SFC WG                                                         G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                                   T. Ao
Expires: 1 October 2021                           Individual contributor
                                                                 Z. Chen
                                                           China Telecom
                                                                K. Leung
                                                            Cisco System
                                                               G. Mishra
                                                            Verizon Inc.
                                                           30 March 2021


                      SFC OAM for path consistency
                  draft-ao-sfc-oam-path-consistency-11

Abstract

   Service Function Chain (SFC) defines an ordered set of service
   functions (SFs) to be applied to packets and/or frames and/or flows
   selected due to classification.  SFC Operation, Administration and
   Maintenance can monitor the continuity of the SFC, i.e., that all SFC
   elements are reachable to each other in the downstream direction.
   But SFC OAM must support verification that the order of traversing
   these SFs corresponds to the state defined by the SFC control plane
   or orchestrator, the metric referred to in this document as the path
   consistency of the SFC.  This document defines a new SFC active OAM
   method to support SFC consistency check, i.e., verification that all
   elements of the given SFC are being traversed in the expected order.

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 1 October 2021.





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Copyright Notice

   Copyright (c) 2021 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
   Provisions Relating to IETF Documents (https://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.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Consistency OAM: Theory of Operation  . . . . . . . . . . . .   3
     3.1.  COAM packet . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  SFF Information Record TLV  . . . . . . . . . . . . . . .   5
     3.3.  SF Information Sub-TLV  . . . . . . . . . . . . . . . . .   6
     3.4.  SF Information Sub-TLV Construction . . . . . . . . . . .   7
       3.4.1.  Multiple SFs as hops of SFP . . . . . . . . . . . . .   7
       3.4.2.  Multiple SFs for load balance . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  COAM Message Types  . . . . . . . . . . . . . . . . . . .   9
     5.2.  SFF Information Record TLV Type . . . . . . . . . . . . .   9
     5.3.  SF Information Sub-TLV Type . . . . . . . . . . . . . . .   9
     5.4.  SF Identifier Types . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informational References  . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Service Function Chain (SFC) is a chain with a series of ordered
   Service Functions (SFs).  Service Function Path (SFP) is a path of a
   SFC.  SFC is described in detail in the SFC architecture document
   [RFC7665].  The SFs in the SFC are ordered, i.e., only when an SF
   processes traffic, then it can be processed by the next SF.  Changes
   in the order are very likely to cause errors.  That's why an operator
   needs to ensure that the order of traversing the SFs is as defined by



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   the control plane or the orchestrator.  This document refers to the
   correlation between the state of the control plane and the SFP itself
   as the SFP consistency.  The need to verify the consistency of the
   particular SFP, using a mechanism of an active OAM protocol, is noted
   in [RFC8924].

   This document defines the method to check the path consistency of the
   SFP.  It is an extension of the SFC Echo-request/Echo-reply specified
   in the [I-D.ietf-sfc-multi-layer-oam].

2.  Conventions used in this document

2.1.  Acronyms

   SFC: Service Function Chain.  An ordered set of some abstract SFs.

   SFF: Service Function Forwarder

   SF: Service Function

   OAM: Operation, Administration and Maintenance

   SFP: Service Function Path

   COAM: Consistency OAM, OAM that can be used to check the consistency
   of the Service Function Path.

   MAC: Message Authentication Code

2.2.  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.  Consistency OAM: Theory of Operation

   Consistency OAM (COAM) uses two functions: COAM Request and COAM
   Reply.  Every SFF that receives the COAM Request MUST perform the
   following actions:

   *  Collect information of the traversed by the COAM Request packet
      SFs and send it to the ingress SFF as COAM Reply packet over IP
      network [I-D.ietf-sfc-multi-layer-oam];





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   *  Forward the COAM Request to the next downstream SFF if the one
      exists.

   As a result, the ingress SFF collects information about all traversed
   SFFs and SFs, information on the actual path the COAM packet has
   traveled.  That information is used to verify the SFC's path
   consistency.  The mechanism for the SFP consistency verification is
   outside the scope of this document.

3.1.  COAM packet

   Consistency OAM introduces two new types of messages to the SFC Echo
   Request/Reply operation defined in [I-D.ietf-sfc-multi-layer-oam]
   with the following values detailed in Section 5.1:

   *  TBA1 - COAM Request

   *  TBA2 - COAM Reply

   Upon receiving the COAM Request, the SFF MUST respond with the COAM
   Reply.  The SFF MUST include the SFs information, as described in
   Section 3.3 and Section 3.2.

   The COAM packet, defined in [I-D.ietf-sfc-multi-layer-oam], is
   displayed 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Version Number        |         Global Flags          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Message Type  |   Reply mode  |  Return Code  | Return S.code |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Sender's Handle                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Sequence Number                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Type     |    Reserved   |           Length              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                             Value                             ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+










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                        Figure 1: COAM Packet Header


   The initiator of COAM Request MAY require the collected information
   in the COAM Reply be sent in the integrity-protected mode using the a
   Message Authentication Code (MAC) Context Header, defined in
   [I-D.ietf-sfc-nsh-integrity].  If the NSH of the received SFC Echo
   Reply includes the MAC Context Header, the authentication of the
   packet MUST be verified before using any data.  If the verification
   fails, the receiver MUST stop processing the SFF Information Record
   TLV and notify an operator.  Specification of the notification
   mechanism is outside the scope of this document.

3.2.  SFF Information Record TLV

   For COAM Request, the SFF MUST include the Information of SFs into
   the SF Information Record TLV in the COAM Reply message.  Every SFF
   sends back a single COAM Reply Message, including information on all
   the SFs attached to the SFF on the SFP as requested in the COAM
   Request message.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |SFF Record TLV |    Reserved   |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       Service Path Identifier (SPI)           |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                   SF Information  Sub-TLV                     |
       ~                                                               ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: SFF Information Record TLV


   SFF Information Record TLV is a variable-length TLV that includes the
   information of all SFFs mapped to the particular SFF instance for the
   specified SFP.  Figure 2 presents the format of an SFC Echo Request/
   Reply TLV, where fields are defined as the following:

      Reserved - one-octet-long field.

      Service Path Identifier (SPI): The identifier of SFP to which all
      the SFs in this TLV belong.




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      SF Information Sub-TLV: The Sub-TLV is as defined in Figure 3.

3.3.  SF Information Sub-TLV

   Every SFF receiving COAM Request packet MUST include the SF
   characteristic data into the COAM Reply packet.  The data format of
   an SF sub-TLV, included in a COAM Reply packet, is displayed in
   Figure 3.

   After the COAM Request message traverses the SFP, all the information
   of the SFs on the SFP is collected from the TLVs included in COAM
   Reply messages.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |SF sub-TLV|    Reserved   |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Service Index  |          SF Type              |   SF ID Type  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          SF Identifiers                       |
       ~                                                               ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 3: Service Function information sub-TLV


   SF sub-TLV Type: Two octets long field.  It indicates that the TLV is
   an SF TLV that contains the information of one SF.

   Length: Two octets long field.  The value of the field is the length
   of the data following the Length field counted in octets.

   Service Index: Indicates the SF's position on the SFP.

   SF Type: Two octets long field.  It is defined in
   [I-D.ietf-bess-nsh-bgp-control-plane] and indicates the type of SF,
   e.g., Firewall, Deep Packet Inspection, WAN optimization controller,
   etc.

   Reserved: For future use.  MUST be zeroed on transmission and MUST be
   ignored on receipt.

   SF ID Type: One octet-long field with values defined as Section 5.4.





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   SF Identifier: An identifier of the SF.  The length of the SF
   Identifier depends on the type of the SF ID Type.  For example, if
   the SF Identifier is its IPv4 address, the SF Identifier should be 32
   bits.  SF ID Type and SF Identifier may be a list, indicating the
   list of the SFs are which are included in a load balance group.

3.4.  SF Information Sub-TLV Construction

   Each SFF in the SFP MUST send one and only one COAM Reply
   corresponding to the COAM Request.  If only one SF is attached to the
   SFF in such SFP, only one SF information sub-TLV is included in the
   COAM Reply.  If several SFs attached to the SFF in the SFP, SF
   Information Sub-TLV MUST be constructed as described below in either
   Section 3.4.1 and Section 3.4.2.

3.4.1.  Multiple SFs as hops of SFP

   Multiple SFs attached to the same SFF are the hops of the SFP.  The
   service indexes of these SFs are different.  Service function types
   of these SFs could be different or be the same.  Information about
   all SFs MAY be included in the COAM Reply message.  Information about
   each SF MUST be listed as separate SF Information Sub-TLVs in the
   COAM Reply message.

   An example of the COAM procedure for this case is shown in Figure 4.
   The Service Function Path(SPI=x) is SF1->SF2->SF4->SF3.  The SF1, SF2
   and SF3 are attached to SFF1, and SF4 is attached to SFF2.  The COAM
   Request message is sent to the SFFs in the sequence of the
   SFP(SFF1->SFF2->SFF1).  Every SFF(SFF1, SFF2) replies with the
   information of SFs belonging to the SFP.  The SF information Sub-TLV
   in Figure 3 contains information for each SF (SF1, SF2, SF3, and
   SF4).

                    SF1         SF2           SF4                SF3
                    +------+------+            |                  |
       COAM Req  ......>  SFF1       ......>  SFF2       ......> SFF1
       (SPI=x)             .                   .                  .
               <............         <..........       <...........
               COAM Reply1(SF1,SF2)  COAM Reply2(SF4)  COAM Reply3(SF3)


            Figure 4: Example 1 for COAM Reply with multiple SFs









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3.4.2.  Multiple SFs for load balance

   Multiple SFs may be attached to the same SFF to balance the load; in
   other words, that means that the particular traffic flow will
   traverse only one of these SFs.  These SFs have the same Service
   Function Type and Service Index.  For this case, the SF identifiers
   and SF ID Type of all these SFs will be listed in the SF Identifiers
   field and SF ID Type in a single SF information sub-TLV of COAM Reply
   message.  The number of these SFs can be calculated according to SF
   ID Type and the value of the Length field of the sub-TLV.

   An example of the COAM procedure for this case is shown in Figure 5.
   The Service Function Path (SPI=x) is SF1a/SF1b->SF2a/SF2b.  The
   Service Functions SF1a and SF1b are attached to SFF1, which balances
   the load among them.  The Service Functions SF2a and SF2b are
   attached to SFF2, which, in turn, balances its load between them.
   The COAM Request message is sent to the SFFs in the sequence of the
   SFP (i.e.  SFF1->SFF2).  Every SFF (SFF1, SFF2) replies with the
   information of SFs belonging to the SFP.  The SF information Sub-TLV
   in Figure 3 contains information for all SFs at that hop.

                               /SF1a                   /SF2a
                               \SF1b                   \SF2b
                                 |                       |
                                SFF1                    SFF2
            COAM Req   .........>  .           .........>  .
            (SPI=x)                .                       .
                       <............        <...............
              COAM Reply1({SF1a,SF1b})   COAM Reply2({SF2a,SF2b})


            Figure 5: Example 2 for COAM Reply with multiple SFs


4.  Security Considerations

   Security considerations discussed in [RFC8300] and
   [I-D.ietf-sfc-multi-layer-oam] apply to this document.

   Also, since Service Function sub-TLV discloses information about the
   SFP the spoofed COAM Request packet may be used to obtain network
   information, it is RECOMMENDED that implementations provide a means
   of checking the source addresses of COAM Request messages, specified
   in SFC Source TLV [I-D.ietf-sfc-multi-layer-oam], against an access
   list before accepting the message.

5.  IANA Considerations




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5.1.  COAM Message Types

   IANA is requested to assign values from its Message Types sub-
   registry in SFC Echo Request/Echo Reply Message Types registry as
   follows:

         +=======+==============================+===============+
         | Value |         Description          | Reference     |
         +=======+==============================+===============+
         | TBA1  | SFP Consistency Echo Request | This document |
         +-------+------------------------------+---------------+
         | TBA2  |  SFP Consistency Echo Reply  | This document |
         +-------+------------------------------+---------------+

             Table 1: SFP Consistency Echo Request/Echo Reply
                              Message Types

5.2.  SFF Information Record TLV Type

   IANA is requested to assign a new type value from SFC OAM TLV Type
   registry as follows:

          +=======+=============================+===============+
          | Value |         Description         | Reference     |
          +=======+=============================+===============+
          | TBA3  | SFF Information Record Type | This document |
          +-------+-----------------------------+---------------+

                      Table 2: SFF-Information Record

5.3.  SF Information Sub-TLV Type

   IANA is requested to assign a new type value from SFC OAM TLV Type
   registry as follows:

                +=======+================+===============+
                | Value |  Description   | Reference     |
                +=======+================+===============+
                | TBA4  | SF Information | This document |
                +-------+----------------+---------------+

                   Table 3: SF-Information Sub-TLV Type









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5.4.  SF Identifier Types

   IANA is requested to create in the registry SF Types the new sub-
   registry SF Identifier Types.  All code points in the range 1 through
   191 in this registry shall be allocated according to the "IETF
   Review" procedure as specified in [RFC8126] and assign values as
   follows:

          +============+=============+=========================+
          | Value      | Description | Reference               |
          +============+=============+=========================+
          | 0          |   Reserved  | This document           |
          +------------+-------------+-------------------------+
          | TBA6       |     IPv4    | This document           |
          +------------+-------------+-------------------------+
          | TBA7       |     IPv6    | This document           |
          +------------+-------------+-------------------------+
          | TBA8       |     MAC     | This document           |
          +------------+-------------+-------------------------+
          | TBA8+1-191 |  Unassigned | IETF Review             |
          +------------+-------------+-------------------------+
          | 192-251    |  Unassigned | First Come First Served |
          +------------+-------------+-------------------------+
          | 252-254    |  Unassigned | Private Use             |
          +------------+-------------+-------------------------+
          | 255        |   Reserved  | This document           |
          +------------+-------------+-------------------------+

                       Table 4: SF Identifier Type

6.  Acknowledgements

   The authors are thankful to John Drake for his review and the
   reference to the work on BGP Control Plane for NSH SFC.  The authors
   express their appreciation to Joel M.  Halpern for his suggestion
   about the load balancing scenario.  The authors also thank Dirk von
   Hugo, for his useful comments.

7.  References

7.1.  Normative References

   [I-D.ietf-sfc-multi-layer-oam]
              Mirsky, G., Meng, W., Khasnabish, B., and C. Wang, "Active
              OAM for Service Function Chaining", Work in Progress,
              Internet-Draft, draft-ietf-sfc-multi-layer-oam-09, 11
              February 2021, <https://tools.ietf.org/html/draft-ietf-
              sfc-multi-layer-oam-09>.



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   [I-D.ietf-sfc-nsh-integrity]
              Boucadair, M., Reddy, T., and D. Wing, "Integrity
              Protection for the Network Service Header (NSH) and
              Encryption of Sensitive Context Headers", Work in
              Progress, Internet-Draft, draft-ietf-sfc-nsh-integrity-05,
              23 March 2021, <https://tools.ietf.org/html/draft-ietf-
              sfc-nsh-integrity-05>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [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>.

7.2.  Informational 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", Work in Progress, Internet-
              Draft, draft-ietf-bess-nsh-bgp-control-plane-18, 21 August
              2020, <https://tools.ietf.org/html/draft-ietf-bess-nsh-
              bgp-control-plane-18>.

   [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>.

   [RFC8924]  Aldrin, S., Pignataro, C., Ed., Kumar, N., Ed., Krishnan,
              R., and A. Ghanwani, "Service Function Chaining (SFC)
              Operations, Administration, and Maintenance (OAM)
              Framework", RFC 8924, DOI 10.17487/RFC8924, October 2020,
              <https://www.rfc-editor.org/info/rfc8924>.




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Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com, gregory.mirsky@ztetx.com


   Ting Ao
   Individual contributor
   No.889, BiBo Road
   Shanghai
   201203
   China

   Phone: +86 17721209283
   Email: 18555817@qq.com


   Zhonghua Chen
   China Telecom
   No.1835, South PuDong Road
   Shanghai
   201203
   China

   Phone: +86 18918588897
   Email: 18918588897@189.cn


   Kent Leung
   Cisco System
   170 West Tasman Drive
   San Jose, CA 95134,
   United States of America

   Email: kleung@cisco.com


   Gyan Mishra
   Verizon Inc.

   Email: gyan.s.mishra@verizon.com








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