TEAS Working Group A. Wang Internet-Draft China Telecom Intended status: Experimental B. Khasanov Expires: May 19, 2021 Yandex LLC Q. Zhao Etheric Networks H. Chen Futurewei November 15, 2020 PCE in Native IP Network draft-ietf-teas-pce-native-ip-13 Abstract This document defines an architecture for providing traffic engineering in a native IP network using multiple BGP sessions and a Path Computation Element (PCE)-based central control mechanism. It defines the Central Control Dynamic Routing (CCDR) procedures and identifies needed extensions for the Path Computation Element Communication Protocol (PCEP). 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/. 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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. CCDR Architecture in Simple Topology . . . . . . . . . . . . 4 4. CCDR Architecture 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 . . . . . . . . . . . . . . . . . . . . 9 7.3. Incremental deployment . . . . . . . . . . . . . . . . . 10 7.4. Loop Avoidance . . . . . . . . . . . . . . . . . . . . . 10 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 11 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 11.1. Normative References . . . . . . . . . . . . . . . . . . 11 11.2. Informative References . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction [RFC8283], based on an extension of the PCE architecture described in [RFC4655] , introduced a broader use applicability for a PCE as a central controller. PCEP is continued to be used as the protocol between PCE and PCC. Building on this work, this document describes a solution using a PCE for centralized control in a native IP network to provide End-to-End(E2E) performance assurance and QoS for traffic. The solution combines the use of distributed routing protocols and a centralized controller, referred to as Centralized Control Dynamic Routing(CCDR). [RFC8735] describes the scenarios and simulation results for traffic engineering in a native IP network based on use of a CCDR architecture. Per [RFC8735], the architecture for traffic engineering in a native IP network should meet the following criteria: o Same solution for native IPv4 and IPv6 traffic. Wang, et al. Expires May 19, 2021 [Page 2] Internet-Draft PCE in Native IP Network November 2020 o Support for intra-domain and inter-domain scenarios. o Achieve End to End traffic assurance, with determined QoS behavior, for traffic requiring a service assurance(prioritized traffic). o No changes in a router's forwarding behavior. o Capability to use the power of centralized control and the flexibility/robustness of a distributed network control plane. o Support different network requirements such as large traffic amount and prefix scale. o Ability to adjust the optimal path dynamically upon the changes of network status. No need for physical links resources reservations to be done in advance. Building on the above documents, this document defines an architecture meeting these requirements by using multiple a BGP session strategy and a PCE as the centralized controller. The architecture depends on the central control (PCE) element to compute the optimal path, and utilizes the dynamic routing behavior of IGP/ BGP protocols for forwarding the traffic. The related PCEP extensions are provided in draft [I-D.ietf-pce-pcep-extension-native-ip]. 2. Terminology This document uses the following terms defined in [RFC5440]: o PCE o PCEP o PCC Other terms are defined in this document: o CCDR: Central Control Dynamic Routing o E2E: End to End o ECMP: Equal-Cost Multipath o RR: Route Reflector Wang, et al. Expires May 19, 2021 [Page 3] Internet-Draft PCE in Native IP Network November 2020 o SDN: Software Defined Network 3. CCDR Architecture in Simple Topology Figure 1 illustrates the CCDR architecture 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 accordingly. +-----+ +----------+ PCE +--------+ | +-----+ | | | | BGP Session 1(lo11/lo21)| +-------------------------+ | | | BGP Session 2(lo12/lo22)| +-------------------------+ PF12 | | PF22 PF11 | | PF21 +---+ +-----+-----+ +-----+-----+ +---+ |SW1+---------+(lo11/lo12)+-------------+(lo21/lo22)+--------------+SW2| +---+ | R1 +-------------+ R2 | +---+ +-----------+ +-----------+ Figure 1: CCDR architecture in simple topology In the Intra-AS scenario, IGP and BGP combined with a PCE are deployed between R1 and R2. In the inter-AS scenario, only the 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 architecture for this simple topology are the following: o Build two BGP sessions between R1 and R2, via the different loopback addresses on these routers. o Using the PCE, set the explicit peer route on R1 and R2 for BGP next hop to different physical link addresses between R1 and R2. The explicit peer route can be set in the format of a static route, which is different from the route learned from the IGP protocol. Wang, et al. Expires May 19, 2021 [Page 4] Internet-Draft PCE in Native IP Network November 2020 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. After the above actions, the bi-directional traffic between the PF11 and PF21, and the bi-directional traffic between PF12 and PF22 will go through different physical links between R1 and R2. 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 next hop for BGP session 2. In this case, the prefixes that are advertised by the BGP peers need not be changed. If, for example, there is bi-directional priority traffic from another address pair (for example prefix PF13/PF23), and the total volume of priority 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-directional traffic between PF13/PF23 will go through the same assigned dedicated physical links as the traffic between PF12/PF22. Such a decoupling philosophy of the IGP/BGP traffic link and the physical link achieves a flexible control capability for the network traffic, achieving the needed QoS assurance to meet the application's requirement. The router needs only support native IP and multiple BGP sessions setup via different loopback addresses. 4. CCDR Architecture in Large Scale Topology When the priority traffic spans across a large scale network, as that illustrated in Figure 2, the multiple BGP sessions cannot be established hop by hop, for example, the iBGP within one AS. For such a scenario, we propose using a Route Reflector (RR) [RFC4456] to achieve a 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 the same as that described in the CCDR architecture for the 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 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 priority traffic) to the selected forwarding address. Wang, et al. Expires May 19, 2021 [Page 5] Internet-Draft PCE in Native IP Network November 2020 +-----+ +----------------+ PCE +------------------+ | +--+--+ | | | | | | | | ++-+ | +------------------+R3+-------------------+ PF12 | +--+ | PF22 PF11 | | PF21 +---+ ++-+ +--+ +--+ +-++ +---+ |SW1+-------+R1+----------+R5+----------+R6+---------+R7+--------+SW2| +---+ ++-+ +--+ +--+ +-++ +---+ | | | | | +--+ +--+ | +------------+R2+----------+R4+-----------+ +--+ +--+ Figure 2: CCDR architecture in large scale network 5. CCDR Multiple BGP Sessions Strategy Generally, different applications may require different QoS criteria, which may include: o Traffic that requires low latency and is not sensitive to packet loss. o Traffic that requires low packet loss and can endure higher latency. o Traffic that requires low jitter. These different traffic requirements can be summarized in the following table: +----------------+-------------+---------------+-----------------+ | 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 Wang, et al. Expires May 19, 2021 [Page 6] Internet-Draft PCE in Native IP Network November 2020 has end to end under-loading links; for Prefix Set No.3, we can let traffic pass over a determined single path, as no Equal Cost Multipath (ECMP) distribution on the parallel links is desired. It is almost impossible to provide an End-to-End (E2E) path efficiently with latency, jitter, and packet loss constraints to meet the above requirements in a large scale IP-based network only using a distributed routing protocol, but these requirements can be met with the assistance of PCE, as that described in [RFC4655] and [RFC8283]. The PCE will have the overall network view, ability to collect the real-time network topology, and the network performance information about the underlying network. The PCE can select the appropriate path to meet the various network performance requirements for different traffic. The architecture to implement the CCDR Multiple BGP sessions strategy is as the follows: The PCE will be responsible for the optimal path computation for the different priority classes of traffic: o PCE collects topology information via BGP-LS [RFC7752] and link utilization information via the existing Network Monitoring System (NMS) from the underlying network. o PCE calculates the appropriate path based upon the application's requirements, and sends the key parameters to edge/RR routers(R1, R7 and R3 in Figure 3) to establish multiple BGP sessions. The loopback addresses used for the BGP sessions should be planned in advance and distributed in the domain. o PCE sends the route information to the routers (R1,R2,R4,R7 in Figure 3) on the 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. o PCE send the prefixes information to the PCC for advertising different prefixes via the specified BGP session. o If the priority traffic prefixes were changed but the total volume of priority traffic does not exceed the physical capacity of the previous E2E path, the PCE needs only change the prefixed advertised via the edge routers (R1,R7 in Figure 3). o If the volume of priority traffic exceeds the capacity of the previous calculated path, the PCE can recalculate and add the appropriate paths to accommodate the exceeding traffic. After Wang, et al. Expires May 19, 2021 [Page 7] Internet-Draft PCE in Native IP Network November 2020 that, the PCE needs to update the on-path routers to build the forwarding path hop by hop. +------------+ | Application| +------+-----+ | +--------+---------+ +----------+SDN Controller/PCE+-----------+ | +--------^---------+ | | | | | | | PCEP | BGP-LS|PCEP | PCEP | | | | +v-+ | +------------------+R3+-------------------+ PF12 | +--+ | PF22 PF11 | | PF21 +---+ +v-+ +--+ +--+ +-v+ +---+ |SW1+-------+R1+----------+R5+----------+R6+---------+R7+--------+SW2| +---+ ++-+ +--+ +--+ +-++ +---+ | | | | | +--+ +--+ | +------------+R2+----------+R4+-----------+ Figure 3: CCDR architecture for Multi-BGP sessions deployment 6. PCEP Extension for Key Parameters Delivery The PCEP protocol needs to be extended to transfer the following key parameters: o Peer information that is used to build the BGP session o Explicit route information to BGP next hop of advertised prefixes o Advertised prefixes and their associated BGP session. Once the router receives such information, it should establish the BGP session with the peer appointed in the PCEP message, build the end to end dedicated path hop by hop, and advertise the prefixes that contained in the corresponding PCEP message. 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 other dynamic protocols. Wang, et al. Expires May 19, 2021 [Page 8] Internet-Draft PCE in Native IP Network November 2020 All above dynamically created states (BGP sessions, Explicit route, Prefix advertised prefix, ) will be cleared on the expiration of state timeout interval which is based on the existing Stateful PCE [RFC8231] and PCECC [RFC8283] mechanism. Regarding the BGP session, it is not different from that configured via the manual or NETCONF/YANG. Different BGP sessions are used mainly for the clarification of the network prefixes, which can be differentiated via the different BGP nexthop. Based on this strategy, if we manipulate the path to the BGP nexthop, then the path to the prefixes that advertised with the BGP sessions will be changed accordingly. Details of communications between PCEP and BGP subsystems in the router's control plane are out of scope of this draft and will be described in a separate draft [I-D.ietf-pce-pcep-extension-native-ip] . 7. Deployment Consideration 7.1. Scalability In the CCDR architecture, only the edge routers that connects with PCE are responsible for the prefixes advertisement via the multiple BGP sessions deployment. The route information for these prefixes within the on-path routers is distributed via the BGP protocol. For multiple domains deployment, the PCE, or the pool of PCEs responsible for these domains, needs only to control the edge router to build the multiple EBGP sessions; all other procedures are the same as within one domain. Unlike the solution from BGP Flowspec, the on-path router needs only to keep the specific policy routes for the BGP next-hop of the differentiate prefixes, not the specific routes to the prefixes themselves. This lessens the burden of the table size of policy based routes for the on-path routers; and has more expandability compared with BGP flowspec or Openflow solutions. 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, whereas the BGP flowspec or Openflow solutions need 1000 policy routes on them. 7.2. High Availability The CCDR architecture is based on the use of the native IP protocol. If the PCE fails, the forwarding plane will not be impacted, as the BGP sessions between all the devices will not flap and the forwarding table remains unchanged. Wang, et al. Expires May 19, 2021 [Page 9] Internet-Draft PCE in Native IP Network November 2020 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 paths to load balance/hot-standby the priority traffic to meet the path failure situation. For ensuring high availability of a PCE/SDN-controllers architecture, an operator should rely on existing high availability solutions for SDN controllers, such as clustering technology and deployment. 7.3. Incremental deployment Not every router within the network will support the PCEP extension defined in [I-D.ietf-pce-pcep-extension-native-ip] simultaneously. For such situations, routers on the edge of a domain can be upgraded first, and then the traffic can be prioritized between different domains. Within each domain, the traffic will be forwarded along the best-effort path. A Service provider can selectively upgrade the routers on each domain in sequence. 7.4. Loop Avoidance A PCE needs to assure calculation of the E2E path based on the status of network and the service requirements in real-time. The PCE needs to consider the explicit route deployment order (for example, from tail rotuer to head rotuer) to eliminate any possible transient traffic loop. 8. Security Considerations The setup of BGP sessions, prefix advertisement, and explicit peer route establishment are all controlled by the PCE. To prevent a bogus PCE sending harmful messages to the network nodes, the network devices should authenticate the validity of the PCE and ensure a secure communication channel between them. Mechanisms described in [RFC8253] should be used. The CCDR architecture does not require the changes of forwarding behavior on the underlay devices, there will no additional security impacts on these devices. 9. IANA Considerations This document does not require any IANA actions. Wang, et al. Expires May 19, 2021 [Page 10] Internet-Draft PCE in Native IP Network November 2020 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, . [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, . [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, . Wang, et al. Expires May 19, 2021 [Page 11] Internet-Draft PCE in Native IP Network November 2020 [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 [I-D.ietf-pce-pcep-extension-native-ip] Wang, A., Khasanov, B., Fang, S., Tan, R., and C. Zhu, "PCEP Extension for Native IP Network", draft-ietf-pce- pcep-extension-native-ip-09 (work in progress), October 2020. Authors' Addresses Aijun Wang China Telecom Beiqijia Town, Changping District Beijing 102209 China Email: wangaj3@chinatelecom.cn Boris Khasanov Yandex LLC Ulitsa Lva Tolstogo 16 Moscow Russia Email: bhassanov@yahoo.com Quintin Zhao Etheric Networks 1009 S CLAREMONT ST SAN MATEO, CA 94402 USA Email: qzhao@ethericnetworks.com Wang, et al. Expires May 19, 2021 [Page 12] Internet-Draft PCE in Native IP Network November 2020 Huaimo Chen Futurewei Boston, MA USA Email: huaimo.chen@futurewei.com Wang, et al. Expires May 19, 2021 [Page 13]