Synonymous Flow Label Framework
draft-bryant-mpls-sfl-framework-05

MPLS                                                           S. Bryant
Internet-Draft                                                G. Swallow
Intended status: Informational                              S. Sivabalan
Expires: April 20, 2016                                    Cisco Systems
                                                               G. Mirsky
                                                                Ericsson
                                                                 M. Chen
                                                                   Z. Li
                                                                  Huawei
                                                        October 18, 2015


                    Synonymous Flow Label Framework
                   draft-bryant-mpls-sfl-framework-00

Abstract

   draft-bryant-mpls-flow-ident describes the requirement for
   introducing flow identities within the MPLS architecture.  This
   document describes a method of accomplishing this by using a
   technique called Synonymous Flow Labels in which labels which mimic
   the behaviour of other labels provide the identification service.
   These identifiers can be used to trigger per-flow operations on the
   on the packet at the receiving label switching router.

Status of This Memo

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

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   This Internet-Draft will expire on April 20, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Synonymous Flow Labels  . . . . . . . . . . . . . . . . . . .   2
   3.  User Service Traffic in the Data Plane  . . . . . . . . . . .   4
     3.1.  Applications Label Present  . . . . . . . . . . . . . . .   4
       3.1.1.  Setting TTL and the Traffic Class Bits  . . . . . . .   4
     3.2.  Single Label Stack  . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Setting TTL and the Traffic Class Bits  . . . . . . .   6
     3.3.  Aggregation of SFL Actions  . . . . . . . . . . . . . . .   6
   4.  Equal Cost Multipath Considerations . . . . . . . . . . . . .   7
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   [I-D.bryant-mpls-flow-ident] describes the requirement for
   introducing flow identities within the MPLS architecture.

   This document describes a method of accomplishing this by using a
   technique called Synonymous Flow Labels (SFL) (see (Section 2)) in
   which labels which mimic the behaviour of other labels provide the
   identification service.  These identifiers can be used to trigger
   per-flow operations on the packet at the receiving label switching
   router.

2.  Synonymous Flow Labels

   An SFL is defined to be a label that causes exactly the same
   behaviour at the egress Label Switching Router (LSR) as the label it
   replaces, but in addition also causes an agreed action to take place
   on the packet.  There are many possible additional actions such as



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   the measurement of the number of received packets in a flow,
   triggering IPFIX inspection, triggering other types of Deep Packet
   Inspection, or identification of the packet source.  In, for example,
   a Performance Monitoring (PM) application, the agreed action could be
   the recording of the receipt of the packet by incrementing a packet
   counter.  This is a natural action in many MPLS implementations, and
   where supported this permits the implementation of high quality
   packet loss measurement without any change to the packet forwarding
   system.

   Consider an MPLS application such as a pseudowire (PW), and consider
   that it is desired to use the approach specified in this document to
   make a packet loss measurement.  By some method outside the scope of
   this text, two labels, synonymous with the PW labels are obtained
   from the egress terminating provider edge (T-PE).  By alternating
   between these SFLs and using them in place of the PW label, the PW
   packets may be batched for counting without any impact on the PW
   forwarding behaviour (note that strictly only one SFL is needed in
   this application, but that is an optimization that is a matter for
   the implementor).

   Now consider an MPLS application that is multi-point to point such as
   a VPN.  Here it is necessary to identify a packet batch from a
   specific source.  This is achieved by making the SFLs source
   specific, so that batches from one source are marked differently from
   batches from another source.  The sources all operate independently
   and asynchronously from each other, independently co-ordinating with
   the destination.  Each ingress is thus able to establish its own SFL
   to identify the sub-flow and thus enable PM per flow.

   Finally we need to consider the case where there is no MPLS
   application label such as occurs when sending IP over an LSP.  In
   this case introducing an SFL that was synonymous with the LSP label
   would introduce network wide forwarding state.  This would not be
   acceptable for scaling reasons.  We therefore have no choice but to
   introduce an additional label.  Where penultimate hop popping (PHP)
   is in use, the semantics of this additional label can be similar to
   the LSP label.  Where PHP is not in use, the semantics are similar to
   an MPLS explicit NULL.  In both of these cases the label has the
   additional semantics of the SFL.

   Note that to achieve the goals set out in Section 1 SFLs need to be
   allocated from the platform label table.








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3.  User Service Traffic in the Data Plane

   As noted in Section 2 it is necessary to consider two cases:

   1.  Applications label present

   2.  Single label stack

3.1.  Applications Label Present

   Figure 1 shows the case in which both an LSP label and an application
   label are present in the MPLS label stack.  Traffic with no SFL
   function present runs over the "normal" stack, and SFL enabled flows
   run over the SFL stack with the SFL used to indicate the packet
   batch.

     +-----------------+          +-----------------+
     |                 |          |                 |
     |      LSP        |          |      LSP        | <May be PHPed
     |     Label       |          |     Label       |
     +-----------------+          +-----------------+
     |                 |          |                 |
     |  Application    |          | Synonymous Flow |
     |     Label       |          |     Label       |
     +-----------------+          +-----------------+ <= Bottom of stack
     |                 |          |                 |
     |   Payload       |          |   Payload       |
     |                 |          |                 |
     +-----------------+          +-----------------+


    "Normal" Label Stack         Label Stack with SFL



    Figure 1: Use of Synonymous Labels In A Two Label MPLS Label Stack

   At the egress LSR the LSP label is popped (if present).  Then the SFL
   is processed in exactly the same way as the corresponding application
   label would have been processed.

3.1.1.  Setting TTL and the Traffic Class Bits

   The TTL and the Traffic Class bits [RFC5462] in the SFL LSE would
   normally be set to the same value as would have been set in the label
   that the SFL is synonymous with.  However it is recognised that there
   may be an applications need to set the SFL to some other value.  An




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   example would be where it was desired to cause the SFL to trigger an
   action in the TTL expiry exception path as part of the label action.

3.2.  Single Label Stack

   Figure 2 shows the case in which only an LSP label is present in the
   MPLS label stack.  Traffic with no SFL function present runs over the
   "normal" stack and SFL enabled flows run over the SFL stack with the
   SFL used to indicate the packet batch.  However in this case it is
   necessary for the ingress LSR to first push the SFL and then to push
   the LSP label.

                                  +-----------------+
                                  |                 |
                                  |      LSP        | <= May be PHPed
                                  |     Label       |
     +-----------------+          +-----------------+
     |                 |          |                 | <= Synonymous with
     |      LSP        |          | Synonymous Flow |    Explicit NULL
     |     Label       |          |     Label       |
     +-----------------+          +-----------------+ <= Bottom of stack
     |                 |          |                 |
     |   Payload       |          |   Payload       |
     |                 |          |                 |
     +-----------------+          +-----------------+


    "Normal" Label Stack         Label Stack with SFL



   Figure 2: Use of Synonymous Labels In A Single Label MPLS Label Stack

   At the receiving LSR it is necessary to consider two cases:

   1.  Where the LSP label is still present

   2.  Where the LSP label is penultimate hop popped

   If the LSP label is present, it processed exactly as it would
   normally processed and then it is popped.  This reveals the SFL which
   in the case of RFC6374 measurements is simply counted and then
   discarded.  In this respect the processing of the SFL is synonymous
   with an Explicit NULL.  As the SFL is the bottom of stack, the IP
   packet that follows is processed as normal.

   If the LSP label is not present due to PHP action in the upstream
   LSR, two almost equivalent processing actions can take place.  Either



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   the SFL can be treated as an LSP label that was not PHPed and the
   additional associated SFL action is taken when the label is
   processed.  Alternatively, it can be treated as an explicit NULL with
   associated SFL actions.  From the perspective of the measurement
   system described in this document the behaviour of two approaches are
   indistinguishable and thus either may be implemented.

3.2.1.  Setting TTL and the Traffic Class Bits

   The TTL and the Traffic Class considerations described in
   Section 3.1.1 apply.

3.3.  Aggregation of SFL Actions

   There are cases where it is desirable to aggregate an SFL action
   against a number of labels.  For example where it is desirable to
   have one counter record the number of packets received over a group
   of application labels, or where the number of labels used by a single
   application is large, and consequently the increase in the number of
   allocated labels needed to support the SFL actions consequently
   becomes too large to be viable.  In these circumstances it would be
   necessary to introduce an additional label in the stack to act as an
   aggregate instruction.  This is not strictly a synonymous action in
   that the SFL is not replacing a existing label, but is somewhat
   similar to the single label case shown in Section 3.2, and the same
   signalling, management and configuration tools would be applicable.

























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                                  +-----------------+
                                  |                 |
                                  |      LSP        | < May be PHPed
                                  |     Label       |
     +-----------------+          +-----------------+
     |                 |          |                 |
     |      LSP        |          |   Aggregate     |
     |     Label       |          |      SFL        |
     +-----------------+          +-----------------+
     |                 |          |                 |
     |  Application    |          |  Application    |
     |     Label       |          |     Label       |
     +-----------------+          +-----------------+ <= Bottom of stack
     |                 |          |                 |
     |   Payload       |          |   Payload       |
     |                 |          |                 |
     +-----------------+          +-----------------+


    "Normal" Label Stack         Label Stack with SFL



                      Figure 3: Aggregate SFL Actions

   The Aggregate SFL is shown in the label stack depicted in Figure 3 as
   preceding the application label, however the choice of position
   before, or after, the application label will be application specific.
   In the case described in Section 3.1, by definition the SFL has the
   full application context.  In this case the positioning will depend
   on whether the SFL action needs the full context of the application
   to perform its action and whether the complexity of the application
   will be increased by finding an SFL following the application label.

   This third SFL case requires further though by the authors and this
   section will be updated in a future version of this draft to reflect
   those thoughts.

4.  Equal Cost Multipath Considerations

   The introduction to an SFL to an existing may cause that flow to take
   a different path through the network under conditions of Equal Cost
   Multipath (ECMP).  This is turn may invalidate the certain uses of
   the SFL such as performance measurement applications.  Where this is
   a problem there are two solutions worthy of consideration:

   1.  The operator can elect to always run with the SFL in place in the
       MPLS label stack.



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   2.  The operator can elect to use [RFC6790] Entropy Labels which, in
       a network that fully supports this type of ECMP, results in the
       ECMP decision being independent of the value of the other labels
       in the label stack.

5.  Privacy Considerations

   Recent IETF concerns on pervasive monitoring are described in
   [RFC7258].  The inclusion of originating and/or flow information in a
   packet provides more identity information and hence potentially
   degrades the privacy of the communication.  Whilst the inclusion of
   the additional granularity does allow greater insight into the flow
   characteristics it does not specifically identify which node
   originated the packet other than by inspection of the network at the
   point of ingress, or inspection of the control protocol packets.
   This privacy threat may be mitigated by encrypting the control
   protocol packets, regularly changing the synonymous labels and by
   concurrently using a number of such labels.  The minimizing the scope
   of the identity indication can be useful in minimizing the
   observability of the flow characteristics.

6.  Security Considerations

   The issue noted in Section 5 is a security consideration.  There are
   no other new security issues associated with the MPLS dataplane.  Any
   control protocol used to request SFLs will need to ensure the
   legitimacy of the request.

7.  IANA Considerations

   This draft makes no IANA requests.

8.  Acknowledgements

   TBD

9.  References

9.1.  Normative References

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
              2009, <http://www.rfc-editor.org/info/rfc5462>.







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9.2.  Informative References

   [I-D.bryant-mpls-flow-ident]
              Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
              Mirsky, "MPLS Flow Identification", draft-bryant-mpls-
              flow-ident-02 (work in progress), September 2015.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <http://www.rfc-editor.org/info/rfc6790>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

Authors' Addresses

   Stewart Bryant
   Cisco Systems

   Email: stbryant@cisco.com


   George Swallow
   Cisco Systems

   Email: swallow@cisco.com


   Siva Sivabalan
   Cisco Systems

   Email: msiva@cisco.com


   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com





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   Zhenbin(Robin)  Li
   Huawei

   Email: lizhenbin@huawei.com















































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