Internet Engineering Task Force V. Govindan
Internet-Draft C. Pignataro
Updates: 5885 (if approved) Cisco Systems
Intended status: Standards Track February 4, 2016
Expires: August 7, 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 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

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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 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:

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.

Bitmask Values for BFD CV Types
Fault Detection Only Fault Detection and Status Signaling
S-BFD, IP/UDP Encapsulation (with IP/UDP Headers) TBD1 (Note1) N/A
S-BFD, PW-ACH Encapsulation when using MPLS PW or L2SS Encapsulation when using L2TP PW (without IP/UDP Headers) TBD2 (Note2) 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 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 S-BFD Reflector Demultiplexing

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

TBD. S-BFD Reflector 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 S-BFD Reflector target discriminators

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

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 (Note1) BFD Only
S-BFD Only None (Note1) S-BFD S-BFD only
Both S-BFD and BFD BFD only S-BFD only Both SBFD and 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.

      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:

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

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

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", Internet-Draft draft-akiya-bfd-seamless-alert-discrim-03, October 2014.
[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-05, June 2015.
[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

[IANA] Internet Assigned Numbers Authority, "Protocol Registries"

Authors' Addresses

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