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Versions: 00 01 draft-ietf-pals-seamless-vccv

Internet Engineering Task Force                              V. Govindan
Internet-Draft                                              C. Pignataro
Updates: 5885 (if approved)                                Cisco Systems
Intended status: Standards Track                           June 30, 2015
Expires: January 1, 2016


                         Seamless BFD for VCCV
                     draft-gp-pals-seamless-vccv-01

Abstract

   This document extends the procedures and Connectivity Verification
   (CV) types already defined for Bidirectional Forwarding Detection
   (BFD) for Virtual Circuit Connectivity Verification (VCCV) to define
   Seamless BFD (S-BFD) for VCCV.  This document will be extended in
   future to include definition of procedures for S-BFD over Tunnels.
   This document extends the CV values defined in RFC5885.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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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 January 1, 2016.

Copyright Notice

   Copyright (c) 2015 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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   publication of this document.  Please review these documents
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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.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  S-BFD Connectivity Verification . . . . . . . . . . . . . . .   3
     2.1.  Co-existence of S-BFD and BFD capabilites . . . . . . . .   4
     2.2.  S-BFD CV Operation  . . . . . . . . . . . . . . . . . . .   4
       2.2.1.  S-BFD Initiator Operation . . . . . . . . . . . . . .   4
       2.2.2.  S-BFD Reflector Operation . . . . . . . . . . . . . .   4
         2.2.2.1.  S-BFD Reflector Demultiplexing  . . . . . . . . .   5
         2.2.2.2.  S-BFD Reflector transmission of control packets .   5
         2.2.2.3.  S-BFD Reflector advertisement of target
                   discriminators using LDP  . . . . . . . . . . . .   5
         2.2.2.4.  S-BFD Reflector advertisement of target
                   discriminators using L2TP . . . . . . . . . . . .   5
         2.2.2.5.  Provisioning of S-BFD Reflector target
                   discriminators  . . . . . . . . . . . . . . . . .   5
         2.2.2.6.  Probing of S-BFD Reflector target discriminators
                   using alert discriminators  . . . . . . . . . . .   5
     2.3.  S-BFD Encapsulation . . . . . . . . . . . . . . . . . . .   6
     2.4.  S-BFD CV Types  . . . . . . . . . . . . . . . . . . . . .   6
   3.  Capability Selection  . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  MPLS CV Types for the VCCV Interface Parameters Sub-TLV .   7
     5.2.  L2TPv3 CV Types for the VCCV Capability AVP . . . . . . .   8
     5.3.  PW Associated Channel Type  . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Background

   BFD for VCCV [RFC5885] defines the CV types for BFD using VCCV,
   protocol operation and the required packet encapsulation formats.
   This document extends those procedures, CV type values to enable
   S-BFD [I-D.ietf-bfd-seamless-base] operation for VCCV.

   The new S-BFD CV Types are PW demultiplexer-agnostic, and hence
   applicable for both MPLS and Layer Two Tunneling Protocol version 3
   (L2TPv3) pseudowire demultiplexers.  This document concerns itself




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   with the S-BFD VCCV operation over single-segment pseudowires (SS-
   PWs).  The scope of this document is as follows:

      This specification describes procedures only for S-BFD
      asynchronous mode.

      S-BFD Echo mode is outside the scope of this specification.

      S-BFD operation for fault detection and status signaling is
      outside the scope of this specification.

1.1.  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
   [RFC2119].

2.  S-BFD Connectivity Verification

   S-BFD protocol provides continuity check services by monitoring the
   S-BFD control packets sent and received over the VCCV channel of the
   PW.  The term <Connectivity Verification> is used throughout this
   document to be consistent with [RFC5885].

   This section defines the CV types to be used for S-BFD.  It also
   defines the procedures for S-BFD discriminator advertisement for the
   SBD reflector and the procedure for S-BFD Initiator operation.

   Two CV Types are defined for S-BFD.  Table 1 summarizes the S-BFD CV
   Types, grouping them by encapsulation (i.e., with versus without IP/
   UDP headers) for fault detection only.  S-BFD for fault detection and
   status signaling is outside the scope of this specification.


















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   +---------------------------------------+-----------+---------------+
   |                                       |   Fault   |     Fault     |
   |                                       | Detection | Detection and |
   |                                       |    Only   |     Status    |
   |                                       |           |   Signaling   |
   +---------------------------------------+-----------+---------------+
   |     S-BFD, IP/UDP Encapsulation (with |    TBD1   |      N/A      |
   |                       IP/UDP Headers) |  (Note1)  |               |
   |                                       |           |               |
   |      S-BFD, PW-ACH Encapsulation when |    TBD2   |      N/A      |
   |   using MPLS PW or L2SS Encapsulation |  (Note2)  |               |
   |    when using L2TP PW (without IP/UDP |           |               |
   |                              Headers) |           |               |
   +---------------------------------------+-----------+---------------+

                 Table 1: Bitmask Values for BFD CV Types

   Two new bits are requested from IANA to indicate S-BFD operation.

2.1.  Co-existence of S-BFD and BFD capabilites

   Since the CV types for S-BFD and BFD are unique, BFD and S-BFD
   capabilities can be advertised concurrently.

2.2.  S-BFD CV Operation

2.2.1.  S-BFD Initiator Operation

   The S-BFD Initiator SHOULD bootstrap S-BFD sessions after it learns
   the discriminator of the remote target identifier through one or more
   of the following methods:

   1.  Advertisements of S-BFD discriminators made through AVP/ TLVs
       defined in L2TP/ LDP.

   2.  Provisioning of S-BFD discriminators.

   3.  Probing remote S-BFD discriminators through S-BFD Alert
       discriminators [I-D.akiya-bfd-seamless-alert-discrim]

   S-BFD Initiator operation MUST be according to the specifications in
   Section 7.2 of [I-D.ietf-bfd-seamless-base].

2.2.2.  S-BFD Reflector Operation

      When as pseudowire signalling protocol such as LDP or L2TPv3 is in
      use the S-BFD Reflector advertises its target discriminators using
      that signalling protocol.  When static PWs are in use the target



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      discriminator of S-BFD needs to be provisioned on the S-BFD
      Initiator nodes.

      All point to point pseudowires are bidirectional, the S-BFD
      Reflector therefore reflects the S-BFD packet back to the
      Initiator using the VCCV channel of the reverse direction of the
      PW on which it was received.

      It is observed that the reflector has enough information to
      reflect the S-BFD Async packet received by it back to the S-BFD
      initiator using the fields of the L2TPv3 headers.

      S-BFD Reflector operation for BFD protocol fields MUST be
      according to the specifications in Section TBD of
      [I-D.ietf-bfd-seamless-base].

2.2.2.1.  S-BFD Reflector Demultiplexing

   TBD

2.2.2.2.  S-BFD Reflector transmission of control packets

   The procedures of S-BFD Reflector described in
   [I-D.ietf-bfd-seamless-base] apply for S-BFD using VCCV.

2.2.2.3.  S-BFD Reflector advertisement of target discriminators using
          LDP

   TBD.

2.2.2.4.  S-BFD Reflector advertisement of target discriminators using
          L2TP

   The S-BFD Reflector MUST use the AVP
   [I-D.gp-l2tpext-sbfd-discriminator] defined for advertising its
   target discriminators using L2TP.

2.2.2.5.  Provisioning of S-BFD Reflector target discriminators

   S-BFD target discriminators MAY be provisioned when static PWs are
   used.

2.2.2.6.  Probing of S-BFD Reflector target discriminators using alert
          discriminators

   S-BFD alert discriminators MAY be used to probe S-BFD target
   discriminators.  If a node implements S-BFD reflector, it SHOULD




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   respond to Alert discriminator requests received from potential S-BFD
   Initiators.

2.3.  S-BFD Encapsulation

   Unless specified differently below, the encapsulation of S-BFD
   packets is the identical the method specified in Sec.3.2 [RFC5885]
   and in [RFC5880] for the encapsulation of BFD packets.

   o  IP/UDP BFD Encapsulation (BFD with IP/UDP Headers)

      *  The destination UDP port for the IP encapsulated S-BFD packet
         MUST be 7784 [I-D.ietf-bfd-seamless-base].

      *  The encapsulation of the S-BFD header fields MUST be according
         to Sec.7.2.2 of [I-D.ietf-bfd-seamless-base].

   o  PW-ACH/ L2SS BFD Encapsulation (BFD without IP/UDP Headers)

      *  The encapsulation of S-BFD packets using this format MUST be
         according to Sec.3.2 of [RFC5885] with the exception of the PW-
         ACH/ L2SS type.

      *  When VCCV carries PW-ACH/ L2SS-encapsulated S-BFD (i.e., "raw"
         S-BFD), the PW-ACH (pseudowire CW's) or L2SS' Channel Type MUST
         be set to TBD2 to indicate "S-BFD Control, PW-ACH/ L2SS-
         encapsulated" (i.e., S-BFD without IP/UDP headers; see
         Section 5.3).  This is to allow the identification of the
         encased S-BFD payload when demultiplexing the VCCV control
         channel.

2.4.  S-BFD CV Types

3.  Capability Selection

   When multiple S-BFD CV Types are advertised, and after applying the
   rules in [RFC5885], the set that both ends of the pseudowire have in
   common is determined.  If the two ends have more than one S-BFD CV
   Type in common, the following list of S-BFD CV Types is considered in
   the order of the lowest list number CV Type to the highest list
   number CV Type, and the CV Type with the lowest list number is used:

   1.  TBD1 - S-BFD IP/UDP-encapsulated, for PW Fault Detection only.

   2.  TBD2 - S-BFD PW-ACH/ L2SS-encapsulated (without IP/UDP headers),
       for PW Fault Detection only.





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   The order of capability selection between S-BFD and BFD is defined as
   follows:

   +--------------------------+-----------+-----------+----------------+
   | Advertised capabilities  |  BFD Only | SBFD Only | Both S-BFD and |
   |       of PE1/ PE2        |           |           |      BFD       |
   +--------------------------+-----------+-----------+----------------+
   |         BFD Only         |    BFD    |    None   |    BFD Only    |
   |                          |           |  (Note1)  |                |
   |                          |           |           |                |
   |        S-BFD Only        |    None   |   S-BFD   |   S-BFD only   |
   |                          |  (Note1)  |           |                |
   |                          |           |           |                |
   |    Both S-BFD and BFD    |  BFD only |   S-BFD   | Both SBFD and  |
   |                          |           |    only   |      BFD       |
   +--------------------------+-----------+-----------+----------------+

          Table 2: Capability Selection Matrix for BFD and S-BFD

   Note1: Can we mandate failing the bringup of the PW in case of a
   capability mismatch?

4.  Security Considerations

   Security measures described in [RFC5885] and
   [I-D.ietf-bfd-seamless-base] are to be followed.

5.  IANA Considerations

5.1.  MPLS CV Types for the VCCV Interface Parameters Sub-TLV

   The VCCV Interface Parameters Sub-TLV codepoint is defined in
   [RFC4446], and the VCCV CV Types registry is defined in [RFC5085].

   This section lists the new BFD CV Types.

   IANA has augmented the "VCCV Connectivity Verification (CV) Types"
   registry in the Pseudowire Name Spaces reachable from [IANA].  These
   are bitfield values.  CV Type values TBD are specified in Section 2
   of this document.











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         MPLS Connectivity Verification (CV) Types:

      Bit (Value)  Description                       Reference
      ===========  ===========                       ==============
      TBD1(0xY)    S-BFD IP/UDP-encapsulated,        this document
                   for PW Fault Detection only
      TBD2(0xZ)    S-BFD PW-ACH/L2SS-encapsulated,   this document
                   for PW Fault Detection only

5.2.  L2TPv3 CV Types for the VCCV Capability AVP

   This section lists the new requests for S-BFD CV Types to be added to
   the existing "VCCV Capability AVP" registry in the L2TP name spaces.
   The Layer Two Tunneling Protocol "L2TP" Name Spaces are reachable
   from [IANA].  IANA is requested to assign the following L2TPv3
   Connectivity Verification (CV) Types in the VCCV Capability AVP
   Values registry.

      VCCV Capability AVP (Attribute Type 96) Values
      ----------------------------------------------

      L2TPv3 Connectivity Verification (CV) Types:

      Bit (Value)  Description                  Reference
      ===========  ===========                  ==============
      TBD1(0xY)    S-BFD IP/UDP-encapsulated,   this document
                   for PW Fault Detection only
      TBD2(0xZ)    S-BFD L2SS-encapsulated,   this document
                   for PW Fault Detection only

5.3.  PW Associated Channel Type

   As per the IANA considerations in [RFC5586], IANA is requested to
   allocate the following Channel Types in the "MPLS Generalized
   Associated Channel (G-ACh) Types" registry:

   IANA has reserved a new Pseudowire Associated Channel Type value as
   follows:

   Registry:
                                                TLV
    Value   Description                         Follows  Reference
    ------  ----------------------------------  -------  ---------------
    TBD2    S-BFD Control, PW-ACH/L2SS          No       [This document]
            encapsulation
            (without IP/UDP Headers)





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6.  Acknowledgements

   Authors would like to thank Nobo Akiya, Stewart Bryant, Pawel
   Sowinski and Greg Mirsky for providing the core inputs of this
   document and for performing thorough reviews and providing number of
   comments.  Authors would also like to thank Yuanlong for comments
   received.

7.  Contributing Authors

   Mallik Mudigonda
   Cisco Systems
   Email: mmudigon@cisco.com

8.  References

8.1.  Normative References

   [I-D.akiya-bfd-seamless-alert-discrim]
              Akiya, N., Pignataro, C., and D. Ward, "Seamless
              Bidirectional Forwarding Detection (S-BFD) Alert
              Discriminator", draft-akiya-bfd-seamless-alert-discrim-03
              (work in progress), October 2014.

   [I-D.gp-l2tpext-sbfd-discriminator]
              Govindan, V. and C. Pignataro, "Advertising S-BFD
              Discriminators in L2TPv3", draft-gp-l2tpext-sbfd-
              discriminator-00 (work in progress), March 2015.

   [I-D.ietf-bfd-seamless-base]
              Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J.
              Networks, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", draft-ietf-bfd-seamless-base-05 (work in
              progress), June 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, February 2006.

   [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
              Emulation (PWE3)", BCP 116, RFC 4446, April 2006.

   [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
              Connectivity Verification (VCCV): A Control Channel for
              Pseudowires", RFC 5085, December 2007.



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   [RFC5586]  Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
              Associated Channel", RFC 5586, June 2009.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC5885]  Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
              Detection (BFD) for the Pseudowire Virtual Circuit
              Connectivity Verification (VCCV)", RFC 5885, June 2010.

8.2.  Informative References

   [IANA]     Internet Assigned Numbers Authority, "Protocol
              Registries", <http://www.iana.org>.

Authors' Addresses

   Vengada Prasad Govindan
   Cisco Systems

   Email: venggovi@cisco.com


   Carlos Pignataro
   Cisco Systems

   Email: cpignata@cisco.com
























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