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Versions: 00 01 02 03 draft-xu-clad-spring-sr-service-chaining

MPLS Working Group                                                 X. Xu
Internet-Draft                                                 S. Bryant
Intended status: Standards Track                                  Huawei
Expires: December 31, 2017                                  H. Assarpour
                                                                Broadcom
                                                                 H. Shah
                                                                   Ciena
                                                            L. Contreras
                                                          Telefonica I+D
                                                              D. Bernier
                                                             Bell Canada
                                                             J. Tantsura
                                                              Individual
                                                                   S. Ma
                                                                 Juniper
                                                            M. Vigoureux
                                                                   Nokia
                                                           June 29, 2017


       Service Chaining using Unified Source Routing Instructions
                   draft-xu-mpls-service-chaining-03

Abstract

   Source Packet Routing in Networking (SPRING) WG is developing an MPLS
   source routing mechanism.  The MPLS source routing mechanism can be
   leveraged to realize a unified source routing instruction which works
   across both IPv4 and IPv6 underlays in addition to the MPLS underlay.
   This document describes how to leverage the unified source routing
   instruction to realize a transport-independent service function
   chaining by encoding the service function path information or service
   function chain information as an MPLS label stack.

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




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   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 December 31, 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
   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
     3.2.  Encoding SFC Information by an MPLS Label Stack . . . . .   7
     3.3.  How to Contain Metadata within an MPLS Packet . . . . . .   9
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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



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   to steer the selected traffic through the required ordered list of
   SFs, the service classifier needs to attach information to the packet
   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.

   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 specific operations on the
   packet.  By leveraging the MPLS source routing mechanism,
   [I-D.xu-mpls-unified-source-routing-instruction] describes a unified
   source routing instruction which works across both IPv4 and IPv6
   underlays in addition to the MPLS underlay.  This document describes
   how to leverage the unified source routing instruction to realize a
   transport-independent service function chaining by encoding the
   service function path information or service function chain
   information as an MPLS label stack.

2.  Terminology

   This memo makes use of the terms defined in
   [I-D.ietf-spring-segment-routing-mpls],
   [I-D.xu-mpls-unified-source-routing-instruction] 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 MPLS labels for their locally
   attached SFs.  For example, SFF1 allocates and advertises a label
   (i.e., L(SF1)) for SF1 while SFF2 allocates and advertises a label (
   i.e., L(SF2)) for SF2.  These labels, which are used to indicate SFs
   are referred to as SF labels.  To encode the SFP information as an



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   MPLS label stack, local MPLS labels are allocated from SFFs' (e.g.,
   SFF1 in Figure 1) label spaces to identify their locally 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 L(SFF1) and L(SFF2) respectively.  In contrast, to
   encode the SFC information by an MPLS label stack, those SF labels
   MUST be domain-wide unique MPLS labels.

   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 and 3.2 describe approaches of leveraging the MPLS- based
   source routing mechanisms to realize the service function chaining by
   encoding the SFP information within an MPLS label stack and by
   encoding the SFC information within an MPLS label stack respectively.
   Since the encoding of the partially specified SFP is just a simple
   combination of the encoding of the SFP and the encoding of the SFC,
   this document would not describe how to encode the partially
   specified SFP anymore.

3.1.  Encoding SFP Information by an MPLS Label Stack





























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

   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
   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



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   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.

   As shown in Figure 3, 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 for MPLS (e.g., MPLS-in-IP/GRE tunnel
   [RFC4023], MPLS-in-UDP tunnel [RFC7510] or MPLS-in-L2TPv3 tunnel
   [RFC4817]) would be used instead, according to the unified source
   routing instruction as described in
   [I-D.xu-mpls-unified-source-routing-instruction].


























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           +----------------------------------------------- ----+
           |                      IP Networks                   |
           |            +---------+       +---------+           |
           |            |   SF1   |       |   SF2   |           |
           |            +----+----+       +----+----+           |
           |  +---------+    |                 |    +---------+ |
           |  | L(SFF2) |    |                 |    |Pkt to D | |
           |  +---------+    |                 |    +---------+ |
           |  | L(SF2)  |    |                 |                |
           |  +---------+    |               ^ | |              |
           |  |Pkt to D | ^  | |             | | |              |
           |  +---------+ |  | |          (5)| | |(6)           |
           |           (2)|  | |(3)          | | V              |
           |       (1)    |  | V     (4)       |      (7)       |
      +----+-----+ ---> +----+----+ ----> +----+----+ --->  +---+---+
      |Classifier+------+  SFF1   +-------+  SFF2   +-------+   D   |
      +----------+      +---------+       +---------+       +---+---+
           |    +---------+      +---------+                    |
           |    |IP Tunnel|      |IP Tunnel|        +---------+ |
           |    |to SFF1  |      | to SFF2 |        |Pkt to D | |
           |    +---------+      +---------+        +---------+ |
           |    | L(SF1)  |      | L(SF2)  |                    |
           |    +---------+      +---------+                    |
           |    | L(SFF2) |      |Pkt to D |                    |
           |    +---------+      +---------+                    |
           |    | L(SF2)  |                                     |
           |    +---------+                                     |
           |    |Pkt to D |                                     |
           |    +---------+                                     |
           +----------------------------------------------------+
               Figure 3: Packet Walk in IP underlay

   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].

3.2.  Encoding SFC 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 an MPLS label stack
   (i.e., L(SF1)->L(SF2)) which indicates that SFC to the packet.  Since
   it's known to the service classifier that SFF1 is attached with an
   instance of SF1, the service classifier would therefore send the MPLS
   encapsulated packet through either an MPLS LSP tunnel or an IP-based
   tunnel towards SFF1 (as shown in Figure 4 and 5 respectively).  When
   the MPLS encapsulated packet arrives at SFF1, SFF1 would know which
   SF should be performed according to the current top label (i.e.,



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   L(SF1)).  Similarly, SFF1 would send the packet returned from SF1 to
   SFF2 through either an MPLS LSP tunnel or an IP-based tunnel towards
   SFF2 since it's known to SFF1 that SFF2 is attached with an instance
   of SF2.  When the encapsulated packet arrives at SFF2, SFF2 would do
   the similar action as what has been done by SFF1.  Since the
   transport (i.e., the underlay) could be IPv4, IPv6 or even MPLS
   networks, the above approach of encoding the SFC information by an
   MPLS label stack is fully transport-independent which is one of the
   major requirements for the SFC encapsulation [RFC7665].

           +----------------------------------------------- ----+
           |                    MPLS Networks                   |
           |            +---------+       +---------+           |
           |            |   SF1   |       |   SF2   |           |
           |            +----+----+       +----+----+           |
           |                 |                 |    +---------+ |
           |                 |                 |    |Pkt to D | |
           |  +---------+    |                 |    +---------+ |
           |  | L(SF2)  |    |                 |                |
           |  +---------+    |               ^ | |              |
           |  |Pkt to D | ^  | |             | | |              |
           |  +---------+ |  | |          (5)| | |(6)           |
           |           (2)|  | |(3)          | | V              |
           |       (1)    |  | V     (4)       |      (7)       |
      +----+-----+ ---> +----+----+ ----> +----+----+ --->  +---+---+
      |Classifier+------+  SFF1   +-------+  SFF2   +-------+   D   |
      +----------+      +---------+       +---------+       +---+---+
           |    +---------+      +---------+        +---------+ |
           |    | L(SFF1) |      | L(SFF2) |        |Pkt to D | |
           |    +---------+      +---------+        +---------+ |
           |    | L(SF1)  |      | L(SF2)  |                    |
           |    +---------+      +---------+                    |
           |    | L(SF2)  |      |Pkt to D |                    |
           |    +---------+      +---------+                    |
           |    |Pkt to D |                                     |
           |    +---------+                                     |
           +----------------------------------------------------+
           Figure 4: Packet Walk in MPLS underlay













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           +----------------------------------------------- ----+
           |                    IP Networks                   |
           |            +---------+       +---------+           |
           |            |   SF1   |       |   SF2   |           |
           |            +----+----+       +----+----+           |
           |                 |                 |    +---------+ |
           |                 |                 |    |Pkt to D | |
           |  +---------+    |                 |    +---------+ |
           |  | L(SF2)  |    |                 |                |
           |  +---------+    |               ^ | |              |
           |  |Pkt to D | ^  | |             | | |              |
           |  +---------+ |  | |          (5)| | |(6)           |
           |           (2)|  | |(3)          | | V              |
           |       (1)    |  | V     (4)       |      (7)       |
      +----+-----+ ---> +----+----+ ----> +----+----+ --->  +---+---+
      |Classifier+------+  SFF1   +-------+  SFF2   +-------+   D   |
      +----------+      +---------+       +---------+       +---+---+
           |    +---------+      +---------+                    |
           |    |IP Tunnel|      |IP Tunnel|        +---------+ |
           |    |to SFF1  |      | to SFF2 |        |Pkt to D | |
           |    +---------+      +---------+        +---------+ |
           |    | L(SF1)  |      | L(SF2)  |                    |
           |    +---------+      +---------+                    |
           |    | L(SF2)  |      |Pkt to D |                    |
           |    +---------+      +---------+                    |
           |    |Pkt to D |                                     |
           |    +---------+                                     |
           +----------------------------------------------------+
           Figure 5: Packet Walk in IP underlay

3.3.  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 an MPLS packet is a potential issue to
   be addressed.  One possible way to address the above issue is: 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.  Another possible
   way is to introduce a protocol identifier field within the MPLS
   packet as described in [I-D.xu-mpls-payload-protocol-identifier].

   More details about how to contain metadata within an MPLS packet
   would be considered in the future version of this draft.





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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.

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-12 (work in progress), February 2017.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-10
              (work in progress), June 2017.





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   [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.

   [I-D.xu-mpls-payload-protocol-identifier]
              Xu, X., "MPLS Payload Protocol Identifier", draft-xu-mpls-
              payload-protocol-identifier-02 (work in progress),
              December 2016.

   [I-D.xu-mpls-unified-source-routing-instruction]
              Xu, X., Bryant, S., Raszuk, R., Chunduri, U., Contreras,
              L., Jalil, L., Assarpour, H., Velde, G., Tantsura, J., and
              S. Ma, "Unified Source Routing Instruction using MPLS
              Label Stack", draft-xu-mpls-unified-source-routing-
              instruction-02 (work in progress), June 2017.

   [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







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   Stewart Bryant
   Huawei

   Email: stewart.bryant@gmail.com


   Hamid Assarpour
   Broadcom

   Email: hamid.assarpour@broadcom.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/


   Daniel Bernier
   Bell Canada

   Email: daniel.bernier@bell.ca


   Jeff Tantsura
   Individual

   Email: jefftant@gmail.com


   Shaowen Ma
   Juniper

   Email: mashaowen@gmail.com






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   Martin Vigoureux
   Nokia

   Email: martin.vigoureux@nokia.com















































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