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SFC WG                                                         G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                                 W. Meng
Expires: November 4, 2017                                ZTE Corporation
                                                           B. Khasnabish
                                                            ZTE TX, Inc.
                                                                 C. Wang
                                                             May 3, 2017


        Multi-Layer OAM for Service Function Chains in Networks
                   draft-wang-sfc-multi-layer-oam-07

Abstract

   This document discusses a multi-layer approach to the task of
   Operation, Administration and Maintenance (OAM) of Service Function
   Chains (SFCs) in networks.  Based on the SFC OAM requirements, a
   multi-layer model is introduced.  A mechanism to detect and localize
   defects using the multi-layer model is also described in this draft.

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 http://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 November 4, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Multi-layer Model of SFC OAM  . . . . . . . . . . . . . . . .   3
   4.  Requirements for SFC OAM Multi-layer Model  . . . . . . . . .   4
   5.  SFC OAM multi-layer model . . . . . . . . . . . . . . . . . .   5
   6.  Gap analysis  . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [RFC7665] defines components necessary to implement Service Function
   Chain (SFC).  These include a classifier which performs
   classification of incoming packets.  A Service Function Forwarder
   (SFF) is responsible for forwarding traffic to one or more connected
   Service Functions (SFs) according to the information carried in the
   SFC encapsulation.  SFF also handles traffic coming back from the SF
   and transports the data packets to the next SFF.  And the SFF serves
   as termination element of the Service Function Path (SFP).  SF is
   responsible for specific treatment of received packets.

   Resulting from that SFC is constructed by a number of these
   components, there are different views from different levels of the
   SFC.  One is the SFC, fully abstract entity, that defines an ordered
   set of SFs that must be applied to packets selected as a result of
   classification.  But SFC doesn't define exact mapping between SFFs
   and SFs.  Thus there exists another semi-abstract entity referred as
   SFP.  SFP is the instantiation of the SFC in the network and provides
   a level of indirection between the fully abstract SFC 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 being
   referred as Rendered Service Path (RSP).  The main difference between
   SFP and RSP is that in the former the authority to select the SFF/SF
   has been delegated to the network.




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   This document proposes the multi-layer model of SFC Operation,
   Administration and Maintenance (OAM) and requirements to improve the
   troubleshooting efficiency.

2.  Conventions

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.2.  Terminology

   Unless explicitly specified in this document, active OAM in SFC and
   SFC OAM are being used interchangeably.

   e2e: End-to-End

   FM: Fault Management

   OAM: Operations, Administration, and Maintenance

   RDI: Remote Defect Indication

   RSP: Rendered Service Path

   SF: Service Function

   SFC: Service Function Chain

   SFF: Service Function Forwarder

   SFP: Service Function Path

3.  Multi-layer Model of SFC OAM

   As described in [I-D.ietf-sfc-oam-framework], multiple layers come
   into play to realize the SFC, including the Service layer, the
   underlying Network layer, as well as the Link layer, which are
   depicted in Figure 1:

   o  The Service layer consists of classifiers and/or service
      functions/SFs.

   o  Network and Transport layers leverage various overlay network
      technologies interconnecting SFs to establish SFP.




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   o  The Link layer is technology specific and reflects the technology
      used in the underlay network.


                      +---+  +---+   +---+  +---+     +---+
                      |SF1|  |SF2|   |SF3|  |SF4|     |SF5|
                      +---+  +---+   +---+  +---+     +---+
                         \    /          \  /           |
      +----------+       +----+         +----+        +----+
      |Classifier|-------|SFF1|---------|SFF2|--------|SFF3|
      +----------+       +----+         +----+        +----+
          0---------------------------------------------0  Service layer
          0----------------0--------------0-------------0  Network layer
          0-------------0------0-------0------0---------0  Link layer


                    Figure 1: SFC OAM Multi-Layer model

4.  Requirements for SFC OAM Multi-layer Model

   To perfrom the OAM task of fault management (FM) in an SFC, that
   inculdes failure detection, defect characterzation and localization,
   this document defines the multi-layer model of OAM, presented in
   Section 3, and set of requirements towards active OAM mechanisms to
   be used on an SFC.

   In example presented in Figure 1 the service SFP1 may be realized
   through two RSPs, RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4--SF6).  To
   perform end-to-end (e2e) FM SFC OAM:

      REQ#1: Packets of active OAM in SFC SHOULD be fate sharing with
      data traffic, i.e. in-band with the monitored traffic, i.e. follow
      exactly the same RSP, in forward direction, i.e. from ingress
      toward egress end point(s) of the OAM test.

      REQ#2: SFC OAM MUST support pro-active monitoring of any element
      in the SFC availability.

   The egress, SFF3 in example in Figure 1, is the entity that detects
   the failure of the SFC.  It must be able to signal the new defect
   state to the ingress, i.e. SFF1.  Hence the following requirement:

      REQ#3: SFC OAM MUST support Remote Defect Indication (RDI)
      notification by egress to the ingress, i.e. source of continuity
      checking.






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

   Once the SFF1 detects the defect objective of OAM switches from
   failure detection to defect characterization and localization.

      REQ#5: SFC OAM MUST support fault localization of Loss of
      Continuity check in the SFC.

      REQ#6: SFC OAM MUST support tracing an SFP in order to realize the
      RSP.

   It is practical, as presented in Figure 1, that several SFs share the
   same SFF.  In such case SFP1 may be realized over two RSPs,
   RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4--SF6).

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

   In process of localizing the SFC failure separating SFC OAM layers is
   very attractive and efficient approach.  To achieve that continuity
   among SFFs that are part of the same SFP should be verified.  Once
   SFFs reacheability along the particular SFP has been confirmed task
   of defect localization may focus on SF reacheability verification.
   Because reacheability of SFFs has already been verified, SFF local to
   the SF may be used as source.

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

   By using the multi-layer model OAM that confirms to the above listed
   requirements is capable to perform efficient defect localization on
   an SFC.

5.  SFC OAM multi-layer model

   Figure 2 presents a use case of applying the proposed SFC OAM multi-
   layer model.  In this scenario operator needs to discover SFFs and
   SFs of the same SFC.  The Layer 1 includes the SFFs that are part of
   the SFP.  The Layer 2 - the SFs along the RSP.  When trying to do SFC
   OAM, classifier or service nodes select and confirm which SFC OAM
   layering they plan to do, then encapsulate the layering information
   in the SFC OAM packets, and send the SFC OAM packets along the
   service function paths to the destination.  When receiving the SFC
   OAM packets, service nodes analyze the layering information and then
   decide whether sending these packets to next SFFs directly without




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   being processed by SFs for Layer 1 process or sending to SFs for
   Layer 2 process.


          +---+ +---+  +----+ +----+  +-----+ +-----+  +------+ +------+
          |SF1|.|SFn|  |SF1'|.|SFn'|  |SF1''|.|SFn''|  |SF1'''|.|SFn'''|
          +---+ +---+  +----+ +----+  +-----+ +-----+  +------+ +------+
              \   /        \   /  |      \     /           \    /   |
  +------+   +----+       +----+  |      +-----+           +-----+  |
  |Class.|---|SFF1|  ...  |SFFn|  |      |SFF1'|   ...     |SFFn'|  |
  +------+   +----+       +----+  |      +-----+           +-----+  |
                             |    |                            |    |
                             |    |                            |    |
                             |----|------Layer 1---------------|    |
                                  |                                 |
                                  |-------------Layer 2-------------|



                  Figure 2: SFC OAM multi-layering model

6.  Gap analysis

   Based on the proposed multi-layer model and the listed requirements
   the following new on-demand functions been defined:

7.  Security Considerations

   It will be considered in a future revision.

8.  IANA Considerations

   It will be considered in a future revision.

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,
              <http://www.rfc-editor.org/info/rfc2119>.

9.2.  Informative References







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   [I-D.ietf-sfc-oam-framework]
              Aldrin, S., Krishnan, R., Akiya, N., Pignataro, C., and A.
              Ghanwani, "Service Function Chaining Operation,
              Administration and Maintenance Framework", draft-ietf-sfc-
              oam-framework-01 (work in progress), February 2016.

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

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


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

   Email: meng.wei2@zte.com.cn,vally.meng@gmail.com


   Bhumip Khasnabish
   ZTE TX, Inc.
   1900 McCarthy Blvd, Suite 205
   Milpitas, CA  95035
   USA

   Email: vumip1@gmail.com, bhumip.khasnabish@ztetx.com


   Cui Wang

   Email: lindawangjoy@gmail.com











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