]> Huawei Technologies

Beijing China c.l@huawei.com

Huawei Technologies

Beijing China shihang9@huawei.com

China Unicom

Beijing China het21@chinaunicom.cn

China Unicom

Beijing China pangran@chinaunicom.cn

Huawei Technologies

Beijing China qianguofeng@huawei.com

Routing Inter-Domain Routing Internet Draft In edge computing, a service may be deployed on multiple instances within one or more sites, called edge service. The edge service is associated with an ANYCAST address in the IP layer, and the route of it with potential service metadata will be distributed to the network. The Edge Service Metadata can be used by ingress routers to make path selections not only based on the routing cost but also the running environment of the edge services. The service route with metadata can be collected by a PCE(Path Compute Element) or an analyzer for calculating the best path to the best site/instance. This draft describes a mechanism to collect information of the service routes and related service metadata in BGP-LS. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Inter-Domain Routing Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction Many services deploy their service instances in multiple sites to get better response time and resource utilization. These sites are often geographically distributed to serve the user demand. For some services such as VR/AR and intelligent transportation, the QoE will depend on both the network metrics and the compute metrics. For example, if the nearest site is overloaded due to the demand fluctuation, then steering the user traffic to another light-loaded site may improve the QoE. describes the BGP extension of distributing service route with network and computing-related metrics. The router connected to the site will receive the service routes and service metadata sent from devices inside the edge site, and then generate the corresponding routes and distribute them to ingress routers. However, the route with service metadata on the router connected to the site can be also collected by a central Controller for calculating the best path to the best site. This document defines an extension of BGP-LS to carry the service metadata along with the service route. Using the service metadata and the service route, the controller can calculate the best site for the traffic, giving each user the best QoE.

Terminology

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.

BGP-LS Extension for Service in a Site The goal of the BGP-LS extension is to collect information of the service prefix and metadata of the service, such as network metrics and compute metrics. A service is identified by a prefix, and this information is carried by the existing prefix NLRI TLV. Other information including service metadata is carried by attributes TLVs.

Prefix NLRI A service is identified by a prefix, and the Prefix NLRI defined in the is used to collect the prefix information of the service. The format of the Prefix NLRI is shown in for better understanding.

The IPv4/IPv6 Topology Prefix NLRI Format

Specifically, the service prefix is carried by the IP Reachability Information TLV() inside the Prefix Descriptor field. The Prefix Length field contains the length of the prefix in bits. The IP Prefix field contains the most significant octets of the prefix.

IP Reachability Information TLV Format

Attributes The following three prefix attribute TLVs are used to carry the metadata of a service instance:

1. Metadata Path Attribute TLV carries the computing metric of the service instances such as site preference, capacity index, and load measurement defined in .
2. Prefix SID TLV carries a Prefix SID associated with the edge site.
3. Color Attribute TLV carries the service requirement level information of the service

Metadata Path Attribute TLV The Metadata Path Attribute TLV is an optional attribute to carry the Edge Service Metadata defined in the . It contains multiple sub-TLVs, with each sub-TLV containing a specific metric of the Edge Service Metadata. This document defines a new TLV in BGP-LS, which reuses the name and the format of Metadata Path Attribute TLV.

Metadata Path Attribute TLV format

• Type: identify the Metadata Path Attribute, to be assigned by IANA.
• Length: the total number of octets of the value field.
• Value: contains multiple sub-TLVs.

There are three types of Edge Service Metadata sub-TLVs defined in :

1. Site Preference Index indicates the preference to choose the site.
2. Capacity Index indicates the capability of a site. One Edge Site can be at full capacity, reduced capacity, or completely out of service.
3. Load Measurement indicates the load level of the site.

To collect this information, this document defines TLVs reusing the name and format of the TLVs defined in .

Prefix SID Attribute TLV In some cases, there may be multiple sites connected to one Edge(egress) router through different interfaces. Generally, an overlay tunnel will be used between the ingress router and the egress for steering the traffic to the best site correctly. In SR-MPLS networks or SRv6 networks, a prefix SID is needed. For example, some SRv6 Endpoint Behaviors such as End.DX6, End.X can be encoded for each site so that the egress router can steer the traffic to the corresponding site. The Prefix SID TLV defined can be used to collect this information. The Prefix SID TLV is an optional TLV to carry the Prefix SID associated with the edge site. The TLV format is illustrated in .

Prefix-SID TLV format

• Type: 1158, identify the Prefix SID Attribute.
• Length: the total number of octets of the value field.
• Value: contains Prefix SID sub-TLV.

Color Attribute TLV Color is used to indicate the service level. For example, different sites may have different levels of service capability which is taken into account by the controller when calculating the path to the egress router. More details can be added in the future revision. The TLV format(shown in ) is similar to the BGP Color Extended Community defined in .

Color Attribute TLV format

• Type: identify the Color Attribute, to be assigned by IANA.
• Length: 6, length of Flags + Color Value.
• Flags and Color are the same as defined in . Color Value: 32 bit value of color.

Security Considerations TBD

IANA Considerations This document requires IANA to assign the following code points from the registry called "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs":

Value	Description	Reference
TBD1	Metadata Path Attribute Type
TBD2	Site Preference Sub-Type
TBD3	Capacity Sub-Type
TBD4	Load Measurement Sub-Type1: Aggregated-Cost
TBD5	Load Measurement Sub-Type2: Raw-Measurements
TBD6	Color Attribute Type

Contributors Xiangfeng Ding email: dingxiangfeng@huawei.com

Normative References In a number of environments, a component external to a network is called upon to perform computations based on the network topology and current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network. This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual IGP links. The mechanism described is subject to policy control. Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs). This document defines a BGP path attribute known as the "Tunnel Encapsulation attribute", which can be used with BGP UPDATEs of various Subsequent Address Family Identifiers (SAFIs) to provide information needed to create tunnels and their corresponding encapsulation headers. It provides encodings for a number of tunnel types, along with procedures for choosing between alternate tunnels and routing packets into tunnels. This document obsoletes RFC 5512, which provided an earlier definition of the Tunnel Encapsulation attribute. RFC 5512 was never deployed in production. Since RFC 5566 relies on RFC 5512, it is likewise obsoleted. This document updates RFC 5640 by indicating that the Load-Balancing Block sub-TLV may be included in any Tunnel Encapsulation attribute where load balancing is desired. Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological subpaths, called "segments". These segments are advertised by routing protocols, e.g., by the link-state routing protocols (IS-IS, OSPFv2, and OSPFv3) within IGP topologies. This document defines extensions to the Border Gateway Protocol - Link State (BGP-LS) address family in order to carry SR information via BGP. This document defines procedures and messages for SRv6-based BGP services, including Layer 3 Virtual Private Network (L3VPN), Ethernet VPN (EVPN), and Internet services. It builds on "BGP/MPLS IP Virtual Private Networks (VPNs)" (RFC 4364) and "BGP MPLS-Based Ethernet VPN" (RFC 7432). Futurewei Microsoft Azure Huawei Technologies Verizon China Mobile This draft describes a new Metadata Path Attribute and some Sub-TLVs for egress routers to advertise the Metadata about the attached edge services (ES). The edge service Metadata can be used by the ingress routers in the 5G Local Data Network to make path selections not only based on the routing cost but also the running environment of the edge services. The goal is to improve latency and performance for 5G edge services. The extension enables an edge service at one specific location to be more preferred than the others with the same IP address (ANYCAST) to receive data flow from a specific source, like a specific User Equipment (UE). 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.

Acknowledgements The authors would like to thank Haibo Wang, Lili Wang, Jianwei Mao for their help.