Network Working Group                              Siva Sivabalan (Ed.)
Internet Draft                                       Sami Boutros (Ed.)
Intended status: Standards Track                         George Swallow
Expires: September 2011                                  Shaleen Saxena
                                                     Cisco Systems, Inc.

                                                         Vishwas Manral
                                                        IPInfusion, Inc.

                                                             Sam Aldrin
                                              Huawei Technologies, Inc.

                                                        October 28, 2011

          Definition of Time-to-Live TLV for LSP-Ping Mechanisms


   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

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   this document are to be interpreted as described in RFC 2119 [3].

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1. Introduction...................................................2
   2. Terminology....................................................3
   3. Time To Live TLV...............................................4
   4. Operation......................................................4
   5. Security Considerations........................................5
   6. IANA Considerations............................................5
   7. References.....................................................5
      7.1. Normative References......................................5
      7.2. Informative References.........Error! Bookmark not defined.
   Author's Addresses................................................7

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

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   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.

   Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119Error!
   Reference source not found.

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 TLV

   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 --------------------->

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

                 Figure 2: Use-case with MS-PWs

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   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
   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-

   Time To Live TLV (See Section 3).

7. References

7.1. Normative References

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

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     [2] T. Nadeau, et. al, "Pseudowire Virtual Circuit Connectivity
           Verification (VCCV): A Control Channel for Pseudowires ", RFC
           5085, December 2007.

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

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Author's Addresses

   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario, K2K 3E8

   Sami Boutros
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose, California 95134

   George Swallow
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough , MASSACHUSETTS 01719
   United States

   Shaleen Saxena
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough , MASSACHUSETTS 01719
   United States

   Vishwas Manral
   IPInfusion, Inc.
   1188 E. Arques Ave.,
   Sunnyvale, CA 94085
   United States

   Sam Aldrin
   Huawei Technologies, Inc.
   1188 Central Express Way,
   Santa Clara, CA 95051
   United States

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