]> China Mobile

Beijing CN yangfeng@chinamobile.com

New H3C Technologies

Beijing CN linchangwang.04414@h3c.com

ops SRops Segment routing (SR) is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. An SR Policy is associated with one or more candidate paths, and each candidate path is either dynamic, explicit or composite. This document describes a policy selection mechanism among the candidate SR Policies based on network quality.

Introduction Segment routing (SR) is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. An SR Policy is associated with one or more candidate paths, and each candidate path is either dynamic, explicit or composite. The specification defines a mechanism for disseminating path delay information across multiple Autonomous Systems (ASes). This information is used for BGP route computation. An SR Policy is associated with one or more candidate paths. A composite candidate path acts as a container for grouping SR Policies. As described in section 2.2 in , the composite candidate path construct enables combination of SR Policies, each with explicit candidate paths and/or dynamic candidate paths with potentially different optimization objectives and constraints, for load-balanced steering of packet flows over its constituent SR Policies. For convenience, the composite candidate path formed by the combination of SR Policies is called parent SR Policy in . Different enterprise applications have varying network performance requirements. For instance, conference is highly sensitive to packet loss and jitter, while CRM applications are not highly demanding in terms of latency and packet loss. This document describes a policy selection mechanism among the candidate SR Policies based on network quality in IPv6 environments.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Terminology The definitions of the basic terms are identical to those found in Segment Routing Policy Architecture . CRM: Customer Relationship Management is a critical application that requires low bandwidth and low latency network connection. Parent SR Policy: Refer to . A Parent SR Policy is the composite candidate path that acts as a container for grouping SR Policies which meet different service optimization objectives and constraints and have the same destination endpoint.

Problem and Requirements Take the network shown in below as an example to illustrate the current problems. CE1 and CE2 are the two access endpoints of the IP telecom network. There are many service flows between CE1 and CE2 that have different requirements for forwarding quality. E.g. CRM and conference traffic have different SLA requirement, and expected be carried by different SR Policies. Generally, from CE1 to CE2, conference services with low latency requirements are forwarded along SR Policy PE1->P1->P2->PE2 and PE1->P3->P4->PE2. The CRM traffic is forwarded along the other SR Policy PE1->P5->P6->PE2. When failure or degradation happened in CRM SR Policy, it should be possible to switchover CRM traffic to conference SR Policy.

Based on such scenario, the following requirements should be met: Maximize failure/degradation protection In case of failure or degradation detected on one SR Policy, it should be possible to do inter-policy protection. Minimal impact after taking repairing action Repair action can be done on flow level to minimize the ripple effect cause by forwarding path switchover. Maximize bandwidth efficiency For some critical applications, it should be possible to forward the traffic over lower class policy in case of higher class SR Policy degradation. Refer to , the services with different forwarding quality requirements to the same destination endpoint can be implemented through parent SR Policy. This document proposes an SR Policy selector for parent SR Policy based on network quality requirement. The head end node of parent SR Policy selects the best constituent SR Policy for the application according to the quality of the constituent SR Policy. Take as an example, there is a parent SR Policy between PE1 to PE2, which has multiple constituent SR Policies. An SR Policy selection mechanism is needed, which should select best constituent SR Policy in the parent SR Policy. When the head node detects the quality degradation of the active constituent SR Policy, it will select another one in the parent SR Policy.

SR Policy Selector

Processing Model A new priority and a new quality threshold is created for the parent SR Policy. The lower the priority number, the higher the priority. That means active constituent SR Policy will be the one with higher priority and meeting the quality threshold. When the network quality degradation is happened on the active constituent SR Policy, such as the packet loss rate exceeds the threshold, switch to the next high priority constituent SR Policy which can meet the threshold value. If the quality of the high priority constituent SR Policy is restored and the specified quality threshold is met, the traffic will be switched back after a period of wait-to-restore time. According to the processing logic, the SR Policy Selector model can be divided into five units, including Flow Classification, Flow Steering, SR Policy Selector, Flow Forwarding, and Network Quality Measurement, as shown in below.

| +--->| Flow | | Classification | | SR Policy Selector | | Forwarding | +----------------+ +----------------------+ +------------+ ^ | +---------+-------+ | Network Quality | | Measurement | +-----------------+ ]]>

The functions of each unit are described below.

Flow Classification After receiving the traffic, the head node first needs to label the traffic with application type according to classification configuration.

SR Policy Selector SR Policy Selector obtains the current quality of each constituent SR Policy from the Network Quality Measurement unit. Based on the quality threshold and the priority, SR Policy Selector selects the active constituent SR Policy.

Each parent SR Policy contains multiple constituent SR Policies. Each constituent SR Policy will include two new configuration parameters, "priority" and "threshold" in this proposal. The constituent SR Policy with the highest priority and qualified threshold will be selected to carry the traffic. To avoid frequent path switching when the network quality is unstable, a wait-to-restore timer is required. Only after automatic restore is allowed and the wait-to-restore timer is timeout, the forwarding path switch from the current constituent SR Policy to the one with higher priority.

Network Quality Measurement The Network Quality Measurement unit regularly monitors the quality of all effective forwarding paths according to the measurement cycle, records the current performance measurement data of the path, and reports it to the SR Policy Selector unit, which decides whether to switch paths. The following network quality parameters can be used: Jitter Latency Packet loss Available bandwidth Bandwidth utilization Current traffic statistics Other forwarding performance parameters The quality parameters can be obtained through active or passive performance measurement methods, such as STAMP, TWAMP, SR bandwidth measurement, etc. The network quality parameters can be calculated by the controller and distributed to the head end node, or calculated by the head end node according to the network measurement data. The measurement method and quality parameter acquisition method are beyond the scope of this document.

Flow Forwarding The service flow is forwarded according to the path determined by the SR Policy Selector unit. When there are multiple paths with the same priority, the traffic will share the load among these SR Policy paths with the same priority according to the weight value.

Examples of SR Policy Selector The application of SR Policy Selector is described in detail in L3VPN over TE scenario. Take the example shown in . There are two services between CE1 and CE2: conference and CRM. The traffic from CE1 to CE2 can be forwarded through two paths: Path1 (PE1->P1->P2->PE2 and PE1->P3->P4->PE2) and Path2 (PE1->P5->P6->PE2). The conference service traffic will be forwarded through Path1 first. The CRM service traffic will be forwarded through Path2 first. When the transmission delay of Path1 exceeds the threshold value and Path2 can meet the delay requirements, switch the conference service to Path2. When the remaining bandwidth of Path2 is less than the bandwidth guarantee threshold, if Path1 still has enough remaining bandwidth, the CRM traffic exceeding the bandwidth will be directed to Path1. The configuration on the head node PE1 includes the following three parts. These configurations can be directly configured on the node or distributed through the controller. Configure the parent SR Policy.

Configure constituent SR Policy.

segment-list sr-policy path2 (color 200, PE2_SID) segment-list ]]>

Define three SR Policy Selector policies, and specify the threshold of network quality, priority.

IANA Considerations This memo includes no request to IANA.

Security Considerations This document does not introduce any security considerations.

Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. Segment Routing (SR) allows a node to steer a packet flow along any path. Intermediate per-path states are eliminated thanks to source routing. SR Policy is an ordered list of segments (i.e., instructions) that represent a source-routed policy. Packet flows are steered into an SR Policy on a node where it is instantiated called a headend node. The packets steered into an SR Policy carry an ordered list of segments associated with that SR Policy. This document updates RFC 8402 as it details the concepts of SR Policy and steering into an SR Policy. A Segment Routing (SR) Policy is an ordered list of segments (also referred to as "instructions") that define a source-routed policy. An SR Policy consists of one or more Candidate Paths (CPs), each comprising one or more segment lists. A headend can be provisioned with these CPs using various mechanisms such as Command-Line Interface (CLI), Network Configuration Protocol (NETCONF), Path Computation Element Communication Protocol (PCEP), or BGP. This document specifies how BGP can be used to distribute SR Policy CPs. It introduces a BGP SAFI for advertising a CP of an SR Policy and defines sub-TLVs for the Tunnel Encapsulation Attribute to signal information related to these CPs. Furthermore, this document updates RFC 9012 by extending the Color Extended Community to support additional steering modes over SR Policy. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. China Mobile Juniper Cisco France Telecom France Telecom Huawei The current BGP specification doesn't use network performance metrics (e.g., network latency) in the route selection decision process. This document describes a performance-aware BGP routing mechanism in which network latency metric is taken as one of the route selection criteria. This routing mechanism is useful for those server providers with global reach to deliver low-latency network connectivity services to their customers. China Mobile China Mobile New H3C Technologies ZTE Corporation Huawei Technologies Segment Routing is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. An SR Policy is associated with one or more candidate paths, and each candidate path is either dynamic, explicit, or composite. This document describes SR Policy Group in MPLS and IPv6 environments and illustrates some use cases for parent SR Policy and SR Policy Group to provide best practice cases for operators.

Acknowledgements The authors would like to thank the following for their valuable contributions of this document. TBD.