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+Internet Engineering Task Force (IETF)                       V. Govindan
+Request for Comments: 7885                                  C. Pignataro
+Updates: 5885                                                      Cisco
+Category: Standards Track                                      July 2016
+ISSN: 2070-1721
+
+
+          Seamless Bidirectional Forwarding Detection (S-BFD)
+          for Virtual Circuit Connectivity Verification (VCCV)
+
+Abstract
+
+   This document defines Seamless BFD (S-BFD) for VCCV by extending the
+   procedures and Connectivity Verification (CV) types already defined
+   for Bidirectional Forwarding Detection (BFD) for Virtual Circuit
+   Connectivity Verification (VCCV).
+
+   This document updates RFC 5885 by extending the CV Type values and
+   the capability selection.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 7841.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/rfc7885.
+
+Copyright Notice
+
+   Copyright (c) 2016 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
+   (http://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.
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 1]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+Table of Contents
+
+   1. Background ......................................................3
+   2. S-BFD Connectivity Verification .................................3
+      2.1. Co-existence of S-BFD and BFD Capabilities .................4
+      2.2. S-BFD CV Operation .........................................4
+           2.2.1. S-BFD Initiator Operation ...........................4
+           2.2.2. S-BFD Reflector Operation ...........................5
+                  2.2.2.1. Demultiplexing .............................5
+                  2.2.2.2. Transmission of Control Packets ............5
+                  2.2.2.3. Advertisement of Target
+                           Discriminators Using LDP ...................5
+                  2.2.2.4. Advertisement of Target
+                           Discriminators Using L2TP ..................6
+                  2.2.2.5. Provisioning of Target Discriminators ......6
+      2.3. S-BFD Encapsulation ........................................6
+   3. Capability Selection ............................................7
+   4. Security Considerations .........................................7
+   5. IANA Considerations .............................................8
+      5.1. MPLS CV Types for the VCCV Interface Parameters Sub-TLV ....8
+      5.2. L2TPv3 CV Types for the VCCV Capability AVP ................8
+      5.3. PW Associated Channel Type .................................9
+   6. References ......................................................9
+      6.1. Normative References .......................................9
+      6.2. Informative References ....................................10
+   Acknowledgements ..................................................11
+   Contributors ......................................................11
+   Authors' Addresses ................................................11
+
+
+
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+Govindan & Pignataro         Standards Track                    [Page 2]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+1.  Background
+
+   Bidirectional Forwarding Detection (BFD) for Virtual Circuit
+   Connectivity Verification (VCCV) [RFC5885] defines the CV Types for
+   BFD using VCCV, protocol operation, and the required packet
+   encapsulation formats.  This document extends those procedures and
+   CV Type values to enable Seamless BFD (S-BFD) [RFC7880] operation
+   for VCCV.
+
+   The new S-BFD CV Types are Pseudowire (PW) demultiplexer agnostic and
+   hence are applicable for both MPLS and Layer Two Tunneling Protocol
+   version 3 (L2TPv3) PW demultiplexers.  This document concerns itself
+   with the S-BFD VCCV operation over Single-Segment PWs (SS-PWs).  The
+   scope of this document is as follows:
+
+   o  This specification describes procedures for S-BFD asynchronous
+      mode only.
+
+   o  S-BFD Echo mode is outside the scope of this specification.
+
+   o  S-BFD operation for fault detection and status signaling is
+      outside the scope of this specification.
+
+   This document specifies the use of a single S-BFD Discriminator per
+   PW.  There are cases where multiple S-BFD Discriminators per PW can
+   be useful.  One such case involves using different S-BFD
+   Discriminators per Flow within a Flow-Aware Transport (FAT) PW
+   [RFC6391]; however, the mapping between Flows and discriminators is a
+   prerequisite.  FAT PWs can be supported as described in Section 7 of
+   [RFC6391], which details Operations, Administration, and Maintenance
+   (OAM) considerations for FAT PWs.
+
+   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
+
+   The 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" (CV) 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 the S-BFD reflector and S-BFD initiator
+   operation.
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 3]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+   Two CV Types are defined for S-BFD.  Table 1 summarizes the S-BFD
+   CV Types, grouping them by encapsulation (i.e., with IP/UDP headers,
+   without IP/UDP headers) for fault detection only.  S-BFD for fault
+   detection and status signaling is outside the scope of this
+   specification.
+
+   +-----------------------------------------+-----------+-------------+
+   |                                         |   Fault   |    Fault    |
+   |                                         | Detection |  Detection  |
+   |                                         |    Only   |  and Status |
+   |                                         |           |  Signaling  |
+   +-----------------------------------------+-----------+-------------+
+   | S-BFD IP/UDP encapsulation (with IP/UDP |    0x40   |     N/A     |
+   |                                headers) |           |             |
+   |                                         |           |             |
+   |   S-BFD PW-ACH encapsulation when using |    0x80   |     N/A     |
+   |   MPLS PW or S-BFD L2-Specific Sublayer |           |             |
+   | (L2SS) encapsulation when using L2TP PW |           |             |
+   |                (without IP/UDP headers) |           |             |
+   +-----------------------------------------+-----------+-------------+
+
+                Table 1: Bitmask Values for S-BFD CV Types
+
+   IANA has assigned two new bits to indicate S-BFD operation.
+
+2.1.  Co-existence of S-BFD and BFD Capabilities
+
+   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.  This can be
+   achieved, for example, through one or more of the following methods.
+   (This list is not exhaustive.)
+
+   1.  Advertisements of S-BFD Discriminators made through a
+       PW signaling protocol -- for example, AVPs/TLVs defined in
+       L2TP/LDP.
+
+   2.  Provisioning of S-BFD Discriminators by manual configuration of
+       the Provider Edge (PE) or L2TP Control Connection Endpoints
+       (LCCEs).
+
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 4]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+   3.  Assignment of S-BFD Discriminators by a controller.
+
+   4.  Probing remote S-BFD Discriminators through a mechanism such as
+       S-BFD Alert Discriminators [SBFD-ALERT-DISCRIM].
+
+   The S-BFD initiator operation MUST be done as specified in
+   Section 7.3 of [RFC7880].
+
+2.2.2.  S-BFD Reflector Operation
+
+   When a PW signaling protocol such as LDP or L2TPv3 is in use, the
+   S-BFD reflector can advertise its target discriminators using that
+   signaling protocol.  When static PWs are in use, the target
+   discriminator of S-BFD needs to be provisioned on the S-BFD
+   initiator nodes.
+
+   All point-to-point PWs 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.
+
+   The reflector has enough information to reflect the S-BFD Async
+   packet received by it back to the S-BFD initiator using the PW
+   context (e.g., fields of the L2TPv3 headers).
+
+   The S-BFD reflector operation for BFD protocol fields MUST be
+   performed as specified in [RFC7880].
+
+2.2.2.1.  Demultiplexing
+
+   Demultiplexing of S-BFD is achieved using the PW context, following
+   the procedures in Section 7.1 of [RFC7880].
+
+2.2.2.2.  Transmission of Control Packets
+
+   S-BFD reflector procedures as described in [RFC7880] apply for S-BFD
+   using VCCV.
+
+2.2.2.3.  Advertisement of Target Discriminators Using LDP
+
+   The advertisement of the target discriminator using LDP is left for
+   further study.  It should be noted that S-BFD can still be used with
+   signaled PWs over an MPLS Packet Switched Network (PSN) by
+   provisioning the S-BFD Discriminators or by learning the S-BFD
+   Discriminators via some other means.
+
+
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 5]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+2.2.2.4.  Advertisement of Target Discriminators Using L2TP
+
+   The S-BFD reflector MUST use the AVP defined in [RFC7886] for
+   advertising its target discriminators using L2TP.
+
+2.2.2.5.  Provisioning of Target Discriminators
+
+   S-BFD target discriminators MAY be provisioned when static PWs
+   are used.
+
+2.3.  S-BFD Encapsulation
+
+   Unless specified differently below, the encapsulation of S-BFD
+   packets is identical to the method specified in Section 3.2 of
+   [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 [RFC7881].
+
+      *  The contents of the S-BFD Control packets MUST be set according
+         to Section 7.3.2 of [RFC7880].
+
+      *  The Time to Live (TTL) (IPv4) or Hop Limit (IPv6) is set
+         to 255.
+
+   o  PW-ACH/L2SS BFD encapsulation (BFD without IP/UDP headers):
+
+      *  The encapsulation of S-BFD packets using this format MUST be
+         performed according to Section 3.2 of [RFC5885], with the
+         exception of the value for the PW-ACH/L2SS type.
+
+      *  When VCCV carries PW-ACH/L2SS-encapsulated S-BFD (i.e., "raw"
+         S-BFD), the Channel Type of PW-ACH (the PW Control Word (CW))
+         or L2SS MUST be set to 0x0008 to indicate "S-BFD Control,
+         PW-ACH/L2SS-encapsulated" (i.e., S-BFD without IP/UDP headers;
+         see Section 5.3).  This is done to allow the identification of
+         the encapsulated S-BFD payload when demultiplexing the VCCV
+         control channel.
+
+
+
+
+
+
+
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 6]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+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 PW 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 order,
+   from 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.  0x40 - S-BFD IP/UDP-encapsulated, for PW Fault Detection only.
+
+   2.  0x80 - S-BFD PW-ACH/L2SS-encapsulated (without IP/UDP headers),
+       for PW Fault Detection only.
+
+   The order of capability selection between S-BFD and BFD is defined as
+   follows:
+
+   +---------------------------+---------+-----------+-----------------+
+   |  Advertised capabilities  |   BFD   |   S-BFD   |  Both S-BFD and |
+   |         of PE1/PE2        |   Only  |    Only   |       BFD       |
+   +---------------------------+---------+-----------+-----------------+
+   |          BFD Only         |   BFD   |    None   |     BFD Only    |
+   |                           |         |           |                 |
+   |         S-BFD Only        |   None  |   S-BFD   |    S-BFD Only   |
+   |                           |         |           |                 |
+   |     Both S-BFD and BFD    |   BFD   |   S-BFD   |  Both S-BFD and |
+   |                           |   Only  |    Only   |       BFD       |
+   +---------------------------+---------+-----------+-----------------+
+
+          Table 2: Capability Selection Matrix for BFD and S-BFD
+
+4.  Security Considerations
+
+   Security considerations for VCCV are addressed in Section 10 of
+   [RFC5085].  The introduction of the S-BFD CV Types does not present
+   any new security risks for VCCV.  Implementations of the additional
+   CV Types defined herein are subject to the same security
+   considerations as those defined in [RFC5085] as well as [RFC7880].
+
+   The IP/UDP encapsulation of S-BFD makes use of the TTL / Hop Limit
+   procedures described in the Generalized TTL Security Mechanism (GTSM)
+   specification [RFC5082] as a security mechanism.
+
+   This specification does not raise any additional security issues
+   beyond these.
+
+
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 7]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+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 "MPLS VCCV Connectivity Verification (CV) Types"
+   registry is defined in [RFC5085].
+
+   This section lists the new S-BFD CV Types.
+
+   IANA has augmented the "MPLS VCCV Connectivity Verification (CV)
+   Types" registry in the "Pseudowire Name Spaces (PWE3)" registry
+   [IANA-PWE3].  These are bitfield values.  CV Type values are
+   specified in Section 2 of this document.
+
+      MPLS VCCV Connectivity Verification (CV) Types:
+
+      Bit (Value)  Description                       Reference
+      ===========  ===========                       ==============
+      6 (0x40)     S-BFD IP/UDP-encapsulated,        RFC 7885
+                   for PW Fault Detection only
+
+      7 (0x80)     S-BFD PW-ACH-encapsulated,        RFC 7885
+                   for PW Fault Detection only
+
+5.2.  L2TPv3 CV Types for the VCCV Capability AVP
+
+   This section lists the new S-BFD "L2TPv3 Connectivity Verification
+   (CV) Types" that have been added to the existing "VCCV Capability AVP
+   (Attribute Type 96) Values" registry in the "Layer Two Tunneling
+   Protocol 'L2TP'" registry [IANA-L2TP].  IANA has assigned the
+   following L2TPv3 Connectivity Verification (CV) Types in the "VCCV
+   Capability AVP (Attribute Type 96) Values" registry.
+
+      VCCV Capability AVP (Attribute Type 96) Values
+      ----------------------------------------------
+
+      L2TPv3 Connectivity Verification (CV) Types:
+
+      Bit (Value)  Description                  Reference
+      ===========  ===========                  ==============
+      6 (0x40)     S-BFD IP/UDP-encapsulated,   RFC 7885
+                   for PW Fault Detection only
+
+      7 (0x80)     S-BFD L2SS-encapsulated,     RFC 7885
+                   for PW Fault Detection only
+
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 8]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+5.3.  PW Associated Channel Type
+
+   As per the IANA considerations in [RFC5586], IANA has allocated a
+   Channel Type in the "MPLS Generalized Associated Channel (G-ACh)
+   Types (including Pseudowire Associated Channel Types)" registry
+   [IANA-G-ACh].
+
+   IANA has assigned a new Pseudowire Associated Channel Type value, as
+   follows:
+
+    Value   Description                          Reference
+    ------  ----------------------------------   ---------------
+    0x0008  S-BFD Control, PW-ACH/L2SS           RFC 7885
+            encapsulation
+            (without IP/UDP Headers)
+
+6.  References
+
+6.1.  Normative References
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119,
+              DOI 10.17487/RFC2119, March 1997,
+              <http://www.rfc-editor.org/info/rfc2119>.
+
+   [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
+              Emulation (PWE3)", BCP 116, RFC 4446,
+              DOI 10.17487/RFC4446, April 2006,
+              <http://www.rfc-editor.org/info/rfc4446>.
+
+   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
+              Pignataro, "The Generalized TTL Security Mechanism
+              (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
+              <http://www.rfc-editor.org/info/rfc5082>.
+
+   [RFC5085]  Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire
+              Virtual Circuit Connectivity Verification (VCCV): A
+              Control Channel for Pseudowires", RFC 5085,
+              DOI 10.17487/RFC5085, December 2007,
+              <http://www.rfc-editor.org/info/rfc5085>.
+
+   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
+              "MPLS Generic Associated Channel", RFC 5586,
+              DOI 10.17487/RFC5586, June 2009,
+              <http://www.rfc-editor.org/info/rfc5586>.
+
+
+
+
+
+
+Govindan & Pignataro         Standards Track                    [Page 9]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
+              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
+              <http://www.rfc-editor.org/info/rfc5880>.
+
+   [RFC5885]  Nadeau, T., Ed., and C. Pignataro, Ed., "Bidirectional
+              Forwarding Detection (BFD) for the Pseudowire Virtual
+              Circuit Connectivity Verification (VCCV)", RFC 5885,
+              DOI 10.17487/RFC5885, June 2010,
+              <http://www.rfc-editor.org/info/rfc5885>.
+
+   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
+              Pallagatti, "Seamless Bidirectional Forwarding Detection
+              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
+              <http://www.rfc-editor.org/info/rfc7880>.
+
+   [RFC7881]  Pignataro, C., Ward, D., and N. Akiya, "Seamless
+              Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6,
+              and MPLS", RFC 7881, DOI 10.17487/RFC7881, July 2016,
+              <http://www.rfc-editor.org/info/rfc7881>.
+
+   [RFC7886]  Govindan, V. and C. Pignataro, "Advertising Seamless
+              Bidirectional Forwarding Detection (S-BFD) Discriminators
+              in the Layer Two Tunneling Protocol Version 3 (L2TPv3)",
+              RFC 7886, DOI 10.17487/RFC7886, July 2016,
+              <http://www.rfc-editor.org/info/rfc7886>.
+
+6.2.  Informative References
+
+   [IANA-G-ACh]
+              Internet Assigned Numbers Authority, "MPLS Generalized
+              Associated Channel (G-ACh) Types (including Pseudowire
+              Associated Channel Types)",
+              <http://www.iana.org/assignments/g-ach-parameters>.
+
+   [IANA-L2TP]
+              Internet Assigned Numbers Authority, "Layer Two Tunneling
+              Protocol 'L2TP'",
+              <http://www.iana.org/assignments/l2tp-parameters>.
+
+   [IANA-PWE3]
+              Internet Assigned Numbers Authority, "Pseudowire Name
+              Spaces (PWE3)",
+              <http://www.iana.org/assignments/pwe3-parameters>.
+
+
+
+
+
+
+
+
+Govindan & Pignataro         Standards Track                   [Page 10]
+
+RFC 7885                  Seamless BFD for VCCV                July 2016
+
+
+   [RFC6391]  Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
+              Regan, J., and S. Amante, "Flow-Aware Transport of
+              Pseudowires over an MPLS Packet Switched Network",
+              RFC 6391, DOI 10.17487/RFC6391, November 2011,
+              <http://www.rfc-editor.org/info/rfc6391>.
+
+   [SBFD-ALERT-DISCRIM]
+              Akiya, N., Pignataro, C., and D. Ward, "Seamless
+              Bidirectional Forwarding Detection (S-BFD) Alert
+              Discriminator", Work in Progress,
+              draft-akiya-bfd-seamless-alert-discrim-03, October 2014.
+
+Acknowledgements
+
+   The authors would like to thank Nobo Akiya, Stewart Bryant, Greg
+   Mirsky, Pawel Sowinski, Yuanlong Jiang, Andrew Malis, and Alexander
+   Vainshtein for providing input to this document, performing thorough
+   reviews, and providing useful comments.
+
+Contributors
+
+   Mallik Mudigonda
+   Cisco Systems, Inc.
+
+   Email: mmudigon@cisco.com
+
+Authors' Addresses
+
+   Vengada Prasad Govindan
+   Cisco Systems, Inc.
+
+   Email: venggovi@cisco.com
+
+
+   Carlos Pignataro
+   Cisco Systems, Inc.
+
+   Email: cpignata@cisco.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+Govindan & Pignataro         Standards Track                   [Page 11]
+