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Versions: 00 01 02 03

Internet Engineering Task Force                                 N. Akiya
Internet-Draft                                              C. Pignataro
Intended status: Standards Track                                 D. Ward
Expires: April 24, 2015                                    Cisco Systems
                                                        October 21, 2014


Seamless Bidirectional Forwarding Detection (S-BFD) Alert Discriminator
               draft-akiya-bfd-seamless-alert-discrim-03

Abstract

   This document defines the Alert Discriminator which operates on the
   Seamless Bidirectional Forwarding Detection (S-BFD), and Alert
   Discriminator Diagnostic Codes which operates on the Alert
   Discriminator.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 http://datatracker.ietf.org/drafts/current/.

   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 April 24, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Extended S-BFD Use Cases  . . . . . . . . . . . . . . . . . .   2
     2.1.  Target S-BFD Discriminator Discovery  . . . . . . . . . .   3
     2.2.  S-BFD Path Tracing  . . . . . . . . . . . . . . . . . . .   3
   3.  Alert Discriminator . . . . . . . . . . . . . . . . . . . . .   4
   4.  Alert Discriminator Diagnostic Codes  . . . . . . . . . . . .   4
     4.1.  Diagnostic Code: Target S-BFD Discriminator Discovery . .   4
     4.2.  Diagnostic Code: S-BFD Path Tracing . . . . . . . . . . .   5
     4.3.  Diagnostic Code: Not Supported  . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Alert Discriminator Diagnostic Codes Registry . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   [I-D.ietf-bfd-seamless-base] defines the Seamless Bidirectional
   Forwarding Detection (S-BFD): a simplified mechanism which uses
   Bidirectional Forwarding Detection (BFD) with large portions of
   negotiation aspects eliminated.

   This document defines the Alert Discriminator which operates on the
   S-BFD, and the Alert Discriminator Diagnostic Codes which operates on
   the Alert Discriminator, for extended S-BFD use cases described in
   Section 2.

2.  Extended S-BFD Use Cases

   This section describes extended S-BFD use cases.








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2.1.  Target S-BFD Discriminator Discovery

   IS-IS ([I-D.ietf-isis-sbfd-discriminator]) and OSPF
   ([I-D.ietf-ospf-sbfd-discriminator]) protocols have been extended to
   advertise S-BFD discriminator values.  These extensions will suffice
   for number of scenarios where S-BFD is used to verify the network
   reachability to other network devices.  Other protocols may be
   extended to support S-BFD in further scenarios.

   There are, however, some scenarios where it is desirable to have a
   mechanism within the S-BFD protocol to discover the target S-BFD
   discriminator value.

   o  In some scenarios, direct protocol communications are
      intentionally kept minimal for reasons such as administrative
      policy.  One such example is the usage of S-BFD across Autonomous
      System (AS) boundaries (i.e. inter-AS).

   o  In some scenarios, there is no control plane which can easily
      advertise S-BFD discriminators.  MPLS-TP and static routes are
      such examples.

   o  In some scenarios, defining and standardizing protocol extensions
      to advertise S-BFD discriminator values may be more work than the
      value it brings.

   To accommodate the two scenarios described, it is desirable to have a
   mechanism within the S-BFD protocol to discover the target S-BFD
   discriminator value.

2.2.  S-BFD Path Tracing

   When a multihop S-BFD session, IP based or MPLS based, determines a
   loss of reachability to the target entity, the responsibility of
   identifying the problematic point in the paths is often left to
   operators.  ICMP echo request/reply (IP Ping/Trace) [RFC0792] and
   MPLS echo request/reply (LSP Ping/Trace) [RFC4379] allow for tracing
   of hops to a specific target, and these are often used by operators,
   manually or automatically, to attempt to isolate faults.  However,
   when it comes to identifying the problematic point that caused the
   S-BFD session to declare the failure, there are couple of issues.

   o  Usage of non-S-BFD packets can result in them being load balanced
      differently along the paths, causing those packets to traverse
      different paths than S-BFD packets did.

   o  Usage of non-S-BFD packets may not identify the problematic points
      which only affect specific flows (which affects S-BFD packets).



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   o  In order to isolate short lived transient issues, it is desirable
      to immediately perform the task of fault isolation.  IP/MPLS Ping/
      Trace implementations often require more processing overhead than
      S-BFD.  Usage of heavier tool to attempt to isolate fault can
      result in missing more instances of identifying short lived
      transient issues.

   Although the task of "fault isolation" does not belong in the BFD/
   S-BFD protocols, if the task of "fault isolation" can be done with
   simple extensions within the S-BFD protocol, the result does provide
   additional benefit to operators.

3.  Alert Discriminator

   This document reserves the value zero of the S-BFD discriminator pool
   as the Alert Discriminator.  A reflector BFD session is to monitor
   incoming S-BFD packets with value zero in the "Your Discriminator"
   field.  The reflector BFD session is to process the S-BFD packets
   according to the value specified in the received "Diagnostic" field.
   Procedures specific to each "Diagnostic" code are described in
   Section 4.

4.  Alert Discriminator Diagnostic Codes

   This section defines the Alert Discriminator Diagnostic Codes, and
   procedures for each defined code point.  The Alert Discriminator
   Diagnostic Codes MUST operate on the Alert Discriminator.
   Specifically:

   o  In the direction from an SBFDInitiator to an SBFDReflector, the
      Alert Discriminator Diagnostic Codes MUST only be used with "Your
      Discriminator" field set to the Alert Discriminator.

   o  In the direction from an SBFDReflector to an SBFDInitiator, the
      Alert Discriminator Diagnostic Code MUST only be used in a reply
      S-BFD packet if received S-BFD packet contained "Your
      Discriminator" field set to the Alert Discriminator.

4.1.  Diagnostic Code: Target S-BFD Discriminator Discovery

   The Alert Discriminator Diagnostic Code 29 is defined for the purpose
   of discovering the target S-BFD discriminator.

     Value  Alert Discriminator Diagnostic Code Name
    ------  ----------------------------------------
        29  Target S-BFD Discriminator Discovery





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   When a reflector BFD session receives an S-BFD packet containing the
   Alert Discriminator and the Alert Discriminator Diagnostic Code of
   29, then the reflector BFD session SHOULD send a reply S-BFD packet.
   The format and the contents of the generated reply S-BFD packet MUST
   follow the definition in the S-BFD protocol documents, except for
   following fields:

   o  "My Discriminator" field MUST be set to one of local S-BFD
      discriminators.

   o  "Diagnostic" field MUST be set to value 29.

4.2.  Diagnostic Code: S-BFD Path Tracing

   The Alert Discriminator Diagnostic Code 30 is defined for the purpose
   of S-BFD path tracing.

     Value  Alert Discriminator Diagnostic Code Name
    ------  ----------------------------------------
        30  S-BFD Path Trace

   When a reflector BFD session receives an S-BFD packet containing the
   Alert Discriminator and the Alert Discriminator Diagnostic Code of
   30, then the reflector BFD session SHOULD send a reply S-BFD packet.
   The format and the contents of the generated reply S-BFD packet MUST
   follow the definition in the S-BFD protocol documents, except for
   following fields:

   o  "My Discriminator" field MUST be set to zero.

   o  "Diagnostic" field MUST be set to value 30.

4.3.  Diagnostic Code: Not Supported

   The Alert Discriminator Diagnostic Code 31 is defined for a reflector
   BFD session to communicate, in reply S-BFD packet, that specified
   Alert Discriminator Diagnostic Code in received S-BFD packet is not
   understood or is not supported.

     Value  Alert Discriminator Diagnostic Code Name
    ------  ----------------------------------------
        31  Not Supported

   When a reflector BFD session receives an S-BFD packet containing the
   Alert Discriminator and an Alert Discriminator Diagnostic Code which
   is not understood or supported by the reflector BFD session, then the
   reflector BFD session SHOULD send a reply S-BFD packet.  The format
   and the contents of the generated reply S-BFD packet MUST follow the



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   definition in the S-BFD protocol documents, except for following
   fields:

   o  "My Discriminator" field MUST be set to zero.

   o  "Diagnostic" field MUST be set to value 31.

   Note that in the direction from an SBFDInitiator to an SBFDReflector,
   the Alert Discriminator Diagnostic Code 31 MUST NOT be used.  If a
   reflector BFD session receives an S-BFD packet with the Alert
   Discriminator and the Alert Discriminator Diagnostic Code 31, then
   the reflector BFD session MUST drop the packet.

5.  Security Considerations

   Conceptually the Alert Discriminator is similar to an IP Router Alert
   Option or an MPLS Router Alert Label.  The Alert Discriminator
   introduces a way which remote network devices can instruct a
   reflector BFD sessions to perform specific tasks corresponding to
   specified Alert Discriminator Diagnostic Codes, and without remote
   network devices knowing a valid S-BFD discriminator on the target
   device.  Hence, it is very critical that reflector BFD session
   services the Alert Discriminator only from trusted sources and for
   allowed Alert Diagnostic Codes for those sources.  Therefore, this
   document RECOMMENDS following security procedures to be implemented:

   o  S-BFD packets with Alert Discriminator is accepted only from
      trusted sources.  An implementation SHOULD provide a mechanism for
      operators to specify an access-list to describe the trusted
      sources.

   o  An implementation SHOULD provide a mechanism for operators to
      specify the Alert Discriminator Diagnostic Codes which are
      supported on the device.  If required, such configuration should
      be set per a trusted source.

   Additionally, it is RECOMMENDED that implementations supporting the
   Alert Discriminator considers the security considerations described
   in [I-D.ietf-bfd-seamless-base], [I-D.ietf-bfd-seamless-ip] and
   [I-D.akiya-bfd-seamless-sr] documents.

6.  IANA Considerations

   This document requests IANA to create a new registry within
   [IANA-BFD] protocol to maintain "Alert Discriminator Diagnostic
   Codes" field.  Initial values are described in immediate sub-section
   to follow.




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6.1.  Alert Discriminator Diagnostic Codes Registry

   The IANA is requested to create and maintain a registry entitled
   "Alert Discriminator Diagnostic Codes" with the following
   registration procedures:

            Registry Name: Alert Discriminator Diagnostic Codes

     Value  Alert Discriminator Diagnostic Code Name  Reference
    ------  ----------------------------------------  -------------
       0-7  Experimental                              This document
      8-28  Reserved                                  This document
        29  Target S-BFD Discriminator Discovery      This document
        30  S-BFD Path Trace                          This document
        31  Not Supported                             This document

   Assignments of Alert Discriminator Diagnostic Codes are via Standards
   Action [RFC5226].

7.  Acknowledgements

   Authors would like to thank Srihari Raghavan and Girija Raghavendra
   Rao for reviewing and providing comments on this document.

8.  Contributing Authors

   Nagendra Kumar
   Cisco Systems
   Email: naikumar@cisco.com

   Mallik Mudigonda
   Cisco Systems
   Email: mmudigon@cisco.com

   Aswatnarayan Raghuram
   AT&T
   Email: ar2521@att.com

   Glenward D.  Hayden
   AT&T
   Email: gh1691@att.com

9.  References








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9.1.  Normative References

   [I-D.akiya-bfd-seamless-sr]
              Akiya, N., Pignataro, C., and N. Kumar, "Seamless
              Bidirectional Forwarding Detection (S-BFD) for Segment
              Routing", draft-akiya-bfd-seamless-sr-03 (work in
              progress), August 2014.

   [I-D.ietf-bfd-seamless-base]
              Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J.
              Networks, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", draft-ietf-bfd-seamless-base-03 (work in
              progress), August 2014.

   [I-D.ietf-bfd-seamless-ip]
              Akiya, N., Pignataro, C., and D. Ward, "Seamless
              Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6
              and MPLS", draft-ietf-bfd-seamless-ip-00 (work in
              progress), September 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

9.2.  Informative References

   [I-D.ietf-isis-sbfd-discriminator]
              Ginsberg, L., Akiya, N., and M. Chen, "Advertising S-BFD
              Discriminators in IS-IS", draft-ietf-isis-sbfd-
              discriminator-01 (work in progress), October 2014.

   [I-D.ietf-ospf-sbfd-discriminator]
              Bhatia, M., Pignataro, C., Aldrin, S., and T. Ranganath,
              "OSPF extensions to advertise S-BFD Target Discriminator",
              draft-ietf-ospf-sbfd-discriminator-00 (work in progress),
              September 2014.

   [IANA-BFD]
              IANA, "Bidirectional Forwarding Detection (BFD)
              Parameters", <http://www.iana.org/assignments/bfd-
              parameters/bfd-parameters.xhtml>.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.




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   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

Authors' Addresses

   Nobo Akiya
   Cisco Systems

   Email: nobo@cisco.com


   Carlos Pignataro
   Cisco Systems

   Email: cpignata@cisco.com


   Dave Ward
   Cisco Systems

   Email: wardd@cisco.com





























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