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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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+
+
+
+
+
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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
+
+
+
+
+
+
+
+
+
+
+
+
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+Govindan & Pignataro Standards Track [Page 11]
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