[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Nits]

Versions: 00 draft-kumarkini-mpls-spring-lsp-ping

MPLS Working Group                                              N. Kumar
Internet-Draft                                                G. Swallow
Intended status: Standards Track                            C. Pignataro
Expires: April 24, 2014                                         N. Akiya
                                                     Cisco Systems, Inc.
                                                                 M. Chen
                                                                  Huawei
                                                        October 21, 2013


Label Switched Path (LSP) Ping/Trace for Segment Routing Networks Using
                             MPLS Dataplane
                  draft-kumar-mpls-spring-lsp-ping-00

Abstract

   Segment Routing architecture leverages the source routing and
   tunneling paradigm and can be directly applied to MPLS dataplane.  A
   node steers a packet through a controlled set of instructions called
   segments, by prepending the packet with Segment Routing header.

   The segment assignment and forwarding semantic nature of Segment
   Routing raises additional consideration for connectivity verification
   and fault isolation in LSP with SPRING architecture.  This document
   illustrates the problem and describe a mechanism to perform LSP Ping
   and Traceroute on Segment Routing network over MPLS dataplane.

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
   and may be updated, replaced, or obsoleted by other documents at any
   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 April 24, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



Kumar, et al.            Expires April 24, 2014                 [Page 1]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Path validation in Segment Routing networks . . . . . . . . .   3
   4.  Segment Routing Sub-TLV Format  . . . . . . . . . . . . . . .   4
     4.1.  IPv4 Prefix Node Segment ID . . . . . . . . . . . . . . .   4
     4.2.  IPv6 Prefix Node Segment ID . . . . . . . . . . . . . . .   6
     4.3.  IGP Adjacency Segment ID  . . . . . . . . . . . . . . . .   7
   5.  Extension to Downstream Mapping TLV . . . . . . . . . . . . .   8
   6.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  FECs in Target FEC Stack TLV  . . . . . . . . . . . . . .   8
     6.2.  FEC Stack Change TLV  . . . . . . . . . . . . . . . . . .   9
     6.3.  PHP, Adjacency SID Pop, Implicit NULL . . . . . . . . . .   9
     6.4.  Segment Protocol Check  . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  11
   10. Contributing Authors  . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   [I-D.filsfils-rtgwg-segment-routing] introduces and explains Segment
   Routing architecture that leverages the source routing and tunneling
   paradigm.  A node steers a packet through a controlled set of
   instructions called segments, by prepending the packet with SR
   header.  A detailed definition about Segment Routing architecture is
   available in draft-filsfils-rtgwg-segment-routing and different use-
   cases are discussed in draft-filsfils-rtgwg-segment-routing-use-
   cases.

   The Segment Routing architecture can be directly applied to MPLS
   dataplane in a way that, the segment will be of 20-bits size and SR
   header is the label stack.



Kumar, et al.            Expires April 24, 2014                 [Page 2]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   [RFC4379] describes the mechanism to perform connectivity
   verification and fault isolation in Label Switched Path (LSP).
   Unlike LDP or RSVP which are the other well-known MPLS control plane
   protocols, segment assignment in Segment Routing architecture is not
   hop-by-hop basis.

   This nature of Segment Routing raises additional consideration for
   connectivity verification and fault isolation in Segment Routing
   network.  This document illustrates the problem and describe a
   mechanism to perform LSP Ping and Traceroute on Segment Routing
   network over MPLS dataplane.

2.  Requirements notation

   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 [RFC2119].

3.  Path validation in Segment Routing networks

   [RFC4379] defines the OAM machinery that helps with connectivity
   check and fault isolation in MPLS dataplane path with the use of
   various Target FEC Stack Sub-TLV that are carried in MPLS Ping
   packets and used by the responder for FEC validation.  While it is
   obvious that new Sub-TLVs need to be assigned, the unique nature of
   SPRING architecture raises a need for additional machinery for path
   validation.  This section discuss the challenges as below:


                         L1
                     +--------+
                     |   L2   |
                     R3-------R6
                    /           \
                   /             \
           R1----R2               R7----R8
                   \             /   L3
                    \           /
                     R4-------R5

             Figure 1: SPRING network

       500x --> Node Segment ID for Router X
                (Ex: 5006 is node segment ID for R6)
       9axy --> Adj Segment ID from Router X to Y over link a
                (Ex: 9136 is Adj segment ID from R3 to R6 via link 1)





Kumar, et al.            Expires April 24, 2014                 [Page 3]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   The forwarding semantic of Adjacency segment is to pop the segment
   and send the packet to a specific neighbor over a specific link.  A
   malfunctioning node may forward packets using Adjacency segment to
   incorrect neighbor or over incorrect link.  Exposed segment (after
   incorrectly forwarded Adjacency segment) might still allow such
   packet to traverse to intended destination, yet intended strict
   traversal has been broken.

   Assume in above topology, R1 sends traffic with segment stack as
   {9124, 5007, 9378} so that the path taken will be R1-R2-R4-R5-R7-R8.
   If the adjacency segment 9124 is misprogrammed in R2 to send the
   packet to R1 or R3, it will still be delivered to R8 but is not via
   the expected path.

   MPLS traceroute may help with detecting such deviation in above
   mentioned scenario.  However, it may not be helpful if R3, due to
   misprogramming, forwards packet with adjacency segment 9236 via link
   L1 while it is expected to be forwarded over Link L2.

   This document defines Target FEC Stack sub-TLVs and explains how they
   can be used to tackle above challenges.

4.  Segment Routing Sub-TLV Format

   The format of the following FEC Sub-TLVs follows the philosophy of
   Target FEC Stack TLV carrying FECs corresponding to each label in the
   label stack.  When operated with the procedures defined in [RFC4379],
   this allows LSP ping/traceroute operations to function when Target
   FEC Stack TLV contains more FECs than received label stack at
   responder nodes.

                   Type  Sub-Type    Value Field
                   ----  --------  ---------------
                       1   TBD1      IPv4 Prefix Node Segment ID
                           TBD2      IPv6 Prefix Node Segment ID
                           TBD3      Adjacency Segment ID



   Service Segments and FRR will be considered in future version.

4.1.  IPv4 Prefix Node Segment ID

   The format is as below:


      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



Kumar, et al.            Expires April 24, 2014                 [Page 4]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         IPv4 Prefix                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Prefix Length  |      Resv     |     Protocol  |  SID Length   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Node Segment ID                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Reserved          |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                Advertising Node Identifier                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   IPv4 Prefix

      This field carries the IPv4 prefix to which the Node Segment ID is
      assigned.

   Prefix Length

      One octet of prefix length in bits.

   Protocol

      Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is
      ISIS.

   SID Length

      Set to 3 or 4 depending on the Segment ID.

   Node Segment ID

      This field carries the Node segment ID.  If the SID Length is 3,
      then the 20 rightmost bits represent the segment.  If length is 4,
      then the value represent a 32 bits Segment ID.

   Advertising Node Identifier

      Specifies the advertising node identifier.When Protocol is set to
      1, then the 32 rightmost bits represent OSPF Router ID and if
      protocol is set to 2, this field carries 48 bit ISIS System ID.









Kumar, et al.            Expires April 24, 2014                 [Page 5]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


4.2.  IPv6 Prefix Node Segment ID

   The format is as below:


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         IPv6 Prefix                           |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Prefix Length  |      Resv     |     Protocol  |  SID Length   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Node Segment ID                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Reserved          |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                Advertising Node Identifier                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   IPv6 Prefix

      This field carries the IPv6 prefix to which the Node Segment ID is
      assigned.

   Prefix Length

      One octet of prefix length in bits.

   Protocol

      Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is
      ISIS.

   SID Length

      Set to 3 or 4 depending on the Segment ID.

   Node Segment ID

      This field carries the Node segment ID.  If the SID Length is 3,
      then the 20 rightmost bits represent the segment.  If length is 4,
      then the value represent a 32 bits Segment ID.




Kumar, et al.            Expires April 24, 2014                 [Page 6]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   Advertising Node Identifier

      Specifies the advertising node identifier.When Protocol is set to
      1, then the 32 rightmost bits represent OSPF Router ID and if
      protocol is set to 2, this field carries 48 bit ISIS System ID.

4.3.  IGP Adjacency Segment ID

   The format is as below:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Local Interface ID                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Remote Interface ID                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Protocol    |    SID Length |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                Advertising Node Identifier                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 IGP Adjacency Segment ID                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




   Local Interface ID

      An identifier that is assigned by local LSR for a link on which
      Adjacency SID is binded.  If the Adj-SID represents parallel
      adjacencies (Section 3.3.2.1 of
      [I-D.filsfils-rtgwg-segment-routing]) this field MUST be set to
      zero.

   Remote Interface ID

      An identifier that is assigned by remote LSR for a link on which
      Adjacency SID is binded.  If the Adj-SID represents parallel
      adjacencies (Section 3.3.2.1 of
      [I-D.filsfils-rtgwg-segment-routing]) this field MUST be set to
      zero.

   Protocol

      Set to 1 if the IGP protocol is OSPF and 2 if IGP protocol is ISIS

   SID Length



Kumar, et al.            Expires April 24, 2014                 [Page 7]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


      Set to 3 or 4 depending on the Segment ID.

   Advertising Node Identifier

      Specifies the advertising node identifier.When Protocol is set to
      1, then the 32 rightmost bits represent OSPF Router ID and if
      protocol is set to 2, this field carries 48 bit ISIS System ID.

   IGP Adjacency Segment ID

      This field carries the adjacency segment ID.

5.  Extension to Downstream Mapping TLV

   In an echo reply, the Downstream Mapping TLV [RFC4379] is used to
   report for each interface over which a FEC could be forwarded.  For
   an FEC, there are multiple protocols that may be used to distribute
   label mapping.  The "Protocol" field of the Downstream Mapping TLV is
   used to return the protocol that is used to distribute a specific a
   label.  The following protocols are defined in section 3.2 of
   [RFC4379]:

   Protocol #        Signaling Protocol
   ----------        ------------------
            0        Unknown
            1        Static
            2        BGP
            3        LDP
            4        RSVP-TE


   With segment routing, OSPF or ISIS can be used for label
   distribution, this document adds two new protocols as follows:

   Protocol #        Signaling Protocol
   ----------        ------------------
            5        OSPF
            6        ISIS


6.  Procedures

   This section describes aspects of LSP ping/traceroute operations that
   require further considerations beyond [RFC4379].

6.1.  FECs in Target FEC Stack TLV





Kumar, et al.            Expires April 24, 2014                 [Page 8]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   When LSP echo request packets are generated by an initiator, FECs
   carried in Target FEC Stack TLV may need to or desire to have
   deviating contents.  This document outlines expected Target FEC Stack
   TLV construction mechanics by initiator for known scenarios.

      Ping

         Initiator MUST include FEC(s) corresponding to the destination
         segment.

         Initiator MAY include FECs corresponding to some or all of
         segments imposed in the label stack by the initiator to
         communicate the segments traversed.

      Traceroute

         Initiator MUST initially include FECs corresponding to all of
         segments imposed in the label stack.

         When a received echo reply contains FEC Stack Change TLV with
         one or more of original segment(s) being popped, initiator MAY
         remove corresponding FEC(s) from Target FEC Stack TLV in the
         next (TTL+1) traceroute request.

         When a received echo reply does not contain FEC Stack Change
         TLV, initiator MUST NOT attempt to remove FEC(s) from Target
         FEC Stack TLV in the next (TTL+1) traceroute request.  Note
         that Downstream Label field of DSMAP/DDMAP contains hints on
         how initiator may be able to update the contents of next Target
         FEC Stack TLV.  However, such hints are ambiguous without full
         understanding of PHP capabilities.

6.2.  FEC Stack Change TLV

   The network node which advertised the node segment ID is responsible
   for generating FEC Stack Change TLV of &pop& operation for node
   segment ID, regardless of if PHP is enabled or not.

   The network node that is immediate downstream of the node which
   advertised the adjacency segment ID is responsible for generating FEC
   Stack Change TLV of &pop& operation for adjacency segment ID.

6.3.  PHP, Adjacency SID Pop, Implicit NULL

   Forwarding behavior of node segment ID PHP is equivalent to usage of
   implicit Null in MPLS protocols that embraces downstream label
   allocation scheme.  Adjacency segment ID is also similar in a sense
   that it can be thought as nexthop destined locally allocated segment



Kumar, et al.            Expires April 24, 2014                 [Page 9]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   that has PHP enabled.  Procedures described in Section 4.4 of
   [RFC4379] relies on Stack-D and Stack-R explicitly having Implicit
   Null value.  It may simplify implementations to reuse Implicit Null
   for node segment ID PHP and adjacency segment ID cases.  However, it
   is technically incorrect for Implicit Null value to externally
   appear.  Therefore, implicit Null MUST NOT be placed in Stack-D and
   Interface and Label Stack TLV for node segment ID PHP and adjacency
   segment ID cases.

6.4.  Segment Protocol Check

      If the Target FEC Sub-TLV at FEC-stack-depth is TBD1 (IPv4 Prefix
      Node Segment ID), set Best return code to (error code TBD) if any
      below conditions fail:

      *  Validate that Advertising Node Identifier of Protocol is a
         local node.

      *  Validate that Node Segment ID is avertised for IPv4 Prefix by
         the Protocol with Advertising Node Identifier.

      *  Validate that Node Segment ID is advertisement of PHP bit.

      If the Target FEC Sub-TLV at FEC-stack-depth is TBD2 (IPv6 Prefix
      Node Segment ID), set Best return code to (error code TBD) if any
      below conditions fail:

      *  Validate that Advertising Node Identifier of Protocol is a
         local node.

      *  Validate that Node Segment ID is advertised for IPv6 Prefix by
         the Protocol with Advertising Node Identifier.

      *  Validate that Node Segment ID is advertised of PHP bit.

      If the Target FEC sub-TLV at FEC-stack-depth is TBD3 (Adjacency
      Segment ID), set Best return code to (error code TBD) if any below
      conditions fail:

      *  Validate that Remote Interface ID matches the local identifier
         of the interface on which the packet was received.

      *  Validate that IGP Adjacency SID is advertised by Advertising
         Node Identifier of Protocol in local IGP database.

7.  IANA Considerations

   To be Updated.



Kumar, et al.            Expires April 24, 2014                [Page 10]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


8.  Security Considerations

   To be Updated.

9.  Acknowledgement

   The authors would like to thank Stefano Previdi for his review and
   comments.

10.  Contributing Authors

   Tarek Saad
   Cisco Systems
   Email: tsaad@cisco.com

   Siva Sivabalan
   Cisco Systems
   Email: msiva@cisco.com

11.  References

11.1.  Normative References

   [I-D.filsfils-rtgwg-segment-routing]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
              "Segment Routing Architecture", draft-filsfils-rtgwg-
              segment-routing-01 (work in progress), October 2013.

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

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

   [RFC6424]  Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
              Performing Label Switched Path Ping (LSP Ping) over MPLS
              Tunnels", RFC 6424, November 2011.

11.2.  Informative References

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291, June 2011.





Kumar, et al.            Expires April 24, 2014                [Page 11]


Internet-Draft        LSP Ping/Trace for SR on MPLS         October 2013


   [RFC6425]  Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
              S., and T. Nadeau, "Detecting Data-Plane Failures in
              Point-to-Multipoint MPLS - Extensions to LSP Ping", RFC
              6425, November 2011.

Authors' Addresses

   Nagendra Kumar
   Cisco Systems, Inc.
   7200 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: naikumar@cisco.com


   George Swallow
   Cisco Systems, Inc.
   1414 Massachusetts Ave
   Boxborough, MA  01719
   US

   Email: swallow@cisco.com


   Carlos Pignataro
   Cisco Systems, Inc.
   7200 Kit Creek Road
   Research Triangle Park, NC  27709-4987
   US

   Email: cpignata@cisco.com


   Nobo Akiya
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, ON  K2K 3E8
   Canada

   Email: nobo@cisco.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com




Kumar, et al.            Expires April 24, 2014                [Page 12]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/