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Network Working Group                                              Z. Hu
Internet-Draft                                                    G. Yan
Intended status: Standards Track                                 X. Chen
Expires: January 1, 2019                                          J. Yao
                                                     Huawei Technologies
                                                           June 30, 2018


               Segment Routing interworking with RSVP-TE
           draft-hu-spring-segment-routing-rsvp-te-interop-00

Abstract

   A Segment Routing (SR) node steers a packet through an ordered list
   of instructions, called segments.  A segment can represent any
   instruction, topological or service-based.  Segment Routing (SR) is a
   protocol designed to forward packets on the network based on the
   concept of source routing.  The Segment Routing architecture can be
   directly applied to the MPLS data plane with no change in the
   forwarding plane.  It simplifies the MPLS control protocol,
   simplifies the configuration of the network, and can achieve SDN
   better.

   Resource Reservation Protocol - Traffic Engineering (RSVP-TE) has the
   ability of path planning and resource reservation.  In the process of
   traditional network evolution to Segment Routing, there will
   inevitably be coexistence of RSVP-TE and Segment Routing.  The
   Document describes how to interact with nodes that support Segment
   Routing capabilities and nodes that support RSVP-TE capabilities.

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 https://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 January 1, 2019.

Copyright Notice

   Copyright (c) 2018 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
   (https://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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   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.  SR to RSVP-TE . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  SR to RSVP-TE . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  SR to RSVP-TE Behavior  . . . . . . . . . . . . . . . . .   5
   3.  RSVP-TE to SR . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  RSVP-TE to SR . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  RSVP-TE to SR Behavior  . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Segment Routing (SR) described in [I-D.ietf-spring-segment-routing]
   leverages the source routing paradigm.  A Segment Routing (SR) node
   steers a packet through an ordered list of instructions, called
   segments.  A segment can represent any instruction, topological or
   service-based.  Segment Routing can be directly applied to the MPLS
   architecture with no change on the forwarding plane
   [I-D.ietf-spring-segment-routing-mpls].  A segment is encoded as an
   MPLS label.  An ordered list of segments is encoded as a stack of
   labels.  The segment to process is on the top of the stack.  A



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   segment can have a semantic local to an SR node or global within an
   SR domain.

   [RFC3209] defines the specification of extensions to RSVP for
   establishing label switched paths (LSPs) in MPLS networks.  The
   signaling protocol model of RSVP uses downstream-on-demand label
   distribution.  The tunnel header node sends the RSVP Path message to
   the tunnel tail node by Path ERO (Explicit Router Object) messages,
   all nodes along the tunnel receive RSVP Path messages and reserve
   resources.  The tunnel tail node sends back a RSVP Resv message to
   allocate labels for the upstream node.  Each node of the tunnel
   completes label assignment and resource reservation through RSVP Path
   messages and RSVP Resv messages.

   Segment Routing- Traffic Engineering (SR-TE) is the technology that
   uses Segment Routing to implement traffic engineering.  In the
   process of traditional network evolution to Segment Routing, there is
   usually a scenario where SR-TE and RSVP-TE interwork to form a
   traffic engineering tunnel.  This document outlines the mechanisms
   through which SR interworks with RSVP-TE in cases where a mix of SR-
   capable and RSVP-capable routers co-exist within the same network and
   more precisely in the same routing domain.

2.  SR to RSVP-TE

   This section describes how to establish a continuous SR-TE tunnel
   across an RSVP-TE domain.  An implementation can be achieved that the
   RSVP-TE domain can be used as the middle part of the SR domain, and
   it can also be used as the tail end part of SR tunnel.

2.1.  SR to RSVP-TE

   This subsection describes the node that supports SR capability as the
   head node of the tunnel to be established and traverses a domain
   which does not support SR capability, but supports RSVP-TE capability
   and how to establish a continuous SR-TE tunnel.















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                    +----------------------+
                    |        Controller    |
                    +----------------------+
                          /              \
                         /                \ BSID
  {102,203,BSID,607,708}/                  \                RSVP-TE Domain
                       /                +---\---------------------------------------------+
                      /                 |    \                                            |
                 +-----+  102 +-----+  203 +-----+      +-----+     +-----+     +-----+ 607 +-----+ 708 +-----+
                 | PE1 |------|  B  |------|  C  |------|  D  |-----|  F  |-----|  G  |-----|  H  |-----| PE3 |
                 +-----+      +-----+   |  +-----+      +-----+     +-----+     +-----+   | +-----+     +-----+
                                        |                                                 |
                                        +-------------------------------------------------+

                                                        Figure 1. SR to RSVP-TE


   In Figure 1, the controller has the ability to collect network
   topology and calculate and arrange user's business demands.

   PE1, B, H and PE3 are network nodes with the capability of Segment
   Routing.

   D and F are network nodes with RSVP-TE capabilities.

   C and G are network devices with both RSVP-TE capability and SR
   capability.

   In SR domain, we assume that the Adjacency-sid between PE1 and B is
   102, Adjacency-sid between B and C is 203, Adjacency-sid between G
   and H is 607, Adjacency-sid between H and PE3 is 708.  All of these
   Adjacency-sids and network topologies are reported to the controller
   via the IGP protocol.

   Now, the traffic must be encapsulated from a PE1 to PE3 through a
   continuous MPLS tunnel.  Therefore, it is necessary to build SR-TE
   tunnel cross over the RSVP-TE domain.

   A RSVP-TE tunnel is firstly built, it can be specifically described :
   Node C calculates the path (C->D->F->G) to Node G through CSPF
   algorithm.  A RSVP-TE tunnel between C and G is established by
   sending RSVP Path messages and receiving RSVP Resv messages, and a
   tunnel Identifier called Binding-sid (BSID) is assigned to the
   established RSVP-TE tunnel at the node C which is handover between
   the RSVP-TE domain and the SR domain.  Through the BGP_LS, the BSID
   is reported to the controller.  When the controller calculates the
   end to end path of A->G to build a SR-TE tunnel, the link in the SR




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   domain is identified by the Adjacency-sids, and the RSVP-TE tunnel is
   identified by the BSID.

   Therefore, the label stack list of SR-TE tunnel can be described with
   { 102, 203, BSID, 607, 708 } .

   When the packet is forwarded, the packet reaches the C.  Node C swap
   the BSID with RSVP-TE tunnel label which is assigned to C by D, and
   then the Traffic is forwarded to G by traditional RSVP-TE label
   swapping hop by hop in the RSVP-TE tunnel.  G receives the packet and
   pops the RSVP-TE tunnel label.  And the packet is continuously
   forwarded to the destination node PE3 through the Adjacency-sids in
   the label stack according to the traditional SR-TE tunnel.

2.2.  SR to RSVP-TE Behavior

   It has to be noted that the nodes C and G in boundary MUST support
   both SR capability and RSVP-TE capability.

   In scenario of SR-TE tunnel crossing over RSVP-TE Domain, a RSVP-TE
   tunnel has to be built firstly in RSVP-TE domain, and a Binding-sid
   (BSID) is generated at the intersection node and reported to the
   controller.  Based on this, the controller can construct the label
   stack and calculate the end-to-end SR-TE tunnel.

3.  RSVP-TE to SR

   This section describes how to establish a continuous RSVP-TE tunnel
   across an SR domain.  An implementation can be achieved that the SR
   domain can be used as the middle part of the RSVP-TE domain, and it
   can also be used as the tail end part of RSVP-TE tunnel.

3.1.  RSVP-TE to SR


















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                    +----------+
                    |Controller|
                    +----------+
                       /
             Path ERO /                                 Segment Routing Domain
                     /                  +-------------------------------------------------+
                    /                   |                                                 |
                 +-----+      +-----+   |  +-----+      +-----+     +-----+     +-----+   | +-----+     +-----+
                 | PE1 |------|  B  |------|  C  |------|  D  |-----|  F  |-----|  G  |-----|  H  |-----| PE3 |
                 +-----+      +-----+   |  +-----+      +-----+     +-----+     +-----+   | +-----+     +-----+
                                        |                                                 |
                                        +-------------------------------------------------+


                                                        Figure 2. RSVP-TE to SR


   In Figure 2, the controller has the ability to collect network
   topology and calculate and arrange user's business demands.

   PE1, B, H and PE3 are network nodes with the capability of RSVP-TE.

   D and F are network nodes with Segment Routing capabilities.

   C and G are network devices with both RSVP-TE capability and SR
   capability.

   Now, the traffic must be encapsulated from PE1 to PE3 through a
   continuous tunnel.  Therefore, it is necessary to establish an RSVP-
   TE tunnel cross over the SR domain.

   There are two methods to get the path information of the tunnel at
   the header node of the tunnel.  One method is to send the Path ERO
   (Explicit Router Object) messages to PE1 which is the tunnel header
   node by the controller.  The other way is to get the Path ERO
   messages through the CSPF algorithm by the tunnel header node.  After
   the path calculation is completed, the header node PE1 sends the RSVP
   Path message hop by hop to the destination node PE3 to request the
   establishment of the RSVP-TE tunnel.

   According to the methods of the controller delivers or the header
   node calculates, PE1 obtains the tunnel path ERO information:
   PE1->B->C->D->F->G->H->PE3.  As shown in Figure 2.  The head node PE1
   establishes a Traffic Engineering (TE) path by sending the RSVP Path
   message according to the path ERO information.

   When the C receives the RSVP Path message, C finds that subsequent
   devices D and F do not support RSVP-TE capabilities, and the node G



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   supports both RSVP-TE and Segment Routing capabilities.  The
   discovery mechanism of Traffic Engineering node capabilities can
   refer to [RFC5073] , which specifies Open Shortest Path First (OSPF)
   and Intermediate System-Intermediate System (IS-IS) traffic
   engineering extensions for the advertisement of control plane and
   data plane traffic engineering node capabilities.

   According to the correspondence between Path ERO information and
   Adjacency-sids or Node-sids of SR domain, node C automatically
   creates a SR-TE tunnel to node G.  The list of label stack
   identifying the SR-TE tunnel may be the Adjacency-sids, the node-
   sids, and the combination of Adjacency-sids and node-sids of SR
   domain.  And a Binding-sid (BSID) is assigned to the SR-TE tunnel as
   a tunnel identifier, which is used to represent the list of label
   stack of SR-TE tunnel.  A BSID is a label that does not conflict
   which is distributed from Segment Routing Local Block (SRLB).  After
   updating the Path message, C sends the Path message to the G through
   the SR-TE tunnel.

   The node G sends the RSVP Path messages to the tail node PE3 of the
   tunnel according to the traditional RSVP-TE mode.

   The tail node PE3 allocates labels for the Label Switched Path (LSP)
   and sends the RSVP Resv message to the upstream node H, and then H
   sends a Resv message hop by hop to the node G.

   Node G assigns a label to the upstream node C and sends it to node C
   through an RSVP Resv message.  Node G acquires that its last hop node
   is C from Record Route Object (RRO) message.  RRO information records
   the path information of RSVP Path messages passing through.

   Node C uses the BSID assigned from the SRLB as a label, puts BSID
   into the Resv message, and sends the Resv message to the upstream
   Node B, and then the Resv message is sent hop by hop to the head node
   PE1.

   At this point, the nodes on the entire ERO have been reserved for
   resources, and a RSVP-TE tunnel crossing over SR domain has been
   established successfully.

   When PE1 needs to bring packets into the RSVP-TE tunnel, PE1 node
   encapsulates the label assigned by the B, B receives the message,
   swaps the label to BSID, and send it to C . C receives the message
   and swap the top label BSID with label stack list of SR-TE tunnel ,
   and the label assigned by node G is reassigned at the bottom of the
   stack.  Packets are forwarded to the node G through the SR-TE tunnel.
   Device G receives the message and forward the message with packets to




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   the destination device PE3 according to the traditional RSVP-TE label
   switching mode.

3.2.  RSVP-TE to SR Behavior

   In the scenario of RSVP-TE crossing over SR domain, the device at the
   junction between RSVP-TE and SR domain can automatically create a SR-
   TE tunnel through Path ERO information, Adjacency-sids and Node-sids.
   This method does not change the way of original tunnel establishment
   of RSVP-TE, and has universal applicability.

4.  IANA Considerations

5.  Security Considerations

   This document does not introduce security issues beyond those
   discussed in [RFC3209] and [I-D.ietf-spring-segment-routing].

6.  Acknowledgements

   The authors of this document would like to thank Gang Yan, Peng Wu
   and Zhenbin Li for their comments and review of this document.

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

7.2.  Informative References

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.

   [I-D.ietf-spring-segment-routing-mpls]
              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-14
              (work in progress), June 2018.






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   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC5073]  Vasseur, J., Ed. and J. Le Roux, Ed., "IGP Routing
              Protocol Extensions for Discovery of Traffic Engineering
              Node Capabilities", RFC 5073, DOI 10.17487/RFC5073,
              December 2007, <https://www.rfc-editor.org/info/rfc5073>.

Authors' Addresses

   Zhibo Hu
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: huzhibo@huawei.com


   Gang Yan
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: yangang@huawei.com


   Xia Chen
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: jescia.chenxia@huawei.com


   Junda Yao
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: yaojunda@huawei.com





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