.  The rate of
   generation of these LSP Ping Echo request messages SHOULD be
   significantly less than the rate of generation of the BFD Control
   packets because LSP Ping requires more processing to validate the
   consistency between the data plane and the control plane.  An
   implementation MAY provide configuration options to control the rate
   of generation of the periodic LSP Ping Echo request messages.

4.2.  Control Plane

   BGP-BFD Attribute [I-D.ietf-bess-mvpn-fast-failover] MAY be used to
   bootstrap multipoint BFD session on a tail.

5.  Security Considerations

   This document does not introduce new security aspects but inherits
   all security considerations from [RFC5880], [RFC5884], [RFC7726],
   [RFC8562], [RFC8029], and [RFC6425].

   Also, BFD for p2mp MPLS LSP MUST follow the requirements listed in
   section 4.1 [RFC4687] to avoid congestion in the control plane or the
   data plane caused by the rate of generating BFD control packets.  An
   operator SHOULD consider the amount of extra traffic generated by
   p2mp BFD when selecting the interval at which the MultipointHead will
   transmit BFD control packets.  Also, the operator MAY consider the
   size of the packet the MultipointHead transmits periodically as using
   IP/UDP encapsulation adds up to 28 octets, which is more than 50% of
   BFD control packet length, comparing to G-ACh encapsulation.








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6.  IANA Considerations

6.1.  Multipoint BFD over MPLS LSP Associated Channel Type

   IANA is requested to allocate value (TBA1) from its MPLS Generalized
   Associated Channel (G-ACh) Types registry.

            +-------+------------------------+---------------+
            | Value |      Description       | Reference     |
            +-------+------------------------+---------------+
            | TBA1  | Multipoint BFD Session | This document |
            +-------+------------------------+---------------+

                Table 1: Multipoint BFD Session G-ACh Type

6.2.  Source MEP ID IP Address Type

   IANA is required to allocate value (TBA2) for the Source MEP ID IP
   Address type from the "CC/CV MEP-ID TLV" registry which is under the
   "MPLS Generalized Associated Channel (G-ACh) Types" registry.

                  +-------+-------------+---------------+
                  | Value | Description | Reference     |
                  +-------+-------------+---------------+
                  | TBA2  |  IP Address | This document |
                  +-------+-------------+---------------+

                Table 2: Source MEP ID IP Address TLV Type

7.  Acknowledgements

   The author sincerely appreciates the comments received from Andrew
   Malis.

8.  References

8.1.  Normative References

   [I-D.ietf-bess-mvpn-fast-failover]
              Morin, T., Kebler, R., and G. Mirsky, "Multicast VPN fast
              upstream failover", draft-ietf-bess-mvpn-fast-failover-05
              (work in progress), February 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.




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   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

   [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>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [RFC6425]  Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
              Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
              Failures in Point-to-Multipoint MPLS - Extensions to LSP
              Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
              <https://www.rfc-editor.org/info/rfc6425>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC7726]  Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
              Aldrin, "Clarifying Procedures for Establishing BFD
              Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726,
              DOI 10.17487/RFC7726, January 2016,
              <https://www.rfc-editor.org/info/rfc7726>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8562]  Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
              Ed., "Bidirectional Forwarding Detection (BFD) for
              Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
              April 2019, <https://www.rfc-editor.org/info/rfc8562>.






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8.2.  Informative References

   [RFC4687]  Yasukawa, S., Farrel, A., King, D., and T. Nadeau,
              "Operations and Management (OAM) Requirements for Point-
              to-Multipoint MPLS Networks", RFC 4687,
              DOI 10.17487/RFC4687, September 2006,
              <https://www.rfc-editor.org/info/rfc4687>.

Author's Address

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com





































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