Network Working Group                                    S. Boutros, Ed.
Internet-Draft                                         S. Sivabalan, Ed.
Intended status: Standards Track                          Cisco Systems
Expires: June 12, 2011                                    V. Manral, Ed.
                                                         IPInfusion Inc.
                                                              G. Swallow
                                                               S. Saxena
                                                           Cisco Systems
                                                       December 09, 2010


         Definition of Time-to-Live TLV for LSP-Ping Mechanisms
                 draft-boutros-mpls-lsp-ping-ttl-tlv-02

Abstract

   LSP-Ping is a widely deployed Operation, Administration, and
   Maintenance (OAM) mechanism in MPLS networks.  However, in the
   present form, this mechanism is inadequate to verify connectivity of
   a segment of a Multi-Segment PseudoWire (MS-PW) from any node on the
   path of the MS-PW.  This document defines a TLV to address this
   shortcoming.

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
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   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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   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 June 12, 2011.

Copyright Notice




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   Copyright (c) 2010 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
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   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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Time to Live (TTL)  . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6
























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1.  Introduction

   A MS-PW can span across multiple service provider networks.  In order
   to allow Service Providers (SP) to verify segments of such MS-PW from
   any node on the path of the MS-PW, any node along the path of the
   MS-PW, should be able to originate an LSP-Ping echo request packet to
   any another node along the path of the MS-PW and receive the
   corresponding echo reply.  If the originator of the echo request is
   at the end of a MS-PW, the receiver of the request can send the reply
   back to the sender without knowing the hop-count distance of the
   originator.  For example, the reply will be intercepted by the
   originator regardless of the TTL value on the reply packet.  But, if
   the originator is not at the end of the MS-PW, the receiver of the
   echo request MAY need to know how many hops away the originator of
   the echo request is so that it can set the TTL value on the MPLS
   header for the echo reply to be intercepted at the originator node.

   In MPLS networks (also applicable to MPLS-TP) for bidirectional co-
   routed LSPs, if it is desired to verify connectivity from any
   intermediate node (LSR) on the LSP to the any other LSR on the LSP
   the receiver may need to know the TTL to send the Echo reply with, so
   as the packet is intercepted by the originator node.

   A new optional TTL TLV is being proposed in this document this TLV
   will be added by the originator of the echo request to inform the
   receiver how many hops away the originator is on the path of the
   MS-PW or Bidirectional LSP.


2.  Terminology

   LSR: Label Switching Router

   MPLS-OAM: MPLS Operations, Administration and Maintenance

   MPLS-TP: MPLS Transport Profile

   MS-PW: Multi-Segment PseudoWire

   PW: PseudoWire

   TLV: Type Length Value

   TTL: Time To Live







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3.  Time to Live (TTL)

      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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  type = TBD                   |   Length = 8                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   value       |
      +-+-+-+-+-+-+-+-+

                  Figure 1: Time To Live TLV format

   The TTL TLV has the format shown in Figure 1.  This TLV shall be
   included in the echo request by the originator of request.  The use
   of this TLV is optional.  If the value field is zero, the LSP Ping
   Echo request packet will be dropped.

   If a receiver does not understand the TTL TLV, it will simply ignore
   the TLV (Type value of TLV is assumed to be in the range of optional
   TLVs which SHOULD be ignored if an implementation does not support or
   understand them).  In the absence of TTL TLV or if TTL TLV is ignored
   by a receiver, the determination of the TTL value used in the MPLS
   label on the echo reply is beyond the scope of this document.

   If a receiver understands the TTL TLV, and the TTL TLV is present in
   the echo request, the receiver MUST use the TTL value specified in
   TLV in the MPLS header of the echo reply.

   In the traceroute mode TTL value in the TLV is successively set to 1,
   2, and so on.


4.  Operation

   In this section, we explain a use case for the TTL TLV with an MPLS
   MS-PW.

                   <------------------MS-PW --------------------->
                   A          B          C           D           E
                   o -------- o -------- o --------- o --------- o
                              ------Echo Request----->
                              <-----Echo Reply--------

                 Figure 2: Use-case with MS-PWs

   Let us assume a MS-PW going through LSRs A, B, C, D, and E.
   Furthermore, assume that an operator wants to perform a connectivity
   check between B and D from B. Thus, an LSP-Ping request with the TTL



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   TLV is originated from B and sent towards D. The echo request packet
   contains the FEC of the PW Segment between C and D. The value field
   of the TTL TLV and the TTL field of the MPLS label are set to 2.  The
   echo request is intercepted at D because of TTL expiry.  D detects
   the TTL TLV in the request, and use the TTL value (i.e., 2) specified
   in the TLV on the MPLS label of the echo reply.  The echo reply will
   be intercepted by B because of TTL expiry.

   The same operation will apply in the case a co-routed bidirectional
   LSP and we want to check connectivity from an intermediate LSR B to
   another LSR D, from B.


5.  Security Considerations

   This draft allows the setting of the TTL value in the MPLS Label of
   an echo reply, so that it can be intercepted by an intermediate
   device.  This can cause a device to get a lot of LSP Ping packets
   which get redirected to the CPU.

   However the same is possible even without the changes mentioned in
   this document.  A device should rate limit the LSP ping packets
   redirected to the CPU so that the CPU is not overwhelmed.


6.  IANA Considerations

   IANA is requested to assign TLV type value to the following TLV from
   the "Multiprotocol Label Switching Architecture (MPLS) Label Switched
   Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub-
   registry.

   Optional Time To Live TLV (See Section 3).  The Suggested value is
   32769 as suggested by RFC 4379 Section 3.


7.  Acknowledgements

   The authors would like to thank Greg Mirsky, Laxmi Narasimaha Reddy
   Devireddy and Mahesh Akula for their comments.


8.  References

8.1.  Normative References

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



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

   [RFC5085]  Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
              Connectivity Verification (VCCV): A Control Channel for
              Pseudowires", RFC 5085, December 2007.

8.2.  Informative References


Authors' Addresses

   Sami Boutros (editor)
   Cisco Systems
   3750 Cisco Way
   San Jose, CA  95134
   US

   Phone: undefined
   Fax:
   Email: sboutros@cisco.com
   URI:


   Siva Sivabalan (editor)
   Cisco Systems
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   Phone: undefined
   Fax:
   Email: msiva@cisco.com
   URI:


   Vishwas Manral (editor)
   IPInfusion Inc.
   1188 E. Arques Ave.
   Sunnyvale, CA  94085
   USA

   Phone: 408-400-1900
   Fax:
   Email: vishwas@ipinfusion.com
   URI:




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   George Swallow
   Cisco Systems
   300 Beaver Brook Road
   Boxborough, MA  01719
   USA

   Phone: undefined
   Fax:
   Email: swallow@cisco.com
   URI:


   Shaleen Saxena
   Cisco Systems
   300 Beaver Brook Road
   Boxborough, MA  01719
   USA

   Phone: undefined
   Fax:
   Email: ssaxena@cisco.com
   URI:





























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