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Versions: (draft-boutros-mpls-lsp-ping-ttl-tlv) 00 01 02 03 04 05 06 07 08 09 10 RFC 7394

Network Working Group                                       Sami Boutros
INTERNET-DRAFT                                            Siva Sivabalan
Intended Status: Standards Track                          George Swallow
                                                          Shaleen Saxena
                                                           Cisco Systems

                                                          Vishwas Manral
                                                     Hewlett Packard Co.

                                                              Sam Aldrin
                                               Huawei Technologies, Inc.

Expires: April 19, 2014                                 October 16, 2013


        Definition of Time-to-Live TLV for LSP-Ping Mechanisms
                draft-ietf-mpls-lsp-ping-ttl-tlv-06.txt


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.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   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
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html



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Copyright and License Notice

   Copyright (c) 2013 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
   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3. Time To Live TLV  . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1. TTL TLV Format  . . . . . . . . . . . . . . . . . . . . . .  4
     3.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1. Traceroute mode . . . . . . . . . . . . . . . . . . . . . .  5
     4.2. Error scenario  . . . . . . . . . . . . . . . . . . . . . .  6
   5. Security Considerations . . . . . . . . . . . . . . . . . . . .  6
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   7. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .  6
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     8.1  Normative References  . . . . . . . . . . . . . . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  7


















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1.  Introduction

   A MS-PW may 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. 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, 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.

   The scope of this TTL TLV is currently limited to MS-PW or
   Bidirectional co-routed MPLS LSPs.

2.  Terminology

   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].

   LSR: Label Switching Router

   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

3.1. TTL TLV Format


      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       |   Reserved    |   Flags                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     Figure 1: Time To Live TLV format

     The TTL TLV has the format shown in Figure 1.

        Value

            The value of the TTL as specified by this TLV

        Flags

            The Flags field is a bit vector with the following format:

             0                   1
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             MBZ             |R|
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            One flag is defined for now, the R flag; the rest of the
            flags are currently undefined and must be zero (MBZ) when
            sending and ignored on receipt.

            The R flag (Reply TTL) is set signify that the value is
            meant to be used as the TTL for the reply packet. Other bits
            may be defined later to enhance the scope of this TLV.

3.2. Usage

   This TLV shall be included in the echo request by the originator of
   request. The use of this TLV is optional. 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 TLV's 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.



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   If a receiver understands the TTL TLV, and the TTL TLV is present in
   the echo request, and if the value field is zero, the LSP Ping Echo
   request packet SHOULD be dropped.

   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 other words, if the
   value of the TTL provided by this TLV does not match the TTL
   determined by other means, such as Switching Point TLV in MS-PW, then
   TTL TLV must be used. This will aid the originator of the echo
   request in analyzing the return path.

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
   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
   choice of the value 2 will be based on the operator input requesting
   the echo request or from the optional LDP switching point TLV. 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.


4.1. Traceroute mode

   In the traceroute mode TTL value in the TLV is successively set to 1,
   2, and so on. This is similar to the TTL values used for the label



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   set on the packet.


4.2. Error scenario

   It is possible that the echo request packet was intercepted before
   the intended destination for reason other than label TTL expiry. This
   could be due network faults, misconfiguration or other reasons. In
   such cases, if the return TTL is set to the value specified in the
   TTL TLV then the echo response packet will continue beyond the
   originating node. This becomes a security issue.

   To prevent this, the label TTL value used in the Echo Reply packet
   must be modified by deducting the incoming label TTL on the received
   packet from TTL TLV value. If the echo request packet is punted to
   the CPU before the incoming label TTL is deducted, then another 1
   must be deducted. In other words:

   Return TTL Value on the Echo Reply packet = (TTL TLV Value)-(Incoming
   Label TTL) + 1

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.

   Time To Live TLV (See Section 3). The value should be assigned from
   the range (32768-49161) of optional TLV's which SHOULD be ignored if
   an implementation does not support or understand them as defined in
   section 3 of RFC 4379 [RFC4379].


7. Acknowledgements




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      The authors would like to thank Greg Mirsky for his comments.

8.  References

8.1  Normative References

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

   [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.




Authors' Addresses



   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario, K2K 3E8
   Canada
   Email: msiva@cisco.com

   Sami Boutros
   Cisco Systems, Inc.
   3750 Cisco Way
   San Jose, California 95134
   USA
   Email: sboutros@cisco.com

   George Swallow
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough , MASSACHUSETTS 01719
   United States
   Email: swallow@cisco.com

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



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   United States
   Email: ssaxena@cisco.com

   Vishwas Manral
   Hewlett Packard Co.
   19111 Pruneridge Ave,
   Cupertino, CA 95014 USA
   United States
   EMail: vishwas.manral@hp.com

   Michael Wildt
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough , MASSACHUSETTS 01719
   United States
   Email: mwildt@cisco.com

   Sam Aldrin
   Huawei Technologies, Inc.
   1188 Central Express Way,
   Santa Clara, CA 95051
   United States
   Email: aldrin.ietf@gmail.com




























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