| TEAS Working Group | A. Wang |
| Internet-Draft | China Telecom |
| Intended status: Experimental | B. Khasanov |
| Expires: December 3, 2020 | Huawei Technologies |
| Q. Zhao | |
| Etheric Networks | |
| H. Chen | |
| Futurewei | |
| June 1, 2020 |
PCE in Native IP Network
draft-ietf-teas-pce-native-ip-07
This document defines the framework for traffic engineering within native IP network, using multiple BGP sessions strategy and PCE -based central control architecture.
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[RFC8735] 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:
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 Central Control Dynamic Routing (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 [I-D.ietf-pce-pcep-extension-native-ip].
This document uses the following terms defined in [RFC5440]: PCE, PCEP
The following terms are used in this document:
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 followings:
After the above actions, the traffic between the PF11 and PF21, and the 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.
If, for example, there is 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 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 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
+---+ +-----+-----+ +-----+-----+ +---+
|SW1+---------+(lo11/lo12)+-------------+(lo21/lo22)+--------------+SW2|
+---+ | R1 +-------------+ R2 | +---+
+-----------+ +-----------+
Figure 1: CCDR framework in simple 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 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 +------------------+
| +--+--+ |
| | |
| | |
| ++-+ |
+------------------+R3+-------------------+
PF12 | +--+ | PF22
PF11 | | PF21
+---+ ++-+ +--+ +--+ +-++ +---+
|SW1+-------+R1+----------+R5+----------+R6+---------+R7+--------+SW2|
+---+ ++-+ +--+ +--+ +-++ +---+
| |
| |
| +--+ +--+ |
+------------+R2+----------+R4+-----------+
+--+ +--+
Figure 2: CCDR framework in large scale network
In general situation, different applications may require different QoS criteria, which may include:
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
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, 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.
+------------+
| 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 framework for Multi-BGP deployment
The PCEP protocol needs to be extended to transfer the following key parameters:
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.
The explicit route created by PCE has the higher priority than the route information created by other protocols, including the route manually configured.
All above dynamically created states (BGP sessions, Prefix advertised prefix, Explict route) will be cleared once the connection between the PCE and network devices is interrupted.
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.
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 domain deployment, the PCE 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 them.
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.
Not every router within the network will support the PCEP extension that defined in [I-D.ietf-pce-pcep-extension-native-ip] simultaneously.
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.
A PCE assures calculations of 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.
This document does not require any IANA actions.
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.
| [I-D.ietf-pce-pcep-extension-native-ip] | Wang, A., Khasanov, B., Fang, S. and C. Zhu, "PCEP Extension for Native IP Network", Internet-Draft draft-ietf-pce-pcep-extension-native-ip-05, February 2020. |