BGP Extension for 5G Edge Service Metadata
draft-ietf-idr-5g-edge-service-metadata-33
| Document | Type | Active Internet-Draft (idr WG) | |
|---|---|---|---|
| Authors | Linda Dunbar , Kausik Majumdar , Cheng Li , Gyan Mishra , Zongpeng Du | ||
| Last updated | 2026-05-29 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-idr-5g-edge-service-metadata-33
Network Working Group L. Dunbar
Internet-Draft Futurewei
Intended status: Standards Track K. Majumdar
Expires: 30 November 2026 Oracle
C. Li
Huawei Technologies
G. Mishra
Verizon
Z. Du
China Mobile
29 May 2026
BGP Extension for 5G Edge Service Metadata
draft-ietf-idr-5g-edge-service-metadata-33
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
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 30 November 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Edge Metadata Influenced Ingress Node Behavior . . . . . . . 5
3.1. Edge Metadata Influenced BGP Path Selection . . . . . . . 6
3.2. Ingress Router Forwarding Behavior . . . . . . . . . . . 6
3.3. Forwarding Behavior when UEs Move . . . . . . . . . . . . 7
3.4. Relationship to Existing BGP Metric/Characteristic
Attributes . . . . . . . . . . . . . . . . . . . . . . . 7
4. Edge Service Metadata Encoding . . . . . . . . . . . . . . . 7
4.1. Edge Metadata Path Attribute . . . . . . . . . . . . . . 7
4.1.1. Edge Metadata Path Attribute Characteristics . . . . 8
4.1.2. Propagation and Attribute Level Processing . . . . . 8
4.1.3. Sub-TLV Handling Rules . . . . . . . . . . . . . . . 9
4.2. The Site Preference Index Sub-TLV . . . . . . . . . . . . 11
4.3. Site Physical Availability Index Metadata Sub-TLV . . . . 12
4.3.1. Site Index Associated to Routes . . . . . . . . . . . 14
4.3.2. BGP UPDATE with standalone Site Availability Index . 14
4.4. Service Delay Prediction Sub-TLV . . . . . . . . . . . . 14
4.5. Raw Measurement Sub-TLV . . . . . . . . . . . . . . . . . 16
4.6. Service-Oriented Capability Sub-TLV . . . . . . . . . . . 19
4.7. Service-Oriented Available Resource Sub-TLV . . . . . . . 20
5. Edge Metadata Processing Capability in BGP OPEN Message . . . 21
6. Service Metadata Propagation Scope . . . . . . . . . . . . . 23
6.1. AS-Scope SubTLV . . . . . . . . . . . . . . . . . . . . . 24
6.1.1. AS-Scope Value Checking Procedure . . . . . . . . . . 25
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7. Policy Based Metadata Integration . . . . . . . . . . . . . . 26
7.1. Policy Application Order . . . . . . . . . . . . . . . . 26
7.2. Metadata Selection by Local Policy . . . . . . . . . . . 26
7.3. Policy-Based Preference Computation . . . . . . . . . . . 26
7.4. Policy Treatment of Routes with Degraded Metadata . . . . 27
7.5. Tie Breaking and ECMP . . . . . . . . . . . . . . . . . . 27
8. Minimum Interval for Metrics Change Advertisement . . . . . . 28
9. Validation and Error Handling . . . . . . . . . . . . . . . . 29
10. Manageability Considerations . . . . . . . . . . . . . . . . 30
11. Security Considerations . . . . . . . . . . . . . . . . . . . 30
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
12.1. Edge Metadata Path Attribute . . . . . . . . . . . . . . 31
12.2. Edge Metadata Capability Code . . . . . . . . . . . . . 32
12.3. Edge Metadata Path Attribute Sub-Types . . . . . . . . . 32
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 33
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
15.1. Normative References . . . . . . . . . . . . . . . . . . 33
15.2. Informative References . . . . . . . . . . . . . . . . . 35
Appendix A. Service Delay Prediction Based on Load
Measurement . . . . . . . . . . . . . . . . . . . . . . . 36
Appendix B. Service Metadata Influenced Decision Process . . . . 37
B.1. Egress Router Behavior . . . . . . . . . . . . . . . . . 37
B.2. Integrating Network Delay with the Service Metrics . . . 38
B.3. Integrating with BGP Route Selection . . . . . . . . . . 38
Appendix C. Deployment Examples for Metadata-Aware Route
Selection . . . . . . . . . . . . . . . . . . . . . . . . 39
C.1. Centralized RR Model . . . . . . . . . . . . . . . . . . 40
C.2. Ingress-Node Decision Model . . . . . . . . . . . . . . . 40
C.3. Consistent Distributed Model . . . . . . . . . . . . . . 40
C.4. Example Policy Weighting Approaches . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
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
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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.
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.
Edge Service Management Function: A local or centralized function
that interprets Edge Metadata Path Attribute values and applies
deployment-specific policy to assist in selecting the preferred
path or egress router for an edge service. How this function is
implemented is outside the scope of this document.
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]
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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
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.
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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.
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
encapsulation appropriate for the address families involved. 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
packets 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.
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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.
3.4. Relationship to Existing BGP Metric/Characteristic Attributes
AIGP [RFC7311] carries accumulated IGP metric information for use in
BGP path selection within an administrative domain. Other IDR work,
such as NHC, has discussed carrying characteristics associated with
the BGP next hop. The Edge Metadata Path Attribute defined in this
document carries different information: service- and site-specific
metadata associated with selected edge-service routes, such as site
preference, site availability, service delay prediction, and service-
oriented resource information.
These metadata values are not accumulated network path metrics and
are not only characteristics of the BGP next hop. Different services
reachable through the same egress router or at the same site may have
different metadata values. Therefore, this document defines a
separate attribute to carry edge-service metadata, while allowing
local policy to combine that metadata with other BGP attributes when
applicable.
4. Edge Service Metadata Encoding
4.1. Edge Metadata Path Attribute
The Edge Metadata Path Attribute is an optional non-transitive BGP
Path attribute that carries metadata associated with edge services
attached to the egress router. The attribute consists of one or more
Edge Metadata Sub-TLVs, where each Sub-TLV encodes one specific
metadata item associated with the advertised route or service.
The Edge Metadata Path Attribute MAY be included in a BGP UPDATE
together with other BGP Path Attributes, such as Communities,
NEXT_HOP, Tunnel Encapsulation Path Attribute, and other applicable
attributes. The choice of which routes carry the Edge Metadata Path
Attribute, and which Sub-TLVs are included for those routes, is
determined by local policy. The fields within the Edge Metadata Path
Attribute and all included Sub-TLVs MUST use network byte order.
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Boundary filtering SHOULD be applied at the administrative boundary
to prevent the Edge Metadata Path Attribute from being distributed
beyond its intended scope.
4.1.1. Edge Metadata Path Attribute Characteristics
The Edge Metadata Path Attribute has the following characteristics:
- The attribute is optional non-transitive.
- The attribute MUST contain at least one Edge Metadata Sub-TLV.
- A single Edge Metadata Path Attribute MAY carry multiple Sub-TLVs.
- The attribute MAY be attached to UPDATE messages for any supported
AFI/SAFI as allowed by local policy and by the capability
negotiation specified in Section 5.
- Only a subset of routes are expected to carry the Edge Metadata
Path Attribute. Which routes carry the attribute is deployment
specific.
4.1.2. Propagation and Attribute Level Processing
A BGP speaker that receives a BGP UPDATE containing the Edge Metadata
Path Attribute and readvertises that route within the same metadata
distribution domain SHOULD propagate the Edge Metadata Path Attribute
without modification, unless local policy explicitly requires
otherwise.
When advertising the route to a peer outside the intended metadata
distribution domain, the speaker SHOULD remove the Edge Metadata Path
Attribute.
If a BGP speaker originates or modifies a route and is configured to
attach Edge Metadata, it MAY add the Edge Metadata Path Attribute to
the UPDATE message, subject to local policy and the capability
negotiation specified in Section 5.
A BGP speaker that receives a malformed Edge Metadata Path Attribute
that cannot be parsed according to the attribute format and length
rules MUST handle the error as specified in Section 9.
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The Edge Metadata Path Attribute is intended to describe the specific
edge service route to which it is attached. This document does not
define aggregation of Edge Metadata Path Attribute values across
multiple BGP routes. A BGP speaker that locally originates an
aggregate route MUST NOT infer or copy Edge Metadata from component
routes unless it explicitly originates new Edge Metadata for the
aggregate route by local policy.
4.1.3. Sub-TLV Handling Rules
When a BGP speaker receives a well-formed Edge Metadata Path
Attribute, it MUST process each included Sub-TLV independently.
An implementation MUST enforce an upper bound on the total number of
Sub-TLVs accepted in a single Edge Metadata Path Attribute. The
bound MAY be configurable and MUST have an implementation-defined
default value. If the number of Sub-TLVs in an Edge Metadata Path
Attribute exceeds the configured or implementation-defined bound, the
receiver MUST treat the Edge Metadata Path Attribute as unusable for
metadata-based route selection and handle the attribute according to
Section 9.
If the attribute contains one or more Sub-TLVs whose types are
recognized by the receiving speaker, the receiving speaker SHOULD
process those recognized Sub-TLVs according to their definitions in
this document and according to local policy.
If the attribute contains a Sub-TLV whose type is unknown or
unsupported by the receiving speaker, the speaker MUST ignore that
Sub-TLV and MUST continue processing the remaining Sub-TLVs. The
presence of an unknown or unsupported Sub-TLV MUST NOT by itself
cause the entire Edge Metadata Path Attribute to be considered
malformed.
If a Sub-TLV type is recognized by the receiving speaker, but the
value carried in that Sub-TLV is invalid according to the definition
of that Sub-TLV, the speaker MUST treat that Sub-TLV as unusable and
MUST ignore it for metadata-based route selection. The speaker
SHOULD continue processing the remaining Sub-TLVs. An invalid value
in one recognized Sub-TLV MUST NOT by itself cause the entire Edge
Metadata Path Attribute to be considered malformed unless the
corresponding Sub-TLV definition explicitly states otherwise.
If the Length field of a Sub-TLV is inconsistent with the encoding
defined for that Sub-TLV, or if the Sub-TLV cannot be fully parsed
based on the encoded length, the Edge Metadata Path Attribute MUST be
treated as malformed, and error handling MUST follow the procedures
specified in Section 9.
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If a recognized Sub-TLV appears more times than allowed by its
definition, the receiver SHOULD use only the first occurrence unless
the specific Sub-TLV definition states otherwise, and SHOULD ignore
the additional occurrences.
A BGP speaker that propagates the Edge Metadata Path Attribute SHOULD
NOT delete unrecognized Sub-TLVs solely because they are
unrecognized. If the route is propagated with the Edge Metadata Path
Attribute, unrecognized Sub-TLVs SHOULD remain unchanged in the
propagated attribute unless local policy requires removal of the
entire attribute.
If some Sub-TLVs are absent, the receiving speaker MUST treat the
attribute as carrying only the metadata explicitly present. The
absence of a particular Sub-TLV MUST NOT be interpreted as a zero
value, an infinite value, a degraded condition, or any other inferred
semantic value unless the specific Sub-TLV definition explicitly
states such behavior.
If none of the included Sub-TLVs are recognized by the receiving
speaker, the speaker MUST treat the Edge Metadata Path Attribute as
present but unusable for local metadata-based route selection. In
that case, the speaker SHOULD fall back to route selection based on
other applicable BGP attributes and local policy.
The same treatment applies when the only recognized Sub-TLVs present
contain invalid values and are ignored according to their Sub-TLV
definitions.
By default, a BGP speaker is not required to report unknown,
unsupported, or unusable Sub-TLVs to its peer. Logging or
notification to a local management system is OPTIONAL.
Ingress nodes that use Edge Metadata for route selection SHOULD apply
a deployment-specific algorithm to the set of recognized Sub-TLVs
that are present and usable in the received attribute. To ensure
consistent route selection, nodes participating in the same
deployment SHOULD use consistent policy regarding which Sub-TLVs are
considered and how their values are incorporated into route
selection.
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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 is not intended to replace LOCAL_PREF or
change the LOCAL_PREF semantics defined by BGP. LOCAL_PREF expresses
operator routing policy according to the BGP deployment in which it
is used. By contrast, the Site Preference Index carries service-
specific site metadata associated with an edge-service route.
Different services at the same site can have different Site
Preference Index values, and local policy may use those values,
together with LOCAL_PREF and other BGP attributes, when selecting
among candidate routes for metadata-aware services.
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 1: Site Preference Index Sub-TLV
- Site-Preference-Index Sub-Type (16 bits): 1 (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 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.
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- 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 Sub-TLV
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
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.
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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.
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 2: 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
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,
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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 Sub-TLV
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:
- 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
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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.
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.
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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 3: 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.
- 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.
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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 4: 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.
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.
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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 5: 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.
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.
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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 6: 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.
- MT (Metric Type)(4 bits): An unsigned 4 bits integer. When the MT
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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 7: 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. Edge Metadata Processing Capability in BGP OPEN Message
The BGP Capabilities Optional Parameter allows a BGP speaker to
advertise, during the BGP OPEN message exchange, the set of
capabilities supported on a session. As specified in [RFC5492], each
capability is encoded as a Capability Code, a Capability Length, and
a Capability Value.
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To enable the exchange of the Edge Metadata Path Attribute on a BGP
session, this document defines a new Edge Metadata Processing
Capability (=78). This capability is used by a BGP speaker to
indicate that it can send and receive the Edge Metadata Path
Attribute for one or more AFI/SAFI pairs on that session.
The Value Field of the Edge Metadata Processing Capability has the
following format:
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|AFI-SAFI-cnt | AFI | SAFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI | SAFI | .. ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Edge Metadata Capability Value Field
Where:
- A Flag(1 bit): When set to 1, this flag indicates that the sender
is willing to send and receive the Edge Metadata Path Attribute
for any AFI/SAFI enabled on the BGP session. When set to 0, the
capability applies only to the AFI/SAFI pairs explicitly listed in
the Capability Value.
- AFI-SAFI-CNT (7 bits): Indicates the number of AFI/SAFI pairs
encoded in the Capability Value.
- AFI (16 bits): Address Family Identifier.
- SAFI (8 bits):Sub-address Family identifier.
When the A Flag is set to 1, the capability applies to any AFI/SAFI
enabled on the BGP session. In this case, AFI-SAFI-CNT SHOULD be set
to 0 and no AFI/SAFI tuples need be present in the Capability Value.
If one or more AFI/SAFI tuples are present when the A Flag is set to
1, the receiver SHOULD ignore those tuples and process the capability
as applying to all AFI/SAFI enabled on the session.
When the A Flag is set to 0, AFI-SAFI-CNT indicates the exact number
of AFI/SAFI pairs listed in the Capability Value, and the capability
applies only to those listed AFI/SAFI pairs.
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A BGP speaker MUST NOT attach the Edge Metadata Path Attribute to any
UPDATE message sent on a BGP session unless both peers have
advertised the Edge Metadata Processing Capability for the
corresponding AFI/SAFI on that session. If one peer has advertised
the capability with the A Flag set to 1, that advertisement is
considered to cover any AFI/SAFI enabled on the session for the
purpose of this check.
If a BGP speaker has not advertised the Edge Metadata Processing
Capability on a session, or has not received this capability from its
peer on that session, the speaker MUST NOT send any UPDATE on that
session that carries the Edge Metadata Path Attribute.
If a BGP speaker receives an UPDATE carrying the Edge Metadata Path
Attribute on a session for which the corresponding Edge Metadata
Processing Capability was not successfully advertised by both peers
for that AFI/SAFI, the receiver SHOULD ignore the Edge Metadata Path
Attribute and process the remainder of the UPDATE according to local
policy and the error-handling procedures specified in Section 9.
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.
6. 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
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.
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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.
6.1. 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 of the value
field, excluding the Sub-Type and Length fields. For the AS-Scope
Sub-TLV, the value field consists of the Reserved field followed
by one or more 32-bit In-Scope AS values. Therefore, the Length
field is 1 + 4*N, where N is the number of In-Scope AS values and
N MUST be at least 1.
- Reserved (8 bits): These bits are reserved for future use and MUST
be set to zero.
- In-Scope AS-Value (32 bits): One or more 32-bit AS values that
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identify ASes within the intended metadata distribution domain.
When multiple ASes are included, they are encoded as consecutive
32-bit AS values within the same AS-Scope Sub-TLV. A receiver
considers the AS-Scope check successful if the local AS, or an AS
recognized by local configuration as part of the same metadata
distribution domain, matches any of the included AS values.
6.1.1. 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:
An AS-Scope value of 0 is invalid and MUST NOT be used. A receiver
that encounters an AS-Scope value of 0 MUST ignore that AS value. If
all AS values carried in the AS-Scope Sub-TLV are invalid, the
receiver MUST treat the AS-Scope check as failed.
When BGP confederations [RFC5065] are used, AS-Scope values refer to
member-AS numbers for sessions within the confederation, and to the
confederation identifier for sessions outside the confederation.
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.
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7. Policy Based Metadata Integration
This section describes how the information carried in the Edge
Metadata Path Attribute can be incorporated into BGP route selection
by local policy. The procedures in this section do not modify the
base BGP decision process defined in [RFC4271]. Instead, they
describe how local policy can use recognized Edge Metadata values
when comparing candidate routes for services configured for metadata-
aware route selection.
7.1. Policy Application Order
To remain consistent with Section 9.1.1 of [RFC4271], metadata-aware
policy evaluation MUST be applied after LOCAL_PREF has been set for
iBGP routes, or after equivalent inbound policy has been applied for
eBGP routes.
The use of Edge Metadata does not replace existing BGP routing
policy. Rather, the Edge Metadata Path Attribute provides additional
inputs that local policy MAY use when comparing candidate routes for
selected services.
7.2. Metadata Selection by Local Policy
A deployment MAY use only a subset of the metadata attributes carried
in the Edge Metadata Path Attribute. Which metadata attributes are
considered, and for which services they are considered, is determined
by local policy.
For example, one deployment may consider only the Service Delay
Prediction Sub-TLV for latency-sensitive services, while another
deployment may consider only availability-related or service-
capability-related Sub-TLVs. A route that carries additional
recognized metadata does not require all such metadata to be used in
route selection.
If none of the recognized metadata carried by a route are selected by
local policy for preference computation, the route is evaluated using
ordinary BGP policy and tie-breaking procedures.
7.3. Policy-Based Preference Computation
For services configured for metadata-aware route selection, local
policy MAY use one or more recognized metadata values carried in the
Edge Metadata Path Attribute, together with other routing attributes,
to derive a preference for each candidate route.
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The procedure for combining recognized metadata with traditional BGP
attributes is deployment specific and outside the scope of this
document. The preference computation MAY be performed at a Route
Reflector (RR), at an ingress node, or at another policy decision
point within the same administrative domain.
When metadata-aware policy is applied to a set of candidate routes,
the route with the most preferred policy outcome is selected. If two
or more routes remain equally preferred after metadata-aware policy
evaluation, the normal BGP tie-breaking procedures defined in
[RFC4271] apply.
This document does not define a default ordering or weighting among
Edge Metadata Sub-TLVs. When more than one recognized metadata Sub-
TLV is present, the local policy MUST specify which Sub-TLVs are used
and how their values are ordered, weighted, or otherwise combined for
preference computation. In the absence of such local policy, a BGP
speaker MUST NOT use the Edge Metadata Path Attribute to alter best-
path selection and MUST evaluate the route using ordinary BGP policy
and tie-breaking procedures.
7.4. Policy Treatment of Routes with Degraded Metadata
Local policy MAY define threshold conditions for one or more metadata
types. When the recognized metadata associated with a route
indicates that such a threshold has been crossed, local policy MAY
reduce the preference of that route or MAY treat the route as
ineligible for metadata-aware service steering.
This document does not mandate a specific action for degraded
metadata values. The action taken, if any, is determined by local
policy. For example, local policy may de-prefer a route whose
Service Delay Prediction exceeds a configured threshold, or a route
whose availability-related metadata falls below a configured level.
If local policy excludes a route from metadata-aware service
steering, the route MAY still remain valid for ordinary BGP
reachability unless separate policy removes or suppresses that route.
7.5. Tie Breaking and ECMP
After metadata-aware policy evaluation, if multiple candidate routes
remain equally preferred, BGP tie-breaking proceeds according to
[RFC4271].
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If the decision process results in multiple equally preferred paths
and the deployment permits Equal Cost Multi Path (ECMP), those paths
MAY be installed in the forwarding plane according to existing BGP
procedures and platform capabilities.
Different local policies may result in different selected paths;
deployments that require consistent route selection across multiple
decision points SHOULD configure consistent metadata-aware policy on
those decision points.
8. 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 and implementation behavior, including any configured
MRAI timer. This document does not rely on a specific MRAI value for
metadata update pacing. 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.
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Measurement-bearing Sub-TLVs, such as the Service Delay Prediction
Sub-TLV and Raw Measurement Sub-TLV, can be derived from local
measurements that change more frequently than BGP UPDATEs should be
advertised. The measurement collection interval is deployment
specific and is independent of the interval at which changed metadata
is advertised in BGP. Implementations SHOULD apply dampening,
hysteresis, or threshold-based change detection before advertising
updated Edge Metadata Path Attribute values, so that small or short-
lived measurement fluctuations do not cause excessive BGP UPDATE
churn.
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. A default minimum interval of 30
seconds for advertising Edge Metadata Path Attribute changes is
RECOMMENDED to balance responsiveness with stability, unless a
deployment configures a different interval. 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.
9. 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.
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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.
If an Edge Metadata Path Attribute does not have any valid Sub-TLVs,
or its Attribute Flags are inconsistent with the optional non-
transitive definition of this attribute, the "attribute discard"
procedure of [RFC7606] is applied.
10. 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 a small subset of services are expected to require the Edge
Metadata Path Attribute. These are typically services for which
metadata-aware route selection is beneficial. The domain in which
such metadata is propagated is typically operated under a common
administrative policy, even when the routers are supplied by
different vendors.
Additional non-normative examples of deployment models and metadata-
aware route-selection procedures are provided in Appendix C.
11. 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.
The Sub-TLV count limit specified in Section 4.1.3 helps reduce
exposure to resource-exhaustion attacks caused by excessively large
Edge Metadata Path Attributes.
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:
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- The Edge Metadata Path Attribute is optional 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
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 ingress
routers to restrict the propagation of BGP UPDATE messages
carrying the Edge Metadata Path Attribute beyond the
administrative domain. Access control lists (ACLs), prefix lists,
or route maps can be used to filter the corresponding BGP routes
for which the Edge Metadata Path Attribute is 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.
12. IANA Considerations
12.1. 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
in the BGP Parameters registry group. The reference for this
assignment is [this document].
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+=======+======================================+=================+
| Value | Description | Reference |
+=======+======================================+=================+
| 42 | Edge Metadata Path Attribute | [this document] |
+-------+--------------------------------------+-----------------+
12.2. Edge Metadata Capability Code
IANA has assigned a Capability Code of 78 from the "BGP Capability
Codes" registry in "Capability Codes registry group" for the Edge
Metadata Capability in the BGP OPEN message.
+=======+======================================+=================+
| Value | Description | Reference |
+=======+======================================+=================+
| 78 | Edge Metadata Capability | [This document] |
+-------+--------------------------------------+-----------------+
12.3. 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:4.2]|
+--------+-----------------------------+-------------------+
| 2 |Site Physical Avail Index |[this document:4.3]|
+--------+-----------------------------+-------------------+
| 3 |Service Delay Predication |[this document:4.4]|
+--------+-----------------------------+-------------------+
| 4 |Raw Measurement |[this document:4.5]|
+--------+-----------------------------+-------------------+
| 5 |Service-Oriented Capability |[this document:4.6]|
+--------+-----------------------------+-------------------+
| 6 |Service-Oriented Available | |
| |Resource |[this document:4.7]|
+--------+-----------------------------+-------------------+
| 7 |AS-Scope |[this document:6.1]|
+--------+-----------------------------+-------------------+
|8-65534 | unassigned | |
+--------+-----------------------------+-------------------+
| 65535 | reserved |[this document] |
+--------+-----------------------------+-------------------+
13. Contributors
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
14. 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.
15. References
15.1. 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>.
[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>.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065,
DOI 10.17487/RFC5065, August 2007,
<https://www.rfc-editor.org/info/rfc5065>.
[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>.
[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>.
[RFC7311] Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
"The Accumulated IGP Metric Attribute for BGP", RFC 7311,
DOI 10.17487/RFC7311, August 2014,
<https://www.rfc-editor.org/info/rfc7311>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
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[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>.
[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>.
[RFC9107] Raszuk, R., Ed., Decraene, B., Ed., Cassar, C., Åman, E.,
and K. Wang, "BGP Optimal Route Reflection (BGP ORR)",
RFC 9107, DOI 10.17487/RFC9107, August 2021,
<https://www.rfc-editor.org/info/rfc9107>.
15.2. Informative References
[ATTRIBUTE-ESCAPE]
J. Haas, "BGP Attribute Escape", July 2023,
<https://datatracker.ietf.org/doc/draft-haas-idr-bgp-
attribute-escape/>.
[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>.
[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.
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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.
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
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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.
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
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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.
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.
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- 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:
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.
Appendix C. Deployment Examples for Metadata-Aware Route Selection
This appendix provides non-normative examples of how a deployment may
apply the procedures described in Section 7.
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C.1. Centralized RR Model
In a deployment where the Route Reflector (RR) is the primary policy
decision point, the RR may apply metadata-aware local policy when
selecting routes for reflection. In such a deployment, routers that
rely on the RR for best-path selection receive routes that already
reflect the policy outcome.
In deployments where the RR is responsible for pre-selecting routes,
the RR may combine recognized Edge Metadata with traditional BGP
attributes when determining the preferred route for a service. The
RR can then reflect only the selected route to its client routers,
such as ingress PEs, in accordance with local policy. This can help
align reflected routes with service-specific requirements while
limiting the number of routes distributed to clients.
Deployments using this model SHOULD consider Optimal Route Reflection
(ORR) [RFC9107] so that route selection reflects the perspective of
ingress routers rather than the physical location of the RR.
C.2. Ingress-Node Decision Model
In some deployments, the RR may reflect multiple candidate routes,
for example by using Add-Paths. In such a deployment, the ingress
node receives those candidate routes and applies local metadata-aware
policy to determine the preferred route for the selected service.
The ingress node may combine recognized metadata values with
traditional BGP attributes when deriving route preference. This
allows the ingress node to make service-specific routing decisions
based on its local policy and on the metadata available for the
candidate routes.
C.3. Consistent Distributed Model
In a deployment where routers exchange iBGP routes directly in
addition to receiving reflected routes, all participating nodes,
including any RR, should apply consistent metadata-aware policy so
that route selection remains aligned across the administrative
domain.
In this model, the RR is not the sole policy decision point.
Instead, each node that performs metadata-aware preference
computation applies consistent policy to the same set of recognized
metadata and routing attributes. This helps reduce the risk of
inconsistent route selection among nodes that receive the same
candidate routes.
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C.4. Example Policy Weighting Approaches
A deployment may choose to assign greater weight to recognized
metadata values than to traditional routing attributes, may weigh
them equally, or may treat metadata only as a secondary refinement
after traditional routing considerations. The weighting method is
deployment specific and is not specified by this document.
For example, one deployment may emphasize service-delay-related
metadata for latency-sensitive services, while another may emphasize
availability-related or resource-related metadata. Another
deployment may use metadata only after candidate routes have already
been narrowed by traditional BGP policy. These examples are
illustrative only and do not impose any required computation method.
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
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Email: duzongpeng@chinamobile.com
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