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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: February 20, 2015                               August 19, 2014


        Definition of Time-to-Live TLV for LSP-Ping Mechanisms
                draft-ietf-mpls-lsp-ping-ttl-tlv-10.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) and/or bidirectional
   co-routed LSP from any node on the path of the MS-PW and/or
   bidirectional co-routed LSP. 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
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   The list of Internet-Draft Shadow Directories can be accessed at



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   http://www.ietf.org/shadow.html


Copyright and License 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
   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 . . . . . . . . . . . . . . . . . . . . . .  6
     4.2. Error scenario  . . . . . . . . . . . . . . . . . . . . . .  6
   5. Security Considerations . . . . . . . . . . . . . . . . . . . .  6
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   7. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .  7
   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 MPLS Echo Request packet to any
   other node along the path of the MS-PW and receive the corresponding
   MPLS Echo Reply. If the originator of the MPLS 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 MPLS
   Echo Request may need to know how many hops away the originator of
   the MPLS Echo Request is so that it can set the TTL value on the MPLS
   header for the MPLS 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 MPLS Echo Reply with, so as the packet is intercepted by the
   originator node.

   A new optional TTL TLV is defined in this document. This TLV will be
   added by the originator of the MPLS Echo Request to inform the
   receiver how many hops away the originator is on the path of the MS-
   PW or Bidirectional LSP.

   This mechanism only works if the MPLS Echo Reply is sent down the co-
   routed LSP, hence the scope of this TTL TLV is currently limited to
   MS-PW or Bidirectional co-routed MPLS LSPs. The presence of the TLV
   implies the use of the return path of the co-routed LSP, if the
   return path is any other mechanism then the TLV in the MPLS Echo
   Request MUST be ignored.

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




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   PW: Pseudowire

   TLV: Type Length Value

   TTL: Time To Live


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 Reserved - 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

   The TTL TLV MAY be included in the MPLS Echo Request by the



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   originator of the request.

   If the TTL TLV is present and the receiver does not understand TTL
   TLVs, it will simply ignore the TLV, as is the case for all optional
   TLVs. If the TTL TLV is not present or is not processed by the
   receiver, any determination of the TTL value used in the MPLS label
   on the LSP-Ping echo reply is beyond the scope of this document.

   If the TTL TLV is present and the receiver understands TTL TLVs, one
   of the following two conditions apply:

    o  If the TTL TLV value field is zero, the LSP-Ping echo request
   packet SHOULD be dropped.

    o  Otherwise, the receiver MUST use the TTL value specified in the
    TTL TLV when it creates the MPLS header of the MPLS Echo Reply.
   The TTL value in the TTL TLV takes precedence over any TTL value
   determined by other means, such as from the Switching Point TLV    in
   the MS-PW.  This precedence will aid the originator of the    LSP-
   Ping 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
                              ---MPLS Echo Request--->
                              <--MPLS 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 MPLS Echo Request with the TTL
   TLV is originated from B and sent towards D. The MPLS 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 MPLS Echo Request or from the optional LDP switching
   point TLV. The MPLS 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 MPLS Echo
   Reply. The MPLS Echo Reply will be intercepted by B because of TTL



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   expiry.

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

4.1. Traceroute mode

   In traceroute mode, the TTL value in the TLV is set to 1 for the
   first Echo Request, then to 2 for the next, and so on. This is
   similar to the TTL values used for the label set on the packet.


4.2. Error scenario

   It is possible that the MPLS 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 MPLS Echo Reply
   packet MUST be modified by deducting the incoming label TTL on the
   received packet from TTL TLV value. If the MPLS Echo Request packet
   is punted to the CPU before the incoming label TTL is deducted, then
   another 1 MUST be added. In other words:

   Return TTL Value on the MPLS 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 MPLS 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.

   The recommendation in [RFC4379] security section applies, to check
   the source address of the MPLS Echo Request, however the source
   address can now be any node along the LSP path.

   A faulty transit node changing the TTL TLV value could make the wrong
   node reply to the MPLS Echo Request, and/or the wrong node to receive



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   the MPLS Echo Reply. An LSP trace may help identify the faulty
   transit node.


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 MUST be assigned from the
   range (32768-49161) of optional TLVs.

   IANA is requested to allocate the value 32769.


7. Acknowledgements

      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



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



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