TEAS Working Group                                               A. Wang
Internet-Draft                                             China Telecom
Intended status: Experimental                                B. Khasanov
Expires: December 10, 2020                           Huawei Technologies
                                                                 Q. Zhao
                                                        Etheric Networks
                                                                 H. Chen
                                                            June 8, 2020

                        PCE in Native IP Network


   This document defines the framework for traffic engineering within
   native IP network, using multiple BGP sessions strategy and PCE
   -based central control architecture.  The procedures described in
   this document are experimental.  The experiment is intended to enable
   research for the usage of PCE in native IP scenarios.  For this
   purpose, this document describe the Central Control Dynamic Routing
   (CCDR) framework and the PCEP extension is specified in draft ietf-

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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  CCDR Framework in Simple Topology . . . . . . . . . . . . . .   4
   4.  CCDR Framework in Large Scale Topology  . . . . . . . . . . .   5
   5.  CCDR Multiple BGP Sessions Strategy . . . . . . . . . . . . .   6
   6.  PCEP Extension for Key Parameters Delivery  . . . . . . . . .   8
   7.  Deployment Consideration  . . . . . . . . . . . . . . . . . .   9
     7.1.  Scalability . . . . . . . . . . . . . . . . . . . . . . .   9
     7.2.  High Availability . . . . . . . . . . . . . . . . . . . .  10
     7.3.  Incremental deployment  . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   [RFC8735] describes the scenarios and simulation results for traffic
   engineering in the native IP network to provide End-to-End (E2E)
   performance assurance and QoS using PCE based central control,
   referred to as Centralized Control Dynamic Routing (CCDR).  Based on
   the various scenarios and analysis as per [RFC8735], the solution for
   traffic engineering in native IP network should have the following

   o  Support native IPv4 and IPv6 traffic simultaneously, no complex
      signaling procedures among network nodes like MPLS-TE and MPLS
      data plane.

   o  Same deployment guidline for intra-domain and inter-domain

   o  Achieve End to End traffic assurance, determined QoS behavior.

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   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.

   o  Adjust the optimal path dynamically upon the change of network
      status.  No physical links resources planning in advance.

   Stateful PCE [RFC8231] specifies a set of extensions to PCEP to
   enable stateful control of paths such as MPLS-TE LSPs between and
   across PCEP sessions in compliance with [RFC4657].  It includes
   mechanisms to affect state synchronization between PCCs and PCEs,
   delegation of control of LSPs to PCEs, and PCE control of timing and
   sequence of path computations within and across PCEP sessions.
   Furthermore, [RFC8281] specifies a mechanism to dynamically
   instantiate LSPs on a PCC based on the requests from a stateful PCE
   or a controller using stateful PCE.  [RFC8283] introduces the
   architecture for PCE as a central controller as an extension of the
   architecture described in [RFC4655] and assumes the continued use of
   PCEP as the protocol used between PCE and PCC.[RFC8283] further
   examines the motivations and applicability for PCEP as a Southbound
   Interface (SBI), and introduces the implications for the protocol.

   This document defines the framework for traffic engineering within
   native IP network, using multiple BGP session strategy, to meet the
   above requirements in dynamical and centrally control mode.  The
   framework is referred as CCDR framework.  It depends on the central
   control (PCE) element to compute the optimal path for selected
   traffic, and utilizes the dynamic routing behavior of traditional
   IGP/BGP protocols to forward such traffic.

   The control messages between PCE and underlying network node are
   transmitted via Path Computation Element Communications Protocol
   (PCEP) protocol.  The related PCEP extensions are provided in draft

2.  Terminology

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

   The following terms are used in this document:

   o  CCDR: Central Control Dynamic Routing

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   o  E2E: End to End

   o  ECMP: Equal Cost Multi Path

   o  RR: Route Reflector

   o  SDN: Software Defined Network

3.  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 prefix PF11(on SW1) and prefix PF21(on SW2) is
   normal traffic, traffic between prefix PF12(on SW1) and prefix
   PF22(on SW2) is priority traffic that should be treated differently.

   In Intra-AS scenario, IGP and BGP are deployed between R1 and R2.  In
   inter-AS scenario, only native BGP protocol is deployed.  The traffic
   between each address pair may change 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 on these routers.

   o  Send different prefixes via the established BGP sessions.  For
      example, PF11/PF21 via the BGP session 1 and PF12/PF22 via the BGP
      session 2.

   o  Set the explicit peer route on R1 and R2 respectively for BGP next
      hop to different physical link addresses between R1 and R2.  Such
      explicit peer route can be set in the format of static route to
      BGP peer address, which is different from the route learned from
      the IGP protocol.

   After the above actions, the bi-direction traffic between the PF11
   and PF21, and the bi-direction traffic between PF12 and PF22 will go
   through different physical links between R1 and R2, each set of
   traffic pass through different dedicated physical links.

   If there is more traffic between PF12 and PF22 that needs to be
   assured , one can add more physical links between R1 and R2 to reach
   the the next hop for BGP session 2.  In this cases the prefixes that
   advertised by the BGP peers need not be changed.

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   If, for example, there is bi-direction traffic from another address
   pair that needs to be assured (for example prefix PF13/PF23), and the
   total volume of assured traffic does not exceed the capacity of the
   previously provisioned physical links, one need only to advertise the
   newly added source/destination prefixes via the BGP session 2.  The
   bi-direction traffic between PF13/PF23 will go through the assigned
   dedicated physical links as the traffic between PF12/PF22.

   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
   signaling procedures like MPLS-TE are introduced, the router needs
   only support native IP and multiple BGP sessions setup via different
   loopback addresses.

                    +----------+ PCE +--------+
                    |          +-----+        |
                    |                         |
                    | BGP Session 1(lo11/lo21)|
                    |                         |
                    | BGP Session 2(lo12/lo22)|
PF12                |                         |                    PF22
PF11                |                         |                    PF21
+---+         +-----+-----+             +-----+-----+              +---+
+---+         |    R1     +-------------+    R2     |              +---+
              +-----------+             +-----------+

           Figure 1: CCDR framework in simple topology

4.  CCDR Framework in Large Scale Topology

   When the assured traffic spans across the large scale network, as
   that illustrated in Figure 2, the multiple 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)
   [RFC4456] to achieve the similar effect.  Every edge router will
   establish two BGP 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 selects the dedicated path as R1-R2-R4-R7, then the operator

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   should set the explicit peer routes via PCEP protocol 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.

               +----------------+ PCE +------------------+
               |                +--+--+                  |
               |                   |                     |
               |                   |                     |
               |                  ++-+                   |
  PF12         |                  +--+                   |          PF22
  PF11         |                                         |          PF21
  +---+       ++-+          +--+          +--+         +-++        +---+
  +---+       ++-+          +--+          +--+         +-++        +---+
               |                                         |
               |                                         |
               |            +--+          +--+           |
                            +--+          +--+
            Figure 2: CCDR framework in large scale network

5.  CCDR Multiple BGP Sessions 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

   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:

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

   It is almost impossible to provide an End-to-End (E2E) path
   efficiently 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, as that described in [RFC4655] and
   [RFC8283] 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.

   The framework to implement the CCDR Multiple BGP sessions 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 via BGP-LS[RFC7752] and link
      utilization information via existing Network Monitor System (NMS)
      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 multiple BGP sessions and advertises
      different prefixes via them.  The loopback addresses used for BGP
      sessions should be planned in advance and distributed in the

   o  PCE sends the route information to the routers (R1,R2,R4,R7 in
      Fig.3) on forwarding path via PCEP
      [I-D.ietf-pce-pcep-extension-native-ip], to build the path to the
      BGP next-hop of the advertised prefixes.

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   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.

                            | Application|
               +----------+SDN Controller/PCE+-----------+
               |          +--------^---------+           |
               |                   |                     |
               |                   |                     |
          PCEP |             BGP-LS|PCEP                 | PCEP
               |                   |                     |
               |                  +v-+                   |
   PF12        |                  +--+                   |          PF22
   PF11        |                                         |          PF21
  +---+       +v-+          +--+          +--+         +-v+        +---+
  +---+       ++-+          +--+          +--+         +-++        +---+
               |                                         |
               |                                         |
               |            +--+          +--+           |

             Figure 3: CCDR framework for Multi-BGP deployment

6.  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

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   the prefixes that contained in the corresponding PCEP message, and
   build the end to end dedicated path hop by hop.

   The dedicated path is preferred by making sure that the explicit
   route created by PCE has the higher priority (lower route preference)
   than the route information created by any other protocols (including
   the route manually configured).

   All above dynamically created states (BGP sessions, Prefix advertised
   prefix, Explicit route) will be cleared on the expiration of state
   timeout interval which is based on the existing Stateful PCE
   [RFC8231] and PCECC [RFC8283] mechanism.

   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.

7.  Deployment Consideration

7.1.  Scalability

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

   For multiple domains deployment, the PCE or the pool of PCEs that
   reponsible for these domains need only control the edge router to
   build multiple eBGP sessions, all other procedures are the same that
   in one domain.

   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.  For
   example, if we want to differentiate 1000 prefixes from the normal
   traffic, CCDR needs only one explicit peer route in every on-path
   router, but the BGP flowspec or Openflow needs 1000 policy routes on

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7.2.  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.

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

7.3.  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.

8.  Security Considerations

   A PCE needs to assure calculation of E2E path based on the status of
   network 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.

   The setup of BGP session, prefix advertisement and explicit peer
   route establishment are all controlled by the PCE.  To prevent the
   bogus PCE to send harmful messages to the network nodes, the network
   devices should authenticate the validity of PCE and keep secures
   communication channel between them.  Mechanism described in [RFC8253]
   should be used to avoid such situation.

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

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9.  IANA Considerations

   This document does not require any IANA actions.

10.  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.

11.  References

11.1.  Normative References

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

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

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,

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   [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,

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,

   [RFC8283]  Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
              Architecture for Use of PCE and the PCE Communication
              Protocol (PCEP) in a Network with Central Control",
              RFC 8283, DOI 10.17487/RFC8283, December 2017,

   [RFC8735]  Wang, A., Huang, X., Kou, C., Li, Z., and P. Mi,
              "Scenarios and Simulation Results of PCE in a Native IP
              Network", RFC 8735, DOI 10.17487/RFC8735, February 2020,

11.2.  Informative References

              Wang, A., Khasanov, B., Fang, S., and C. Zhu, "PCEP
              Extension for Native IP Network", draft-ietf-pce-pcep-
              extension-native-ip-05 (work in progress), February 2020.

Authors' Addresses

   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209

   Email: wangaj3@chinatelecom.cn

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

   Email: khasanov.boris@huawei.com

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   Quintin Zhao
   Etheric Networks
   SAN MATEO, CA  94402

   Email: qzhao@ethericnetworks.com

   Huaimo Chen
   Boston, MA

   Email: huaimo.chen@futurewei.com

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