Service Function Chaining (SFC) Operations, Administration and Maintenance (OAM) Framework
draft-ietf-sfc-oam-framework-15

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Internet Engineering Task Force                                S. Aldrin
Internet-Draft                                                    Google
Intended status: Informational                         C. Pignataro, Ed.
Expires: November 26, 2020                                 N. Kumar, Ed.
                                                                   Cisco
                                                             R. Krishnan
                                                                  VMware
                                                             A. Ghanwani
                                                                    Dell
                                                            May 25, 2020

                    Service Function Chaining (SFC)
       Operations, Administration and Maintenance (OAM) Framework
                    draft-ietf-sfc-oam-framework-15

Abstract

   This document provides a reference framework for Operations,
   Administration and Maintenance (OAM) for Service Function Chaining
   (SFC).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on November 26, 2020.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Document Scope  . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Acronyms and Terminology  . . . . . . . . . . . . . . . .   4
       1.2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . .   4
       1.2.2.  Terminology . . . . . . . . . . . . . . . . . . . . .   5
   2.  SFC Layering Model  . . . . . . . . . . . . . . . . . . . . .   5
   3.  SFC OAM Components  . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  The SF Component  . . . . . . . . . . . . . . . . . . . .   8
       3.1.1.  SF Availability . . . . . . . . . . . . . . . . . . .   8
       3.1.2.  SF Performance Measurement  . . . . . . . . . . . . .   9
     3.2.  The SFC Component . . . . . . . . . . . . . . . . . . . .   9
       3.2.1.  SFC Availability  . . . . . . . . . . . . . . . . . .   9
       3.2.2.  SFC Performance Measurement . . . . . . . . . . . . .  10
     3.3.  Classifier Component  . . . . . . . . . . . . . . . . . .  10
     3.4.  Underlay Network  . . . . . . . . . . . . . . . . . . . .  10
     3.5.  Overlay Network . . . . . . . . . . . . . . . . . . . . .  10
   4.  SFC OAM Functions . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Connectivity Functions  . . . . . . . . . . . . . . . . .  11
     4.2.  Continuity Functions  . . . . . . . . . . . . . . . . . .  11
     4.3.  Trace Functions . . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Performance Measurement Functions . . . . . . . . . . . .  12
   5.  Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Existing OAM Functions  . . . . . . . . . . . . . . . . .  13
     5.2.  Missing OAM Functions . . . . . . . . . . . . . . . . . .  14
     5.3.  Required OAM Functions  . . . . . . . . . . . . . . . . .  14
   6.  Operational Aspects of SFC OAM at the Service Layer . . . . .  14
     6.1.  SFC OAM Packet Marker . . . . . . . . . . . . . . . . . .  14
     6.2.  OAM Packet Processing and Forwarding Semantic . . . . . .  15
     6.3.  OAM Function Types  . . . . . . . . . . . . . . . . . . .  16
   7.  Candidate SFC OAM Tools . . . . . . . . . . . . . . . . . . .  16
     7.1.  ICMP  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.2.  BFD/Seamless-BFD  . . . . . . . . . . . . . . . . . . . .  16
     7.3.  In-Situ OAM . . . . . . . . . . . . . . . . . . . . . . .  17
     7.4.  SFC Traceroute  . . . . . . . . . . . . . . . . . . . . .  17
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  18
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   12. Contributing Authors  . . . . . . . . . . . . . . . . . . . .  20
   13. Informative References  . . . . . . . . . . . . . . . . . . .  20

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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Service Function Chaining (SFC) enables the creation of composite
   services that consist of an ordered set of Service Functions (SF)
   that are to be applied to any traffic selected as a result of
   classification [RFC7665].  SFC is a concept that provides for more
   than just the application of an ordered set of SFs to selected
   traffic; rather, it describes a method for deploying SFs in a way
   that enables dynamic ordering and topological independence of those
   SFs as well as the exchange of metadata between participating
   entities.  The foundations of SFC are described in the following
   documents:

   o  SFC Problem Statement [RFC7498]

   o  SFC Architecture [RFC7665]

   The reader is assumed to be familiar with the material in [RFC7665].

   This document provides a reference framework for Operations,
   Administration and Maintenance (OAM, [RFC6291]) of SFC.
   Specifically, this document provides:

   o  In Section 2, an SFC layering model;

   o  In Section 3, aspects monitored by SFC OAM;

   o  In Section 4, functional requirements for SFC OAM;

   o  In Section 5, a gap analysis for SFC OAM.

   o  In Section 6, operational aspects of SFC OAM at the service layer.

   o  In Section 7, applicability of various OAM tools.

   o  In Section 8, manageability considerations for SF and SFC.

   SFC OAM solution documents should refer to this document to indicate
   the SFC OAM component and the functionality they target.

   OAM controllers are SFC-aware network devices that are capable of
   generating OAM packets.  They should be within the same
   administrative domain as the target SFC enabled domain.

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1.1.  Document Scope

   The focus of this document is to provide an architectural framework
   for SFC OAM, particularly focused on the aspect of the Operations
   component within OAM.  Actual solutions and mechanisms are outside
   the scope of this document.

1.2.  Acronyms and Terminology

1.2.1.  Acronyms

   SFC: Service Function Chain

   SFF: Service Function Forwarder

   SF: Service Function

   SFP: Service Function Path

   RSP: Rendered Service Path

   NSH: Network Service Header

   VM: Virtual Machines

   OAM: Operations, Administration and Maintenance

   IPPM: IP Performance Measurement

   BFD: Bidirectional Forwarding Detection

   NVO3: Network Virtualization over Layer3

   SNMP: Simple Network Management Protocol

   NETCONF: Network Configuration Protocol

   E-OAM: Ethernet OAM

   MPLS_PM: MPLS Performance Measurement

   POS: Packet over SONET

   DWDM: Dense Wavelength Division Multiplexing

   hSFC: Hierarchical Service Function Chaining

   IBN: Internal Boundary Node

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   MPLS: Multiprotocol Label Switching

   TRILL: Transparent Interconnection of Lots of Links

   CLI: Command Line Interface

1.2.2.  Terminology

   This document uses the terminologies defined in [RFC7665], [RFC8300],
   and so the readers are expected to be familiar with the
   terminologies.

2.  SFC Layering Model

   Multiple layers come into play for implementing the SFC.  These
   include the service layer and the underlying layers (Network Layer,
   Link Layer, etc.).

   o  The service layer, which consists of SFC data plane elements that
      includes classifiers, Service Functions (SF), Service Function
      Forwarders (SFF), and SFC Proxies.  This layer uses the overlay
      network layer for ensuring connectivity between SFC data plane
      elements.

   o  The overlay network layer, which leverages various overlay network
      technologies (e.g., VxLAN)interconnecting SFC data plane elements
      and allows establishing Service Function Paths (SFPs).  This layer
      is mostly transparent to the SFC data plane elements as not all
      the data plane elements process the overlay header.

   o  The underlay network layer, which is dictated by the networking
      technology deployed within a network (e.g., IP, MPLS)

   o  The link layer, which is tightly coupled with the physical
      technology used.  Ethernet is one such choice for this layer, but
      other alternatives are deployed (e.g.  POS, DWDM).  In a virtual
      environment, virtualized I/O technologies such as SR-IOV or
      similar are also applicable for this layer.  The same or distinct
      link layer technologies may be used in each leg shown in Figure 1.

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      o----------------------Service Layer----------------------o

   +------+   +---+   +---+   +---+   +---+   +---+   +---+   +---+
   |Classi|---|SF1|---|SF2|---|SF3|---|SF4|---|SF5|---|SF6|---|SF7|
   |fier  |   +---+   +---+   +---+   +---+   +---+   +---+   +---+
   +------+
                <------VM1------>       <--VM2-->       <--VM3-->

      ^-----------------^-------------------^---------------^  Overlay
                                                               Network

      o-----------------o-------------------o---------------o  Underlay
                                                               Network

      o--------o--------o--------o----------o-------o-------o  Link

                Figure 1: SFC Layering Example

   In Figure 1, the service layer elements such as classifier and SF are
   depicted as virtual entities that are interconnected using an overlay
   network.  The underlay network may comprise multiple intermediate
   nodes not shown in the figure that provide underlay connectivity
   between the service layer elements.

   While Figure 1 depicts an example where SFs are enabled as virtual
   entities, the SFC architecture does not make any assumptions on how
   the SFC data plane elements are deployed.  The SFC architecture is
   flexible and accommodates physical or virtual entity deployment.  SFC
   OAM accounts for this flexibility and accordingly it is applicable
   whether SFC data plane elements are deployed directly on physical
   hardware, as one or more Virtual entities, or any combination
   thereof.

3.  SFC OAM Components

   The SFC operates at the service layer.  For the purpose of defining
   the OAM framework, the service layer is broken up into three distinct
   components:

   1.  SF component: OAM functions applicable at this component include
       testing the SFs from any SFC-aware network device (e.g.,
       classifiers, controllers, other service nodes).  Testing an SF
       may be more expansive than just checking connectivity to the SF
       such as checking if the SF is providing its intended service.
       Refer to Section 3.1.1 for a more detailed discussion.

   2.  SFC component: OAM functions applicable at this component include
       (but are not limited to) testing the service function chains and

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       the SFPs, validation of the correlation between an SFC and the
       actual forwarding path followed by a packet matching that SFC,
       i.e. the Rendered Service Path (RSP).  Some of the hops of an SFC
       may not be visible when Hierarchical Service Function Chaining
       (hSFC) [RFC8459] is in use.  In such schemes, it is the
       responsibility of the Internal Boundary Node (IBN) to glue the
       connectivity between different levels for end-to-end OAM
       functionality.

   3.  Classifier component: OAM functions applicable at this component
       include testing the validity of the classification rules and
       detecting any incoherence among the rules installed when more
       than one classifier is used as explained in Section 2.2 of
       [RFC7665] .

   Figure 2 illustrates an example where OAM for the three defined
   components are used within the SFC environment.

 +-Classifier  +-Service Function Chain OAM
 | OAM         |
 |             |        ___________________________________________
 |              \      /\          Service Function Chain          \
 |               \    /  \      +---+      +---+     +-----+  +---+ \
 |                \  /    \     |SF1|      |SF2|     |Proxy|--|SF3|  \
 |      +------+   \/      \    +---+      +---+     +-----+  +---+   \
 +----> |      |....(+->    )     |          |         |               )
        |Classi|    \      /   +-----+    +-----+    +-----+          /
        |fier  |     \    /    | SFF1|----| SFF2|----| SFF3|         /
        |      |      \  /     +--^--+    +-----+    +-----+        /
        +----|-+       \/_________|________________________________/
             |                    |
             +-------SF_OAM-------+
                                      +---+   +---+
                              +SF_OAM>|SF3|   |SF5|
                              |       +-^-+   +-^-+
                       +------|---+     |       |
                       |Controller|     +-SF_OAM+
                       +----------+
                            Service Function OAM (SF_OAM)

              Figure 2: SFC OAM Components

   It is expected that multiple SFC OAM solutions will be defined, each
   targeting one specific component of the service layer.  However, it
   is critical that SFC OAM solutions together provide the coverage of
   all three SFC OAM components: the SF component, the SFC component,
   and the classifier component.

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3.1.  The SF Component

3.1.1.  SF Availability

   One SFC OAM requirement for the SF component is to allow an SFC-aware
   network device to check the availability of a specific SF (instance),
   located on the same or different network device(s).  For cases where
   multiple instances of an SF are used to realize a given SF for the
   purpose of load sharing, SF availability can be performed by checking
   the availability of any one of those instances, or the availability
   check may be targeted at a specific instance.  SF availability is an
   aspect that raises an interesting question: How does one determine
   that a service function is available?  On one end of the spectrum,
   one might argue that an SF is sufficiently available if the service
   node (physical or virtual) hosting the SF is available and is
   functional.  On the other end of the spectrum, one might argue that
   the SF's availability can only be concluded if the packet, after
   passing through the SF, was examined and it was verified that the
   packet did indeed get the expected service.

   The former approach will likely not provide sufficient confidence to
   the actual SF availability, i.e. a service node and an SF are two
   different entities.  The latter approach is capable of providing an
   extensive verification, but comes at a cost.  Some SFs make direct
   modifications to packets, while others do not.  Additionally, the
   purpose of some SFs may be to, conditionally, drop packets
   intentionally.  In such cases, it is normal behavior that certain
   packets will not be egressing out from the service function.  The OAM
   mechanism needs to take into account such SF specifics when assessing
   SF availability.  Note that there are many flavors of SFs available,
   and many more that are likely be introduced in future.  Even a given
   SF may introduce a new functionality (e.g., a new signature in a
   firewall).  The cost of this approach is that the OAM mechanism for
   some SF will need to be continuously modified in order to "keep up"
   with new functionality being introduced: lack of extensibility.

   The SF availability check can be performed using a generalized
   approach (i.e., an adequate granularity to provide a basic SF
   service).  The task of evaluating the true availability of a Service
   Function is a complex activity, currently having no simple, unified
   solution.  There is currently no standard means of doing so.  Any
   such mechanism would be far from a typical OAM function, so it is not
   explored as part of the analysis in Sections 4 and 5.

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3.1.2.  SF Performance Measurement

   The second SFC OAM requirement for the SF component is to allow an
   SFC-aware network device to check the performance metrics such as
   loss and delay induced by a specific SF for processing legitimate
   traffic.  The performance can be a passive measurement by using live
   traffic, an active measurement by using synthetic probe packets or
   can be a hybrid method that use a combination of active and passive
   measurement.  More details about this OAM function is explained in
   Section 4.4.

   On the one hand, the performance of any specific SF can be quantified
   by measuring the loss and delay metrics of the traffic from SFF to
   the respective SF, while on the other hand, the performance can be
   measured by leveraging the loss and delay metrics from the respective
   SFs.  The latter requires SF involvement to perform the measurement
   while the former does not.  For cases where multiple instances of an
   SF are used to realize a given SF for the purpose of load sharing, SF
   performance can be quantified by measuring the metrics for any one
   instance of SF or by measuring the metrics for a specific instance.

   The metrics measured to quantify the performance of the SF component
   are not just limited to loss and delay.  Other metrics such as
   throughput also exist and the choice of metrics for performance
   measurement is outside the scope of this document.

3.2.  The SFC Component

3.2.1.  SFC Availability

   An SFC could comprise varying SFs and so the OAM layer is required to
   perform validation and verification of SFs within an SFP, in addition
   to connectivity verification and fault isolation.

   In order to perform service connectivity verification of an SFC/SFP,
   the OAM functions could be initiated from any SFC-aware network
   device of an SFC-enabled domain for end-to-end paths, or partial
   paths terminating on a specific SF, within the SFC/SFP.  The goal of
   this OAM function is to ensure the SFs chained together have
   connectivity as was intended at the time when the SFC was
   established.  The necessary return codes should be defined for
   sending back in the response to the OAM packet, in order to complete
   the verification.

   When ECMP is in use at the service layer for any given SFC, there
   must be the ability to discover and traverse all available paths.

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   A detailed explanation of the mechanism is outside the scope of this
   document and is expected to be included in the actual solution
   document.

3.2.2.  SFC Performance Measurement

   Any SFC-aware network device should have the ability to make
   performance measurements over the entire SFC (i.e., end-to-end) or to
   a specific segment of SFs within the SFC.

3.3.  Classifier Component

   A classifier maintains the classification rules that map a flow to a
   specific SFC.  It is vital that the classifier is correctly
   configured with updated classification rules and is functioning as
   expected.  The SFC OAM must be able to validate the classification
   rules by assessing whether a flow is appropriately mapped to the
   relevant SFC and detect any misclassification.  Sample OAM packets
   can be presented to the classifiers to assess the behavior with
   regard to a given classification entry.

   The classifier availability check may be performed to check the
   availability of the classifier to apply the rules and classify the
   traffic flows.  Any SFC-aware network device should have the ability
   to perform availability checking of the classifier component for each
   SFC.

   Any SFC-aware network device should have the ability to perform
   performance measurement of the classifier component for each SFC.
   The performance can be quantified by measuring the performance
   metrics of the traffic from the classifier for each SFC/SFP.

3.4.  Underlay Network

   The underlay network provides connectivity between the SFC components
   so the availability or the performance of the underlay network
   directly impacts the SFC OAM.

   Any SFC-aware network device may have the ability to perform
   availability check or performance measurement of the underlay network
   using any existing OAM functions listed in Section 5.1.

3.5.  Overlay Network

   The overlay network provides connectivity for service plane between
   the SFC components and is mostly transparent to the SFC data plane
   elements.

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   Any SFC-aware network device may have the ability to perform
   availability check or performance measurement of the overlay network
   using any existing OAM functions listed in Section 5.1.

4.  SFC OAM Functions

   Section 3 described SFC OAM components and the associated OAM
   operations on each of them.  This section explores SFC OAM functions
   that are applicable for more than one SFC component.

   The various SFC OAM requirements listed in Section 3 highlighted the
   need for various OAM functions at the service layer.  As listed in
   Section 5.1, various OAM functions are in existence that are defined
   to perform OAM functionality at different layers.  In order to apply
   such OAM functions at the service layer, they need to be enhanced to
   operate a single SF/SFF to multiple SFs/SFFs spanning across one or
   more SFCs.

4.1.  Connectivity Functions

   Connectivity is mainly an on-demand function to verify that the
   connectivity exists between certain network elements and that the SFs
   are available.  For example, LSP Ping [RFC8029] is a common tool used
   to perform this function for an MPLS network.  Some of the OAM
   functions performed by connectivity functions are as follows:

   o  Verify the Path MTU from a source to the destination SF or through
      the SFC.  This requires the ability for the OAM packet to be of
      variable length.

   o  Detect any packet re-ordering and corruption.

   o  Verify that an SFC or SF is applying the expected policy.

   o  Verification and validation of forwarding paths.

   o  Proactively test alternate or protected paths to ensure
      reliability of network configurations.

4.2.  Continuity Functions

   Continuity is a model where OAM messages are sent periodically to
   validate or verify the reachability of a given SF within an SFC or
   for the entire SFC.  This allows a monitoring network device (such as
   the classifier or controller) to quickly detect failures such as link
   failures, network element failures, SF outages, or SFC outages.  BFD
   [RFC5880] is one such function which helps in detecting failures

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   quickly.  OAM functions supported by continuity functions are as
   follows:

   o  Ability to provision a continuity check to a given SF within an
      SFC or for the entire SFC.

   o  Proactively test alternate or protected paths to ensure
      reliability of network configurations.

   o  Notifying other OAM functions or applications of the detected
      failures so they can take appropriate action.

4.3.  Trace Functions

   Tracing is an OAM function that allows the operation to trigger an
   action (e.g. response generation) from every transit device (e.g.
   SFF, SF, SFC Proxy) on the tested layer.  This function is typically
   useful for gathering information from every transit device or for
   isolating the failure point to a specific SF within an SFC or for an
   entire SFC.  Some of the OAM functions supported by trace functions
   are:

   o  Ability to trigger an action from every transit device at the SFC
      layer, using TTL or other means.

   o  Ability to trigger every transit device at the SFC layer to
      generate a response with OAM code(s), using TTL or other means.

   o  Ability to discover and traverse ECMP paths within an SFC.

   o  Ability to skip SFs that do not support OAM while tracing SFs in
      an SFC.

4.4.  Performance Measurement Functions

   Performance measurement functions involve measuring of packet loss,
   delay, delay variance, etc.  These performance metrics may be
   measured pro-actively or on-demand.

   SFC OAM should provide the ability to measure packet loss for an SFC.
   On-demand measurement can be used to estimate packet loss using
   statistical methods.  To ensure accurate estimations, one needs to
   ensure that OAM packets are treated the same and also share the same
   fate as regular data traffic.

   Delay within an SFC could be measured based on the time it takes for
   a packet to traverse the SFC from the ingress SFC node to the egress
   SFF.  Measurement protocols such as One-way Active Measurement

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   Protocol (OWAMP) [RFC4656] and Two-way Active Measurement Protocol
   (TWAMP) [RFC5357] can be used to measure the characteristics.  As
   SFCs are unidirectional in nature, measurement of one-way delay
   [RFC7679] is important.  In order to measure one-way delay, time
   synchronization must be supported by means such as NTP, GPS,
   Precision Time Protocol (PTP), etc.

   One-way delay variation [RFC3393] could also be calculated by sending
   OAM packets and measuring the jitter for traffic passing through an
   SFC.

   Some of the OAM functions supported by the performance measurement
   functions are:

   o  Ability to measure the packet processing delay induced by a single
      SF or the one-way delay to traverse an SFP bound to a given SFC.

   o  Ability to measure the packet loss [RFC7680] within an SF or an
      SFP bound to a given SFC.

5.  Gap Analysis

   This section identifies various OAM functions available at different
   layers introduced in Section 2.  It also identifies various gaps that
   exist within the current toolset for performing OAM functions
   required for SFC.

5.1.  Existing OAM Functions

   There are various OAM tool sets available to perform OAM functions
   within various layers.  These OAM functions may be used to validate
   some of the underlay and overlay networks.  Tools like ping and trace
   are in existence to perform connectivity check and tracing of
   intermediate hops in a network.  These tools support different
   network types like IP, MPLS, TRILL, etc.  Ethernet OAM (E-OAM)
   [Y.1731] [EFM] and Connectivity Fault Management (CFM) [DOT1Q] offer
   OAM mechanisms such as an Ethernet continuity check for Ethernet
   links.  There is an effort around NVO3 OAM to provide connectivity
   and continuity checks for networks that use NVO3.  BFD is used for
   the detection of data plane forwarding failures.  The IPPM framework
   [RFC2330] offers tools such as OWAMP [RFC4656] and TWAMP [RFC5357]
   (collectively referred as IPPM in this section) to measure various
   performance metrics.  MPLS Packet Loss Measurement (LM) and Packet
   Delay Measurement (DM) (collectively referred as MPLS_PM in this
   section) [RFC6374] offers the ability to measure performance metrics
   in MPLS network.  There is also an effort to extend the tool set to
   provide connectivity and continuity checks within overlay networks.

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   BFD is another tool which helps in detecting data forwarding
   failures.  Table 3 below is not exhaustive.

                    Table 3: OAM Tool GAP Analysis
   +----------------+--------------+-------------+--------+------------+
   | Layer          | Connectivity |  Continuity |  Trace | Performance|
   +----------------+--------------+-------------+--------+------------+
   | Underlay N/w   | Ping         |E-OAM, BFD   |  Trace | IPPM,      |
   |                |              |             |        | MPLS_PM    |
   +----------------+--------------+-------------+--------+------------+
   | Overlay N/w    | Ping         | BFD,        |        |            |
   |                |              | NVO3 OAM    | Trace  | IPPM       |
   +----------------+--------------+-------------+--------+------------+
   | Classifier     | Ping         | BFD         | Trace  | None       |
   +----------------+--------------+-------------+--------+------------+
   | SF             | None         | None        | None   | None       |
   +----------------+--------------+-------------+--------+------------+
   | SFC            | None         | None        | None   | None       |
   +----------------+--------------+-------------+--------+------------+

5.2.  Missing OAM Functions

   As shown in Table 3, there are no standards-based tools available at
   the time of this writing that can be used natively (i.e. without
   enhancement) for the verification of SFs and SFCs.

5.3.  Required OAM Functions

   Primary OAM functions exist for underlying layers.  Tools like ping,
   trace, BFD, etc. exist in order to perform these OAM functions.

   As depicted in Table 3, toolsets and solutions are required to
   perform the OAM functions at the service layer.

6.  Operational Aspects of SFC OAM at the Service Layer

   This section describes the operational aspects of SFC OAM at the
   service layer to perform the SFC OAM function defined in Section 4
   and analyzes the applicability of various existing OAM toolsets in
   the service layer.

6.1.  SFC OAM Packet Marker

   SFC OAM messages should be encapsulated with necessary SFC header and
   with OAM markings when testing the SFC component.  SFC OAM messages

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   may be encapsulated with the necessary SFC header and with OAM
   markings when testing the SF component.

   The SFC OAM function described in Section 4 performed at the service
   layer or overlay network layer must mark the packet as an OAM packet
   so that relevant nodes can differentiate an OAM packet from data
   packets.  The base header defined in Section 2.2 of [RFC8300] assigns
   a bit to indicate OAM packets.  When NSH encapsulation is used at the
   service layer, the O bit must be set to differentiate the OAM packet.
   Any other overlay encapsulations used at the service layer must have
   a way to mark the packet as OAM packet.

6.2.  OAM Packet Processing and Forwarding Semantic

   Upon receiving an OAM packet, SFC-aware SFs may choose to discard the
   packet if it does not support OAM functionality or if the local
   policy prevents them from processing the OAM packet.  When an SF
   supports OAM functionality, it is desirable to process the packet and
   provide an appropriate response to allow end-to-end verification.  To
   limit performance impact due to OAM, SFC-aware SFs should rate limit
   the number of OAM packets processed.

   An SFF may choose not to forward the OAM packet to an SF if the SF
   does not support OAM or if the policy does not allow to forward OAM
   packets to an SF.  The SFF may choose to skip the SF, modify the
   header and forward to the next SFC node in the chain.  It should be
   noted that skipping an SF might have implications on some OAM
   functions (e.g. the delay measurement may not be accurate).  The
   method by which an SFF detects if the connected SF supports or is
   allowed to process OAM packets is outside the scope of this document.
   It could be a configuration parameter instructed by the controller or
   it can be done by dynamic negotiation between the SF and SFF.

   If the SFF receiving the OAM packet bound to a given SFC is the last
   SFF in the chain, it must send a relevant response to the initiator
   of the OAM packet.  Depending on the type of OAM solution and tool
   set used, the response could be a simple response (such as ICMP
   reply) or could include additional data from the received OAM packet
   (like statistical data consolidated along the path).  The details are
   expected to be covered in the solution documents.

   Any SFC-aware node that initiates an OAM packet must set the OAM
   marker in the overlay encapsulation.

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6.3.  OAM Function Types

   As described in Section 4, there are different OAM functions that may
   require different OAM solutions.  While the presence of the OAM
   marker in the overlay header (e.g., O bit in the NSH header)
   indicates it as an OAM packet, it is not sufficient to indicate what
   OAM function the packet is intended for.  The Next Protocol field in
   the NSH header may be used to indicate what OAM function is intended
   or what toolset is used.  Any other overlay encapsulations used at
   the service layer must have a similar way to indicate the intended
   OAM function.

7.  Candidate SFC OAM Tools

   As described in Section 5.1, there are different tool sets available
   to perform OAM functions at different layers.  This section describe
   the applicability of some of the available toolsets in the service
   layer.

7.1.  ICMP

   [RFC0792] and [RFC4443] describe the use of ICMP in IPv4 and IPv6
   networks respectively.  It explains how ICMP messages can be used to
   test the network reachability between different end points and
   perform basic network diagnostics.

   ICMP could be leveraged for connectivity functions (defined in
   Section 4.1) to verify the availability of an SF or SFC.  The
   Initiator can generate an ICMP echo request message and control the
   service layer encapsulation header to get the response from the
   relevant node.  For example, a classifier initiating OAM can generate
   an ICMP echo request message, can set the TTL field in the NSH header
   [RFC8300] to 63 to get the response from the last SFF, and thereby
   test the SFC availability.  Alternatively, the initiator can set the
   TTL to some other value to get the response from a specific SFs and
   thereby partially test SFC availability or the initiator could send
   OAM packets with sequentially incrementing TTL in the NSH to trace
   the SFP.

   It could be observed that ICMP at its current stage may not be able
   to perform all required SFC OAM functions, but as explained above, it
   can be used for some of the connectivity functions.

7.2.  BFD/Seamless-BFD

   [RFC5880] defines the Bidirectional Forwarding Detection (BFD)
   mechanism for failure detection.  [RFC5881] and [RFC5884] define the
   applicability of BFD in IPv4, IPv6 and MPLS networks.  [RFC7880]

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   defines Seamless BFD (S-BFD), a simplified mechanism of using BFD.
   [RFC7881] explains its applicability in IPv4, IPv6 and MPLS network.

   BFD or S-BFD could be leveraged to perform the continuity function
   for SF or SFC.  An initiator could generate a BFD control packet and
   set the "Your Discriminator" value to identify the last SFF in the
   control packet.  Upon receiving the control packet, the last SFF in
   the SFC will reply back with the relevant DIAG code.  The TTL field
   in the NSH header could be used to perform a partial SFC availability
   check.  For example, the initiator can set the "Your Discriminator"
   value to identify the SF that is intended to be tested and set the
   TTL field in the NSH header in a way that it expires at the relevant
   SF.  How the initiator gets the Discriminator value to identify the
   SF is outside the scope of this document.

7.3.  In-Situ OAM

   [I-D.ietf-sfc-ioam-nsh] defines how In-Situ OAM data fields
   [I-D.ietf-ippm-ioam-data] are transported using the NSH header.
   [I-D.ietf-sfc-proof-of-transit] defines a mechanism to perform proof
   of transit to securely verify if a packet traversed the relevant SFP
   or SFC.  While the mechanism is defined inband (i.e., it will be
   included in data packets), IOA Option-Types such as IOAM Trace
   Option-Types can also be used to perform other SFC OAM function such
   as SFC tracing.

   In-Situ OAM could be leveraged to perform SF availability and SFC
   availability or performance measurement.  For example, if SFC is
   realized using NSH, the O-bit in the NSH header could be set to
   indicate the OAM traffic as defined in Section 4.2
   [I-D.ietf-sfc-ioam-nsh].

7.4.  SFC Traceroute

   [I-D.penno-sfc-trace] defines a protocol that checks for path
   liveliness and traces the service hops in any SFP.  Section 3 of
   [I-D.penno-sfc-trace] defines the SFC trace packet format while
   Sections 4 and 5 of [I-D.penno-sfc-trace] defines the behavior of SF
   and SFF respectively.  While [I-D.penno-sfc-trace] has expired, the
   proposal is implemented in Open Daylight and is available.

   An initiator can control the Service Index Limit (SIL) in SFC trace
   packet to perform SF and SFC availability test.

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8.  Manageability Considerations

   This document does not define any new manageability tools but
   consolidates the manageability tool gap analysis for SF and SFC.
   Table 4 below is not exhaustive.

                   Table 4: OAM Tool GAP Analysis
  +----------------+--------------+-------------+--------+-------------+
  | Layer          |Configuration |Orchestration|Topology|Notification |
  +----------------+--------------+-------------+--------+-------------+
  | Underlay N/w   |CLI, NETCONF  | CLI, NETCONF| SNMP   |SNMP, Syslog,|
  |                |              |             |        |NETCONF      |
  +----------------+--------------+-------------+--------+-------------+
  | Overlay N/w    |CLI, NETCONF  | CLI, NETCONF| SNMP   |SNMP, Syslog |
  |                |              |             |        |NETCONF      |
  +----------------+--------------+-------------+--------+-------------+
  | Classifier     |CLI, NETCONF  | CLI, NETCONF| None   | None        |
  +----------------+--------------+-------------+--------+-------------+
  | SF             |CLI, NETCONF  | CLI, NETCONF| None   | None        |
  +----------------+--------------+-------------+--------+-------------+
  | SFC            |CLI, NETCONF  | CLI, NETCONF| None   | None        |
  +----------------+--------------+-------------+--------+-------------+

   Configuration, orchestration and other manageability tasks of SF and
   SFC could be performed using CLI, NETCONF [RFC6241] , etc.

   While the NETCONF capabilities are readily available as depicted in
   Table 4, the information and data models are needed for
   configuration, manageability and orchestration for SFC.  With
   virtualized SF and SFC, manageability needs to be done
   programmatically.

9.  Security Considerations

   Any security considerations defined in [RFC7665] and [RFC8300] is
   applicable for this document.

   The OAM information from the service layer at different components
   may collectively or independently reveal sensitive information.  The
   information may reveal the type of service functions hosted in the
   network, the classification rules and the associated service chains,
   specific service function paths, etc.  The sensitivity of the
   information from the SFC layer raises a need for careful security
   considerations.

   The mapping and the rules information at the classifier component may
   reveal the traffic rules and the traffic mapped to the SFC.  The SFC

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   information collected at an SFC component may reveal the SFs
   associated within each chain and this information together with
   classifier rules may be used to manipulate the header of synthetic
   attack packets that may be used to bypass the SFC and trigger any
   internal attacks.

   The SF information at the SF component may be used by a malicious
   user to trigger Denial of Service (DoS) attack by overloading any
   specific SF using rogue OAM traffic.

   To address the above concerns, SFC and SF OAM should provide
   mechanisms for mitigating:

   o  Misuse of the OAM channel for denial-of-services,

   o  Leakage of OAM packets across SFC instances, and

   o  Leakage of SFC information beyond the SFC domain.

   The documents proposing the OAM solution for SF components should
   provide rate-limiting the OAM probes at a frequency guided by the
   implementation choice.  Rate-limiting may be applied at the
   Classifier, SFF or the SF . The OAM initiator may not receive a
   response for the probes that are rate-limited resulting in false
   negatives and the implementation should be aware of this.  To
   mitigate any attacks that leverage OAM packets, future documents
   proposing OAM solutions should describe the use of any technique to
   detect and mitigate anomalies and various security attacks.

   The documents proposing the OAM solution for any service layer
   components should consider some form of message filtering to control
   the OAM packets entering the administrative domain or prevent leaking
   any internal service layer information outside the administrative
   domain.

10.  IANA Considerations

   No action is required by IANA for this document.

11.  Acknowledgements

   We would like to thank Mohamed Boucadair, Adrian Farrel, Greg Mirsky,
   Tal Mizrahi, Martin Vigoureux, Tirumaleswar Reddy, Carlos Bernados,
   Martin Duke, Barry Leiba, Eric Vyncke, Roman Danyliw, Erik Kline,
   Benjamin Kaduk, Robert Wilton, Frank Brockner, Alvaro Retana, Murray
   Kucherawy, and Alissa Cooper for their review and comments.

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12.  Contributing Authors

   Nobo Akiya
   Ericsson
   Email: nobo.akiya.dev@gmail.com

13.  Informative References

   [DOT1Q]    IEEE, "Standard for Local and Metropolitan Area Networks--
              Bridges and Bridged Networks, IEEE Std 802.1Q-2014,
              November 2014".

   [EFM]      IEEE, "IEEE Standard for Ethernet (Clause 57 for
              Operations, Administration, and Maintenance), IEEE Std
              802.3-2018, June 2018".

   [I-D.ietf-ippm-ioam-data]
              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., remy@barefootnetworks.com, r., daniel.bernier@bell.ca,
              d., and J. Lemon, "Data Fields for In-situ OAM", draft-
              ietf-ippm-ioam-data-09 (work in progress), March 2020.

   [I-D.ietf-sfc-ioam-nsh]
              Brockners, F. and S. Bhandari, "Network Service Header
              (NSH) Encapsulation for In-situ OAM (IOAM) Data", draft-
              ietf-sfc-ioam-nsh-03 (work in progress), March 2020.

   [I-D.ietf-sfc-proof-of-transit]
              Brockners, F., Bhandari, S., Mizrahi, T., Dara, S., and S.
              Youell, "Proof of Transit", draft-ietf-sfc-proof-of-
              transit-04 (work in progress), November 2019.

   [I-D.penno-sfc-trace]
              Penno, R., Quinn, P., Pignataro, C., and D. Zhou,
              "Services Function Chaining Traceroute", draft-penno-sfc-
              trace-03 (work in progress), September 2015.

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

   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              DOI 10.17487/RFC2330, May 1998,
              <https://www.rfc-editor.org/info/rfc2330>.

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   [RFC3393]  Demichelis, C. and P. Chimento, "IP Packet Delay Variation
              Metric for IP Performance Metrics (IPPM)", RFC 3393,
              DOI 10.17487/RFC3393, November 2002,
              <https://www.rfc-editor.org/info/rfc3393>.

   [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>.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
              <https://www.rfc-editor.org/info/rfc4656>.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, DOI 10.17487/RFC5357, October 2008,
              <https://www.rfc-editor.org/info/rfc5357>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <https://www.rfc-editor.org/info/rfc5881>.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291,
              DOI 10.17487/RFC6291, June 2011,
              <https://www.rfc-editor.org/info/rfc6291>.

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

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,
              <https://www.rfc-editor.org/info/rfc7498>.

   [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>.

   [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Delay Metric for IP Performance Metrics
              (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
              2016, <https://www.rfc-editor.org/info/rfc7679>.

   [RFC7680]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Loss Metric for IP Performance Metrics
              (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
              2016, <https://www.rfc-editor.org/info/rfc7680>.

   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
              <https://www.rfc-editor.org/info/rfc7880>.

   [RFC7881]  Pignataro, C., Ward, D., and N. Akiya, "Seamless
              Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6,
              and MPLS", RFC 7881, DOI 10.17487/RFC7881, July 2016,
              <https://www.rfc-editor.org/info/rfc7881>.

   [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>.

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   [RFC8459]  Dolson, D., Homma, S., Lopez, D., and M. Boucadair,
              "Hierarchical Service Function Chaining (hSFC)", RFC 8459,
              DOI 10.17487/RFC8459, September 2018,
              <https://www.rfc-editor.org/info/rfc8459>.

   [Y.1731]   ITU-T, "OAM Functions and mechanisms for Ethernet based
              networks",
              <https://www.itu.int/rec/T-REC-G.8013-201508-I/en>.

Authors' Addresses

   Sam K. Aldrin
   Google

   Email: aldrin.ietf@gmail.com

   Carlos Pignataro (editor)
   Cisco Systems, Inc.

   Email: cpignata@cisco.com

   Nagendra Kumar (editor)
   Cisco Systems, Inc.

   Email: naikumar@cisco.com

   Ram Krishnan
   VMware

   Email: ramkri123@gmail.com

   Anoop Ghanwani
   Dell

   Email: anoop@alumni.duke.edu

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