



Network Working Group                                          L. Dunbar
Internet-Draft                                                 Futurewei
Intended status: Standards Track                             K. Majumdar
Expires: 16 September 2026                                        Oracle
                                                                   C. Li
                                                     Huawei Technologies
                                                               G. Mishra
                                                                 Verizon
                                                                   Z. Du
                                                            China Mobile
                                                           15 March 2026


               BGP Extension for 5G Edge Service Metadata
               draft-ietf-idr-5g-edge-service-metadata-31

Abstract

   This draft describes a new Edge Metadata Path Attribute and some Sub-
   TLVs for egress routers to advertise the Edge 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).

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
   [RFC2119] [RFC8174] when, and only when, they appear in all capitals,
   as shown here.

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/.



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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   This Internet-Draft will expire on 16 September 2026.

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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
   3.  Edge Metadata Influenced Ingress Node Behavior  . . . . . . .   4
     3.1.  Edge Metadata Influenced BGP Path Selection . . . . . . .   5
     3.2.  Ingress Router Forwarding Behavior  . . . . . . . . . . .   6
     3.3.  Forwarding Behavior when UEs Move . . . . . . . . . . . .   6
   4.  Edge Service Metadata Encoding  . . . . . . . . . . . . . . .   6
     4.1.  Edge Metadata Path Attribute  . . . . . . . . . . . . . .   7
       4.1.1.  Edge Metadata Path Attribute Characteristics  . . . .   7
       4.1.2.  Edge Metadata Path Attribute Processing . . . . . . .   8
       4.1.3.  Sub-TLVs Data Processing  . . . . . . . . . . . . . .   8
       4.1.4.  Edge Metadata Path Attribute Handling Procedure . . .   9
       4.1.5.  Edge Metadata Processing Capability in BGP OPEN
               Message . . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  The Site Preference Index Sub-TLV . . . . . . . . . . . .  10
     4.3.  Site Physical Availability Index Metadata . . . . . . . .  11
       4.3.1.  Site Index Associated to Routes . . . . . . . . . . .  13
       4.3.2.  BGP UPDATE with standalone Site Availability Index  .  13
     4.4.  Service Delay Prediction  . . . . . . . . . . . . . . . .  13
       4.4.1.  Service Delay Prediction Sub-TLV  . . . . . . . . . .  15
     4.5.  Raw Measurement Sub-TLV . . . . . . . . . . . . . . . . .  16
     4.6.  Service-Oriented Capability Sub-TLV . . . . . . . . . . .  18
     4.7.  Service-Oriented Available Resource Sub-TLV . . . . . . .  19
   5.  Service Metadata Propagation Scope  . . . . . . . . . . . . .  20
     5.1.  AS-Scope SubTLV . . . . . . . . . . . . . . . . . . . . .  21



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       5.1.1.  AS-Scope Value Checking Procedure . . . . . . . . . .  22
   6.  Policy Based Metadata Integration . . . . . . . . . . . . . .  22
   7.  Minimum Interval for Metrics Change Advertisement . . . . . .  26
   8.  Validation and Error Handling . . . . . . . . . . . . . . . .  27
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  27
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  27
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
     11.1.  Edge Metadata Path Attribute . . . . . . . . . . . . . .  28
     11.2.  Edge Metadata Capability Code  . . . . . . . . . . . . .  29
     11.3.  Edge Metadata Path Attribute Sub-Types . . . . . . . . .  29
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  30
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  30
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     14.2.  Informative References . . . . . . . . . . . . . . . . .  32
   Appendix A.  Service Delay Prediction Based on Load
           Measurement . . . . . . . . . . . . . . . . . . . . . . .  33
   Appendix B.  Service Metadata Influenced Decision Process . . . .  34
     B.1.  Egress Router Behavior  . . . . . . . . . . . . . . . . .  34
     B.2.  Integrating Network Delay with the Service Metrics  . . .  35
     B.3.  Integrating with BGP Route Selection  . . . . . . . . . .  36
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

1.  Introduction

   This document describes a new Edge Metadata Path Attribute added to a
   BGP UPDATE message [RFC4271] for egress routers to advertise the
   Metadata about 5G low latency edge services directly attached to the
   egress routers. 5G [TS.23.501-3GPP]is characterized by having edge
   services closer to the Cell Towers reachable by Local Data Networks
   (LDN).  From an IP network perspective, the 5G LDN is a limited
   domain [RFC8799] with edge services a few hops away from the ingress
   nodes.  Only selective UE services are considered as 5G low latency
   edge services.

   Note: The proposed edge service Metadata Path Attribute are not
   intended for the best-effort services reachable via the public
   Internet.  The information carried by the Edge Metadata Path
   Attribute can be used by the ingress routers to make path selections
   for selective low latency services based on not only the network
   distance but also the running environment of the edge cloud sites.
   The goal is to improve latency and performance for 5G ultra-low
   latency services.








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   This extension is targeted for a single domain with a BGP Route
   Reflector (RR) [RFC4456] controlling the propagation of the BGP
   UPDATEs.  The edge service Metadata Path Attribute is only attached
   to the low latency services (routes) hosted in the 5G edge cloud
   sites.  These routes are only a small subset of services initiated
   from UEs, not for UEs accessing many internet sites.

   While the proposed Edge Metadata Path Attribute is particularly
   beneficial for low latency services, the Edge Metadata Path
   Attributes can be expanded to propagate information about GPU
   availability, power, or other resources necessary for compute-
   intensive services such as AI and machine learning.  This flexibility
   makes it a valuable tool for a wide range of applications beyond just
   low latency services when used within a limited domain network.

2.  Conventions used in this document

   The following conventions are used in this document.

   Edge DC:  Edge Data Center, which provides the hosting environment
      for the edge services.  An Edge DC might host 5G core functions in
      addition to the frequently used edge services.

   gNB:  next generation Node B [TS.23.501-3GPP]

   RTT:  Round-trip Time

   PSA:  PDU Session Anchor (UPF) [TS.23.501-3GPP]

   UE:  User Equipment

   UPF:  User Plane Function [TS.23.501-3GPP]

   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 [RFC8174] when, and only when, they appear in all capitals, as
   shown here.

3.  Edge Metadata Influenced Ingress Node Behavior

   The goal of this edge service Metadata Path Attribute is for egress
   routers to propagate the metrics about the running environment for a
   subset of edge services to ingress routers so that the ingress
   routers can make path selections based on not only the routing cost
   but also the running environment for those edge services.  The BGP
   speakers that do not support the Edge Metadata Path Attribute can
   ignore the Edge Metadata Path Attribute in a BGP UPDATE Message.  All



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   intermediate nodes can forward the entire BGP UPDATE as it is.
   Multiple metrics can be attached to one Metadata Path Attribute.  One
   Metadata Path Attribute can contain computing service capability
   information, computing service states, computing resource states of
   the corresponding edge site, or more.  Computing service capability
   information can be used to record information of the computing power
   node or initialization deployment information for computing service
   initialization.  Computing service states can include one of the
   service connection numbers, service duration, and so on.  Computing
   resource states can be detailed information on computing resources
   such as CPU/GPU.  They can also be an abstract metric from these
   detailed parameters to indicate the resource status of the edge site.
   There could be more metrics about the running environment being
   attached to the Metadata Path Attribute; e.g., some of the metrics
   being discussed by the IETF CATS Working Group.  This document
   illustrates a few examples of Sub-TLVs of the metrics under the edge
   service Metadata Path Attribute:

   -  the site physical availability index,

   -  the site preference index,

   -  the service delay predication index x, and

   -  the raw load measurement.

   This section specifies how those Metadata impact the ingress node's
   path selections.

3.1.  Edge Metadata Influenced BGP Path Selection

   When an ingress router receives BGP UPDATEs for the same IP prefix
   from multiple egress routers, all these egress routers' loopback
   addresses are considered as the next hops for the IP prefix.  For the
   selected low latency edge services, the ingress router BGP engine
   would call an edge service Management function that can select paths
   based on the edge service Metadata received.  Section 5.1 has an
   exemplary algorithm to compute the weighted path cost based on the
   edge service Metadata carried by the Sub-TLV(s) specified in this
   document.

   Section 5 has the detailed description of the edge service Metadata
   influenced optimal path selection.








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3.2.  Ingress Router Forwarding Behavior

   When the ingress router receives a packet and does a lookup on the
   route in the FIB, it determines the destination prefix's entire path
   including the optimal egress node.  The ingress router encapsulates
   the packet destined towards the optimal egress router.  For routes
   that carry the Metadata Path Attribute but lack the Tunnel
   Encapsulation Path Attribute [RFC9012], it is recommended that the
   ingress router encapsulate the original packet using an IP-in-IP
   header.  This encapsulation ensures that intermediate nodes not
   supporting the Metadata Path Attribute do not forward the packet to
   unintended destinations.  The outer header SHOULD set the destination
   address to the optimal egress router and the source address to the
   ingress router.

   For routes without the Metadata Path Attribute, no changes are
   required.  Packets are forwarded according to existing behavior:
   encapsulation is applied when Tunnel Attributes are present, and
   parkets are forwarded without encapsulation when they are not.

   For subsequent packets belonging to the same flow, the ingress router
   needs to forward them to the same egress router unless the selected
   egress router is no longer reachable.  Forwarding packets for a
   particular flow to the same egress router, also known as Flow
   Affinity, is supported by many commercial routers.  Most registered
   EC services have relatively short-lived flows.

   How Flow Affinity is implemented is out of the scope for this
   document.

3.3.  Forwarding Behavior when UEs Move

   When a UE moves to a new 5G gNB which is anchored to the same UPF,
   the packets from the UE traverse to the same ingress router.  Path
   selection and forwarding behavior are same as before.

   If the UE maintains the same IP address when anchored to a new UPF,
   the directly connected ingress router might use the information
   passed from a neighboring router to derive the optimal BGP Next Hop
   for this route.  The detailed algorithm is out of the scope of this
   document.

4.  Edge Service Metadata Encoding








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4.1.  Edge Metadata Path Attribute

   The Edge Metadata Path Attribute is an optional non-transitive BGP
   Path attribute that carries metrics and Metadata about the edge
   services attached to the egress router.  The Edge Metadata Path
   Attribute (TBD1) consists of a set of Sub-TLVs, and each Sub-TLV
   contains information for specific metrics of the edge services.

   BGP Peers that intend to exchange the Edge Metadata Path Attribute
   SHOULD indicate this by signaling the Edge Metadata Capability (TBD2)
   in the Open Capabilities field with the format described in
   Section 4.1.5.  The web of BGP peers that exchange the Edge Metadata
   Path Attributes forms a limited domain, either within a single AS or
   within a group of ASes under a single Administrative Authority.

   The fields within the Edge Metadata Path Attribute and its Sub-TLVs
   MUST use network byte order (big-endian), where the most significant
   byte is transmitted first.

4.1.1.  Edge Metadata Path Attribute Characteristics

   Only a small subset of BGP UPDATE messages include the Edge Metadata
   Path Attribute.  The choice of which prefix to carry the Edge
   Metadata Path Attribute is determined by local policies.  The Edge
   Metadata Path Attribute can be included in a BGP UPDATE message
   [RFC4271] together with other BGP Path Attributes [IANA-BGP-PARAMS],
   such as Communities [RFC4360], NEXT_HOP, Tunnel Encapsulation Path
   Attribute [RFC9012], and other BGP attributes.

   The Edge Metadata Path Attribute has the following characteristics:

   -  Non-transitive

   -  Boundary node filtering SHOULD be deployed to remove the BGP Edge
      Metadata Path Attribute at the administrative boundary to prevent
      the distribution of the BGP Edge Metadata Path Attribute beyond
      its intended scope of applicability.

   -  Can be packed in an UPDATE with both IPv4 and IPv6 NLRI
      corresponding to SAFI values 1 (Unicast)[RFC4760], 2 (Multicast)
      [RFC4760], 4 (MPLS Labels)[RFC8277], 65 (VPN) [RFC4364], 128
      (MPLS-labeled VPN) [RFC4364] [RFC8277], 129 (Multicast VPN)
      [RFC6513], 133 (MPLS-based VPLS) [RFC4761], 134 (EVPN) [RFC7432],
      and IPv6 Anycast [RFC4786].

   -  MUST contain at least one Edge Metadata Sub-TLV.  Multiple Edge





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      Metadata Sub-TLVs can be included in a Edge Metadata Path
      Attribute in one BGP UPDATE message.  The choice of the Sub-TLVs
      present in the BGP Edge Metadata Path Attribute is determined by
      the local policies.  Multiple Sub-TLVs may be carried by a single
      BGP Edge Metadata Path Attribute.

4.1.2.  Edge Metadata Path Attribute Processing

   A BGP speaker that advertises a BGP UPDATE message received from one
   of its neighbors SHOULD advertise the BGP Edge Metadata Path
   Attribute received with the UPDATE message without modification only
   when forwarding to peers within the same domain.  Otherwise, the Edge
   Metadata Path Attribute SHOULD be removed.  If the UPDATE message did
   not come with a BGP Edge Metadata Path Attribute, the speaker MAY
   attach a BGP Edge Metadata Path Attribute to the UPDATE message, if
   configured to do so, provided that the modification adheres to the
   domain's policies and security guidelines.

   A BGP Peer receiving a BGP Edge Metadata Path Attribute SHOULD ignore
   Sub-TLVs with unknown types and process the recognized Sub-TLVs.  BGP
   Peers SHOULD not delete any Sub-TLV from the BGP Edge Metadata Path
   Attribute.

   To prevent forwarding loops and ensure consistent routing decisions,
   it is essential that all BGP peers within an Autonomous System (AS)
   adopt a unified approach to handling BGP Edge Metadata Path
   Attributes.  Specifically, BGP peers SHOULD consistently ignore Sub-
   TLVs with unknown types while processing the recognized Sub-TLVs.
   Additionally, BGP peers SHOULD refrain from deleting any Sub-TLV from
   the BGP Edge Metadata Path attribute.  This ensures that all peers
   have a common understanding of the routing information and reduces
   the risk of routing inconsistencies that could lead to forwarding
   loops.

4.1.3.  Sub-TLVs Data Processing

   By default, a BGP speaker does not report any unrecognized Sub-TLVs
   within a Edge Metadata Path Attribute unless configured to send a
   notification to its management system.  The ingress node SHOULD be
   configured with an algorithm to combine the recognized metrics
   carried by the Sub-TLVs within a Edge Metadata Path Attribute of the
   received BGP UPDATE message.









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   To ensure consistent route selection, a deployment specific algorithm
   SHOULD be configured across all ingress nodes to factor in the Edge
   Metadata's contribution alongside existing policies.  This will help
   the ingress node make informed decisions about the optimal path to
   the next-hop, considering both traditional routing factors and the
   additional insights provided by the Edge Metadata.

4.1.4.  Edge Metadata Path Attribute Handling Procedure

   The Edge Metadata Path Attribute MUST contain at least one Edge
   Metadata Sub-TLV.  Multiple Edge Metadata Sub-TLVs can be included in
   a Edge Metadata Path Attribute in one BGP UPDATE message.  The
   content of the Sub-TLVs present in the BGP Edge Metadata Path
   Attribute is determined by configuration.  The domain ingress nodes
   SHOULD process the recognized Sub-TLVs carried by the Edge Metadata
   Path Attribute and ignore the unrecognized Sub-TLVs.  By default, a
   BGP speaker does not report any unrecognized Sub-TLVs within a Edge
   Metadata Path Attribute unless configured to send a notification to
   its management system.  The ingress router SHOULD be configured with
   an algorithm to consider the recognized metrics carried by the Sub-
   TLVs within a Edge Metadata Path Attribute of the received BGP UPDATE
   message.

4.1.5.  Edge Metadata Processing Capability in BGP OPEN Message

   The "Capabilities Optional Parameter" [RFC5492] allows a BGP speaker
   to indicate its capabilities during the BGP OPEN message exchange.
   The Capabilities Optional Parameter is a triple that includes a one-
   octet Capability Code, a one-octet Capability length, and a variable-
   length Capability Value.

   To enable support for the Edge Metadata Path Attribute, a new Edge
   Metadata Processing Capability code (TBD2) is defined.  This
   capability allows a BGP speaker to communicate its ability to process
   the Edge Metadata Path Attribute for specified AFI and SAFI pairs.

   The Value Field of the Edge Metadata Processing Capability:


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |A| NLRI-cnt    |      AFI                      |  SAFI         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              AFI              |    SAFI       |     ..        ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 1: Edge Metadata Capability Value Field



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   Where:

   -  A Flag(1 bit): Set to 1 indicates that the Edge Metadata attribute
      can be attached to any AFI/SAFI.  Set to 0 indicates that the Edge
      Metadata attribute is restricted to specific AFI/SAFI pairs listed
      in the remainder of the Open Capabilities.

   -  NLRI-CNT (7 bits): Indicates the number of AFI/SAFI pairs
      specified in the OPEN Capability.

   -  AFI (16 bits): Address Family Identifier.

   -  SAFI (8 bits):Sub-address Family identifier.

   If a BGP speaker does not include the Edge Metadata Processing
   Capability in its BGP OPEN message for a specific BGP session, or if
   it does not receive the Edge Metadata Processing Capability from its
   peer on that session, it MUST NOT send any BGP UPDATE message on that
   session that bind the Edge Metadata Path Attribute to any prefix.

4.2.  The Site Preference Index Sub-TLV

   Different services might have different preference index values
   configured for the same site.  For example, Service-A requires high
   computing power, Service-B requires high bandwidth among its
   microservices, and Service-C requires high volume storage capacity.
   For a DC with relatively low storage capacity but high bisectional
   bandwidth, its preference index value for Service-B is higher and
   lower for Service-C.  Site Preference Index can also be used to
   achieve stickiness for some services.

   It is out of the scope of this document how the preference index is
   determined or configured.

   The Site Preference Index Sub-TLV has the following format:


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Site-Preference-Index Sub-Type | Length        | Reserved      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                Site Preference Index value                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2: Site Preference Index Sub-TLV

   -  Site-Preference-Index Sub-Type (16 bits): 1 (specified in this
      document).



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   -  Length (8 bits): Specifies the total length in octets of the value
      field (not including the Type and Length fields).  For the Site-
      Preference-Index Sub-Type, the length SHOULD be set to 5.

   -  Reserved: Reserved for future use.  In this version of the
      document, the Reserved field MUST be set to zero and MUST be
      ignored upon receipt.  Received values MUST be propagated without
      change.

   -  Site Preference Index value: 1 .. (2^32-1); the higher the value,
      the more preference for the site.  Site Preference Index value ==
      0 is reserved, and the Site-Preference-Index Sub-TLV SHOULD be
      ignored when 0 is received..

4.3.  Site Physical Availability Index Metadata

   The Site Physical Availability Index indicates the percentage of
   impact on a group of routes associated with a common physical
   characteristic, for example, a pod, a row of server racks, a floor,
   or an entire DC.  The purpose is to use one UPDATE message to
   indicate a group of routes of different NLRIs impacted by a physical
   event.  For example, a power outage to a pod can cause the Site
   Physical Availability Index to be 0% for all the routes in the pod.
   Partial fiber cut to a row of shelves can cause the Site Physical
   Availability Index to be 50% for all the routes in those shelves.
   The value is 0-100, with 100% indicating the site is fully
   functional, 0% indicating the site is entirely out of service, and
   50% indicating the site is 50% degraded.

   It is recommended to assign each route with one Site-ID.  When a
   route is associated with multiple Site-IDs, the latest BGP UPDATE
   will override any previous associations.  For example, one DC can use
   POD number as Site-ID, another DC can use Row of Shelves as the Site-
   ID.

   Cloud Site/Pod failures and degradation include, but are not limited
   to, a site degradation or an entire site going down caused by a
   variety of reasons.  Examples include fiber cuts impacting a site or
   among pods, cooling failures, insufficient backup power, cyber
   threats attacks, too many changes outside of the maintenance window,
   etc.  Fiber-cuts are not uncommon within a Cloud site or between
   sites.

   When a physical failure occurs at an edge site (or a pod), many
   instances can be affected, and the associated routes (i.e., IP
   addresses) may not be easily aggregated.  Instead of sending numerous
   BGP UPDATE messages to ingress routers for each impacted instance,
   the egress router can send a single BGP UPDATE to indicate the site's



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   physical capacity availability.  Based on this update, ingress
   routers can decide to reroute all or some of the affected instances,
   depending on the extent of the site's degradation.  This approach
   significantly improves efficiency, particularly when fault detection
   within an edge site relies on proprietary or deployment-specific
   mechanisms.

   The BGP UPDATE for the individual instances (i.e., the routes) can
   include the Capacity Availability Index solely for ingress routers to
   associate the routes with the Side-ID.  The actual Capacity
   Availability Index value, i.e., the percentage for all the routes
   associated with the Side-ID, is generated by the egress routers with
   the egress routers' loopback address as the NLRI.

   The Site Physical Availability Index Sub-TLV has fixed length of 8
   Octets, including the Type field.  Therefore a Length field is not
   needed.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      PhyAvailIdx Sub-Type     |     Length    |I|   Reserved  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Site-ID (2 octets)     | Site Availability Percentage  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 3: Site Physical Availability Index Sub-TLV

   - PhyAvailIdx Sub-Type (16 bits):  Indicates teh Site-Physical-
      Availability-Index Sub-Type=2 (Specified in this document).

   -  Length (8 bits): Specifies the total length in octets of the value
      field (not including the Type and Length fields).  For the
      PhyAvailIdx Sub-Type, the length SHOULD be set to 5.

   Route-Flag I (1 bit):  is a flag bit.  When set to 1, the Site
      Availability Index is for BGP speakers (receivers) to associate
      the routes with the Site-ID.  The Site Availability Percentage
      value is ignored.  When set to 0, the BGP speakers (receivers)
      SHOULD apply the Site Availability Index value to all the routes
      associated with the Site-ID.

   Reserved (7 bits):  Reserved for future use.  The bits are set to
      zero upon transmission, and ignored upon reception.

   - Site ID (16 bits):  is an identifier for a group of routes





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      associated with a common physical characteristic, for example, a
      pod, a row of server racks, a floor, or an entire DC.  The purpose
      is to use one UPDATE message to indicate a group of routes
      impacted by a physical event.  Those routes might be from
      different address families or NLRIs.  There could be multiple
      sites connected to one egress router (a.k.a. Edge DC GW).

   - Site Availability Percentage (16 bits):  When the RouteFlag-I is 1,
      the Site Availability Percentage is ignored by the Ingress
      routers.  When the RouteFlag I is set to 0, the Site Availability
      Percentage represents the percentage of the site availability for
      all the routes associated with the Site-ID; e.g., 100%, 50%, or
      0%. When a site goes dark, the Index is set to 0. 50 means 50%
      functioning.  When the value is outside the 0-100% range, the
      value carried in this Sub-TLV is ignored.

4.3.1.  Site Index Associated to Routes

   An egress router sets itself as the next hop for a BGP peer before
   sending an UPDATE with the Edge Metadata Path Attribute that includes
   the Site Physical Availability Index Sub-TLV.  The Site Physical
   Availability Index Sub-TLV (with RouteFlag-I=1) is for ingress
   routers to associate the Site Identifier with the prefixes.

4.3.2.  BGP UPDATE with standalone Site Availability Index

   A BGP UPDATE that includes the Site Availability Index Sub-TLV
   without specifying attached routes in the NLRI, but instead using the
   egress router's loopback address in the NLRI, is referred to as a
   standalone Site Availability Index BGP UPDATE.  When an ingress
   router receives such a BGP UPDATE containing the Edge Metadata Path
   Attribute with the standalone Site Physical Availability Index Sub-
   TLV from Router-X or its RR with the Originator-ID equal to Router-X,
   the ingress router SHOULD use the site availability index to
   efficiently reduce or increase the preference for all BGP routes
   attached to Router-X.

   The BGP UPDATE with a standalone Site Availability Index is NOT
   intended for resolving NextHop.

4.4.  Service Delay Prediction

   It is desirable for an ingress router to select a site with the
   shortest processing time for an ultra-low latency service.  However,
   it is not easy to predict which site has "the fastest processing
   time" or "the shortest processing delay" for an incoming service
   request because:




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   -  The given service instance shares the same physical infrastructure
      with many other applications and service instances.  Service
      requests by other applications, UEs, or applications running
      behavior can impact the processing time for the given service
      instance.

   -  The given service instance can be served by a cluster of servers
      behind a Load Balancer.  To the network, the service is identified
      by one service ID.

   -  The service complexity is different.  One service may call many
      microservices, need to access multiple backend databases, and need
      to go through sophisticated security scrubbing functions, etc.
      Another service can be processed by a few simple steps.  Without
      the application internal logic, it is not easy to estimate the
      processing time for future service requests.

   Even though utilization measurements, like those below, are collected
   by most data centers, they cannot indicate which site has the
   shortest processing time.  A service request might be processed
   faster on Site-A even if Site-A is overutilized.

   -  Server utilization for the server where the instance is
      instantiated.

   -  The network utilization for the links to the server where the
      instance is instantiated.

   -  The number of databases that the service instance will access.

   -  The memory utilization of the databases.

   The remaining available resource at a site is a more reasonable
   indication of process delay for future service requests.

   -  The remaining available Server resources.

   -  The remaining available network utilization for the links to the
      server where the instance is instantiated.

   -  The number of databases that the service instance will access.

   -  The remaining storage available for the databases.

   The Service Delay Prediction Index is a value that predicts
   processing delays at the site for future service requests.  The
   higher the value, the longer of the delay.




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4.4.1.  Service Delay Prediction Sub-TLV

   While out of scope, we assume there is an algorithm that can derive
   the Service Delay Prediction Index that can be assigned to the egress
   router.  When the Service Delay Prediction value is updated, which
   can be triggered by the available resources change, etc., the egress
   router can attach the updated Service Delay Predication value in a
   Sub-TLV under the Edge Metadata Path Attribute of the BGP Route
   UPDATE message to the ingress routers.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ServiceDelayPredict Sub-Type  |   Length      |F|L|Reserved   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Service Delay Predication Value                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 4: Service Delay Prediction Index Sub-TLV

   - ServiceDelayPredict Sub-Type (16 bits):  3 (specified in this
      document).

   - Length (8 bits):  specifies the total length in octets of the value
      field, not including the sub-Type and Length field.  The value of
      Length can be 5 or 9 depends on what format the Service Delay
      Prediction Vlaue uses.

   - Flag (F) (1 bit):  Indicates whether the Service Delay is a timer
      value (F=0) or a relative value (F=1) where a higher value
      represents a longer delay

   - Flag (L) (1 bit):  Indicates the unit of measurement for the
      Service Delay Prediction Value.  When the F-flag is set to 0, L=0
      specifies the 64-bit NTP Timestamp format, and L=1 indicates
      milliseconds.  If the F-flag is set to 1, the L-flag value is
      ignored.

   - Reserved (6 bits):  These bits are reserved for future use and MUST
      be set to zero.  Future documents may specify different uses for
      these bits.

   - Service Delay Predication Value (when the Flag bit is set to 1):
      an integer in the range of 0-100, with 0 indicating that the
      service delay is negligible and 100 indicating that the site has
      the most significant delay compared to all other sites for the
      same service.  When the value is outside the 0-100 range, the
      value carried in this Sub-TLV is ignored.



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   - Service Delay Predication Value (when the Flag bit is set to 0):
      the estimated delay time encoded in the NTP Format as defined in
      [RFC5905].  When the L-flag is 1, then it is a 64-bit format,
      otherwise it is a 32-bit short format.

4.5.  Raw Measurement Sub-TLV

   When ingress routers have embedded analytics tool relying on the raw
   measurements, it is useful for the egress router to send the raw
   measurement.

   Raw Measurement Sub-TLV has the following format:


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Raw-Measurement Sub-Type      | Length        |  Reserved     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Value                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 5: Service Delay Prediction Raw Measurements Sub-TLV

   - Raw-Measurement Sub-Type (16 bits): 4 (specified in this document).
   Indicating raw measurements Metadata associated with the edge service
   address.

   - Length (8 bits): specifies the total length, in octets, of the
   value field, excluding the Sub-Type and the Length fields.  For the
   Raw-Measurement Sub-Type, the length is determined by the Value
   field, which carries one or more types of raw measurement.

   - Reserved (8 bits): These bits are reserved for future use and MUST
   be set to zero.  Future documents may specify different uses for
   these bits.

   - Value: The value filed can contain multiple types of raw
   measurements, each represented as a Sub-Sub-TLV.

   One example of a raw measurement Metadata Sub-sub-TLV is defined
   below to convey the total number of packets or bytes transmitted over
   a specified period for a particular edge service address.  When a
   Data DC GW router cannot directly access the internal state of an
   edge service, the volume of incoming traffic can be a reliable
   indicator of its load.  A sudden increase in packets or bytes can
   signal a surge in requests, potentially leading to performance issues
   or resource constraints on the service side.




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   To differentiate this measurement from others that may be defined in
   the future, this document assigns a Sub-sub-Type value of 1 to
   represent the total packets or bytes transmitted to an edge service
   address.

   Future documents may define additional Sub-sub-types of raw
   measurement metadata.  Each type of raw measurement will have a
   unique Sub-sub-type value assigned at the time of its specification.


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |RawPacketsMeasure Sub-sub-Type | Length        |B|Reserved     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   total number of packets (or bytes) to the Edge Service      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   total number of packets (or bytes) from the Edge Service    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 6: Packets or Bytes Measurements Sub-TLV

   - RawPacketsMeasure Sub-sub-Type (8 bits): 1 (specified in this
   document).  Indicating raw measurements of packets or bits
   transmitted to or from the edge service address.

   - Length (8 bits): specifies the total length in octets of the value
   field, excluding the Sub-sub-Type and the Length fields.  For the raw
   measurements of packets transmitted to or from the edge service
   address Sub-sub-Type, the length SHOULD be 22.

   - B flag (1 bit): If set to 0, the raw measurement is the number of
   packets.  If set to 1, the raw measurement is the number of bytes.

   - Reserved (7 bits): These bits are reserved for future use and MUST
   be set to zero.

   - Measurement Period: BGP Update period in Seconds or user-specified
   period.

   - Total number of packets to the Edge Service (32 bits): This field
   specifies the total number of packets transmitted to the edge service
   address over the specified measurement period.

   - Total number of packets from the Edge Service (32 bits): This field
   specifies the total number of packets from the edge service address
   over the specified measurement period.



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   The receiver nodes can compute the needed metrics, such as the
   Service Delay Prediction, for the service based on the raw
   measurements sent from the egress router and preconfigured
   algorithms.

4.6.  Service-Oriented Capability Sub-TLV

   The service-oriented capability Sub-TLV is for distributing
   information regarding the capabilities of a specific service in a
   deployment environment.  Depending on the deployment, a deployment
   environment can be an edge site or other types of environments.  This
   information provides ingress routers or controllers with the
   available resources for the specific service in each deployment
   environment.  It enables them to make well-informed decisions for the
   optimal paths to the selected deployment environment.

   Currently, the Sub-TLV only has an abstract value derived from
   various metrics, although the specifics of this derivation are beyond
   the scope of this document.  Importantly, this value is significant
   only when comparing multiple data center sites for the same service.
   This value is not meaningful when comparing different services,
   meaning the capability value relevant to Service A cannot be directly
   compared with that for Service B.  Future enhancements may expand
   this sub-TLV to include more types of metrics or even raw data that
   represents direct metrics.  This information is important in 5G
   network environments where efficient resource utilization is crucial
   for enhancing performance and service quality.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ServiceOriented Cap Sub-Type  |   Length      | Res   |  MT   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       SO-CapValue                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 7: Service-Oriented Capability Sub-TLV

   - ServiceOriented Cap Sub-Type (16 bits):  5 (specified in this
      document).

   - Length (8 bits):  Specifies the total length in octets, excluding
      the sub-Type and Length fields.  For the ServiceOriented Cap Sub-
      Type, the Length SHOULD be 5.

   - Res (4 bits):  These bits are reserved for future use and MUST be
      set to zero.




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   - MT (Metric Type)(4 bits):  An unsigned 4 bits integer.  When the MT
      value is set to 0, it indicates the SoCapValue field contains a
      normalized metric derived from multiple metric types.  The rules
      for deriving this normalized metric are out of scope of this
      document and defined by per-service.  Additional metric types may
      be defined in future documents.

   - SO-CapValue (32 bits):  The Service-Oriented Capability Abstract
      Value is an integer between 0 and 2^32-1.  A larger number means
      higher capability, and a value of 0 indicates the site has the
      lowest relative capability for the service.  The method used to
      derive this value is beyond the scope of this document.

   Multiple Service-Oriented Capability Sub-TLVs with different metric
   types can be encoded in a Edge Metadata Path Attribute, indicating
   that multiple metrics are carried.  However, if more than one
   Service-Oriented Capability Sub-TLVs with the same metric type are
   encoded in a Edge Metadata Path Attribute, only the first one will be
   processed and the others will be ignored in processing.

4.7.  Service-Oriented Available Resource Sub-TLV

   The "Service-Oriented Available Resource Sub-TLV" is for distributing
   a metric that measures the real-time avaiable resources allocated for
   processing specific services or applications at an edge site.  This
   Sub-TLV complements the "Service-Oriented Capability Sub-TLV"
   described in Section 4.6, which addresses the static resource
   capability of a site for a service.  While the Capability Abstract
   Value provides a baseline understanding of a site's potential to
   handle a service, the Available Resource metric offers a dynamic
   perspective by quantifying how much of this capacity is currently
   available.  This distinction is crucial for managing resource
   efficiency and responsiveness in network operations, ensuring that
   capabilities are not only available but also optimally used to meet
   the actual service demands.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |ServiceOriented Avail Sub-Type |   Length      |P| Res |  MT   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SO-AvailRes                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 8: Service-Oriented Available Resource Sub-TLV

   - ServiceOriented Avail (Service-Oriented Available Resource) Sub-
   Type:  6 (specified in this document).



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   - Length (8 bits)  Specifies the total length in octets, excluding
      the sub-Type and the length field.  For the ServiceOriented
      Available Resource Sub-Type, the Length SHOULD be 5.

   - Flag (P):  Is a single-bit Percentage flag.  When it is set to 1,
      it indicates the value is the Service-Oriented Available Resource
      in percentage.  When the "P" flag is set to 0, the value in this
      Sub-TLV is the abstract value of the available resource.

   - Res (3 bits):  These bits are reserved for future use and MUST be
      set to zero.

   - MT (4 bits)  Metric Type.  This document defines a default metric
      type as value 0, indicating this is the normalized metric derived
      by multiple type of metrics.  The rules to derive the normalized
      metric are out of scope of this document and defined by the
      service.  Other Metric Types could be defined by other documents
      in the future.

   - SO-AvailRes (32 bits):  When the P-Flag bit is set to 1, Service-
      Oriented Available Resource Value is a percentage (0-100), with 0
      indicating that 0% of the capability is available and 100
      indicating that 100% of the capability is available.  When the
      value is outside the 0-100 range, the value carried in this Sub-
      TLV is ignored.  For example, Capacity value is 50 and the SO-
      AvailRes is 50 when P-flag is set, it means 50% of 50 unit of
      resource is available, while 25 unit of resource is available in
      this site for the service.  When the P-flag is 0, then the value
      of this filed is the abstract value of the available resource.
      For example, When the capacity value is 50, and the SO-AvailRes is
      50, it means all the resource is available.

   Multiple Service-Oriented Available Resource Sub-TLVs with different
   metric types can be encoded in a Edge Metadata Path Attribute,
   indicating that multiple metrics are carried.  However, if more than
   one Service-Oriented Available Resource Sub-TLVs with the same metric
   type are encoded in a Edge Metadata Path Attribute, only the first
   one will be processed and the others will be ignored in processing.

5.  Service Metadata Propagation Scope

   The propagation scope of the Edge Metadata Path Attribute needs
   careful consideration to ensure it does not inadvertently leak to
   other BGP domains.  According to Section 3 of [ATTRIBUTE-ESCAPE], it
   is necessary for the Route Reflector (RR) to be upgraded to constrain
   the propagation scope when propagating the metadata path attributes.
   Therefore, the Edge Metadata Path Attribute originator sets the
   attribute as Non-transitive when sending the BGP UPDATE message to



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   its corresponding RR.  Non-transitive attributes are only guaranteed
   to be dropped during BGP route propagation by implementations that do
   not recognize them, ensuring that the Edge Metadata path attributes
   do not propagate beyond the intended scope.

   The RR can append the NO-ADVERTISE well-known community to the BGP
   UPDATE message with the Edge Metadata Path Attribute when forwarding
   it to the ingress routers.  This signals to the ingress nodes that
   the associated route's Metadata Path Attribute SHOULD not be further
   advertised beyond their scope.  This precautionary measure ensures
   that the receiver of the BGP UPDATE message refrains from forwarding
   the received update to its peers, preventing the undesired
   propagation of the information carried by the Metadata Path
   Attribute.

5.1.  AS-Scope SubTLV

   To address the potential issue where the NO-ADVERTISE well-known
   community of the BGP UPDATE message can be dropped by some routers, a
   new AS-Scope Sub-TLV can be included in the Metadata Path Attribute
   to prevent the Metadata Path Attribute from being leaked to
   unintended Autonomous Systems (ASes).  The AS-Scope Sub-TLV will
   enforce stricter control over the propagation of the metadata by
   associating it with specific AS numbers.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        AS-Scope Sub-Type      |   Length      | Reserved      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         In-Scope AS-Value                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 9: AS-Scope Sub-TLV

   - AS-Scope Sub-Type (16 bits):  7 (specified in this document).

   - Length (8 bits)  Specifies the total length in octets, excluding
      the sub-Type and the length field.  For the AS-Scope Sub-Type, the
      Length SHOULD be 6.

   - Reserved (8 bits):  These bits are reserved for future use and MUST
      be set to zero.

   - In-Scope AS-Value (32 bits):  AS value that is recognized by the
      BGP speaker in the domain.





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5.1.1.  AS-Scope Value Checking Procedure

   When a router receives a BGP UPDATE message containing the AS-Scope
   Sub-TLV, it must perform the following steps to process the AS-Scope
   value:

   - AS Recognition: The router will check the AS value in the AS-Scope
   Sub-TLV.

   - If the AS value matches the local AS or a recognized AS in its
   configuration, the router will process the update as usual.  If the
   AS value does not match or is not recognized, the router SHOULD NOT
   process the Edge Metadata Path Attribute values in the BGP UDPATE and
   SHOULD NOT propagate the received BGP UPDATE to other nodes.  I.e.,
   treat-as-withdraw behavior will be used.

   Example Usage:

   Consider a scenario where a router in AS 65001 advertises a BGP
   UPDATE message with the AS-Scope Sub-TLV set to AS 65001.  When
   another router in AS 65002 receives this UPDATE, it will check the
   AS-Scope Sub-TLV value:

   Since AS 65002 does not match the AS value 65001, the router in AS
   65002 will drop the UPDATE, preventing the metadata from leaking into
   AS 65002.

   This mechanism ensures that the metadata remains confined to the
   intended ASes, enhancing the security and control over the
   propagation of BGP metadata.

6.  Policy Based Metadata Integration

   This section describes how the information carried in the Edge
   Metadata Path Attribute is integrated into the BGP route selection
   process.  RR and Ingress nodes can incorporate metadata into their
   route selection, depending on the network deployment and local policy
   configuration.  To ensure compliance with Section 9.1.1 of [RFC4271],
   metadata-based preferences must be applied after the LOCAL_PREF
   attribute is set for iBGP routes or after local policies are applied
   for eBGP routes.

   Deployment Specific Attribute Selection:








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   Each deployment, by the local policy, chooses the subset of available
   metadata attributes to use in setting the local preference for the
   route.  This tailors the route selection process to the specific
   needs and policies of the network.  Both RRs and Ingress nodes can
   selectively integrate metadata attributes into their computations
   based on these policies.

   To ensure consistent routing decisions when integrating Edge Metadata
   Path Attributes, two deployment models are described:

   -  Centralized RR Model:

      If the RR is acting as the deployment's "server" for best paths,
      it is recommended that routers in the AS ONLY peer through the RR.
      This ensures that the RR serves as the single point of policy-
      based computation, and all ingress routers receive consistent
      routes that account for the Edge Metadata Path Attribute.

   -  Consistent Distributed Model:

      If routers in the AS are partially meshed and allowed to exchange
      iBGP routes directly, the RR must be treated as just another node.
      In this case: All nodes, including the RR, must implement the same
      policy for integrating the Edge Metadata Path Attribute and
      computing route preference.  The procedure for combining metadata
      and traditional BGP attributes SHOULD be consistent across all
      nodes, ensuring that all routers converge on the same "best" path
      when presented with the same set of routes and metadata.

   Influence on the BGP Decision Process:

   -  At the Route Reflector (RR):

      In deployments where RRs are responsible for pre selecting routes,
      the RR integrates metadata and traditional BGP attributes when
      determining the "best" route.  The RR reflects only the selected
      route to its client routers (e.g., Ingress PEs), ensuring
      alignment with service specific requirements.  To mitigate hot
      potato routing issues, deployments SHOULD consider Optimal Route
      Reflection (ORR) as specified in [RFC9107], which enables the RR
      to compute and advertise routes based on ingress routers'
      perspectives rather than the RR's own location.

   -  At the Ingress Node:

      When the RR reflects multiple routes (e.g., using Add Paths), the





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      Ingress node receives all candidate routes.  It then integrates
      metadata attributes with traditional BGP attributes to compute the
      preference for a route.  This allows the Ingress node to make
      service specific routing decisions based on its local policy and
      visibility into metadata.

   Policy Driven Combined Preference Evaluation:

   The preference for a route is computed based on a weighted
   combination of metadata attributes and traditional BGP attributes.
   The weights are determined by local policy:

   -  Metadata and traditional BGP attributes are integrated into a
      single preference value using a deployment specific algorithm.

   -  Either the RR or the Ingress node selects the route with the
      highest computed preference value for reflection or traffic
      steering.

   Handling Degraded Metrics:

   When critical metadata metrics, such as the Capacity Availability
   Index or Service Delay Prediction Index, degrade beyond a configured
   threshold, local BGP policy may treat the affected route as
   ineligible for traffic steering.  This behavior is equivalent to BGP
   local policy declaring the route is not eligible for route selection.
   This ensures that traffic is not routed to service instances that not
   capable to process the services, preserving the quality of service
   for critical applications.

   Example Scenarios for Policy Based Route Selection:

   A BGP peer uses local policy run over the route (prefix plus
   attribute) to select the best route and then use tie breaking based
   on [RFC4271].  This section simply provides 3 examples of how local
   policy might weigh the Metadata metrics during that policy selection.

   Scenario 1: Local Policy Prioritizes Metadata Metrics Over
   Traditional BGP Attributes.

   The local policy assigns a higher weight to metadata metrics when
   computing the preference for routes.  The selection process follows
   these steps:

   -  Compute a preference value based on the weighted combination of
      metadata attributes and traditional BGP attributes, with metadata
      metrics having higher weight.




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   -  Prefer the route with the highest computed preference value.

   -  Resolve remaining ties using traditional BGP tie breaking criteria
      (e.g., eBGP over iBGP, lowest IGP metric, oldest route, lowest
      route ID).

   Scenario 2: Local Policy Weighs Metadata Metrics and Traditional BGP
   Attributes Equally.

   The local policy assigns equal weight to metadata and traditional BGP
   attributes during preference computation.  The selection process is
   as follows:

   -  Compute a preference value by equally weighing metadata derived
      metrics and traditional BGP attributes.

   -  Prefer the route with the highest computed preference value.

   -  Resolve remaining ties using traditional BGP tie breaking
      criteria.

   Scenario 3: Local Policy Prioritizes Traditional BGP Attributes Over
   Metadata Metrics

   The local policy assigns a higher weight to traditional BGP
   attributes.  The selection process follows these steps:

   -  Compute a preference value based on the weighted combination of
      metadata attributes and traditional BGP attributes, with
      traditional attributes having higher weight.

   -  Prefer the route with the highest computed preference value.

   -  Resolve remaining ties using traditional BGP tie breaking
      criteria.

   Equal Cost Multi Path (ECMP) in BGP Route Selection:

   When the BGP decision process identifies multiple paths with equal
   preference after considering both Edge Metadata Path Attributes and
   traditional BGP attributes, BGP can pass these paths to the
   forwarding engine to enable ECMP.

   This Policy Based Metadata Integration approach enables network
   operators to incorporate Edge Metadata Path Attributes into BGP route
   selection based on their specific operational goals and requirements,
   while maintaining compatibility with traditional BGP operations.




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7.  Minimum Interval for Metrics Change Advertisement

   Route Churn Considerations

   While the mechanism detailed in this document aims to provide dynamic
   metrics like Capacity Availability Index, Site Delay Prediction
   Index, Service Delay Prediction Index, and Raw Measurement to
   optimize path selection, it is essential to consider the broader
   implications of metric-induced churn.  Particularly, in the context
   of routes used for BGP nexthop resolution (e.g., labeled unicast),
   frequent changes in these metrics can lead to significant churn not
   only for the prefixes carrying the data but also for dependent
   routes.

   In normal operation, the metadata associated with a prefix is
   propagated along with BGP UPDATE messages as per standard BGP
   behavior.  The advertisement interval is governed by the underlying
   BGP mechanisms, such as the MRAI timer (typically 30 seconds for
   iBGP).  This document does not propose a new periodic advertisement
   mechanism independent of routing updates.  If metadata attributes
   (e.g., compute availability, service locality) change, a BGP UPDATE
   is triggered accordingly.  If there is no change to the advertised
   metadata, no additional UPDATE is sent, in order to avoid unnecessary
   update churn and to comply with BGP best practices.  Any active or
   proactive refresh mechanisms for metadata would require explicit
   triggers and change detection mechanisms, which are outside the scope
   of this document.

   This behavior is analogous to the impacts observed with RSVP auto-
   bandwidth, which can introduce considerable instability within a
   network.  Such route churn can propagate through the network, causing
   a cascade of UPDATEs and potential route flaps, thereby affecting
   overall network stability and performance.

   To mitigate these effects, network operators SHOULD carefully manage
   the advertisement intervals of these dynamic metrics, ensuring they
   are set to avoid unnecessary churn.  The default minimum interval for
   metrics change advertisement, set at 30 seconds, is designed to
   balance responsiveness with stability.  However, in scenarios with
   higher sensitivity to route stability, operators may consider
   increasing this interval further to reduce the frequency of UPDATEs.

   Significant load changes at EC data centers can be triggered by
   short-term gatherings of UEs, like conventions, lasting a few hours
   or days.  Therefore, a high metrics change rate can persist for hours
   or days.





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8.  Validation and Error Handling

   The Edge Metadata Path Attribute is an optional non-transitive BGP
   Path attribute that carries metrics and metadata about the edge
   services attached to the egress router.  The Edge Metadata Path
   Attribute, to be assigned by IANA , consists of a set of Sub-TLVs,
   and each Sub-TLV contains information for specific metrics of the
   edge services.

   When more than one sub-TLV is present in a Metadata Path Attribute,
   they are processed independently.  Suppose a Edge Metadata Path
   Attribute can be parsed correctly but contains a Sub-TLV whose type
   is not recognized by a particular BGP speaker; that BGP speaker MUST
   NOT consider the attribute malformed.  Instead, it MUST interpret the
   attribute as if that Sub-TLV had not been present.  Logging the error
   locally or to a management system is optional.  If the route carrying
   the Edge Metadata path attribute is propagated with the attribute,
   the unrecognized Sub-TLV remains in the attribute.

9.  Manageability Considerations

   The edge service Metadata described in this document are only
   intended for propagating between ingress and egress routers of one
   single BGP Administrative Domain [RFC1136].  A single BGP
   Administrative Domain can consist of one AS or multiple ASes.

   Only the selective services by UEs are considered as 5G edge
   services.  The 5G LDN is usually managed by one operator, even though
   the routers can be by different vendors.

10.  Security Considerations

   The proposed edge service Metadata are advertised within the trusted
   domain of 5G LDN's ingress and egress routers.  The ingress routers
   SHOULD not propagate the edge service Metadata to any nodes that are
   not within the trusted domain.

   To prevent the BGP UPDATE receivers (a.k.a. ingress routers in this
   document) from leaking the Edge Metadata Path Attribute by accident
   to nodes outside the trusted domain [ATTRIBUTE-ESCAPE], the following
   practice SHOULD be enforced:

   -  The Edge Metadata Path Attribute is non-transitive.  Per
      [RFC4271], non-transitive Path Attributes are dropped during BGP
      route propagation by implementations that do not recognize them.

   -  Route Reflectors can append the NO-ADVERTISE well-known community




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      to the BGP UPDATE message with Edge Metadata Path Attribute when
      forwarding to the ingress routers.  By doing so, the Route
      Reflector signals to ingress nodes that the routes with the Edge
      Metadata Path Attribute SHOULD not be further advertised beyond
      their scope.  This precautionary measure ensures that the receiver
      of the BGP UPDATE message refrains from forwarding the received
      UPDATE to its peers, preventing the undesired propagation of the
      information carried by the Edge Metadata Path Attribute.

   BGP Route Filtering or BGP Route Policies [RFC5291] can also be used
   to ensure that BGP UPDATE messages with Edge Metadata Path Attribute
   attached do not get forwarded out of the administrative domain.  BGP
   route filtering [RFC5291] allows network administrators to control
   the advertisements and acceptance of BGP routes, ensuring that
   specific routes do not leak outside the intended administrative
   domain.  Here are the steps to achieve this:

   -  Use Route Filtering: Implement route filtering policies on the
      ingress routers to restrict the propagation of BGP UPDATE messages
      for the registered 5G edge services beyond the administrative
      domain.  You can use access control lists (ACLs), prefix lists, or
      route maps to filter the BGP routes classified as the 5G edge
      services, which need the Edge Metadata Path Attributes to be
      distributed from egress routers to ingress routers.

   -  Filter by Prefix: Use prefix filtering to specify which IP
      prefixes SHOULD be advertised to peers and which SHOULD be
      suppressed.  This step ensures that only authorized routes are
      sent to external peers.

   -  Use Route Maps: Route maps provide a flexible way to filter and
      manipulate BGP route advertisements.  You can create route maps to
      match specific conditions and then apply them to the BGP
      configuration.

11.  IANA Considerations

11.1.  Edge Metadata Path Attribute

   IANA has done early allocation [RFC7120] of the codepoint 42 to the
   "Edge Metadata Path Attribute" in the "BGP Path Attributes" registry.
   The reference for this assignment is [this document].

      +=======+======================================+=================+
      | Value |             Description              |    Reference    |
      +=======+======================================+=================+
      |  42   |   Edge Metadata Path Attribute       | [this document] |
      +-------+--------------------------------------+-----------------+



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11.2.  Edge Metadata Capability Code

   IANA has assigned a Capability Code of 78 from the "BGP Capability
   Codes" registry for the Edge Metadata Capability in the BGP OPEN
   message.

      +=======+======================================+=================+
      | Value |             Description              |    Reference    |
      +=======+======================================+=================+
      |  78   |     Edge Metadata Capability         | [This document] |
      +-------+--------------------------------------+-----------------+


11.3.  Edge Metadata Path Attribute Sub-Types

   IANA is requested to create a new sub-registry under the Edge
   Metadata Path Attribute registry as follows:

   Name:  Sub-TLVs under the "Edge Metadata Path Attribute"

   Registration Procedure:  Expert Review [RFC8126].

      Detailed Expert Review procedure will be added per [RFC8126].

   Reference:  [this document]


























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   +========+=============================+===================+
   |Sub-Type|   Description               | Reference         |
   +========+=============================+===================+
   |      0 |reserved                     |[this document ]   |
   +--------+-----------------------------+-------------------+
   |      1 |Site Preference Index        |[this document:4.3]|
   +--------+-----------------------------+-------------------+
   |      2 |Site Physical Avail Index    |[this document:4.4]|
   +--------+-----------------------------+-------------------+
   |      3 |Service Delay Predication    |[this document:4.5]|
   +--------+-----------------------------+-------------------+
   |      4 |Raw Measurement              |[this document:4.6]|
   +--------+-----------------------------+-------------------+
   |      5 |Service-Oriented Capability  |[this document:4.7]|
   +--------+-----------------------------+-------------------+
   |      6 |Service-Oriented Available   |                   |
   |        |Resource                     |[this document:4.8]|
   +--------+-----------------------------+-------------------+
   |      7 |AS-Scope                     |[this document:5.1]|
   +--------+-----------------------------+-------------------+
   |8-65534 | unassigned                  |                   |
   +--------+-----------------------------+-------------------+
   |  65535 | reserved                    |[this document]    |
   +--------+-----------------------------+-------------------+

12.  Contributors


   Changwang Lin

   New H3C Technologies

   China

   Email: linchangwang.04414@h3c.com



13.  Acknowledgements

   Acknowledgements to Jeff Haas, Tom Petch, Adrian Farrel, Alvaro
   Retana, Robert Raszuk, Sue Hares, Shunwan Zhuang, Donald Eastlake,
   Dhruv Dhody, Cheng Li, DongYu Yuan, and Vincent Shi for their
   suggestions and contributions.

14.  References

14.1.  Normative References



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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <https://www.rfc-editor.org/info/rfc4360>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast
              Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
              December 2006, <https://www.rfc-editor.org/info/rfc4786>.

   [RFC5291]  Chen, E. and Y. Rekhter, "Outbound Route Filtering
              Capability for BGP-4", RFC 5291, DOI 10.17487/RFC5291,
              August 2008, <https://www.rfc-editor.org/info/rfc5291>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <https://www.rfc-editor.org/info/rfc5492>.

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.



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   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <https://www.rfc-editor.org/info/rfc7120>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
              <https://www.rfc-editor.org/info/rfc8277>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

14.2.  Informative References

   [ATTRIBUTE-ESCAPE]
              J. Haas, "BGP Attribute Escape", July 2023,
              <https://datatracker.ietf.org/doc/draft-haas-idr-bgp-
              attribute-escape/>.

   [IANA-BGP-PARAMS]
              IANA, "BGP Path Attributes", BGP Path Attributes 
              https://www.iana.org/assignments/bgp-parameters/.

   [RFC1136]  Hares, S. and D. Katz, "Administrative Domains and Routing
              Domains: A model for routing in the Internet", RFC 1136,
              DOI 10.17487/RFC1136, December 1989,
              <https://www.rfc-editor.org/info/rfc1136>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <https://www.rfc-editor.org/info/rfc4456>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.




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   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
              <https://www.rfc-editor.org/info/rfc8799>.

   [TS.23.501-3GPP]
              3rd Generation Partnership Project (3GPP), "System
              Architecture for 5G System; Stage 2, 3GPP TS 23.501
              v2.0.1", December 2017.

Appendix A.  Service Delay Prediction Based on Load Measurement

   When data centers detailed running status are not exposed to the
   network operator, historic traffic patterns through the egress
   routers can be utilized to predict the load to a specific service.
   For example, when traffic volume to one service at one data center
   suddenly increases a huge percentage compared with the past 24 hours
   average, it is likely caused by a larger than normal demand for the
   service.  When this happens, another data center with lower-than-
   average traffic volume for the same service might have a shorter
   processing time for the same service.

   Here are some measurements that can be utilized to derive the Service
   Delay Predication for a service ID:

   -  Total number of packets to the attached service instance
      (ToPackets);

   -  Total number of packets from the attached service instance
      (FromPackets);

   -  Total number of bytes to the attached service instance (ToBytes);

   -  Total number of bytes from the attached service instance
      (FromBytes);

   -  The actual load measurement to the service instance attached to an
      egress router can be based on one of the metrics above or
      including all four metrics with different weights applied to each,
      such as:

      LoadIndex = w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes

      Where w1/w2/w3/w4 are between 0-1. w1+ w2+ w3+ w4 = 1;

      The weights of each metric contributing to the index of the
      service instance attached to an egress router can be configured or
      learned by self-adjusting based on user feedbacks.




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   The Service Delay Prediction Index can be derived from
   LoadIndex/24Hour-Average.  A higher value means a longer delay
   prediction.  The egress router can use the ServiceDelayPred sub-TLV
   to indicate to the ingress routers of the delay prediction derived
   from the traffic pattern.

   Note: The proposed IP layer load measurement is only an estimate
   based on the amount of traffic through the egress router, which might
   not truly reflect the load of the servers attached to the egress
   routers.  They are listed here only for some special deployments
   where those metrics are helpful to the ingress routers in selecting
   the optimal paths.

Appendix B.  Service Metadata Influenced Decision Process

B.1.  Egress Router Behavior

   Multiple instances of the same service could be attached to one
   egress router.  When all instances of the same service are grouped
   behind one application layer load balancer, they appear as one single
   route to the egress router, i.e., the application loader balancer's
   prefix.  Under this scenario, the compute metrics for all those
   instances behind one application layer balancer are aggregated under
   the application load balancer's prefix.  In this case, the compute
   metrics aggregated by the Load Balancer are visible to the egress
   router as associated with the Load Balancer's prefix.  However, how
   the application layer Load Balancers distribute the traffic among
   different instances is out of the scope of this document.  When
   multiple instances of the same service have different paths or links
   reachable from the egress router, multiple groups of metrics from
   respective paths could be exposed to the egress router.  The egress
   router can have preconfigured policies on aggregating various metrics
   from different paths and the corresponding policies in selecting a
   path for forwarding the packets received from ingress routers.  The
   aggregated metrics can be carried in the BGP UPDATE messages instead
   of detailed measurements to reduce the entries advertised by the
   control plane and dampen the routes update in the forwarding plane.
   Upon receiving packets from ingress routers, the egress router can
   use its policies to choose an optimal path to one service instance.
   It is out of the scope of this document how the measurements are
   aggregated on egress routers and how ingress routers are configured
   with the algorithms to integrate the aggregated metrics with network
   layer metrics.

   Many measurements could impact and correspondingly reflect service
   performance.  In order to simplify an optimal selection process,
   egress routers can have preconfigured policies or algorithms to
   aggregate multiple metrics into one simple one to ingress routers.



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   Though out of the scope of this document, an egress router can also
   have an algorithm to convert multiple metrics to network metrics, an
   IGP cost for each instance, to pass to ingress nodes.  This decision-
   making process integrates network metrics computed by traditional
   IGP/BGP and the service delay metrics from egress routers to achieve
   a well-informed and adaptive routing approach.  This intelligent
   orchestration at the edge enhances the service's overall performance
   and optimizes resource utilization across the distributed
   infrastructure.  When the egress has merged the compute metrics from
   the local sites behind it, it can include one or more aggregated
   compute metrics in the Metadata Path Attribute in the BGP UPDATE to
   the Ingress.  Also, an identifier or flag can be carried to indicate
   that the metrics are merged ones.  After receiving the routes for the
   Service ID with the identifier, the ingress would do the route
   selection based on pre-configured algorithms (see Section 3 of this
   document).

B.2.  Integrating Network Delay with the Service Metrics

   As the service metrics and network delays are in different units,
   here is an exemplary algorithm for an ingress router to compare the
   cost to reach the service instances at Site-i or Site-j.

                   ServD-i * CP-j               Pref-j * NetD-i
   Cost-i=min(w *(----------------) + (1-w) *(------------------))
                   ServD-j * CP-i               Pref-i * NetD-j


   CP-i:  Capacity Availability Index at Site-i.  A higher value means
      higher capacity available.

   NetD-i:  Network latency measurement (RTT) to the Egress Router at
      the site-i.

   Pref-i:  Preference Index for Site-i, a higher value means higher
      preference.

   ServD-i:  Service Delay Predication Index at Site-i for the service,
      i.e., the ANYCAST address [RFC4786] for the service.

   w:  Weight is a value between 0 and 1.  If smaller than 0.5, Network
      latency and the site Preference have more influence; otherwise,
      Service Delay and capacity availability have more influence.








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   When a set of service Metadata is converted to a simple metric, a
   decision process is determined by the metric semantics and deployment
   situations.  The goal is to integrate the conventional network
   decision process with the service Metadata into a unified decision-
   making process for path selection.

B.3.  Integrating with BGP Route Selection

   Not all metadata attributes specified in this document are intended
   for use in every deployment.  Each deployment may choose to consider
   only a subset of the available metadata attributes based on its
   specific service requirements.

   - Deployment-Specific Attribute Selection:

   A deployment may prioritize only certain metadata attributes relevant
   to its operational needs.  For example, one deployment might only use
   the Service Delay Prediction Index for latency-sensitive
   applications, while another might focus solely on the Capacity
   Availability Index to manage resource availability.

   - Influence on BGP Decision Process:

   The edge service Metadata influences next-hop selection differently
   from traditional BGP metrics (e.g., Local Preference, MED).  Unlike a
   general next-hop metric that can affect many routes, edge service
   Metadata selectively impacts optimal next-hop selection for specific
   routes configured to consider these service-specific attributes.
   This targeted influence allows for optimized path selection without
   disrupting broader route decisions.

   - Handling Degraded Metrics (Policy-Based):

   If a service-specific metric degrades beyond a configured threshold
   (e.g., the Service Delay Prediction Index exceeds an acceptable delay
   threshold or the Capacity Availability Index drops below a required
   level), the ingress router will treat that route as ineligible for
   traffic steering.  This is similar to a BGP route withdrawal, where
   the degraded route is deprioritized or ignored, even if traditional
   BGP attributes would otherwise favor it.  This ensures that traffic
   is directed only to service instances that meet the defined
   performance criteria.

   - Fallback to Non-Metadata Routes:







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   If no suitable routes with the required metadata are available, the
   BGP decision process defaults to traditional attribute evaluation
   [RFC4271], ensuring consistent routing even when metadata-specific
   paths are absent.

   This approach provides flexibility and adaptability in routing
   decisions, allowing each deployment to apply relevant metadata
   attributes and enforce performance thresholds for improved service
   quality.

Authors' Addresses

   Linda Dunbar
   Futurewei
   Dallas, TX,
   United States of America
   Email: ldunbar@futurewei.com


   Kausik Majumdar
   Oracle
   California,
   United States of America
   Email: kausik.majumdar@oracle.com


   Cheng Li
   Huawei Technologies
   Beijing
   China
   Email: c.l@huawei.com


   Gyan Mishra
   Verizon
   United States of America
   Email: gyan.s.mishra@verizon.com


   Zongpeng Du
   China Mobile
   Beijing
   China
   Email: duzongpeng@chinamobile.com







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