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MPLS Working Group                                                Y. Liu
Internet-Draft                                                 G. Mirsky
Intended status: Standards Track                         ZTE Corporation
Expires: January 13, 2021                                  July 12, 2020


     MPLS-based Service Function Path(SFP) Consistency Verification
                 draft-lm-mpls-sfc-path-verification-00

Abstract

   This document proposes a method to verify the correlation between
   Service Function Chaining control and/or management plane view of the
   specified Service Function Path and the state of its data.  It works
   for both SR service programming and MPLS-based NSH SFC.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 13, 2021.

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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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  MPLS-based SFP Consistency Verification . . . . . . . . . . .   3
     3.1.  MPLS-based SFP Consistency Verification . . . . . . . . .   4
     3.2.  SFC Info Sub-TLV  . . . . . . . . . . . . . . . . . . . .   4
     3.3.  SFC Basic Unit FEC Sub-TLV  . . . . . . . . . . . . . . .   6
     3.4.  Theory of Operation . . . . . . . . . . . . . . . . . . .   6
       3.4.1.  MPLS-based service programming  . . . . . . . . . . .   7
       3.4.2.  RFC 8595 path consistency . . . . . . . . . . . . . .   7
     3.5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Service Function Chain (SFC) defines an ordered set of service
   functions (SFs) to be applied to packets and/or frames, and/or flows
   selected as a result of classification.

   SFC can be achieved through a variety of encapsulation methods, such
   as NSH [RFC8300], SR service programming
   [I-D.ietf-spring-sr-service-programming] and MPLS-based NSH SFC
   [RFC8595].

   This document describes extensions to MPLS LSP ping [RFC8029]
   mechanisms to support verification between the control/management
   plane and the data plane state for both SR-MPLS service programming
   and MPLS-based NSH SFC.

2.  Conventions used in this document

2.1.  Acronyms

   SFC: Service Function Chain

   SFF: Service Function Forwarder

   SF: Service Function

   SFP: Service Function Path

   RSP: Rendered Service Path




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3.  MPLS-based SFP Consistency Verification

   MPLS echo request and reply messages [RFC8029] can be extended to
   support the verification of the consistency of an MPLS-based Service
   Function Path (SFP).

   SR-MPLS/MPLS can be used to realize an SFP.  Two methods have been
   defined:

   o  [I-D.ietf-spring-sr-service-programming] describes how to achieve
      service function chaining in SR-enabled MPLS and IPv6 networks.
      In an SR-MPLS network, each SF is associated with an MPLS label.
      As a result, an SFP can be encoded as a stack of MPLS labels and
      pushed on top of the packet.

   o  [RFC8595] provides another method to realize SFC in an MPLS
      network by means of using a logical representation of the Network
      Service Header (NSH) in an MPLS label stack.  When an MPLS label
      stack is used to carry a logical NSH, a basic unit of
      representation is used, which can be present one or more times in
      the label stack.  This unit comprises two MPLS labels, one carries
      a label to provide a context within the SFC scope (the SFC Context
      Label), and the other carries a label to show which SF is to be
      enacted (the SF Label).  This two-label unit is shown in Figure 1.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           SFC Context Label           | TC  |S|       TTL     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           SF Label                    | TC  |S|       TTL     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 1: The Basic Unit of MPLS Label Stack for SFC

   In MPLS Label Switched Paths (LSPs), MPLS LSP ping [RFC8029] is used
   to check the correctness of the data plane functioning and to verify
   the data plane against the control plane.

   The proposed extension of MPLS LSP ping allows verification of the
   correlation between the control/management (if data model-based
   central controller used) plane and the data plane state in SR-MPLS/
   MPLS-based SFC.

   Generally, except for the designed specific functions, the packet
   processing functions supported by SFs are limited.  SFs may not
   support MPLS OAM protocols like LSP ping, so SFFs are responsible for
   MPLS echo request processing.



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3.1.  MPLS-based SFP Consistency Verification

   An MPLS SFC validation request/reply is an MPLS echo request/reply
   that includes an SFC validation TLV.

   Nodes examine and process the TLV only if configured to do so; other
   nodes MUST ignore the TLV and process the packet as a standard MPLS
   echo packet.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     TLV Type=TBA1             |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                    SFC Information Sub-TLV(s)                 |
       ~                                                               ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: SFC Validation TLV

   SFC Information Sub-TLV: The Sub-TLV, as defined in Figure 3, MUST
   NOT be included in an MPLS SFC validation request.

3.2.  SFC Info Sub-TLV

   Upon receiving the SFC validation request, the SFF MUST respond with
   an echo reply, which includes the SFC detailed information.

   The SFC detailed information is recorded in SFC info sub-TLV.

   Two types of sub-TLVs are defined in this section, and those are used
   in MPLS-based service programming
   [I-D.ietf-spring-sr-service-programming] and MPLS-based NSH [RFC8595]
   respectively.















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     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      sub-TLV Type=TBA1        |          Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        SFF Label                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        SF Label                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     SF Type                   |     SR Proxy Type             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 3: SFC Info Sub-TLV for SR-MPLS-based Service Programming

   Type TBA1 sub-TLV: used in SR-MPLS-based service programming

   SFF Label: represents the SID of the SFF

   SF Label: represents the service SID of the SF or SR proxy

   SF Type: indicates the type of SF, such as DPI, firewall, etc.

   SR Proxy Type: It is defined in
   [I-D.ietf-spring-sr-service-programming] and indicates the type of SR
   proxy if it exists.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      sub-TLV Type=TBA2        |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    SFC-FWD Type               |       Reserved                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     SFC context Label                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SF Label                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SF Type                   |      Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 4: SFC Info Sub-TLV for MPLS-based NSH

   Type TBA2 sub-TLV: used in MPLS-based NS

   SFC-FWD Type: indicates the forwarding type of the data plane, and
   has the following values:

   0x10: MPLS-based NSH [RFC8595] label swapping



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   0x11: MPLS-based NSH [RFC8595] label stacking

   SFC context Label: The meaning of the SFC context label depends on
   the SFC Type.  If SFC-FWD Type is 0x10, the SFC context Label
   represents SPI.  If SFC-FWD Type is 0x11, the SFC context Label
   represents the context label [RFC8595].

   SF Label: The meaning of the SF label depends on the SFC-FWD Type.
   If SFC Type is 0x10, the SF Label represents SI.  If SFC Type is
   0x11, the SF Label represents the SFI index [RFC8595].

   SF Type: It is defined in [I-D.ietf-bess-nsh-bgp-control-plane] and
   indicates the type of SF, such as DPI, firewall, etc.

3.3.  SFC Basic Unit FEC Sub-TLV

   Unlike standard MPLS forwarding, which is based on a single label, in
   [RFC8595], packet forwarding is based on the basic unit of MPLS label
   stack for SFC(SFC Context Label+SF Label).  A new FEC sub-TLV is
   defined in this document, which can be used to carry the
   corresponding FEC of the basic unit.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Route Distinguisher (RD)                     |
   |                      (8 octets)                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         SF Type               |       Reserved                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 5: SFC Basic Unit sub-TLV

   Route Distinguisher (RD): 8 octets field in SFIR Route Type specific
   NLRI [I-D.ietf-bess-nsh-bgp-control-plane] .

   SF Type: 2 octets.  It is defined in [I-D.ietf-bess-nsh-bgp-control-
   plane] and indicates the type of SF, such as DPI, firewall, etc.

   A node that receives an LSP ping with the new FEC will check if it is
   its Route Distinguisher and whether it advertised that Service
   Function Type.

3.4.  Theory of Operation

   An MPLS SFC validation request is an MPLS echo request with an SFC
   validation TLV, and the echo request is sent with a label stack
   corresponding to the SFP being tested.



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   Sending an SFC echo request to the control plane is triggered by one
   of the following packet processing exceptions: IP TTL expiration,
   MPLS TTL expiration, or the receiver is the terminal SFF for an SFP.

   After general packet sanity verifying[RFC8029], section 3.4.1 and
   section 3.4.2 in this document separately describe the following
   processing procedures in service programming and MPLS-based NSH.

   After all SFFs on the SFP send back MPLS echo reply, the sender
   collects information about all traversed SFFs and SFs on the rendered
   service path (RSP).

3.4.1.  MPLS-based service programming

   [I-D.ietf-spring-sr-service-programming] describes how a service can
   be associated with a SID to achieve service function chaining.  In an
   SR-MPLS network, the SFP is encoded as a stack of MPLS labels.  That
   stack is pushed on top of the packet.

   If an SFC validation TLV is present in the received echo request, an
   SFF MUST parse through the label stack until the next label is not a
   local service SID to get all the SFs attached to the SFF on the SFP
   and record the corresponding Label-stack-depth.

   The SFF then sends an MPLS echo reply with all the SF information
   recorded in SFC Information Sub-TLV, including the service SID and
   the SF type.

3.4.2.  RFC 8595 path consistency

   [RFC8595] describes how Service Function Chaining (SFC) can be
   achieved in an MPLS network using a logical representation of the
   Network Service Header (NSH) in an MPLS label stack.

   SFC forwarding can be achieved by label swapping, label stacking, or
   the mix of both.  When an SFF receives a packet containing an MPLS
   label stack, it examines the top basic unit of MPLS label stack for
   SFC, {SPI, SI} or {context label, SFI index}, to determine where to
   send the packet next.

   Upon receiving the SFC validation request, an SFF checks the MPLS
   label stack to get all the locally attached basic units for SFC.
   Then, the SFF sends back a reply message, including SFC info sub-
   TLVs, for each basic unit local to the SFF.







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3.5.  Discussion

   In [RFC8595], it says, "when an SFF receives a packet from any
   component of the SFC system (classifier, SFI, or another SFF), it
   MUST discard any packets with TTL set to zero".  To trace SFC, it
   should be changed to allow punting the packet to the control plane
   though under throttling control.

4.  References

4.1.  Normative References

   [I-D.ietf-bess-nsh-bgp-control-plane]
              Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
              Jalil, "BGP Control Plane for the Network Service Header
              in Service Function Chaining", draft-ietf-bess-nsh-bgp-
              control-plane-15 (work in progress), June 2020.

   [I-D.ietf-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
              d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
              Henderickx, W., and S. Salsano, "Service Programming with
              Segment Routing", draft-ietf-spring-sr-service-
              programming-02 (work in progress), March 2020.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

   [RFC8595]  Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
              Forwarding Plane for Service Function Chaining", RFC 8595,
              DOI 10.17487/RFC8595, June 2019,
              <https://www.rfc-editor.org/info/rfc8595>.

4.2.  Informative References

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.




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Authors' Addresses

   Liu Yao
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: liu.yao71@zte.com.cn


   Greg Mirsky
   ZTE Corporation

   Email: gregimirsky@gmail.com




































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