Internet Engineering Task Force V. Govindan
Internet-Draft C. Pignataro
Updates: 5885 (if approved) Cisco Systems
Intended status: Standards Track February 22, 2016
Expires: August 25, 2016

Seamless BFD for VCCV


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 updates RFC 5885, extending the CV Values and the Capability Selection.

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 working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 August 25, 2016.

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 ( 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.

Table of Contents

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 Pseudowire (PW) demultiplexer-agnostic, and hence applicable for both MPLS and Layer Two Tunneling Protocol version 3 (L2TPv3) pseudowire demultiplexers. This document concerns itself with the S-BFD VCCV operation over single-segment pseudowires (SS-PWs). The scope of this document is as follows:

This document specifies the use of a single S-BFD discriminator per Pseudowire. There are cases where multiple S-BFD discriminators per PW can be useful. One such cases is using different S-BFD discriminators per Flow within a 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].

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 the S-BFD reflector and 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.

Bitmask Values for BFD CV Types
Fault Detection Only Fault Detection and Status Signaling
S-BFD, IP/UDP Encapsulation (with IP/UDP Headers) TBD1 N/A
S-BFD, PW-ACH Encapsulation when using MPLS PW or L2-Specific Sublayer (L2SS) Encapsulation when using L2TP PW (without IP/UDP Headers) TBD2 N/A

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. This can be achieved, for example but not limited to, through one or more of the following methods:

  1. Advertisements of S-BFD discriminators made through a PW signaling protocol, for example AVP/TLVs defined in L2TP/LDP.
  2. Provisioning of S-BFD discriminators by manual configuration of the PE/LCCEs.
  3. Assignment of S-BFD discriminators by a controller.
  4. Probing remote S-BFD discriminators through a mechanism such as 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 Demultiplexing

Demultiplexing of S-BFD is achieved using the PW context, following the procedures in Section 7.1 of [I-D.ietf-bfd-seamless-base]. Transmission of Control Packets

The procedures of S-BFD Reflector described in [I-D.ietf-bfd-seamless-base] apply for S-BFD using VCCV. 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 PSN, by provisioning of the S-BFD discriminators or by learning the S-BFD discriminators by other means. Advertisement of Target Discriminators Using L2TP

The S-BFD Reflector MUST use the AVP [I-D.ietf-l2tpext-sbfd-discriminator] defined for advertising its target discriminators using L2TP. 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 [RFC5885] and in [RFC5880] for the encapsulation of BFD packets.

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.

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

Capability Selection Matrix for BFD and S-BFD
Advertised capabilities of PE1/ PE2 BFD Only SBFD Only Both S-BFD and BFD
BFD Only BFD None BFD Only
S-BFD Only None S-BFD S-BFD only
Both S-BFD and BFD BFD only S-BFD only Both SBFD and BFD

4. Security Considerations

Security considerations for VCCV are addressed in Section 10 of [RFC5085]. The introduction of the S-BFD Connectivity Verification (CV) Types introduces no new security risks for VCCV. Routers that implement the additional CV Types defined herein are subject to the same security considerations as defined in [RFC5085], as well as [I-D.ietf-bfd-seamless-base].

This specification does not raise any additional security issues beyond these.

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 "MPLS VCCV Connectivity Verification (CV) Types" registry in the Pseudowire Name Spaces reachable from [IANA-PWE3]. These are bitfield values. CV Type values are specified in Section 2 of this document.

      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-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 "L2TPv3 Connectivity Verification (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-L2TP]. 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:

 Value   Description                         Follows  Reference
 ------  ----------------------------------  -------  ---------------
 TBD3    S-BFD Control, PW-ACH/L2SS          No       [This document]
         (without IP/UDP Headers)

6. Acknowledgements

The authors would like to thank Nobo Akiya, Stewart Bryant, Greg Mirsky, and Pawel Sowinski, Yuanlong, Andrew Malis, and Alexander Vainshtein for providing input to this document and for performing thorough reviews and useful comments.

7. Contributing Authors

Mallik Mudigonda
Cisco Systems

8. References

8.1. Normative References

[I-D.ietf-bfd-seamless-base] Akiya, N., Pignataro, C., Ward, D., Bhatia, M. and J. Networks, "Seamless Bidirectional Forwarding Detection (S-BFD)", Internet-Draft draft-ietf-bfd-seamless-base-07, February 2016.
[I-D.ietf-bfd-seamless-ip] Akiya, N., Pignataro, C. and D. Ward, "Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6 and MPLS", Internet-Draft draft-ietf-bfd-seamless-ip-03, February 2016.
[I-D.ietf-l2tpext-sbfd-discriminator] Govindan, V. and C. Pignataro, "Advertising S-BFD Discriminators in L2TPv3", Internet-Draft draft-ietf-l2tpext-sbfd-discriminator-02, January 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, DOI 10.17487/RFC4446, April 2006.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085, December 2007.
[RFC5586] Bocci, M., Vigoureux, M. and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, June 2009.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010.
[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV)", RFC 5885, DOI 10.17487/RFC5885, June 2010.

8.2. Informative References

[I-D.akiya-bfd-seamless-alert-discrim] Akiya, N., Pignataro, C. and D. Ward, "Seamless Bidirectional Forwarding Detection (S-BFD) Alert Discriminator", Internet-Draft draft-akiya-bfd-seamless-alert-discrim-03, October 2014.
[IANA-L2TP] Internet Assigned Numbers Authority, "Layer Two Tunneling Protocol "L2TP"", May 2015.
[IANA-PWE3] Internet Assigned Numbers Authority, "Pseudowire Name Spaces (PWE3)", January 2016.
[RFC6391] Bryant, S., 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.

Authors' Addresses

Vengada Prasad Govindan Cisco Systems EMail:
Carlos Pignataro Cisco Systems EMail: