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MPLS Working Group                                                 X. Xu
Internet-Draft                                                 S. Bryant
Intended status: Standards Track                                  Huawei
Expires: April 16, 2017                                     H. Assarpour
                                                                Broadcom
                                                                 H. Shah
                                                                   Ciena
                                                            L. Contreras
                                                          Telefonica I+D
                                                              D. Bernier
                                                             Bell Canada
                                                        October 13, 2016


               Service Chaining using MPLS Source Routing
                   draft-xu-mpls-service-chaining-00

Abstract

   Source Packet Routing in Networking (SPRING) WG is developing an MPLS
   source routing mechanism.  This MPLS source routing mechanism can be
   leveraged to realize the service path layer functionality of the
   service function chaining (i.e., steering the selected traffic
   through a particular service function path) by encoding the service
   function path information as an MPLS label stack.  This document
   describes how to use the MPLS source routing mechanism as developed
   by the SPRING WG to realize the service path layer functionality of
   service function chaining.

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].

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




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   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 April 16, 2017.

Copyright Notice

   Copyright (c) 2016 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
   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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution Description  . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Encoding SFP Information by an MPLS Label Stack . . . . .   4
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   When applying a particular Service Function Chain (SFC) [RFC7665] 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.  In order
   to steer the selected traffic through the required ordered list of
   SFs, the service classifier needs to attach information to the packet
   specifying which Service Function Forwarders (SFFs) and which SFs are
   to be visited by the selected traffic.  The Source Packet Routing in
   Networking (SPRING) WG is developing an MPLS source routing mechanism
   which can be used to steer traffic through an ordered set of routers
   (i.e., an explicit path) and instruct nodes on that path to execute



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   specific operations on the packet.  This MPLS source routing
   mechanism thus 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 a label stack.  This document
   describes how to use the MPLS 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 [RFC7665].

2.  Terminology

   This memo makes use of the terms defined in
   [I-D.ietf-spring-segment-routing-mpls] and [RFC7665].

3.  Solution Description

           +----------------------------------------------- ----+
           |               MPLS SPRING Networks                 |
           |            +---------+       +---------+           |
           |            |   SF1   |       |   SF2   |           |
           |            +----+----+       +----+----+           |
           |               ^ | |(3)          ^ | |(6)           |
           |       (1)  (2)| | V     (4)  (5)| | V     (7)      |
      +----+-----+ ---> +----+----+ ----> +----+----+ --->  +---+---+
      |Classifier+------+  SFF1   +-------+  SFF2   +-------+   D   |
      +----------+      +---------+       +---------+       +---+---+
           |                                                    |
           +----------------------------------------------------+
        Figure 1: Service Function Chaining in MPLS-SPRING Networks

   As shown in Figure 1, SFF1 and SFF2 are two MPLS-SPRING-capable
   nodes.  They are also SFFs, each with one SF attached.  In addition,
   they have allocated and advertised Segment IDs (SID) for their
   locally attached SFs.  In the MPLS-SPRING context, SIDs are encoded
   as MPLS labels.  For example, SFF1 allocates and advertises a 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 as an MPLS
   label stack, those SF SIDs as mentioned above would be interpreted as
   local MPLS labels.  More specifically, local MPLS labels are
   allocated from SFFs' (e.g., SFF1 in Figure 1) label spaces to
   identify their attached SFs (e.g., SF1 in Figure 1), whilst the SFFs
   are identified by either nodal SIDs or adjacency SIDs depending on
   how strictly the network path needs to be specified.  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



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   destination D.  Section 3.1 describes how to use the MPLS-based
   source routing mechanism to realize the service path functionality of
   the service function chaining (i.e., by encoding the SFP information
   within an MPLS label stack).

3.1.  Encoding SFP Information by an MPLS Label Stack

           +----------------------------------------------- ----+
           |               MPLS SPRING Networks                 |
           |            +---------+       +---------+           |
           |            |   SF1   |       |   SF2   |           |
           |            +----+----+       +----+----+           |
           |  +---------+    |                 |    +---------+ |
           |  |SID(SFF2)|    |                 |    |Pkt to D | |
           |  +---------+    |                 |    +---------+ |
           |  |SID(SF2) |    |                 |                |
           |  +---------+    |               ^ | |              |
           |  |Pkt to D | ^  | |             | | |              |
           |  +---------+ |  | |          (5)| | |(6)           |
           |           (2)|  | |(3)          | | V              |
           |       (1)    |  | V     (4)       |      (7)       |
      +----+-----+ ---> +----+----+ ----> +----+----+ --->  +---+---+
      |Classifier+------+  SFF1   +-------+  SFF2   +-------+   D   |
      +----------+      +---------+       +---------+       +---+---+
           |    +---------+      +---------+        +---------+ |
           |    |SID(SFF1)|      |SID(SFF2)|        |Pkt to D | |
           |    +---------+      +---------+        +---------+ |
           |    |SID(SF1) |      |SID(SF2) |                    |
           |    +---------+      +---------+                    |
           |    |SID(SFF2)|      |Pkt to D |                    |
           |    +---------+      +---------+                    |
           |    |SID(SF2) |                                     |
           |    +---------+                                     |
           |    |Pkt to D |                                     |
           |    +---------+                                     |
           +----------------------------------------------------+
           Figure 2: Packet Walk in MPLS Source Routing based SFC

   As shown in Figure 2, 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 represented by an 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 [RFC7665].
   When the encapsulated packet arrives at SFF1, SFF1 would know which
   SF should be performed according to the top label (i.e., SID (SF1))
   of the received MPLS packet.  We first consider the case where SF1 is



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   an encapsulation aware SF, i.e., it understands how to process a
   packet with a pre-pended MPLS label stack.  In this case the packet
   would be sent to SF1 by SFF1 with the label stack SID(SFF2)->
   SID(SF2).  SF1 would perform the required service function on the
   received MPLS packet where the payload is constrained to be an IP
   packet, and the SF needs to process both IPv4 and IPv6 packets (note
   that the SF would use the first nibble of the MPLS payload to
   identify the payload type).  After the MPLS packet is returned from
   SF1, SFF1 would send it to SFF2 according to the top label (i.e., SID
   (SFF2) ).

   If SF1 is a legacy SF, i.e. one that is unable to process the MPLS
   label stack, the remaining MPLS label stack (i.e.,
   SID(SFF2)->SID(SF2)) MUST be saved and stripped from the packet
   before sending the packet to SF1.  When the packet is returned from
   SF1, SFF1 would re-impose the MPLS label stack which had been
   previously stripped and then send the packet to SFF2 according to the
   current top label (i.e., SID (SFF2) ).  As for how to associate the
   corresponding MPLS label stack with the packets returned from legacy
   SFs, those mechanisms as described in
   [I-D.song-sfc-legacy-sf-mapping] could be considered.

   When the encapsulated packet arrives at SFF2, SFF2 would perform the
   similar action to that described above.

   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-UDP tunnel
   [RFC7510] or MPLS-in-L2TPv3 tunnel [RFC4817]) would be used instead
   (for more details about this special usage, please refer to
   [I-D.xu-mpls-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 [RFC7665].

4.  Acknowledgements

   The authors would like to thank Loa Andersson, Andrew G.  Malis,
   Adrian Farrel, Alexander Vainshtein and Joel M.  Halpern for their
   valuable comments and suggestions on the document

5.  IANA Considerations

   This document makes no request of IANA.






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6.  Security Considerations

   It is fundamental to the SFC design that the classifier is a trusted
   resource which determines the processing that the packet will be
   subject to, including for example the firewall.  It is also
   fundamental to the SPRING design that packets are routed through the
   network using the path specified by the node imposing the SIDs.
   Where an SF is not encapsulation aware the packet may exist as an IP
   packet, however this is an intrinsic part of the SFC design which
   needs to define how a packet is protected in that environment.  Where
   a tunnel is used to link two non-MPLS domains, the tunnel design
   needs to specify how it is secured.  Thus the secutity
   vulnerabilities are addressed in the underlying technologies used by
   this design, which itself does not introduce any new security
   vulnerabilities.

7.  References

7.1.  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>.

7.2.  Informative References

   [I-D.ietf-sfc-nsh]
              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-10 (work in progress), September 2016.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R.,
              jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
              with MPLS data plane", draft-ietf-spring-segment-routing-
              mpls-05 (work in progress), July 2016.

   [I-D.song-sfc-legacy-sf-mapping]
              Song, H., You, J., Yong, L., Jiang, Y., Dunbar, L.,
              Bouthors, N., and D. Dolson, "SFC Header Mapping for
              Legacy SF", draft-song-sfc-legacy-sf-mapping-08 (work in
              progress), September 2016.








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   [I-D.xu-mpls-spring-islands-connection-over-ip]
              Xu, X., Raszuk, R., Chunduri, U., Contreras, L., and L.
              Jalil, "Connecting MPLS-SPRING Islands over IP Networks",
              draft-xu-mpls-spring-islands-connection-over-ip-00 (work
              in progress), October 2016.

   [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>.

   [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

   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com


   Stewart Bryant
   Huawei

   Email: stewart.bryant@gmail.com


   Hamid Assarpour
   Broadcom

   Email: hamid.assarpour@broadcom.com







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   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/


   Daniel Bernier
   Bell Canada

   Email: daniel.bernier@bell.ca






























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