| TEAS Working Group | A. Wang |
| Internet-Draft | China Telecom |
| Intended status: Experimental | Q. Zhao |
| Expires: December 28, 2018 | B. Khasanov |
| H. Chen | |
| P. Mi | |
| Huawei Technologies | |
| R. Mallya | |
| Juniper Networks | |
| S. Peng | |
| ZTE Corporation | |
| June 26, 2018 |
PCE in Native IP Network
draft-ietf-teas-pce-native-ip-01
This document defines the framework for CCDR traffic engineering within Native IP network, using Dual/Multi-BGP session 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 CCDR traffic engineering 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 scenario and simulation results for the CCDR traffic engineering. In summary, the requirements for CCDR traffic engineering in Native IP network are the following:
[I-D.ietf-pce-pcep-extension-native-ip].
This document defines the framework for CCDR traffic engineering within Native IP network, using Dual/Multi-BGP session strategy and CCDR architecture, to meet the above requirements in dynamical and central control mode. Future 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] .
Dual-BGP framework for simple topology is illustrated in Fig.1, which is comprised by SW1, SW2, R1, R2. There are multiple physical links between R1 and R2. Traffic between IP11 and IP21 is normal traffic, traffic between IP12 and IP22 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 timely and the corresponding source/destination addresses of the traffic may also change dynamically.
The key idea of the Dual-BGP framework for this simple topology is the following:
So, 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 type of traffic occupy the different dedicated physical links.
If there is more traffic between IP12 and IP22 that needs to be assured , one can add more physical links on 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 two BGP peer need not be changed.
If, for example, there is traffic from another address pair that needs to be assured (for example IP13/IP23), but the total volume of assured traffic does not exceed the capacity of the previous appointed physical links, then one need only to advertise the newly added source/destination prefixes via the BGP peer pair2, then the traffic between IP13/IP23 will go through the assigned dedicated physical links as the traffic between IP12/IP22.
Such decouple philosophy gives the network operator more flexible control ability on the network traffic, get the determined QoS assurance effect to meet the application’s requirement. No complex MPLS signal procedures is introduced, the router need 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 Design Philosophy for Dual-BGP Framework
When the assured traffic spans across one 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 Dual-BGP effect, select one router which performs the role of RR (for example R3 in Fig.2), every other edge router will establish two BGP peer sessions with the RR, using their different loopback addresses respectively. The other two steps for traffic differentiation are same as one described in the Dual-BGP simple topology usage case.
For the example shown in Fig.2, if we select the R1-R2-R4-R7 as the dedicated path, then we 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 actual address of the physical link.
+------------R3--------------+
| |
SW1-------R1-------R5---------R6-------R7--------SW2
| | | |
+-------R2---------R4--------+
Fig.2 Dual-BGP Framework for large scale network
In general situation, several additional traffic differentiation criteria exist, including:
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 difficult and almost impossible to provide an end-to-end (E2E) path with latency, latency variation, packet loss, and bandwidth utilization constraints to meet the above requirements in large scale IP-based network via the traditional distributed routing protocol, but these requirements can be solved using the CCDR architecture since 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 the various network performance requirements of different traffic type.
With the advent of SDN concepts towards pure IP networks, it is possible now to accomplish the central and dynamic control of network traffic according to the application’s various requirements. The procedure to implement the dynamic deployment of Multi-BGP strategy is the following:
+----+
***********+ PCE+*************
* +--*-+ *
* / * \ *
* * *
PCEP* BGP-LS/SNMP *PCEP
* * *
* * \ * /
\ * / * \ */
\*/-----------R3--------------*
| |
| |
SW1-------R1-------R5---------R6-------R7--------SW2
| | | |
| | | |
+-------R2---------R4--------+
Fig.3 PCE based framework for Multi-BGP deployment
The PCEP protocol needs to be extended to transfer the following key parameters:
[I-D.ietf-pce-pcep-extension-native-ip] .
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
The reason why 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, there 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 to influence the edge routers for the prefixes differentiation via the multi-BGP deployment. The route information for these prefixes within the on-path routers were distributed via the traditional 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 scalability when comparing with the solution from BGP flowspec or Openflow.
CCDR framework is based on the traditional 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 the same. 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.
From PCE/SDN-controller HA side we will rely on existing HA solutions of SDN controllers such as clustering.
Not every router within the network support 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 sub domain can be upgraded first, and then the traffic can be assured between different sub domains. Within each sub domain, the traffic will be forwarded along the best-effort path. Service provider can selectively upgrade the routers on each sub-domain in sequence.
Solution described in this draft puts more requirements on the function of PCE and its communication with the underlay devices. 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 also to consider the router order during deployment to eliminate the possible transient traffic loop.
This solution does not require the change of forward behavior on the underlay devices, then there will no additional security impact for the devices.
When deploy the solution on network, service provider should also consider more on the protection of SDN controller and their communication with the underlay devices, which described in document [RFC5440] and [RFC8253]
This document does not require any IANA actions.