| TEAS Working Group | A. Wang |
| Internet-Draft | China Telecom |
| Intended status: Experimental | Q. Zhao |
| Expires: October 18, 2019 | B. Khasanov |
| H. Chen | |
| Huawei Technologies | |
| R. Mallya | |
| Juniper Networks | |
| April 16, 2019 |
PCE in Native IP Network
draft-ietf-teas-pce-native-ip-03
This document defines the framework for traffic engineering within native IP network, using Dual/Multi-BGP sessions strategy and PCE-based central control architecture. The proposed central mode control framework conforms to the concept that defined in [RFC8283]. The scenario and simulation results of traffic engineering in Native IP network is described in draft [I-D.ietf-teas-native-ip-scenarios].
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Draft [I-D.ietf-teas-native-ip-scenarios] describes the scenarios, simulation results and suggestions 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 followings criteria:
[I-D.ietf-pce-pcep-extension-native-ip].
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(Centrally Control Dynamic Routing, abbreviated as CCDR ). The related PCEP protocol extensions to transfer the key parameters between PCE and the underlying network devices(PCC) are provided in draft
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] .
Fig.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 IGP/BGP protocol is deployed between R1 and R2. 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 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 changed.
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 ability 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.
| BGP Peer Pair2 |
+------------------+
|lo1 lo1 |
| |
| BGP Peer Pair1 |
+------------------+
IP12 |lo0 lo0 | IP22
IP11 | | IP21
SW1-------R1-----------------R2-------SW2
Links Group
Fig.1 CCDR framework in simple topology
When the assured traffic spans across the large scale network, as that illustrated in Fig.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 Fig.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.
+----------R3(RR)------------+
| |
SW1-------R1-------R5---------R6-------R7--------SW2
| | | |
+-------R2---------R4--------+
Fig.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:
+----------+-------------+---------------+-----------------+
| 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
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 controller, 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 Multi-BGP strategy are the followings:
+----+
***********+ PCE+*************
* +--*-+ *
* / * \ *
* * *
PCEP* BGP-LS/SNMP *PCEP
* * *
* * \ * /
\ * / * \ */
\*/-----------R3--------------*
| |
| |
SW1-------R1-------R5---------R6-------R7--------SW2
| | | |
| | | |
+-------R2---------R4--------+
Fig.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.
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 selected 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 requires by OpenFlow is hardly achievable in many today’s 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 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.
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 unchaned.
If one node on the optimal path is failed, the assurance traffic will fall over to the best-effort forwarding path. One can even design several assurance paths to load balance/hot-standby the assurance traffic to meet the path failure situation, as done in MPLS FRR.
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.
The PCE should have the capability to calculate the loop-free end to end 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 SDN controller and their communication with the underlay devices, which is described in document [RFC5440] and
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.
Penghui Mi and Shaofu Peng contribute the contents of this draft.
The author would like to thank Deborah Brungard, Adrian Farrel, Huaimo Chen, Vishnu Beeram, Lou Berger, Dhruv Dhody and Jessica Chen for their supports and comments on this draft.