[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06

Network Working Group                                              X. Xu
Internet-Draft                                                     Z. Li
Intended status: Standards Track                                  Huawei
Expires: March 12, 2016                                          H. Shah
                                                                   Ciena
                                                            L. Contreras
                                                          Telefonica I+D
                                                       September 9, 2015


              Service Function Chaining Using MPLS-SPRING
                   draft-xu-sfc-using-mpls-spring-04

Abstract

   Source Packet Routing in Networking (SPRING) WG specifies a special
   source routing mechanism.  Such source routing mechanism can be
   leveraged to realize the service path layer functionality of the
   service function chaining (i.e, steering traffic through a particular
   service function path) by encoding the service function path or the
   service function chain information as the explicit path information.
   This document describes how to leverage the MPLS-based source routing
   mechanism as developed by the SPRING WG to realize the service path
   layer functionality of the service function chaining.

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 March 12, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





Xu, et al.               Expires March 12, 2016                 [Page 1]


Internet-Draft                                            September 2015


   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
   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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution Description  . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Encoding SFP Information by an MPLS Label Stack . . . . .   4
     3.2.  How to Contain Metadata within an MPLS Packet . . . . . .   5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   When applying a particular Service Function Chain (SFC)
   [I-D.ietf-sfc-architecture] to the traffic selected by a service
   classifier, the traffic need to be steered through an ordered set of
   Service Functions (SF) in the network.  This ordered set of SFs in
   the network indicates the Service Function Path (SFP) associated with
   the above SFC.  To steer the selected traffic through an ordered list
   of SFs in the network, the traffic need to be attached by the service
   classifier with the information about the SFP (i.e., specifying
   exactly which Service Function Forwarders (SFFs) and which SFs are to
   be visited by traffic), the SFC, or the partially specified SFP which
   is in between the former two extremes.  Source Packet Routing in
   Networking (SPRING) WG specifies a special source routing mechanism
   which can be used to steer traffic through an ordered set of routers
   (i.e., an explicit path).  Such source routing mechanism can be
   leveraged to realize the service path layer functionality of the SFC
   (i.e., steering traffic through a particular SFP) by encoding the SFP
   information as the explicit path information contained in packets.
   The source routing mechanism specified by the SPRING WG can be
   applied to the MPLS data plane
   [I-D.ietf-spring-segment-routing-mpls].  This document describes how



Xu, et al.               Expires March 12, 2016                 [Page 2]


Internet-Draft                                            September 2015


   to leverage the MPLS-based source routing mechanisms to realize the
   service path layer functionality of the service function chaining.
   Note that this approach is aligned with the Transport Derived SFF
   mode as described in Section 4.3.1 of [I-D.ietf-sfc-architecture].

1.1.  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 RFC 2119 [RFC2119].

2.  Terminology

   This memo makes use of the terms defined in
   [I-D.ietf-spring-segment-routing] and [I-D.ietf-sfc-architecture].

3.  Solution Description

           +----------------------------------------------- ----+
           |                  SPRING Networks                   |
           |            +---------+       +---------+           |
           |            |   SF1   |       |   SF2   |           |
           |            +----+----+       +----+----+           |
           |                 |                 |                |
           |       (1)       |      (2)        |      (3)       |
      +----+-----+ ---> +----+----+ ----> +----+----+ --->  +---+---+
      |Classifier+------+  SFF1   +-------+  SFF2   +-------+   D   |
      +----------+      +---------+       +---------+       +---+---+
           |                                                    |
           +----------------------------------------------------+
            Figure 1: Service Function Chaining in SPRING Networks

   As shown in Figure 1, assume SFF1 and SFF2 are two MPLS-SPRING-
   capable nodes.  They are also Service Function Forwarders (SFF) to
   which two SFs (i.e., SF1 and SF2) are attached respectively.  In
   addition, they have allocated and advertised Segment IDs (SID) for
   their locally attached SFs.  In the MPLS-SPRING context, SIDs are
   intercepted as MPLS labels.  For example, SFF1 allocates and
   advertises an SID (i.e., SID(SF1)) for SF1 while SFF2 allocates and
   advertises an SID ( i.e., SID(SF2)) for SF2.  These SIDs which are
   used to indicate SFs are referred to as SF SIDs.  To encode the SFP
   information by an MPLS label stack, those SF SIDs as mentioned above
   would be interpreted as local MPLS labels.  In addition, assume node
   SIDs for SFF1 and SFF2 are SID(SFF1) and SID(SFF2) respectively.  Now
   assume a given traffic flow destined for destination D is selected by
   the service classifier to go through a particular SFC (i.e., SF1->
   SF2) before reaching its final destination D.  Section 3.1 describes
   how to leverage the MPLS- based source routing mechanisms to realize



Xu, et al.               Expires March 12, 2016                 [Page 3]


Internet-Draft                                            September 2015


   the service path functionality of the service function chaining
   (i.e., by encoding the SFP information within an MPLS label stack).
   Section 3.2 describes how to carry metadata over MPLS packets.

3.1.  Encoding SFP Information by an MPLS Label Stack

   Since the selected packet needs to travel through an SFC (i.e.,
   SF1->SF2), the service classifier would attach a segment list of
   (i.e., SID(SFF1)->SID(SF1)->SID(SFF2)-> SID(SF2)) which indicates the
   corresponding SFP to the packet.  This segment list is actually
   represented by a MPLS label stack.  To some extent, the MPLS label
   stack here could be looked as a specific implementation of the SFC
   encapsulation used for containing the SFP information
   [I-D.ietf-sfc-architecture].  When the encapsulated packet arrives at
   SFF1, SFF1 would know which SF should be performed according to the
   current top label (i.e., SID (SF1)) of the received MPLS packet.  If
   SF1 is an SFC encapsulation-aware SF, the MPLS packet would be sent
   to SF1 after the top label is poped.  After receiving the MPLS packet
   returned from SF1, SFF1 would send it to SFF2 according to the
   current top label (i.e., SID (SFF2) ).  If SF1 is a legacy SF which
   could not process the MPLS label stack, the whole MPLS label stack
   (i.e., SID(SFF2)->SID(SF2)) MUST be stripped before sending the
   packet to SF1.  After receiving the packet returned from SF1, SFF1
   would re-impose the MPLS label stack which had been stripped before
   to the packet and then send it to SFF2 according to the current top
   label (i.e., SID (SFF2) ).  When the encapsulated packet arrives at
   SFF2, SFF2 would perform the similar action as what has been done by
   SFF1.

   If there is no MPLS LSP towards the next node segment (i.e., the next
   SFF identified by the current top label), the corresponding IP-based
   tunnel (e.g., MPLS-in-IP/GRE tunnel [RFC4023], MPLS-in-L2TPv3 tunnel
   [RFC4817] or MPLS-in-UDP tunnel [RFC7510]) could be used instead (For
   more details about this special usage, please refer to
   [I-D.xu-spring-islands-connection-over-ip]).  Since the transport
   (i.e., the underlay) could be IPv4, IPv6 or even MPLS networks, the
   above approach of encoding the SFP information by an MPLS label stack
   is fully transport-independent which is one of the major requirements
   for the SFC encapsulation [I-D.ietf-sfc-architecture].

   In addition, the service classifier could further impose metadata on
   the MPLS packet through the Network Service Header (NSH)
   [I-D.ietf-sfc-nsh] (As for how to contain the NSH within a MPLS
   packet, please see Section 3.3).  Here the Service Path field wihin
   the NSH would not be used for the path selection purpose anymore and
   therefore it MUST be set to a particular value to indicate such
   particular usage.  In addition, the service index value within the
   NSH is set to a value indicating the total number of SFs within the



Xu, et al.               Expires March 12, 2016                 [Page 4]


Internet-Draft                                            September 2015


   service function path.  The service index SHOULD be decreased by one
   on each SF or SFC-proxy on behalf of the corresponding legacy SF.
   When the service index become zero, the NSH MUST be removed from the
   packet by the SF or SFC-proxy on behalf of the corresponding legacy
   SF.

3.2.  How to Contain Metadata within an MPLS Packet

   Since the MPLS encapsulation has no explicit protocol identifier
   field to indicate the protocol type of the MPLS payload, how to
   indicate the presence of metadata (i.e., the NSH which is only used
   as a metadata containner) in MPLS packets is a potential issue.
   There is a possible way to address the above issue: SFFs allocate two
   different labels for a given SF, one indicates the presence of NSH
   while the other indicates the absence of NSH.  This approach has no
   change to the current MPLS architecture but it would require more
   than one label binding for a given SF.  More details about how to
   contain metadata within an MPLS packet would be considered in the
   future version of this draft.

4.  Acknowledgements

   The authors would like to thank Loa Andersson and Andrew G.  Malis
   for their valuable comments and suggestions on the draft.  The
   authors would like to thank Adrian Farrel, Stewart Bryant, Alexander
   Vainshtein, Joel M.  Halpern for their comments on how to indicate
   the presence of metadata within an MPLS packet.

5.  IANA Considerations

   TBD.

6.  Security Considerations

   TBD

7.  References

7.1.  Normative References

   [I-D.ietf-sfc-architecture]
              Halpern, J. and C. Pignataro, "Service Function Chaining
              (SFC) Architecture", draft-ietf-sfc-architecture-11 (work
              in progress), July 2015.







Xu, et al.               Expires March 12, 2016                 [Page 5]


Internet-Draft                                            September 2015


   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
              and E. Crabbe, "Segment Routing with MPLS data plane",
              draft-ietf-spring-segment-routing-mpls-01 (work in
              progress), May 2015.

   [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>.

7.2.  Informative References

   [I-D.ietf-sfc-nsh]
              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-01 (work in progress), July 2015.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and r. rjs@rob.sh, "Segment Routing Architecture", draft-
              ietf-spring-segment-routing-04 (work in progress), July
              2015.

   [I-D.xu-spring-islands-connection-over-ip]
              Xu, X., Raszuk, R., Chunduri, U., and L. Contreras,
              "Connecting MPLS-SPRING Islands over IP Networks", draft-
              xu-spring-islands-connection-over-ip-04 (work in
              progress), March 2015.

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
              <http://www.rfc-editor.org/info/rfc4023>.

   [RFC4817]  Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
              J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
              Protocol Version 3", RFC 4817, DOI 10.17487/RFC4817, March
              2007, <http://www.rfc-editor.org/info/rfc4817>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,
              <http://www.rfc-editor.org/info/rfc7510>.







Xu, et al.               Expires March 12, 2016                 [Page 6]


Internet-Draft                                            September 2015


Authors' Addresses

   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com


   Zhenbin Li
   Huawei

   Email: lizhenbin@huawei.com


   Himanshu Shah
   Ciena

   Email: hshah@ciena.com


   Luis M. Contreras
   Telefonica I+D
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid,  28050
   Spain

   Email: luismiguel.contrerasmurillo@telefonica.com
   URI:   http://people.tid.es/LuisM.Contreras/






















Xu, et al.               Expires March 12, 2016                 [Page 7]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/