SFC WG                                                         G. Mirsky
Internet-Draft                                                 ZTE Corp.
Updates: 8300 (if approved)                                      W. Meng
Intended status: Standards Track                         ZTE Corporation
Expires: 5 December 2021                                   B. Khasnabish
                                                                 C. Wang
                                                  Individual contributor
                                                             3 June 2021


                Active OAM for Service Function Chaining
                   draft-ietf-sfc-multi-layer-oam-12

Abstract

   A set of requirements for active Operation, Administration, and
   Maintenance (OAM) of Service Function Chains (SFCs) in a network is
   presented in this document.  Based on these requirements, an
   encapsulation of active OAM messages in SFC and a mechanism to detect
   and localize defects are described.

   This document updates RFC 8300.  Particularly, it updates the
   definition of O (OAM) bit in the Network Service Header (NSH) and
   defines how an active OAM message is identified in the NSH.

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 5 December 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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.  Terminology and Conventions . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements for Active OAM in SFC Network  . . . . . . . . .   4
   4.  Active OAM Identification in the NSH  . . . . . . . . . . . .   6
   5.  Echo Request/Echo Reply for SFC . . . . . . . . . . . . . . .   8
     5.1.  Return Codes  . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  Authentication in Echo Request/Reply  . . . . . . . . . .  11
     5.3.  SFC Echo Request Transmission . . . . . . . . . . . . . .  11
     5.4.  SFC Echo Request Reception  . . . . . . . . . . . . . . .  12
       5.4.1.  Errored TLVs TLV  . . . . . . . . . . . . . . . . . .  12
     5.5.  SFC Echo Reply Transmission . . . . . . . . . . . . . . .  13
     5.6.  SFC Echo Reply Reception  . . . . . . . . . . . . . . . .  14
     5.7.  Tracing an SFP  . . . . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     8.1.  SFC Active OAM Protocol . . . . . . . . . . . . . . . . .  16
     8.2.  SFC Active OAM Message Type . . . . . . . . . . . . . . .  16
     8.3.  SFC Echo Request/Echo Reply Parameters  . . . . . . . . .  17
     8.4.  SFC Echo Request/Echo Reply Message Types . . . . . . . .  17
     8.5.  SFC Echo Reply Modes  . . . . . . . . . . . . . . . . . .  18
     8.6.  SFC Echo Return Codes . . . . . . . . . . . . . . . . . .  20
     8.7.  SFC TLV Type  . . . . . . . . . . . . . . . . . . . . . .  21
     8.8.  SFC OAM UDP Port  . . . . . . . . . . . . . . . . . . . .  21
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   [RFC7665] defines data plane elements necessary to implement a
   Service Function Chaining (SFC).  These include:





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   1.  Classifiers that perform the classification of incoming packets.
       Such classification may result in associating a received packet
       to a service function chain.

   2.  Service Function Forwarders (SFFs) that are responsible for
       forwarding traffic to one or more connected Service Functions
       (SFs) according to the information carried in the SFC
       encapsulation and handling traffic coming back from the SFs and
       forwarding it to the next SFF.

   3.  SFs that are responsible for executing specific service treatment
       on received packets.

   There are different views from different levels of the SFC.  One is
   the service function chain, an entirely abstract view, which defines
   an ordered set of SFs that must be applied to packets selected based
   on classification rules.  But service function chain doesn't specify
   the exact mapping between SFFs and SFs.  Thus, another logical
   construct used in SFC is a Service Function Path (SFP).  According to
   [RFC7665], SFP is the instantiation of the SFC in the network and
   provides a level of indirection between the entirely abstract SFCs
   and a fully specified ordered list of SFFs and SFs identities that
   the packet will visit when it traverses the SFC.  The latter entity
   is referred to as Rendered Service Path (RSP).  The main difference
   between SFP and RSP is that the former is the logical construct,
   while the latter is the realization of the SFP via the sequence of
   specific SFC data plane elements.

   This document defines how active Operation, Administration and
   Maintenance (OAM), per [RFC7799] definition of active OAM, is
   identified when Network Service Header (NSH) is used as the SFC
   encapsulation.  Following the analysis of SFC OAM in [RFC8924], this
   document applies and, when necessary, extends requirements listed in
   Section 4 of [RFC8924] for the use of active OAM in an SFP supporting
   fault management and performance monitoring.  Active OAM tools,
   conformant to the requirements listed in Section 3, improve, for
   example, troubleshooting efficiency and defect localization in SFP
   because they specifically address architectural principles of NSH.
   For that purpose, SFC Echo Request and Echo Reply are specified in
   the document.  This mechanism enables on-demand Continuity Check,
   Connectivity Verification among other operations over SFC in
   networks, addresses functionalities discussed in Sections 4.1, 4.2,
   and 4.3 of [RFC8924].  Also, this document updates Section 2.2 of
   [RFC8300] in part of the definition of O bit in the (NSH).







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2.  Terminology and Conventions

   The terminology defined in [RFC7665] is used extensively throughout
   this document.  The reader is expected to be familiar with it.

   In this document, SFC OAM refers to an active OAM [RFC7799] in an SFC
   architecture.

2.1.  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.

2.2.  Acronyms

   E2E: End-to-End

   FM: Fault Management

   NSH: Network Service Header

   OAM: Operations, Administration, and Maintenance

   RSP: Rendered Service Path

   SF: Service Function

   SFC: Service Function Chain

   SFF: Service Function Forwarder

   SFP: Service Function Path

   MAC: Message Authentication Code

3.  Requirements for Active OAM in SFC Network

   As discussed in [RFC8924], SFC-specific means are needed to perform
   the OAM task of fault management (FM) in an SFC architecture,
   including failure detection, defect characterization, and
   localization.  This document defines the set of requirements for
   active FM OAM mechanisms to be used in an SFC architecture.






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                 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
                 |SFI11| |SFI12| |SFI21| |SFI22| |SFI31| |SFI32|
                 +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
                     \    /          \   /           \    /
      +----------+   +----+         +----+          +----+
      |Classifier|---|SFF1|---------|SFF2|----------|SFF3|
      +----------+   +----+         +----+          +----+


                   Figure 1: An Example of SFC Data Plane

   Regarding the reference model depicted in Figure 1, consider a
   service function chain that includes three distinct service
   functions.  In this example, the SFP traverses SFF1, SFF2, and SFF3,
   each SFF being connected to two instances of the same service
   function.  End-to-end (E2E) SFC OAM has the Classifier as the
   ingress, and SFF3 - as its egress.  Segment SFC OAM is between two
   elements that are part of the same SFP.  Following are the
   requirements for an FM SFC OAM, whether with the E2E or segment
   scope:

      REQ#1: Packets of active SFC OAM in SFC SHOULD be fate sharing
      with the monitored SFC data, in the forward direction from ingress
      toward egress endpoint(s) of the OAM test.

   The fate sharing, in the SFC environment, is achieved when a test
   packet traverses the same path and receives the same treatment in the
   transport layer as an SFC NSH packet.

      REQ#2: SFC OAM MUST support monitoring of the continuity of the
      SFP between any of its elements.

   A network failure might be declared when several consecutive test
   packets are not received within a pre-determined time.  For example,
   in the E2E SFC OAM FM case, the egress, SFF3, in the example in
   Figure 1, could be the entity that detects the SFP's failure by
   monitoring a flow of periodic test packets.  The ingress may be
   capable of recovering from the failure, e.g., using redundant SFC
   elements.  Thus, it is beneficial for the egress to signal the new
   defect state to the ingress, which in this example is the Classifier.
   Hence the following requirement:

      REQ#3: SFC OAM MUST support Remote Defect Indication notification
      by the egress to the ingress.

      REQ#4: SFC OAM MUST support connectivity verification of the SFP.
      Definition of the misconnection defect, entry and exit criteria
      are outside the scope of this document.



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   Once the SFF1 detects the defect, the objective of the SFC OAM
   changes from the detection of a defect to defect characterization and
   localization.

      REQ#5: SFC OAM MUST support fault localization of the Loss of
      Continuity Check within an SFP.

      REQ#6: SFC OAM MUST support an SFP tracing to discover the RSP.

   In the example presented in Figure 1, two distinct instances of the
   same service function share the same SFF.  In this example, the SFP
   can be realized over several RSPs that use different instances of SF
   of the same type.  For example, RSP1(SFI11--SFI21--SFI31) and
   RSP2(SFI12--SFI22--SFI32).  Available RSPs can be discovered using
   the trace function discussed in Section 4.3 [RFC8924].

      REQ#7: SFC OAM MUST have the ability to discover and exercise all
      available RSPs in the network.

   The SFC OAM layer model described in [RFC8924] offers an approach for
   a defect localization within a service function chain.  As the first
   step, the SFP's continuity for SFFs that are part of the same SFP
   could be verified.  After the reachability of SFFs has already been
   verified, SFFs that serve an SF may be used as a test packet source.
   In such a case, SFF can act as a proxy for another element within the
   service function chain.

      REQ#8: SFC OAM MUST be able to trigger on-demand FM with responses
      being directed towards the initiator of such proxy request.

4.  Active OAM Identification in the NSH

   The O bit in the NSH is defined in [RFC8300] as follows:

      O bit: Setting this bit indicates an OAM packet.

   This document updates that definition as follows:

      O bit: Setting this bit indicates an OAM command and/or data in
      the NSH Context Header or packet payload.

   Active SFC OAM is defined as a combination of OAM commands and/or
   data included in a message that immediately follows the NSH.  To
   identify the active OAM message, the Next Protocol field's value MUST
   be set to Active SFC OAM (TBA1) (Section 8.1).  The rules for
   interpreting the values of the O bit and the Next Protocol field are
   as follows:




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   *  O bit set and the Next Protocol value is not one of identifying
      active or hybrid OAM protocol (per [RFC7799] definitions), e.g.,
      defined in this specification Active SFC OAM:

         - a Fixed-Length Context Header or Variable-Length Context
         Header(s) contain an OAM command or data.

         - the type of payload is determined by the Next Protocol field.

   *  O bit set and the Next Protocol value is one of identifying active
      or hybrid OAM protocol:

         - the payload that immediately follows the NSH MUST contain an
         OAM command or data.

   *  O bit is clear:

         - no OAM in a Fixed-Length Context Header or Variable-Length
         Context Header(s).

         - the payload determined by the Next Protocol field's value
         MUST be present.

   *  O bit is clear and the Next Protocol field's value identifies
      active or hybrid OAM protocol MUST be identified and reported as
      the erroneous combination.  An implementation MAY have control to
      enable processing of the OAM payload.

   One conclusion from the above-listed rules of processing the O bit
   and the Next Protocol field's value is to avoid the combination of
   OAM in an NSH Context Header (Fixed-Length or Variable-Length) and
   the payload immediately following the NSH because there is no
   unambiguous way to identify such combination using the O bit and the
   Next Protocol field.

   As demonstrated in Section 4 [RFC8924] and Section 3 of this
   document, SFC OAM is required to perform multiple tasks.  Several
   active OAM protocols could be used to address all the requirements.
   When IP/UDP encapsulation of an SFC OAM control message is used,
   protocols can be demultiplexed using the Destination UDP port number.
   But extra IP/UDP headers, especially in an IPv6 network, add
   noticeable overhead.  This document defines Active OAM Header
   (Figure 2) to demultiplex active OAM protocols on an SFC.








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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | V | Msg Type  |     Flags     |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~              SFC Active OAM Control Packet                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 2: SFC Active OAM Header

      V - two-bit-long field indicates the current version of the SFC
      active OAM header.  The current value is 0.

      Msg Type - six bits long field identifies OAM protocol, e.g., Echo
      Request/Reply or Bidirectional Forwarding Detection.

      Flags - eight bits long field carries bit flags that define
      optional capability and thus processing of the SFC active OAM
      control packet, e.g., optional timestamping.

      Length - two octets long field that is the length of the SFC
      active OAM control packet in octets.

5.  Echo Request/Echo Reply for SFC

   Echo Request/Reply is a well-known active OAM mechanism that is
   extensively used to verify a path's continuity, detect
   inconsistencies between a state in control and the data planes, and
   localize defects in the data plane.  ICMP ([RFC0792] for IPv4 and
   [RFC4443] for IPv6 networks respectively) and [RFC8029] are examples
   of broadly used active OAM protocols based on Echo Request/Reply
   principle.  The SFC NSH Echo Request/Reply defined in this document
   addresses several requirements listed in Section 3.  Specifically, as
   defined in this specification, it can be used to check the continuity
   of an SFP, trace an SFP, localize the failure of the SFP.  The SFC
   NSH Echo Request/Reply control message format is presented in
   Figure 3.














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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | V |        Reserved           |         Global Flags          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Message Type  |   Reply mode  |  Return Code  |Return Subcode |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Sender's Handle                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Sequence Number                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                              TLVs                             ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: SFC Echo Request/Reply Format

   The interpretation of the fields is as follows:

      Version (V) is a two-bit field that indicates the current version
      of the SFC Echo Request/Reply.  The current value is 0.  The
      version number is to be incremented whenever a change is made that
      affects the ability of an implementation to parse or process
      control packet correctly.

      Reserved - fourteen-bit field.  It MUST be zeroed on transmission
      and ignored on receipt.

      The Global Flags is a two-octet bit vector field.

      The Message Type is a one-octet field that reflects the packet
      type.  Value TBA3 identifies Echo Request and TBA4 - Echo Reply.

      The Reply Mode is a one-octet field.  It defines the type of the
      return path requested by the sender of the Echo Request.

      Return Codes and Subcodes are one-octet fields each.  These can be
      used to inform the sender about the result of processing its
      request.  Initial Return Code values are according to Table 1.
      For all Return Code values defined in this document, the value of
      the Return Subcode field MUST be set to zero.

      The Sender's Handle is a four-octet field.  It is filled in by the
      sender of the Echo Request and returned unchanged by the Echo
      Reply sender.  The sender of the Echo Request MAY use a pseudo-
      random number generator to set the value of the Sender's Handle
      field.





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      The Sequence Number is a four-octet field.  It is assigned by the
      sender and can be (for example) used to detect missed replies.
      The value of the Sequence Number field SHOULD be monotonically
      increasing in the course of the test session.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Type     |    Reserved   |           Length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                            Value                              ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 4: SFC Echo Request/Reply TLV Format

   TLV is a variable-length field.  Multiple TLVs MAY be placed in an
   SFC Echo Request/Reply packet.  Additional TLVs may be enclosed
   within a given TLV, subject to the semantics of the (outer) TLV in
   question.  If more than one TLV is to be included, the value of the
   Type field of the outmost outer TLV MUST be set to Multiple TLVs Used
   (TBA12), as assigned by IANA according to Section 8.7.  Figure 4
   presents the format of an SFC Echo Request/Reply TLV, where fields
   are defined as the following:

      Type - a one-octet-long field that characterizes the
      interpretation of the Value field.  Type values allocated
      according to Section 8.7.

      Reserved - one-octet-long field.  The value of the Type field
      determines its interpretation and encoding.

      Length - two-octet-long field equal to the Value field's length in
      octets.

      Value - a variable-length field.  The value of the Type field
      determines its interpretation and encoding.

5.1.  Return Codes

   The value of the Return Code field is set to zero by the sender of an
   Echo Request.  The receiver of said Echo Request can set it to one of
   the values listed in Table 1 in the corresponding Echo Reply that it
   generates.







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          +=======+============================================+
          | Value |                Description                 |
          +=======+============================================+
          | 0     |               No Return Code               |
          +-------+--------------------------------------------+
          | 1     |      Malformed Echo Request received       |
          +-------+--------------------------------------------+
          | 2     | One or more of the TLVs was not understood |
          +-------+--------------------------------------------+
          | 3     |           Authentication failed            |
          +-------+--------------------------------------------+

                      Table 1: SFC Echo Return Codes

5.2.  Authentication in Echo Request/Reply

   Authentication can be used to protect the integrity of the
   information in SFC Echo Request and/or Echo Reply.  In the
   [I-D.ietf-sfc-nsh-integrity] a variable-length Context Header has
   been defined to protect the integrity of the NSH and the payload.
   The header can also be used for the optional encryption of the
   sensitive metadata.  MAC#1 Context Header is more suitable for the
   integrity protection of active SFC OAM, particularly of the defined
   in this document SFC Echo Request and Echo Reply.  On the other hand,
   using MAC#2 Context Header allows the detection of mishandling of the
   O-bit by a transient SFC element.

5.3.  SFC Echo Request Transmission

   SFC Echo Request control packet MUST use the appropriate transport
   encapsulation of the monitored SFP.  If the NSH is used, Echo Request
   MUST set O bit, as defined in [RFC8300].  NSH MUST be immediately
   followed by the SFC Active OAM Header defined in Section 4.  The
   Message Type field's value in the SFC Active OAM Header MUST be set
   to SFC Echo Request/Echo Reply value (TBA2) per Section 8.2.

   Value of the Reply Mode field MAY be set to:

   *  Do Not Reply (TBA5) if one-way monitoring is desired.  If the Echo
      Request is used to measure synthetic packet loss; the receiver may
      report loss measurement results to a remote node.  Note that ways
      of learning the identy of that node is otside the scope of this
      specification.

   *  Reply via an IPv4/IPv6 UDP Packet (TBA6) value likely will be the
      most used.





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   *  Reply via Application Level Control Channel (TBA7) value if the
      SFP may have bi-directional paths.

   *  Reply via Specified Path (TBA8) value to enforce the use of the
      particular return path specified in the included TLV to verify bi-
      directional continuity and also increase the robustness of the
      monitoring by selecting a more stable path.
      [I-D.ao-sfc-oam-return-path-specified] provides an example of the
      defining a specific path for the Echo Reply.

5.4.  SFC Echo Request Reception

   Sending an SFC Echo Request to the control plane is triggered by one
   of the following packet processing exceptions: NSH TTL expiration,
   NSH Service Index (SI) expiration, or the receiver is the terminal
   SFF for an SFP.

   Firstly, if the SFC Echo Request is authenticated, the receiving SFF
   MUST verify the authentication.  If the verification fails, the
   receiver SFF MUST send an SFC Echo Reply with the Return Code set to
   "Authentication failed" and the Subcode set to zero.  Then, the SFF
   that has received an SFC Echo Request verifies the received packet's
   general sanity.  If the packet is not well-formed, the receiver SFF
   SHOULD send an SFC Echo Reply with the Return Code set to "Malformed
   Echo Request received" and the Subcode set to zero.  If there are any
   TLVs that SFF does not understand, the SFF MUST send an SFC Echo
   Reply with the Return Code set to 2 ("One or more TLVs was not
   understood") and set the Subcode to zero.  In the latter case, the
   SFF MAY include an Errored TLVs TLV (Section 5.4.1) that, as sub-
   TLVs, contains only the misunderstood TLVs.  The header field's
   Sender's Handle, Sequence Number are not examined but are included in
   the SFC Echo Reply message.  If the sanity check of the received Echo
   Request succeeded, then the SFF at the end of the SFP MUST set the
   Return Code value to 5 ("End of the SFP") and the Subcode set to
   zero.  If the SFF is not at theend of the SFP and the TTL value is 1,
   the value of the Return Code MUST be set to 4 ("TTL Exceeded") and
   the Subcode set to zero.

5.4.1.  Errored TLVs TLV

   If the Return Code for the Echo Reply is determined as 2 ("One or
   more TLVs was not understood"), then the Errored TLVs TLV MAY be
   included in an Echo Reply.  The use of this TLV allows informing the
   sender of an Echo Request of mandatory TLVs either not supported by
   an implementation or parsed and found to be in error.






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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Errored TLVs |    Reserved   |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             Value                             |
       .                                                               .
       .                                                               .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 5: Errored TLVs TLV

   where

      The Errored TLVs Type MUST be set to TBA14 Section 8.7.

      Reserved - one-octet-long field.

      Length - two-octet-long field equal to the length of the Value
      field in octets.

      The Value field contains the TLVs, encoded as sub-TLVs, that were
      not understood or failed to be parsed correctly.

5.5.  SFC Echo Reply Transmission

   The Reply Mode field directs whether and how the Echo Reply message
   should be sent.  The sender of the Echo Request MAY use TLVs to
   request that the corresponding Echo Reply is transmitted over the
   specified path.  [I-D.ao-sfc-oam-return-path-specified] provides an
   example of a TLV that can be used to specify the path of the Echo
   Reply.  Value TBA3 is referred to as the "Do not reply" mode and
   suppresses the Echo Reply packet transmission.  The default value
   (TBA6) for the Reply mode field requests the responder to send the
   Echo Reply packet out-of-band as IPv4 or IPv6 UDP packet.

   Responder to the SFC Echo Request sends the Echo Reply over IP
   network if the Reply mode is Reply via an IPv4/IPv6 UDP Packet.
   Because the NSH does not identify the ingress node that generated the
   Echo Request, the source ID MUST be included in the message and used
   as the IP destination address for IP/UDP encapsulation of the SFC
   Echo Reply.  The sender of the SFC Echo Request MUST include SFC
   Source TLV Figure 6.






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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Source ID  |    Reserved   |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Value                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 6: SFC Source TLV

   where

      Source ID Type is a one-octet-long field and has the value of
      TBA13 Section 8.7.

      Reserved - one-octet-long field.

      Length is a two-octets-long field, and the value equals the length
      of the Value field in octets.

      Value field contains the IP address of the sender of the SFC OAM
      control message, IPv4 or IPv6.

   The UDP destination port for SFC Echo Reply TBA15 will be allocated
   by IANA Section 8.8.

5.6.  SFC Echo Reply Reception

   An SFF SHOULD NOT accept SFC Echo Reply unless the received passes
   the following checks:

   *  the received SFC Echo Reply is well-formed;

   *  it has an outstanding SFC Echo Request sent from the UDP port that
      matches destination UDP port number of the received packet;

   *  if the matching to the Echo Request found, the value of the
      Sender's Handle in the Echo Request sent is equal to the value of
      Sender's Handle in the Echo Reply received;

   *  if all checks passed, the SFF checks if the Sequence Number in the
      Echo Request sent matches to the Sequence Number in the Echo Reply
      received.








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5.7.  Tracing an SFP

   SFC Echo Request/Reply can be used to isolate a defect detected in
   the SFP and trace an RSP.  As for ICMP echo request/reply [RFC0792]
   and MPLS echo request/reply [RFC8029], this mode is referred to as
   "traceroute".  In the traceroute mode, the sender transmits a
   sequence of SFC Echo Request messages starting with the NSH TTL value
   set to 1 and is incremented by 1 in each next Echo Request packet.
   The sender stops transmitting SFC Echo Request packets when the
   Return Code in the received Echo Reply equals 5 ("End of the SFP").

   Suppose a specialized information element (e.g., IPv6 Flow Label
   [RFC6437] or Flow ID [I-D.ietf-sfc-nsh-tlv]) is used for distributing
   the load across Equal Cost Multi-Path or Link Aggregation Group
   paths.  In that case, such an element MAY also be used for the SFC
   OAM traffic.  Doing so is meant to control whether the SFC Echo
   Request follows the same RSP as the monitored flow.

6.  Security Considerations

   When the integrity protection for SFC active OAM, and SFC Echo
   Request/Reply in particular, is required, it is RECOMMENDED to use
   one of Context Headers defined in [I-D.ietf-sfc-nsh-integrity].
   MAC#1 (Message Authentication Code) Context Header could be more
   suitable for active SFC OAM because it does not require re-
   calculation of the MAC when the value of the NSH Base Header's TTL
   field is changed.  The integrity protection for SFC active OAM can
   also be achieved using mechanisms in the underlay data plane.  For
   example, if the underlay is an IPv6 network, IP Authentication Header
   [RFC4302] or IP Encapsulating Security Payload Header [RFC4303] can
   be used to provide integrity protection.  Confidentiality for the SFC
   Echo Request/Reply exchanges can be achieved using the IP
   Encapsulating Security Payload Header [RFC4303].  Also, the security
   needs for SFC Echo Request/Reply are similar to those of ICMP ping
   [RFC0792], [RFC4443] and MPLS LSP ping [RFC8029].

   There are at least three approaches to attacking a node in the
   overlay network using the mechanisms defined in the document.  One is
   a Denial-of-Service attack, sending an SFC Echo Request to overload
   an element of the SFC.  The second may use spoofing, hijacking,
   replying, or otherwise tampering with SFC Echo Requests and/or
   replies to misrepresent, alter the operator's view of the state of
   the SFC.  The third is an unauthorized source using an SFC Echo
   Request/Reply to obtain information about the SFC and/or its
   elements, e.g., SFF or SF.






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   It is RECOMMENDED that implementations throttle the SFC ping traffic
   going to the control plane to mitigate potential Denial-of-Service
   attacks.

   Reply and spoofing attacks involving faking or replying to SFC Echo
   Reply messages would have to match the Sender's Handle and Sequence
   Number of an outstanding SFC Echo Request message, which is highly
   unlikely.  Thus the non-matching reply would be discarded.

   To protect against unauthorized sources trying to obtain information
   about the overlay and/or underlay, an implementation MAY check that
   the source of the Echo Request is indeed part of the SFP.

7.  Acknowledgments

   Authors greatly appreciate thorough review and the most helpful
   comments from Dan Wing, Dirk von Hugo, and Mohamed Boucadair.

8.  IANA Considerations

8.1.  SFC Active OAM Protocol

   IANA is requested to assign a new type from the SFC Next Protocol
   registry as follows:

                +=======+================+===============+
                | Value |  Description   | Reference     |
                +=======+================+===============+
                | TBA1  | SFC Active OAM | This document |
                +-------+----------------+---------------+

                     Table 2: SFC Active OAM Protocol

8.2.  SFC Active OAM Message Type

   IANA is requested to create a new registry called "SFC Active OAM
   Message Type".  All code points in the range 1 through 32767 in this
   registry shall be allocated according to the "IETF Review" procedure
   specified in [RFC8126].  The remaining code points to be allocated
   according to Table 3:











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         +===============+=============+=========================+
         | Value         | Description | Reference               |
         +===============+=============+=========================+
         | 0             |   Reserved  |                         |
         +---------------+-------------+-------------------------+
         | 1 - 32767     |   Reserved  | IETF Consensus          |
         +---------------+-------------+-------------------------+
         | 32768 - 65530 |   Reserved  | First Come First Served |
         +---------------+-------------+-------------------------+
         | 65531 - 65534 |   Reserved  | Private Use             |
         +---------------+-------------+-------------------------+
         | 65535         |   Reserved  |                         |
         +---------------+-------------+-------------------------+

                    Table 3: SFC Active OAM Message Type

   IANA is requested to assign a new type from the SFC Active OAM
   Message Type registry as follows:

          +=======+=============================+===============+
          | Value |         Description         | Reference     |
          +=======+=============================+===============+
          | TBA2  | SFC Echo Request/Echo Reply | This document |
          +-------+-----------------------------+---------------+

                 Table 4: SFC Echo Request/Echo Reply Type

8.3.  SFC Echo Request/Echo Reply Parameters

   IANA is requested to create a new SFC Echo Request/Echo Reply
   Parameters registry.

8.4.  SFC Echo Request/Echo Reply Message Types

   IANA is requested to create in the SFC Echo Request/Echo Reply
   Parameters registry the new sub-registry Message Types.  All code
   points in the range 1 through 175 in this registry shall be allocated
   according to the "IETF Review" procedure specified in [RFC8126].
   Code points in the range 176 through 239 in this registry shall be
   allocated according to the "First Come First Served" procedure
   specified in [RFC8126].  The remaining code points are allocated
   according to Table 5: as specified in Table 5.









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               +===========+==============+===============+
               | Value     | Description  | Reference     |
               +===========+==============+===============+
               | 0         |   Reserved   | This document |
               +-----------+--------------+---------------+
               | 1- 175    |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 176 - 239 |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 240 - 251 | Experimental | This document |
               +-----------+--------------+---------------+
               | 252 - 254 | Private Use  | This document |
               +-----------+--------------+---------------+
               | 255       |   Reserved   | This document |
               +-----------+--------------+---------------+

                   Table 5: SFC Echo Request/Echo Reply
                              Message Types

   IANA is requested to assign values as listed in Table 6.

               +=======+==================+===============+
               | Value |   Description    | Reference     |
               +=======+==================+===============+
               | TBA3  | SFC Echo Request | This document |
               +-------+------------------+---------------+
               | TBA4  |  SFC Echo Reply  | This document |
               +-------+------------------+---------------+

                   Table 6: SFC Echo Request/Echo Reply
                           Message Types Values

8.5.  SFC Echo Reply Modes

   IANA is requested to create in the SFC Echo Request/Echo Reply
   Parameters registry the new sub-registry Reply Mode.  All code points
   in the range 1 through 175 in this registry shall be allocated
   according to the "IETF Review" procedure specified in [RFC8126].
   Code points in the range 176 through 239 in this registry shall be
   allocated according to the "First Come First Served" procedure
   specified in [RFC8126].  The remaining code points are allocated
   according to Table 7: as specified in Table 7.









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               +===========+==============+===============+
               | Value     | Description  | Reference     |
               +===========+==============+===============+
               | 0         |   Reserved   | This document |
               +-----------+--------------+---------------+
               | 1- 175    |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 176 - 239 |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 240 - 251 | Experimental | This document |
               +-----------+--------------+---------------+
               | 252 - 254 | Private Use  | This document |
               +-----------+--------------+---------------+
               | 255       |   Reserved   | This document |
               +-----------+--------------+---------------+

                       Table 7: SFC Echo Reply Mode

   All code points in the range 1 through 191 in this registry shall be
   allocated according to the "IETF Review" procedure specified in
   [RFC8126] and assign values as listed in Table 8.

      +=======+====================================+===============+
      | Value |            Description             | Reference     |
      +=======+====================================+===============+
      | 0     |              Reserved              |               |
      +-------+------------------------------------+---------------+
      | TBA5  |            Do Not Reply            | This document |
      +-------+------------------------------------+---------------+
      | TBA6  | Reply via an IPv4/IPv6 UDP Packet  | This document |
      +-------+------------------------------------+---------------+
      | TBA7  |    Reply via Application Level     | This document |
      |       |          Control Channel           |               |
      +-------+------------------------------------+---------------+
      | TBA8  |      Reply via Specified Path      | This document |
      +-------+------------------------------------+---------------+
      | TBA9  | Reply via an IPv4/IPv6 UDP Packet  | This document |
      |       | with the data integrity protection |               |
      +-------+------------------------------------+---------------+
      | TBA10 |    Reply via Application Level     | This document |
      |       |   Control Channel with the data    |               |
      |       |        integrity protection        |               |
      +-------+------------------------------------+---------------+
      | TBA11 | Reply via Specified Path with the  | This document |
      |       |     data integrity protection      |               |
      +-------+------------------------------------+---------------+

                   Table 8: SFC Echo Reply Mode Values



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8.6.  SFC Echo Return Codes

   IANA is requested to create in the SFC Echo Request/Echo Reply
   Parameters registry the new sub-registry Return Codes as described in
   Table 9.

            +=========+=============+=========================+
            | Value   | Description | Reference               |
            +=========+=============+=========================+
            | 0-191   |  Unassigned | IETF Review             |
            +---------+-------------+-------------------------+
            | 192-251 |  Unassigned | First Come First Served |
            +---------+-------------+-------------------------+
            | 252-254 |  Unassigned | Private Use             |
            +---------+-------------+-------------------------+
            | 255     |   Reserved  |                         |
            +---------+-------------+-------------------------+

                       Table 9: SFC Echo Return Codes

   Values defined for the Return Codes sub-registry are listed in
   Table 10.

        +=======+=================================+===============+
        | Value |           Description           | Reference     |
        +=======+=================================+===============+
        | 0     |          No Return Code         | This document |
        +-------+---------------------------------+---------------+
        | 1     | Malformed Echo Request received | This document |
        +-------+---------------------------------+---------------+
        | 2     | One or more of the TLVs was not | This document |
        |       |            understood           |               |
        +-------+---------------------------------+---------------+
        | 3     |      Authentication failed      | This document |
        +-------+---------------------------------+---------------+
        | 4     |           TTL Exceeded          | This document |
        +-------+---------------------------------+---------------+
        | 5     |          End of the SFP         | This document |
        +-------+---------------------------------+---------------+

                   Table 10: SFC Echo Return Codes Values










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8.7.  SFC TLV Type

   IANA is requested to create the SFC OAM TLV Type registry.  All code
   points in the range 1 through 175 in this registry shall be allocated
   according to the "IETF Review" procedure specified in [RFC8126].
   Code points in the range 176 through 239 in this registry shall be
   allocated according to the "First Come First Served" procedure
   specified in [RFC8126].  The remaining code points are allocated
   according to Table 11:

               +===========+==============+===============+
               | Value     | Description  | Reference     |
               +===========+==============+===============+
               | 0         |   Reserved   | This document |
               +-----------+--------------+---------------+
               | 1- 175    |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 176 - 239 |  Unassigned  | This document |
               +-----------+--------------+---------------+
               | 240 - 251 | Experimental | This document |
               +-----------+--------------+---------------+
               | 252 - 254 | Private Use  | This document |
               +-----------+--------------+---------------+
               | 255       |   Reserved   | This document |
               +-----------+--------------+---------------+

                   Table 11: SFC OAM TLV Type Registry

   This document defines the following new values in SFC OAM TLV Type
   registry:

              +=======+====================+===============+
              | Value |    Description     | Reference     |
              +=======+====================+===============+
              | TBA12 | Multiple TLVs Used | This document |
              +-------+--------------------+---------------+
              | TBA13 |   Source ID TLV    | This document |
              +-------+--------------------+---------------+
              | TBA14 |    Errored TLVs    | This document |
              +-------+--------------------+---------------+

                      Table 12: SFC OAM Type Values

8.8.  SFC OAM UDP Port

   IANA is requested to allocate UDP port number according to





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   +=============+============+===================+============+=====================+=============+
   |Service Name |Port Number |Transport Protocol |Description |Semantics Definition |Reference    |
   +=============+============+===================+============+=====================+=============+
   |SFC OAM      |TBA15       |UDP                |SFC OAM Echo|Section 5.5          |This document|
   |             |            |                   |Reply       |                     |             |
   +-------------+------------+-------------------+------------+---------------------+-------------+

                           Table 13: SFC OAM Port

9.  References

9.1.  Normative References

   [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>.

   [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>.

9.2.  Informative References

   [I-D.ao-sfc-oam-return-path-specified]
              Mirsky, G., Ao, T., Chen, Z., and G. Mishra, "Controlled
              Return Path for Service Function Chain (SFC) OAM", Work in
              Progress, Internet-Draft, draft-ao-sfc-oam-return-path-
              specified-09, 30 March 2021, <https://tools.ietf.org/html/
              draft-ao-sfc-oam-return-path-specified-09>.

   [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>.








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   [I-D.ietf-sfc-nsh-tlv]
              Wei, Y. (., Elzur, U., Majee, S., and C. Pignataro,
              "Network Service Header Metadata Type 2 Variable-Length
              Context Headers", Work in Progress, Internet-Draft, draft-
              ietf-sfc-nsh-tlv-06, 12 May 2021,
              <https://tools.ietf.org/html/draft-ietf-sfc-nsh-tlv-06>.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <https://www.rfc-editor.org/info/rfc792>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [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>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [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>.







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   [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>.

   [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>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

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


   Wei Meng
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing,
   China

   Email: meng.wei2@zte.com.cn


   Bhumip Khasnabish
   Individual contributor

   Email: vumip1@gmail.com


   Cui Wang
   Individual contributor

   Email: lindawangjoy@gmail.com













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