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Versions: (draft-gp-l2tpext-sbfd-discriminator) 00 01 02 03 04 05 RFC 7886

Networking Working Group                                     V. Govindan
Internet-Draft                                              C. Pignataro
Intended status: Standards Track                                   Cisco
Expires: October 17, 2016                                 April 15, 2016


    Advertising Seamless Bidirectional Forwarding Detection (S-BFD)
   Discriminators in Layer Two Tunneling Protocol, Version 3 (L2TPv3)
                draft-ietf-l2tpext-sbfd-discriminator-05

Abstract

   This document defines a new Attribute Value Pair (AVP) that allows
   L2TP Control Connection Endpoints (LCCEs) to advertise one or more
   Seamless Bidirectional Forwarding Detection (S-BFD) Discriminator
   values using the Layer Two Tunneling Protocol, Version 3 (L2TPv3).

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
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   This Internet-Draft will expire on October 17, 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
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  S-BFD Target Discriminator ID AVP . . . . . . . . . . . . . .   2
     2.1.  Encoding Format . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [I-D.ietf-bfd-seamless-base] defines a simplified mechanism to use
   Bidirectional Forwarding Detection (BFD) [RFC5880], referred to as
   Seamless Bidirectional Forwarding Detection (S-BFD).  The S-BFD
   mechanisms depend on network nodes knowing the BFD discriminators
   which each node in the network has reserved for this purpose.  S-BFD
   requires the usage of unique discriminators within an administrative
   domain.  The use of Layer Two Tunneling Protocol, Version 3 (L2TPv3)
   [RFC3931] is one possible means of advertising these discriminators.

   This document specifies the encoding to be used when S-BFD
   discriminators are advertised using L2TPv3.

1.1.  Terminology

   The reader is expected to be very familiar with the terminology and
   protocol constructs defined in S-BFD (see Section 2 of
   [I-D.ietf-bfd-seamless-base]) and L2TPv3 (see Section 1.3 of
   [RFC3931]).

2.  S-BFD Target Discriminator ID AVP

   The "S-BFD Target Discriminator ID" AVP is exchanged using the ICRQ
   (Incoming-Call-Request), ICRP (Incoming-Call-Reply), OCRQ (Outgoing-




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   Call-Request), and OCRP (Outgoing-Call-Reply) control messages during
   session negotiations.

2.1.  Encoding Format

   The S-BFD Target Discriminator Identifier (ID) Attribute Value Pair
   (AVP), Attribute Type "TBA by IANA", is an identifier used to
   advertise the S-BFD Target Discriminator(s) supported by an LCCE for
   the S-BFD Reflector operation.  This AVP indicates that the
   advertiser implements an S-BFD reflector supporting the specified
   target discriminator(s) and is ready for S-BFD Reflector operation.
   The receiving LCCE MAY use this AVP if it wants to monitor
   connectivity to the advertising LCCE using S-BFD.

   The Attribute Value field for this AVP has the following format:

   S-BFD Target Discriminator ID (ICRQ, ICRP, OCRQ, OCRP):

                                          No. of octets
      +-----------------------------+
      | Discriminator Value(s)      |     4/Discriminator
      :                             :
      +-----------------------------+

   An LCCE MAY include the S-BFD Discriminator Advertisement AVP in a
   L2TP Control Protocol message (ICRQ, ICRP, OCRQ, OCRP) [RFC3931].  If
   the other LCCE does not wish to monitor connectivity using S-BFD, it
   MAY safely discard this AVP without affecting the rest of session
   negotiation.  While [I-D.ietf-bfd-seamless-base] concerns itself with
   the advertisement of only one discriminator unless the mapping to
   discriminators to entities is specified, the AVP encoding allows the
   specification of an arbitrary number of S-BFD Discriminators (at
   least one) for extensibility.

   When an LCCE uses the S-BFD Target Discriminator ID AVP, multiple
   S-BFD Discriminators MAY be included, and at least one S-BFD
   Discriminator MUST be included.  When one S-BFD Discriminator is
   advertised, such S-BFD Discriminator is associated with the L2TPv3
   Session.  When multiple S-BFD discriminators are advertised how a
   given discriminator is mapped to a specific use case is out of scope
   for this document.

   The S-BFD Target Discriminator ID AVP allows for advertising at least
   one S-BFD Discriminator value:







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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Discriminator 1                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Discriminator 2 (Optional)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               ...                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Discriminator n (Optional)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The M bit of the L2TP Control Protocol Message (ICRQ, ICRP, OCRQ,
   OCRP) [RFC3931] MUST NOT be set inside the S-BFD Target Discriminator
   ID AVP advertisement.

3.  IANA Considerations

   IANA maintains a sub-registry "Message Type AVP (Attribute Type 0)
   Values" in the "Control Message Attribute Value Pairs" as per
   [RFC3438].  IANA is requested to assign the first free value from
   this sub-registry as the Message typ AVP for "S-BFD Target
   Discriminator ID".

   A summary of the new AVPs requested for Attribute Type 0 follows:

   Control Message Attribute Value Pairs

         Attribute
         Type          Description
         -----------   ------------------
         TBA by IANA   S-BFD Target Discriminator ID


4.  Security Considerations

   Security concerns for L2TP are addressed in [RFC3931].  Introduction
   of the S-BFD Discriminator Advertisement AVP introduces no new
   security risks for L2TP.

   Advertisement of the S-BFD discriminators does make it possible for
   attackers to initiate S-BFD sessions using the advertised
   information.  The vulnerabilities this poses and how to mitigate them
   are discussed in the Security Considerations section of
   [I-D.ietf-bfd-seamless-base].






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5.  Acknowledgements

   Authors would like to thank Nobo Akiya, Stewart Bryant and Pawel
   Sowinski for providing core inputs for the document and for
   performing thorough reviews and providing number of comments.
   Authors would like to thank Nagendra Kumar for his reviews.

6.  Contributing Authors

   Mallik Mudigonda
   Cisco Systems, Inc.

   Email: mmudigon@cisco.com

7.  References

7.1.  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)", draft-ietf-bfd-seamless-base-09 (work in
              progress), April 2016.

   [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>.

   [RFC3438]  Townsley, W., "Layer Two Tunneling Protocol (L2TP)
              Internet Assigned Numbers Authority (IANA) Considerations
              Update", BCP 68, RFC 3438, DOI 10.17487/RFC3438, December
              2002, <http://www.rfc-editor.org/info/rfc3438>.

   [RFC3931]  Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
              "Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
              RFC 3931, DOI 10.17487/RFC3931, March 2005,
              <http://www.rfc-editor.org/info/rfc3931>.

7.2.  Informative References

   [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>.







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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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