TEAS Working Group                                               A. Wang
Internet-Draft                                             China Telecom
Intended status: Experimental                                    Q. Zhao
Expires: July 13, 2020                                       B. Khasanov
                                                     Huawei Technologies
                                                                 H. Chen
                                                        January 10, 2020

                        PCE in Native IP Network


   This document defines the framework for traffic engineering within
   native IP network, using Dual/Multi-Border Gateway Protocol (BGP)
   sessions strategy and Path Computation Engine (PCE) -based central
   control architecture.

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   This Internet-Draft will expire on July 13, 2020.

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   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  CCDR Framework in Simple Topology . . . . . . . . . . . . . .   3
   5.  CCDR Framework in Large Scale Topology  . . . . . . . . . . .   5
   6.  CCDR Multi-BGP Strategy . . . . . . . . . . . . . . . . . . .   5
   7.  CCDR Framework for Multi-BGP Strategy . . . . . . . . . . . .   6
   8.  PCEP Extension for Key Parameters Delivery  . . . . . . . . .   7
   9.  Deployment Consideration  . . . . . . . . . . . . . . . . . .   8
     9.1.  Scalability . . . . . . . . . . . . . . . . . . . . . . .   8
     9.2.  High Availability . . . . . . . . . . . . . . . . . . . .   8
     9.3.  Incremental deployment  . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   9
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Draft [I-D.ietf-teas-native-ip-scenarios] describes the scenarios and
   simulation results for traffic engineering in native IP network.  To
   meet the requirements of various scenarios, the solution for traffic
   engineering in native IP network should have the following criteria:

   o  No complex Multiprotocol Label Switching (MPLS) signaling

   o  End to End traffic assurance, determined Quality of Service (QoS)

   o  Same deployment method for intra-domain and inter-domain.

   o  No upgrade to forwarding behavior of the router.

   o  Can exploit the power of centrally control and flexibility/
      robustness of distributed control protocol.

   o  Coping with the differentiation requirements for large amount
      traffic and prefixes.

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   o  Flexible deployment and automation control.

   This document defines the framework for traffic engineering within
   native IP network, using Dual/Multi-BGP session strategy, to meet the
   above requirements in dynamical and centrally control mode.  The
   framework is referred as Central Control Dynamic Routing (CCDR)
   framework.  The related Path Computation Element Communications
   Protocol (PCEP) extensions to transfer the key parameters between PCE
   and the underlying network devices are provided in draft

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119] .

3.  Terminology

   This document uses the following terms defined in [RFC5440]: PCE,

   The following terms are defined in this document:

   o  CCDR: Central Control Dynamic Routing

   o  E2E: End to End

   o  ECMP: Equal Cost Multi Path

   o  QoS: Quality of Service

   o  RR: Route Reflector

   o  SDN: Software Definition Network

4.  CCDR Framework in Simple Topology

   Figure 1 illustrates the CCDR framework for traffic engineering in
   simple topology.  The topology is comprised by four devices which are
   SW1, SW2, R1, R2.  There are multiple physical links between R1 and
   R2.  Traffic between IP11(on SW1) and IP21(on SW2) is normal traffic,
   traffic between IP12(on SW1) and IP22(on SW2) is priority traffic
   that should be treated differently.

   Only native Interior Gateway Protocol (IGP) /BGP protocol is deployed
   between R1 and R2.  The traffic between each address pair may change

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   in real time and the corresponding source/destination addresses of
   the traffic may also change dynamically.

   The key ideas of the CCDR framework for this simple topology are the

   o  Build two BGP sessions between R1 and R2, via the different
      loopback addresses lo0, lo1 on these routers.

   o  Send different prefixes via the established BGP sessions.  For
      example, IP11/IP21 via the BGP pair 1 and IP12/IP22 via the BGP
      pair 2.

   o  Set the explicit peer route on R1 and R2 respectively for BGP next
      hop of lo0, lo1 to different physical link addresses between R1
      and R2.

   After the above actions, the traffic between the IP11 and IP21, and
   the traffic between IP12 and IP22 will go through different physical
   links between R1 and R2, each set of traffic occupies different
   dedicated physical links.

   If there is more traffic between IP12 and IP22 that needs to be
   assured , one can add more physical links between R1 and R2 to reach
   the loopback address lo1(also the next hop for BGP Peer pair2).  In
   this cases the prefixes that advertised by the BGP peers need not be

   If, for example, there is traffic from another address pair that
   needs to be assured (for example IP13/IP23), and the total volume of
   assured traffic does not exceed the capacity of the previous
   appointed physical links, one need only to advertise the newly added
   source/destination prefixes via the BGP peer pair2.  The traffic
   between IP13/IP23 will go through the assigned dedicated physical
   links as the traffic between IP12/IP22.

   Such decouple philosophy gives network operator flexible control
   capability on the network traffic, achieve the determined QoS
   assurance effect to meet the application's requirement.  No complex
   MPLS signal procedures is introduced, the router needs only support
   native IP protocol.

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                                   |  BGP Peer Pair2  |
                                   |lo1           lo1 |
                                   |                  |
                                   |  BGP Peer Pair1  |
                        IP12       |lo0           lo0 |       IP22
                        IP11       |                  |       IP21
                                       Links Group

                      Figure 1: CCDR framework in simple topology

5.  CCDR Framework in Large Scale Topology

   When the assured traffic spans across the large scale network, as
   that illustrated in Figure 2, the Dual-BGP sessions cannot be
   established hop by hop, especially for the iBGP within one AS.

   For such scenario, we should consider to use the Route Reflector (RR)
   to achieve the similar effect.  Every edge router will establish two
   BGP peer sessions with the RR via different loopback addresses
   respectively.  The other steps for traffic differentiation are same
   as that described in the CCDR framework for simple topology.

   As shown in Figure 2, if we select R3 as the RR, every edge router(R1
   and R7 in this example) will build two BGP session with the RR.  If
   the PCE calculates select the dedicated path as R1-R2-R4-R7, then the
   operator should set the explicit peer routes on these routers
   respectively, pointing to the BGP next hop (loopback addresses of R1
   and R7, which are used to send the prefix of the assured traffic) to
   the selected forwarding address.

                         |                            |
                         |        |          |        |

                Figure 2: CCDR framework in large scale network

6.  CCDR Multi-BGP Strategy

   In general situation, different applications may require different
   QoS criteria, which may include:

   o  Traffic that requires low latency and is not sensitive to packet

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   o  Traffic that requires low packet loss and can endure higher

   o  Traffic that requires low jitter.

   These different traffic requirements can be summarized in the
   following table:

         | Flow No. |    Latency  |  Packet Loss  |   Jitter        |
         |  1       |    Low      |   Normal      |   Don't care    |
         |  2       |   Normal    |   Low         |   Dont't care   |
         |  3       |   Normal    |   Normal      |   Low           |
                    Table 1. Traffic Requirement Criteria

   For Flow No.1, we can select the shortest distance path to carry the
   traffic; for Flow No.2, we can select the path that is comprised by
   under loading links from end to end; For Flow No.3, we can let all
   assured traffic pass the determined single path, no Equal Cost
   Multipath (ECMP) distribution on the parallel links is desired.

   It is almost impossible to provide an End-to-End (E2E) path with
   latency, jitter, packet loss constraints to meet the above
   requirements in large scale IP-based network via the distributed
   routing protocol, but these requirements can be solved with the
   assistance of PCE, because the PCE has the overall network view, can
   collect real network topology and network performance information
   about the underlying network, select the appropriate path to meet
   various network performance requirements of different traffics.

7.  CCDR Framework for Multi-BGP Strategy

   The framework to implement the CCDR Multi-BGP strategy are the
   followings.  Here PCE is the main component of the Software
   Definition Network (SDN) controller and is responsible for optimal
   path computation for priority traffic.

   o  SDN controller gets topology and link utilization information from
      the underlying network.

   o  PCE calculates the appropriate path upon application's
      requirements, sends the key parameters to edge/RR routers(R1, R7
      and R3 in Fig.3) to establish multi-BGP peer sessions and
      advertises different prefixes via them.

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   o  PCE sends the route information to the routers (R1,R2,R4,R7 in
      Fig.3) on forwarding path via PCEP, to build the path to the BGP
      next-hop of the advertised prefixes.

   o  If the assured traffic prefixes were changed but the total volume
      of assured traffic does not exceed the physical capacity of the
      previous E2E path, PCE needs only change the prefixed advertised
      via the edge routers (R1,R7 in Fig.3).

   o  If the volume of assured traffic exceeds the capacity of previous
      calculated path, PCE can recalculate and add the appropriate paths
      to accommodate the exceeding traffic.  After that, PCE needs to
      update on-path routers to build the forwarding path hop by hop.

                        *          +---*---+         *
                        *           / * \            *
                        *             *              *
                    PCEP*       BGP-LS/SNMP          *PCEP
                        *             *              *
                        *             *           \  * /
                      \ * /           *            \ */
                        |                            |
                        |                            |
                        |        |          |        |
                        |        |          |        |

              Figure 3: CCDR framework for Multi-BGP deployment

8.  PCEP Extension for Key Parameters Delivery

   The PCEP protocol needs to be extended to transfer the following key

   o  Peer addresses pair that is used to build the BGP session

   o  Advertised prefixes and their associated BGP session.

   o  Explicit route information to BGP next hop of advertised prefixes.

   Once the router receives such information, it should establish the
   BGP session with the peer appointed in the PCEP message, advertise
   the prefixes that contained in the corresponding PCEP message, and
   build the end to end dedicated path hop by hop.

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   Details of communications between PCEP and BGP subsystems in router's
   control plane are out of scope of this draft and will be described in
   separate draft [I-D.ietf-pce-pcep-extension-native-ip] .

   The reason that we select PCEP as the southbound protocol instead of
   OpenFlow, is that PCEP is suitable for the changes in control plane
   of the network devices, while OpenFlow dramatically changes the
   forwarding plane.  We also think that the level of centralization
   that required by OpenFlow is hardly achievable in SP networks so
   hybrid BGP+PCEP approach looks much more interesting.

9.  Deployment Consideration

9.1.  Scalability

   In CCDR framework, PCE needs only influence the edge routers for the
   prefixes advertisement via the multi-BGP deployment.  The route
   information for these prefixes within the on-path routers were
   distributed via the BGP protocol.

   Unlike the solution from BGP Flowspec, the on-path router need only
   keep the specific policy routes to the BGP next-hop of the
   differentiate prefixes, not the specific routes to the prefixes
   themselves.  This can lessen the burden from the table size of policy
   based routes for the on-path routers, and has more expandability when
   comparing with the solution from BGP flowspec or Openflow.

9.2.  High Availability

   The CCDR framework is based on the distributed IP protocol.  If the
   PCE failed, the forwarding plane will not be impacted, as the BGP
   session between all devices will not flap, and the forwarding table
   will remain unchanged.

   If one node on the optimal path is failed, the priority traffic will
   fall over to the best-effort forwarding path.  One can even design
   several assurance paths to load balance/hot-standby the priority
   traffic to meet the path failure situation, as done in MPLS Fast
   Reroute (FRR).

   For high availability of PCE/SDN-controller, operator should rely on
   existing HA solutions for SDN controller, such as clustering
   technology and deployment.

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9.3.  Incremental deployment

   Not every router within the network will support the PCEP extension
   that defined in [I-D.ietf-pce-pcep-extension-native-ip]

   For such situations, router on the edge of domain can be upgraded
   first, and then the traffic can be assured between different domains.
   Within each domain, the traffic will be forwarded along the best-
   effort path.  Service provider can selectively upgrade the routers on
   each domain in sequence.

10.  Security Considerations

   The PCE should have the capability to calculate the loop-free E2E
   path upon the status of network condition and the service
   requirements in real time.

   The PCE need consider the explicit route deployment order (for
   example, from tail router to head router) to eliminate the possible
   transient traffic loop.

   CCDR framework described in this draft puts more requirements on the
   function of PCE and its communication with the underlay devices.
   Service provider should consider more on the protection of PCE and
   their communication with the underlay devices, which is described in
   document [RFC5440] and [RFC8253]

   CCDR framework does not require the change of forward behavior on the
   underlay devices, then there will no additional security impact on
   the devices.

11.  IANA Considerations

   This document does not require any IANA actions.

12.  Acknowledgement

   The author would like to thank Deborah Brungard, Adrian Farrel,
   Vishnu Beeram, Lou Berger, Dhruv Dhody, Raghavendra Mallya , Mike
   Koldychev, Haomian Zheng, Penghui Mi, Shaofu Peng and Jessica Chen
   for their supports and comments on this draft.

13.  References

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13.1.  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,

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,

13.2.  Informative References

              Wang, A., Khasanov, B., Cheruathur, S., Zhu, C., and S.
              Fang, "PCEP Extension for Native IP Network", draft-ietf-
              pce-pcep-extension-native-ip-04 (work in progress), August

              Wang, A., Huang, X., Qou, C., Li, Z., and P. Mi,
              "Scenarios and Simulation Results of PCE in Native IP
              Network", draft-ietf-teas-native-ip-scenarios-12 (work in
              progress), October 2019.

Authors' Addresses

   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209

   Email: wangaj3@chinatelecom.cn

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   Quintin Zhao
   Huawei Technologies
   125 Nagog Technology Park
   Acton, MA  01719

   Email: quintin.zhao@huawei.com

   Boris Khasanov
   Huawei Technologies
   Moskovskiy Prospekt 97A
   St.Petersburg  196084

   Email: khasanov.boris@huawei.com

   Huaimo Chen
   Boston, MA

   Email: huaimo.chen@futurewei.com

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