SRv6 Policy Selector

SRv6 Policy Selector China Mobile

Beijing CN yangfeng@chinamobile.com

New H3C Technologies

Beijing CN linchangwang.04414@h3c.com

ops srv6ops 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 SRv6 Policies based on network quality in IPv6 environments.

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 SRv6 Policy is associated with one or more candidate paths. A composite candidate path acts as a container for grouping SRv6 Policies. As described in section 2.2 in , the composite candidate path construct enables combination of SRv6 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 SRv6 Policies. For convenience, the composite candidate path formed by the combination of SRv6 Policies is called parent SRv6 Policy in . Different enterprise applications have varying network performance requirements. For instance, voice is highly sensitive to packet loss and jitter, while OA applications are not highly demanding in terms of latency and packet loss. This document describes a policy selection mechanism among the candidate SRv6 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 . Office Automation: OA, which stands for "Office Automation," is a collaborative office and internal management platform built using network and software technologies. 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 Requriements Take the networking 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. OA and voice traffic have different SLA requirement, and expected be carried by different SRv6 Policies. Generally, from CE1 to CE2, voice services with low latency requirements are forwarded along the highly reliable path PE1->PE2->CE2. The OA traffic is forwarded along the normal path PE3->P5->P6->PE2->CE2. When failure or degradation happened in voice traffic SRv6 Policy, there should be possible to assure basic communication for voice traffic by using OA bandwidth. In single SRv6 Policy, there are many mechanism provide failure/degrade protection, such as TILFA, VPN FRR. However, it is not clear how to handle failure or degradation between multiple SRv6 Policies in a parent SR Policy.

Based on such scenarios, the following requirements are proposed: Maximize failure/degradation protection In case of failure or degradation detected on one SRv6 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 SRv6 Policy degradation. Refer to , the services with different forwarding quality requirements to the same destination endpoint can be implemented through parent SRv6 Policy group. This document proposes an SRv6 Policy selector for parent SRv6 Policy based on network quality requirement. The head end node selects the best constituent SRv6 Policy for the application according to the quality of the constituent SRv6 Policy. Take as an example, there is a parent SRv6 Policy between CE1 to CE2, which has multiple constituent SRv6 Policies. A new SRv6 Policy Selector is defined for the application in the parent SRv6 Policy, which will select best constituent SRv6 Policy in the parent SRv6 Policy. When the head node detects the quality degradation of the active constituent SRv6 Policy, it will select another constituent SRv6 Policy in the parent SRv6 Policy.

SRv6 Policy Selector

Processing Model A new priority and a new quality threshold is created for each constituent SRv6 Policy. The lower the priority number, the higher the priority. That means avtive constituent SRv6 Policy will be the one with higher priority and meeting the quality threshold. When the network quality degradation is happened on the active constituent SRv6 Policy, such as the packet loss rate exceeds the threshold, switch to the next high priority constituent SRv6 Policy. If the quality of the high priority forwarding constituent SRv6 Policy is restored and the specified quality threshold is met, the traffic will be switched back to the high priority constituent SRv6 Policy after a period of wait-to-restore time. According to the processing logic, the SRv6 Policy Policy Selector model can be divided into five units, including Flow Classification, Flow Steering, Policy Selector, Flow Forwarding, and Network Quality Measurement, as shown in below.

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

Flow Steering According to the application type determined by the Flow classification, the header node selects the parent SRv6 Policy for traffic forwarding.

Policy Selector SRv6 Policy Selector obtains the current quality of each constituent SRv6 Policy from the Network Quality Measurement unit. Based on the quality threshold and the priority, SRv6 Policy Selector selects the active constituent SRv6 Policy.

| +-------------+ | | | +------------+ | SRv6 | +-------------+---+ | | | Classified | | Policy | / | | | +->| Selector |<-Measurement-+ | | | Traffic | | | \ | | +------------+ | | + ------------+---+ | | | +->| +-------------+ | | | | | | Active Path | | | | +----------+ | +-------------+ | | | | +-------------+ | | | | | Standby Path| | | | | +-------------+ | | | | Constituent | | | | SRv6 Policy | | | | (lower priority)| | | + ----------------+ | +---------------------------------------------------+ ]]> Each parent SRv6 Policy contains multiple constituent SRv6 Policies. Each constituent SRv6 Policy will include two new configuration parameters, "priority" and "threshold". A lower priority value indicates a higher precedence. The constituent SRv6 Policy with the highest priority and qualified threshold will be active. 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 SRv6 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 SRv6 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 iOAM, STAMP, TWAMP, SRv6 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 Policy Selector unit. When there are multiple paths with the same priority, the traffic will share the load among these SRv6 Policy paths with the same priority according to the weight value.

Examples of Policy Selector The application of Policy Selector is described in detail in L3VPN over TE scenario. The networking is shown in Figure 4 below. CE1 and CE2 belong to the same L3VPN and access the public network through PE1, PE2 and PE3 respectively. There are two services between CE1 and CE2: voice and OA. The traffic from CE1 to CE2 can be forwarded through two paths: Path1 (PE1->PE2->CE2) and Path2 (PE3->P5->P6->PE2->CE2). Among them, the reliability of path 1 is high and the transmission delay is low. Path 2 has a large bandwidth. The voice service traffic will be forwarded through Path1 first. The OA 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 voice service to Path2. When the remaining bandwidth of Path2 is less than the bandwidth guarantee threshold, if Path1 still has enough remaining bandwidth, the OA traffic exceeding the bandwidth will be directed to Path1.

The configuration on the head node CE1 includes the following three parts. These configurations can be directly configured on the node or distributed through the controller. Define three Policy Selector policies, and specify the threshold of network quality, path priority and the corresponding path color value for routing.

Configure forwarding paths.

sr-policy policy-B (color 200, CE2_SID) segment-list ]]> Configure corresponding Policy Selector policies for services with specified characteristics in the parent SRv6 Policy group.

IANA Considerations This memo includes no request to IANA.

Security Considerations This document does not introduce any security considerations.

Segment Routing Architecture 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 Policy Architecture 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. Advertising Segment Routing Policies in BGP 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. Key words for use in RFCs to Indicate Requirement Levels 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. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words 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. BGP Performance-aware Routing Mechanism 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. SR Policy Group 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. Measurement Method for Bandwidth of SRv6 Forwarding Path China Mobile New H3C Technologies New H3C Technologies ZTE Corporation Ruijie Networks This document proposes a method for measuring the actual bandwidth of SRv6 forwarding paths. Carrying the bandwidth information from bottleneck nodes along the packet path in the IPv6 extension header of data packets or active measurement packets, the SRv6 headend node and controller can obtain the actual minimum available bandwidth of the forwarding path in real-time.

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