The Correspondence between Packets and SRv6 Tunnels

Introduction In SRv6 networks, the software-defined network (SDN) controller serves as a core component, responsible for the centralized management and dynamic configuration of network resources. It is crucial for achieving network flexibility and intelligence. In SR, a path must be identified for several use cases, such as binding bidirectional paths [I-D.ietf-pce-sr-bidir-path] and end-to-end performance measurement [I-D.gandhi-spring-udp-pm]. Currently, the controller's perception of SRv6 message paths relies solely on theoretical derivation, which is limited in terms of timeliness and accuracy. Specifically, there is an inherent latency in the controller's update of the network state, and the state acquisition mechanism can occasionally malfunction, necessitating a secondary refresh for validation. This poses a significant challenge for scenarios that rely heavily on real-time state information for path computation and decision-making processes. Using the configuration of multipath tunnels as an example, ideally, it should dynamically adjust traffic routing based on the master-standby relationships and priority levels of the three preconfigured tunnels. This adjustment is crucial for ensuring the high availability and operational efficiency of the network. However, in practical applications, due to latency in the controller's state sensing, it may fail to promptly react to real-time alterations in network linkages. This delay leads to inaccurate path determinations, impacting the efficacy of operations such as traffic metering and appropriate traffic direction. Moreover, in scenarios involving load balancing across tunnels, where a single path encompasses multiple parallel sub-paths, traffic distribution strategies based on hashing rules or random device allocation can enhance bandwidth utilization efficiency. However, they also increase the complexity of operational maintenance monitoring. This is because the current mechanisms struggle to track and validate the actual forwarding routes of packets in real-time, thereby complicating the operation and maintenance oversight. To address these issues, this paper defines a new SRH extension header called "SRv6 Policy Key," which is used to identify the tunnel. This identifier is conveyed through the message header and communicated to the controller by the network node. This process empowers the controller to discern the SR path, thereby enhancing its state-aware capabilities within the Segment Routing domain. As a result, the controller can apprehend the network's real-time status with greater speed and accuracy, significantly aiding in the facilitation of operational maintenance decision-making processes.

Conventions and Definitions 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 RFC2119 when, and only when, they appear in all capitals, as shown here.

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.

SRv6 Policy KEY

Format of an SRv6 Policy KEY

SRv6 Policy KEY TLV

Type: An 8-bit code point.
Length: The length of the variable-length data field in bytes 6.
Flags: 8bit, marks list.
Preference: 32bit, marks SRv6 Policy Candidate Path.
Policy Color: 32bit, a Color of SRv6 Policy.
Headend: 128bit, first node of SRv6 Policy.
Endpoint: 128bit, destination address of SRv6 Policy.

Functional Description

Function1: Path Consistency Verification The awareness of actual paths ensures the controller can accurately evaluate the congruence between the factual routes of data transmission and the pre-established ideal paths. This procedure encompasses a systematic comparison of network packets'forwarding trajectories against the planned routes, aiming to detect and rectify potential deviations in path. Consequently, this boosts the network's reliability and operational efficiency.

Function2: Service flow analysis function A network node can document the traversal of SRv6 Policies, Candidate Paths, and Lists, and accumulate statistics in accordance with the service logic at these three hierarchical levels. In instances of node upgrade or relocation, the impacted services can thus be identified. Network nodes are capable of gathering traffic statistics based on the SRv6 Policies, Candidate Paths, and Lists that traverse the node, correlating these statistics with the service logic at the three tiers.

Function3: Controller path visualization The controller gathers the header information from packets processed at each network node and conducts statistical analyses, thereby enriching the visibility and manageability of network path data.

Use Case

Case 1: Enhancing Real-Time Path Recognition The controller cannot sense packet paths in real-time. The SRv6 Policy Key addresses this limitation by providing distinctive identifiers for each path, thereby enhancing the controller's ability to identify actual paths in real-time. The accuracy of deducing real paths is impeded by the latency in sensing path information. In light of the challenges posed by delays in link state updates and the necessity for revalidation of initially detected anomalies, coupled with the issue of delayed updates to network device configurations, the SRv6 Policy Key fortifies the controller's capability for instantaneous path recognition. By embedding a unique identifier for each path, the SRv6 Policy Key effectively mitigates the difficulties associated with making path decisions reliant on immediate information. This enhancement ensures the accuracy and efficiency of network control, facilitating superior decision-making based on real-time data. This is evident in two scenarios: - In the architectural design featuring triple-redundant tunnels, achieving a seamless switch-over between the primary and backup tunnels necessitates precise awareness of the state of each path to uphold uninterrupted service delivery. - Under the policy of single-tunnel multipath, traffic is dynamically distributed based on link conditions and priority levels. This requires accurate path awareness to ensure efficient traffic handling and optimization, thereby maximizing network performance.

Case 2： Improving Path Visibility The controller cannot sense the actual paths in real-time. In intricate network load-balancing scenarios, a single path is bifurcated into three concurrent sub-paths to collaboratively bear the traffic load, with allocation executed randomly by devices following designated hash rules. While this mechanism enhances bandwidth utilization, it presents the challenge of not being able to deduce the actual path taken, thereby introducing complexities to Operation & Maintenance (O&M) management and hindering fault diagnosis and resolution. Through the SRv6 Policy Key, the controller can attain real-time visibility of paths, thereby overcoming the uncertainty and unpredictability of paths engendered by the original random allocation mechanism.

Security Considerations TBD.

IANA Considerations TBD.