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rfc:rfc7885

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

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]

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