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MPLS Working Group                                             S. Bryant
Internet-Draft                               Futurewei Technologies Inc.
Intended status: Standards Track                              G. Swallow
Expires: July 6, 2020                          Southend Technical Center
                                                            S. Sivabalan
                                                           Cisco Systems
                                                        January 03, 2020


                A Simple Control Protocol for MPLS SFLs
                    draft-bryant-mpls-sfl-control-06

Abstract

   In draft-ietf-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,
   withdraw, 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 https://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 July 6, 2020.

Copyright Notice

   Copyright (c) 2020 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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   to this document.  Code Components extracted from this document must
   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 Procedures  . . . . . . . . . . . . . . . . .   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.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Allocation of MPLS Generalized Associated Channel (G-ACh)
           Type  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.2.  Creation of SFL Simple Control Code Registry  . . . . . .  11
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   In [I-D.ietf-mpls-sfl-framework] the concept of MPLS synonymous flow
   labels (SFL) was introduced.  This document describes a simple
   control protocol, for use in a well-managed MPLS network, that runs
   over an associated control header to request, withdraw, 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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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.



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   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.

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:
















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   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      (6 bits) Used where the SFLs for this Session
                  Identifier are 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 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 Flags.




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   The meanings of the flag bits are:

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

   0x0: SFL Request. This indicates that the responder is requested
   to allocate the set of SFLs marked with the R LFlag in this
   message.

   0x1: SFL Refresh. This indicates that the responder is requested
   to refresh the set of SFLs marked with the V LFlag in this message.

   0x2: SFL 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.

   For a Response:

   Codes 0x0-0xF are reserved for non-error responses.

   0x1: SFL Grant. This indicates that the responder allocated the
   set of SFLs marked with the A LFlag in this Message.

   0x2: SFL 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.

   0x3: SFL Withdraw-Ack. This indicates that the responder has
   received the Withdraw message and will withdraw the SFLs

   0x10: Unspecified Error.  Indicates that the operation
   failed for an unspecified reason.

   0x11: 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.

   Editors Note - We need to revisit the RFC6374 errors and the protocol
   to see if we need some more error codes.

   The LFlags field is defined as follows:



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        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:

   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 Procedures

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.  The Querier sets the Control
   Message Flag to Query and the Control Code to Request.  The Querier
   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.



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   The Querier sets the requested lifetime.  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
   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:

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

   For each SFL with an R flag set, the Responder 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.




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   A Querier MUST wait a configured time (suggested wait of 60 seconds)
   before re-attempting 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.

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.  The
   Querier sets the Control Message Flag to Query and the Control Code
   to Refresh.  The Querier uses the session identifier and the SFL
   Batch identifier that it used to request this SFL batch.

   The Querier sets the requested lifetime.  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 Querier sets the Num SFL field to the SFL batch size.

   The Querier sets each SFL 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:

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

   The Responder 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.





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

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.
   The Querier 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 Querier sets the requested lifetime to zero.

   The Querier sets the Num SFL field 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 field is determined and filled in.

   The Responder proceeds as follows:

   The Responder 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 re-attempting 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




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   significantly beyond nominal expiry.  A margin of the order of
   minutes is RECOMMENDED.

4.  Return Path

   Where the LSP (or other MPLS construct) is multi-point to point, or
   multi-point to multi- point 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.  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.

6.  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 packets.  The control protocol described in this memo
   thus introduced no additional MPLS security vulnerabilities.

7.  IANA Considerations

7.1.  Allocation of MPLS Generalized Associated Channel (G-ACh) Type

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

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

   A value of 0x5A is suggested.







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7.2.  Creation of SFL Simple Control Code Registry

   IANA is requested to created a new "SFL Simple Control Code" registry
   within the Generic Associated Channel (G-ACh) Parameters namespace.
   This registry is divided into two separate parts, one for Query Codes
   and the other for Response Codes, with formats and initial
   allocations as follows:

   Query Codes

   Code Description                         Reference
   ---- ----------------------------------- ---------
   0x0  SFL Request                         This
   0x1  SFL Refresh                         This
   0x2  SFL Withdraw                        This

   Response Codes

   Code Description                         Reference
   ---- ----------------------------------- ---------
   0x0  Reserved                            This
   0x1  SFL Grant                           This
   0x2  SFL Refresh-Ack                     This
   0x3  SFL Withdraw-Ack                    This
   0x10 Unspecified Error                   This
   0x11 SFL-Unable

   IANA should indicate that the values 0x0 - 0xF in the Response Code
   section are reserved for non-error response codes.

   The range of the Code field is 0 - 255.

   The allocation policy for this registry is IETF Review.

8.  Acknowledgments

   The authors thank Haomian Zheng for his review comments.

   RFC Editor please remove this note which is used to force the
   following references to appear [RFC3032] [RFC5036]

9.  References

9.1.  Normative References







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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://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,
              <https://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, <https://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,
              <https://www.rfc-editor.org/info/rfc5586>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [I-D.ietf-mpls-sfl-framework]
              Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
              and G. Mirsky, "Synonymous Flow Label Framework", draft-
              ietf-mpls-sfl-framework-06 (work in progress), October
              2019.

Authors' Addresses

   Stewart Bryant
   Futurewei Technologies Inc.

   Email: stewart.bryant@gmail.com


   George Swallow
   Southend Technical Center

   Email: swallow.ietf@gmail.com



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   Siva Sivabalan
   Cisco Systems

   Email: msiva@cisco.com















































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