IDR X. Yi, Ed. Internet-Draft M. Han, Ed. Intended status: Standards Track China Unicom Expires: 7 January 2027 C. Li, Ed. G. Zeng, Ed. Huawei Technologies 6 July 2026 Distribution of Service Metadata in BGP FlowSpec draft-yi-idr-bgp-fs-edge-service-metadata-06 Abstract In edge computing and distributed cloud environments, a service may be deployed on multiple instances across one or more sites, referred to as an edge service. The edge service is typically associated with an ANYCAST IP address. With the emergence of Computing-Aware Traffic Steering (CATS) requirements, there is a growing need to consider both network and computing metrics when making traffic steering decisions. Traditional routing protocols lack the capability to convey compute-related information, necessitating extensions to existing protocols. This draft defines a mechanism to distribute service routes along with computing-related metadata using BGP FlowSpec. The service metadata, including compute resource status and performance metrics, can be collected by a central controller, processed, and then distributed to ingress routers using BGP FlowSpec extensions. This enables ingress routers to make path selections based not only on routing cost but also on the running environment and resource availability of edge services, thereby optimizing Quality of Experience (QoE). The mechanism is aligned with the CATS architecture and metric framework by allowing the advertised metadata to represent either selected original service metrics or an aggregated Level 2 (L2) metric. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Yi, et al. Expires 7 January 2027 [Page 1] Internet-Draft Service Metadata in BGP FlowSpec July 2026 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 7 January 2027. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.3. Relationship to CATS . . . . . . . . . . . . . . . . . . 3 2. BGP FlowSpec Extension for Service Metadata . . . . . . . . . 4 2.1. Metadata Path Attribute TLV . . . . . . . . . . . . . . . 5 2.2. Aggregated Metric Path Attribute TLV . . . . . . . . . . 5 3. Metadata Distribution and Selection Behavior . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 7.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction The proliferation of edge computing and multi-cloud deployments has led to services being distributed across numerous geographically dispersed sites. These deployments support applications such as VR/ AR, intelligent transportation, and distributed AI workloads, which require low latency and high reliability. In such environments, multiple service instances are replicated across various sites to ensure sufficient capacity and maintain the required QoE. Yi, et al. Expires 7 January 2027 [Page 2] Internet-Draft Service Metadata in BGP FlowSpec July 2026 Computing-Aware Traffic Steering (CATS) [I-D.ietf-cats-framework] has been proposed as a traffic engineering approach that optimizes traffic steering to service instances by considering both network and compute resources. The CATS use cases and requirements [I-D.ietf-cats-usecases-requirements] describe service deployment scenarios in which multiple service instances may be reachable through different network paths and may have different compute status. However, existing routing protocols like BGP focus primarily on network-layer metrics (e.g., AS paths, hop count) and lack the ability to convey compute-related information such as CPU utilization, memory capacity, or service load. This gap creates a critical challenge: without compute-aware metrics, networks cannot make optimal steering decisions. For example, a user might be routed to the nearest site based on network latency, only to find it overloaded, while a lighter-loaded site with slightly higher latency could provide better overall QoE. To address this, there is a need to extend BGP FlowSpec to carry both service routes and compute-related metadata, enabling ingress routers to make informed decisions based on a holistic view of network and compute resources. This document defines an extension to BGP FlowSpec that allows the distribution of service metadata alongside service routes. The extension leverages the metrics framework defined in [I-D.ietf-cats-metric-definition], particularly the Level 2 (L2) normalized metrics, to provide a scalable and efficient way to convey compute-related information. 1.1. Terminology 1.2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 1.3. Relationship to CATS The CATS architecture defines a control-plane function that collects service and network information, computes traffic steering decisions, and provides the information required by the forwarding nodes. In the deployment model considered by this document, a BGP FlowSpec controller acts as the entity that receives or derives the service metadata and distributes it to ingress routers together with the service route information. Yi, et al. Expires 7 January 2027 [Page 3] Internet-Draft Service Metadata in BGP FlowSpec July 2026 The metadata advertised by this document is intended to be used as input to the ingress router's service instance selection process. It does not define a new CATS computation algorithm. Instead, it provides a BGP FlowSpec encoding by which the result of metric collection, normalization, and aggregation can be made available to the ingress routers that steer traffic toward the selected egress router or service site. 2. BGP FlowSpec Extension for Service Metadata The goal of the BGP FlowSpec extension is to distribute the information of the service route and metadata. A service is identified by a prefix and this information is carried using the existing Destination Prefix Component specified in [RFC8955] and [RFC8956]. [I-D.ietf-idr-ts-flowspec-srv6-policy] defines that the Color Extended Community and BGP Prefix-SID attribute is carried in the context of the FlowSpec NLRI. In addition to that, this document proposes to carry the service metadata attribute(See Figure 1). The ingress router can compare the compute metric of different sites and steer the traffic into the best one using the SR policy. The metadata can be original values defined in [I-D.ietf-idr-5g-edge-service-metadata] or an aggregated one calculated using original values. +------------+ | BGP FS | | Controller | +------------+ | FlowSpec route to Ingress: | NLRI: Destination Prefix | Redirect to IPv6 Nexthop: Egress's Address | Policy Color: C1 | PrefixSID: End.X1 | Service Metadata: Compute metric | .-----. | ( ) V .--( )--. +-------+ ( ) +------+ +---------+ | |_( SRv6 Core Network )_| | (End.X1) | | |Ingress| ( ================> ) |Egress|----------| Site | +-------+ (SR List) +------+ +---------+ '--( )--' ( ) '-----' Figure 1: Example of using BGP FlowSpec to distribute the service route and metadata Yi, et al. Expires 7 January 2027 [Page 4] Internet-Draft Service Metadata in BGP FlowSpec July 2026 2.1. Metadata Path Attribute TLV The Metadata Path Attribute TLV is the same as defined in [I-D.ietf-idr-5g-edge-service-metadata], including the following three sub-TLVs: 1. Site Preference Index sub-TLV indicates the preference to choose the site. 2. Capacity Index sub-TLV indicates the capability of a site. One Edge Site can be in full capacity, reduced capacity, or completely out of service. 3. Load Measurement sub-TLV indicates the load level of the site. 2.2. Aggregated Metric Path Attribute TLV To align with the metrics framework defined in [I-D.ietf-cats-metric-definition], this document introduces an Aggregated Metric Path Attribute TLV(See Figure 2) that carries a Level 2 (L2) normalized metric. The L2 metric is a single normalized value that represents the overall performance of a service instance, derived from lower-level metrics (L0 or L1) using aggregation and normalization functions. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Aggregated Metadata Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Aggregated Metric Value (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Aggregated Metric Path Attribute TLV format * Type: identify the Aggregated Metadata Attribute, to be assigned by IANA. * Length: the total number of the octets of the value field. * Value: value of Aggregated Computing metric. The Aggregated Metric Value is a 32-bit unsigned integer that carries a normalized L2 metric. The detailed normalization and aggregation functions are outside the scope of this document and are expected to follow the metric semantics and aggregation model defined in [I-D.ietf-cats-metric-definition]. Unless otherwise specified by local policy, a lower value indicates a more preferable service Yi, et al. Expires 7 January 2027 [Page 5] Internet-Draft Service Metadata in BGP FlowSpec July 2026 instance. All candidate service instances compared by the same ingress router MUST use the same metric semantics and normalization function. An implementation MAY use the Aggregated Metric Path Attribute TLV together with the Metadata Path Attribute TLV defined in [I-D.ietf-idr-5g-edge-service-metadata]. When both original metadata and the aggregated metric are present, the aggregated metric SHOULD be used for fast comparison among service instances, while the original metadata MAY be used for policy constraints, troubleshooting, or local tie-breaking. 3. Metadata Distribution and Selection Behavior A BGP FlowSpec controller that advertises the metadata defined in this document SHOULD ensure that the metadata and the associated service route describe the same service instance or site. If the controller aggregates multiple original metrics into one L2 metric, it SHOULD apply the same aggregation policy to all service instances that are candidates for the same service prefix. An ingress router receiving multiple FlowSpec routes for the same service prefix can use the received metadata as part of its local selection process. The exact selection algorithm is a matter of local policy. A typical policy can first filter out service instances that are administratively unavailable or out of capacity, then compare the aggregated metric, and finally apply local tie- breakers such as network path preference, SR Policy color, or configured site preference. The metadata is expected to be dynamic. To avoid route churn, the controller SHOULD apply thresholding, hysteresis, damping, or rate limiting before advertising metadata changes. The ingress router SHOULD treat withdrawn or expired metadata as unavailable for compute-aware selection and fall back to local routing or policy behavior. 4. Security Considerations TBD. 5. IANA Considerations This document requests IANA to assign the following code point from the registry called "BGP Path Attributes": Yi, et al. Expires 7 January 2027 [Page 6] Internet-Draft Service Metadata in BGP FlowSpec July 2026 +=======+==========================+=============+ | Value | Description | Reference | +=======+==========================+=============+ | TBD1 | Aggregated Metadata Type | Section 2.2 | +-------+--------------------------+-------------+ Table 1 6. Contributors Tao He China Unicom Email: het21@chinaunicom.cn Hang Shi Huawei Technologies Email: shihang9@huawei.com Xiangfeng Ding Huawei Technologies Email: dingxiangfeng@huawei.com Haibo Wang Huawei Technologies Email: rainsword.wang@huawei.com Zicheng Wang Inspur Email: wangzicheng01@inspur.com 7. References 7.1. Normative References [RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M. Bacher, "Dissemination of Flow Specification Rules", RFC 8955, DOI 10.17487/RFC8955, December 2020, . [RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed., "Dissemination of Flow Specification Rules for IPv6", RFC 8956, DOI 10.17487/RFC8956, December 2020, . [I-D.ietf-idr-5g-edge-service-metadata] Dunbar, L., Majumdar, K., Li, C., Mishra, G. S., and Z. Du, "BGP Extension for 5G Edge Service Metadata", Work in Progress, Internet-Draft, draft-ietf-idr-5g-edge-service- metadata-33, 29 May 2026, . [I-D.ietf-cats-metric-definition] Yao, K., Li, C., Contreras, L. M., Ros-Giralt, J., and G. Zeng, "CATS Metrics Definition", Work in Progress, Internet-Draft, draft-ietf-cats-metric-definition-10, 22 June 2026, . Yi, et al. Expires 7 January 2027 [Page 7] Internet-Draft Service Metadata in BGP FlowSpec July 2026 [I-D.ietf-idr-ts-flowspec-srv6-policy] Wenying, J., Liu, Y., Zhuang, S., Mishra, G. S., and S. Chen, "Traffic Steering using BGP FlowSpec with SR Policy", Work in Progress, Internet-Draft, draft-ietf-idr- ts-flowspec-srv6-policy-10, 18 March 2026, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 7.2. Informative References [I-D.ietf-cats-framework] Li, C., Du, Z., Boucadair, M., Contreras, L. M., and J. Drake, "A Framework for Computing-Aware Traffic Steering (CATS)", Work in Progress, Internet-Draft, draft-ietf- cats-framework-24, 2 April 2026, . [I-D.ietf-cats-usecases-requirements] Yao, K., Contreras, L. M., Shi, H., Zhang, S., and Q. An, "Computing-Aware Traffic Steering (CATS) Problem Statement, Use Cases, and Requirements", Work in Progress, Internet-Draft, draft-ietf-cats-usecases-requirements-14, 2 February 2026, . Authors' Addresses Xinxin Yi (editor) China Unicom Beijing China Email: yixx3@chinaunicom.cn Mengyao Han (editor) China Unicom Beijing China Yi, et al. Expires 7 January 2027 [Page 8] Internet-Draft Service Metadata in BGP FlowSpec July 2026 Email: hanmy12@chinaunicom.cn Cheng Li (editor) Huawei Technologies Beijing China Email: c.l@huawei.com Guanming Zeng (editor) Huawei Technologies Beijing China Email: zengguanming@huawei.com Yi, et al. Expires 7 January 2027 [Page 9]