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Versions: 00 01

MPLS Working Group                                             S. Bryant
Internet-Draft                                                    Huawei
Intended status: Standards Track                              G. Swallow
Expires: September 11, 2017                                 S. Sivabalan
                                                           Cisco Systems
                                                          March 10, 2017


                MPLS Flow Identification Considerations
                    draft-bryant-mpls-sfl-control-01

Abstract

   In draft-bryant-mpls-sfl-framework the concept of MPLS synonymous
   flow labels (SFL) was introduced.  This document describes a control
   protocol that runs over an associated control header to request,
   withdrawn and extend the lifetime of such labels.

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 September 11, 2017.

Copyright Notice

   Copyright (c) 2017 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
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  SFL Control . . . . . . . . . . . . . . . . . . . . . . . . .   2
     3.1.  SFL Control Message . . . . . . . . . . . . . . . . . . .   3
     3.2.  SFL Control Proceedures . . . . . . . . . . . . . . . . .   6
       3.2.1.  Request/Grant . . . . . . . . . . . . . . . . . . . .   6
       3.2.2.  Refresh . . . . . . . . . . . . . . . . . . . . . . .   8
       3.2.3.  Withdraw  . . . . . . . . . . . . . . . . . . . . . .   9
       3.2.4.  Timer Accuracy  . . . . . . . . . . . . . . . . . . .   9
   4.  Return Path . . . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Manageability Considerations  . . . . . . . . . . . . . . . .  10
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  10
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   In [I-D.bryant-mpls-sfl-framework] the concept of MPLS synonymous
   flow labels (SFL) was introduced.  This document describes a simple
   control protocol that runs over an associated control header to
   request, withdrawn and extend the lifetime of such labels.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

3.  SFL Control

   This section describes the process by which the RFC6374 Querier
   requests SFLs, the process by which the RFC6374 Responder sends them
   to the Querier, and the process for managing the SFL lifetime.  SFL
   Control Messages are carried over the SFL Control ACH.  The SFL ACH
   is carried over a Pseudowire(PW) in place of the PW Control Word
   (CW), over an MPLS LSP using the GAL, or over some other mutually
   agreed path.  Similarly the response may be returned over a PW, over
   a bidirectional LSP or over some other mutually agreed path.  See
   Section 4.




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3.1.  SFL Control Message

   The format of an SFL Control message, which follows the Associated
   Channel Header (ACH), is as follows:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version| Flags |  Control Code |        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Session Identifier          | SFL Batch |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Lifetime (seconds)              |   Num SFL     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 SFL 0                 |      LFlags           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 SFL n                 |      LFlags           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Forwarding Equivalence Class (FEC)            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: SFL Control Message Format

   Reserved fields MUST be set to 0 and ignored upon receipt.  The
   possible values for the remaining fields are as follows:

   Version        Protocol version.  Set to zero in this specification.

   Flags          Message control flags.

   Control Code   Code identifying the query or response type.

   Message Length Total length of this message in bytes.

   Session Identifier  Set arbitrarily by the querier and used as a
                  message handle.

   SFL Batch      Used where the SFLs for this Session Identifier
                  managed across multiple SFL Control Messages.  A given
                  set of SFLs MUST be retained in the same batch.

   Lifetime       The lifetime in seconds of the SFLs in this message.
                  In a Query message it is the requested lifetime.  In a
                  Response message it is the lifetime that the SFLs have
                  been allocated for by the Responder.  The Querier MUST



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                  NOT use an SFL after expiry of its lifetime, a
                  Responder MUST make the SFL available for at least its
                  lifetime.

   Num SFL        The number of SFLs in this SFL Batch.  This MUST be
                  constant for the lifetime of the batch.

   SFL n          The n'th SFL carried in this TLV.  This is an MPLS
                  label which is a component of a label stack entry as
                  defined in Section 2.1 of [RFC3032].  The position of
                  a label within a batch is constant for the lifetime of
                  the batch.  Enumeration starts at zero.

   LFlags         The set of flags associated with the immediately
                  preceding SFL.  See below.

   FEC            The Forwarding Equivalence Class that the SFLs in this
                  TLV correspond to.  This is encoded as per
                  Section 3.4.1 of [RFC5036].

   Flags: The format of the Flags field is shown below.

                              +-+-+-+-+
                              |R|0|0|0|
                              +-+-+-+-+

                        SFL Control Message Flag

   R: Query/Response indicator.  Set to 0 for a Query and 1 for a
      Response.

   0: Set to zero by the Sender and ignored by the Receiver.

   Control Code: Set as follows according to whether the message is a
   Query or a Response as identified by the R flag.

   For a Query:

   Request  This indicates that the responder is requested to allocate
      the set of SFLs marked with the R LFlag in this Message.

   Refresh  This indicates that the responder is requested to refresh
      the set of SFLs marked with the V LFlag in this Message.

   Withdraw  This indicates that the querier will no longer use the set
      of SFLs marked with the V Lflag and the responder may expire their
      lifetime.




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   For a Response:

   Grant  This indicates that the responder allocated the set of SFLs
      marked with the A LFlag in this Message.

   Refresh-Ack  This indicates that the responder has refreshed the set
      of SFLs marked with the V LFlag in this Message, and the lifetime
      is now as indicated by the lifetime field.

   Withdraw-Ack  This indicates that the responder has received the
      Withdraw message and will withdraw the SFLs

   SFL-Unable  The Responder was unable to satisfy the SFL Request.  The
      details of the failure can be determined by comparing the Request
      and Grant messages.

   Further error codes are for future study.

   The LFlags field is defined as follows:

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

                      Figure 2: LFlags Bit Definition

   Where:






















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   0 (Valid (V))  The Label value of the corresponding SFL is valid.  In
                  an SFL Request setting the V Lflag indicates a request
                  for the specified label value.  Where an SFL has a
                  valid flag clear in a request message this indicates
                  that any SFL value is acceptable.

   1 (Request (R))  Indicates to the Querier that this member of the SFL
                  batch is requested.  Where a value is specified in the
                  request, but the Responder is unable honour that
                  request, no SFL is allocated and the corresponding A
                  flag MUST be cleared.

   2 (Allocated (A)  Indicates to the Querier that this SFL was
                  allocated.

   3 (Withdraw (W))  Indicates to the Responser that this SFL is to be
                  withdrawn and to the Querier that the withdrawal has
                  been carried out.

   MBZ            MUST be sent as zero and ignored on receive.

   A flag value of one is true/set and a flag value of zero is false/
   clear.  The use of these bits is described in more detail in the
   following sub-sections.

3.2.  SFL Control Proceedures

3.2.1.  Request/Grant

   To request a batch of SFLs the Querier constructs an SFL Control
   Request, encapsulates it in an SFL Control ACH and sends it to the
   Responder via an appropriate path.  It sets the Control Message Flag
   to Query and the Control Code to Request.  It chooses a session
   identifier as a handle for this transaction and as a way of binding
   this batch of SFLs to other operations that will use members of this
   SFL batch.  Since members of the batch are treated as a group, the
   SFL Batch identifier is used to identify different SFL batches used
   in conjunction with the same session identifier.

   The requested lifetime is set.  This is the number of seconds from
   the time of the query to the time when the batch of SFLs will expire
   unless refreshed.

   The Num SFL field is set to the SFL batch size.

   Each SFL is set as follows: if a specific value is requested (for
   example for continuity across system restarts) this is written into
   the SFV n field and the V LFlag set.  Otherwise, and including spare



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   SFLs where an allocation is not requested, the label value is set to
   zero and the V LFlag is cleared.  For each SFL entry where an
   allocation is requested the R LFlag is set.  All other LFlags are
   cleared.

   The Forwarding Equivalence Class (FEC) is set to the FEC for which
   the SFLs are requested.

   The Message Length is determined and filled in.

   The Responder proceeds as follows:

   It sets the control Message Flag to Response and initially sets the
   Control Code to Grant.

   For each SFL with an R flag set, it determines whether it can honour
   the request, if so sets the A Lflag, and if the SFL value in the
   query was zero it overwrites it with the allocated SFL label value.
   In all other cases it leaves the SFL value and LFlag unchanged.

   The lifetime field is updated with the lifetime of the SFLs if this
   is different from the requested lifetime.

   All other fields in the Query message are left unchanged and the
   message is sent back to the Querier using the signaled or previously
   agreed message path.

   Where the offered lifetime is other than the requested lifetime the
   Querier may accept the proposed value, or withdraw the SFLs and
   attempt to negotiate a new set of SFLs with a different lifetime.

   If the Responder is unable to allocate all of the requested SFLs it
   MUST respond with a response code of SFL-Unable.  The Querier MUST
   determine whether the allocated SFLs were adequate for its purposes
   and MUST send a withdraw if there are not adequate.  A Querier MUST
   NOT attempt to hoard labels in the hope that the residual labels
   needed may become available in the future.

   A Querier MUST wait a configured time (suggested wait of 60 seconds)
   before reattempting negotiation for a resource.  Any failure to
   negotiate the required resources MUST be notified through the
   management interface of both Querier and Responder.

   A Querier MUST NOT send an expired SFL to a Responder since to do so
   may invalidate another SFL operation.






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3.2.2.  Refresh

   To request the lifetime refresh of a batch of SFLs the Querier
   constructs an SFL Refresh Request, encapsulates it in an SFL Control
   ACH and sends it to the Responder via an appropriate path.  It sets
   the Control Message Flag to Query and the Control Code to Refresh.
   It uses the session identifier and the SFL Batch identifier that it
   used to request this SFL batch.

   The requested lifetime is set.  This is the number of seconds from
   the time of the query to the time when the batch of SFLs will expire
   unless refreshed.

   The Num SFL field is set to the SFL batch size.

   Each SFL is set as follows: the allocated SFL label value is written
   into the SFL n field and the V LFlag set.  All other LFlags are
   cleared.

   The Forwarding Equivalence Class (FEC) is set to the FEC for which
   the SFLs are requested.

   The Message Length is determined and filled in.

   The Responder proceeds as follows:

   It sets the control Message Flag to Response and sets the Control
   Code to Refresh-Ack.

   It sets the lifetime to the lifetime of the SFL.

   All other fields in the Query message are left unchanged and the
   message is sent back to the Querier using the signaled or previously
   agreed message path.

   Where the offered lifetime is other than the requested lifetime the
   Querier may accept the proposed value, or withdraw the SFLs and
   attempt to negotiate a new set of SFLs with a different lifetime.

   A Querier MUST wait a configured time (suggested wait of 60 seconds)
   before reattempting negotiation for a resource.  Any failure to
   negotiate the required resources MUST be notified through the
   management interface of both Querier and Responder.








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3.2.3.  Withdraw

   To request the withdrawal of some or all of a batch of SFLs the
   Querier constructs an SFL Withdraw Request, encapsulates it in an SFL
   Control ACH and sends it to the Responder via an appropriate path.
   It sets the Control Message Flag to Query and the Control Code to
   Withdraw.  It uses the session identifier and the SFL Batch
   identifier that it used to request this SFL batch.

   The requested lifetime is set to zero.

   The Num SFL field is set to the SFL batch size.

   Each SFL being withdrawn is set as follows: the allocated SFL label
   value is written into the SFL n field and the V and W LFlags set.
   All other LFlags are cleared.

   The Forwarding Equivalence Class (FEC) is set to the FEC for which
   the SFLs are requested.

   The Message Length is determined and filled in.

   The Responder proceeds as follows:

   It sets the control Message Flag to Response and sets the Control
   Code to Withdraw-Ack.

   All other fields in the Query message are left unchanged and the
   message is sent back to the Querier using the signaled or previously
   agreed message path.

   A Querier MUST wait a configured time (suggested wait of 60 seconds)
   before reattempting a Withdraw request.  No more than three Withdraw
   requests should be made.

3.2.4.  Timer Accuracy

   The lifetime of SFLs is expected to be sufficiently long that there
   are no significant constraints on timer accuracy.  A node should be
   conservative in its assumptions concerning the lifetime of an SFL.  A
   Querier MUST stop using a SFL significantly before the expiry of its
   lifetime and a Responder must maintain an SFL in active operation
   significantly beyond nominal expiry.  A margin of the order of
   minutes is RECOMMENDED.







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4.  Return Path

   Where the LSP is a mulit-point to point, or multi-point to multi-
   point MPLS LSP (or other MPLS construct) the RFC6374 Address TLV MUST
   be included in Query packet, even if the response is requested in-
   band, since this is needed to provide the necessary return address
   for this request.

5.  Manageability Considerations

   This may be provided in a future version of this memo.

6.  Privacy Considerations

   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.

7.  Security Considerations

   It is assumed that this protocol is run in a well managed MPLS
   network with strict access controls preventing unwanted parties from
   generating MPLS OAM packets.  The control protocol described in this
   memo thus introduced no additional MPLS security vulnerabilities.

8.  IANA Considerations

   As per the IANA considerations in [RFC5586], IANA is requested to
   allocate the following Channel Types in the "MPLS Generalized
   Associated Channel (G-ACh) Types" registry:

   Value  Description                              TLV Follows Reference
   ------ ---------------------------------------- ----------- ---------
   0x0XXX SFL Control                              No          This

   A value of 0x60 is suggested.

   Force references to appear with mkd [RFC3032] [RFC5036]






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9.  Normative References

   [I-D.bryant-mpls-sfl-framework]
              Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
              and G. Mirsky, "Synonymous Flow Label Framework", draft-
              bryant-mpls-sfl-framework-03 (work in progress), March
              2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <http://www.rfc-editor.org/info/rfc3032>.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <http://www.rfc-editor.org/info/rfc5036>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <http://www.rfc-editor.org/info/rfc5586>.

Authors' Addresses

   Stewart Bryant
   Huawei

   Email: stewart.bryant@gmail.com


   George Swallow
   Cisco Systems

   Email: swallow.ietf@gmail.com


   Siva Sivabalan
   Cisco Systems

   Email: msiva@cisco.com






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