BGP Extension for 5G Edge Service Metadata
draft-ietf-idr-5g-edge-service-metadata-25
The information below is for an old version of the document.
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| Authors | Linda Dunbar , Kausik Majumdar , Cheng Li , Gyan Mishra , Zongpeng Du | ||
| Last updated | 2024-12-03 (Latest revision 2024-10-14) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-idr-5g-edge-service-metadata-25
Network Working Group L. Dunbar
Internet-Draft Futurewei
Intended status: Standards Track K. Majumdar
Expires: 6 June 2025 Oracle
C. Li
Huawei Technologies
G. Mishra
Verizon
Z. Du
China Mobile
3 December 2024
BGP Extension for 5G Edge Service Metadata
draft-ietf-idr-5g-edge-service-metadata-25
Abstract
This draft describes a new Metadata Path Attribute and some Sub-TLVs
for egress routers to advertise the Metadata about the attached edge
services (ES). The edge service Metadata can be used by the ingress
routers in the 5G Local Data Network to make path selections not only
based on the routing cost but also the running environment of the
edge services. The goal is to improve latency and performance for 5G
edge services.
The extension enables an edge service at one specific location to be
more preferred than the others with the same IP address (ANYCAST) to
receive data flow from a specific source, like a specific User
Equipment (UE).
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 6 June 2025.
Copyright Notice
Copyright (c) 2024 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. Metadata Influenced Ingress Node Behavior . . . . . . . . . . 4
3.1. Metadata Influenced BGP Path Selection . . . . . . . . . 5
3.2. Ingress Router Forwarding Behavior . . . . . . . . . . . 5
3.3. Forwarding Behavior when UEs Move . . . . . . . . . . . . 6
4. Edge Service Metadata Encoding . . . . . . . . . . . . . . . 6
4.1. Metadata Path Attribute . . . . . . . . . . . . . . . . . 6
4.1.1. Metadata Path Attribute Characteristics . . . . . . . 7
4.1.2. Metadata Path Attribute Processing . . . . . . . . . 7
4.1.3. Sub-TLVs Data Processing . . . . . . . . . . . . . . 8
4.1.4. Metadata Path Attribute Handling Procedure . . . . . 8
4.1.5. 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 . . . . . . . . . . 14
4.5. Raw Measurement Sub-TLV . . . . . . . . . . . . . . . . . 15
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
5.1.1. AS-Scope Value Checking Procedure . . . . . . . . . . 22
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6. Policy Based Metadata Integration . . . . . . . . . . . . . . 22
7. Minimum Interval for Metrics Change Advertisement . . . . . . 25
8. Validation and Error Handling . . . . . . . . . . . . . . . . 26
9. Manageability Considerations . . . . . . . . . . . . . . . . 26
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
11.1. Metadata Path Attribute . . . . . . . . . . . . . . . . 28
11.2. Metadata Path Attribute Sub-Types . . . . . . . . . . . 28
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.1. Normative References . . . . . . . . . . . . . . . . . . 29
14.2. Informative References . . . . . . . . . . . . . . . . . 31
Appendix A. Service Delay Prediction Based on Load
Measurement . . . . . . . . . . . . . . . . . . . . . . . 32
Appendix B. Service Metadata Influenced Decision Process . . . . 33
B.1. Egress Router Behavior . . . . . . . . . . . . . . . . . 33
B.2. Integrating Network Delay with the Service Metrics . . . 34
B.3. Integrating with BGP Route Selection . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
This document describes a new 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 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.
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.
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While the proposed Metadata Path Attribute is particularly beneficial
for low latency services, the 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. 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 Metadata Path Attribute can ignore
the 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
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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. 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
header. This encapsulation ensures that intermediate nodes not
supporting the Metadata Path Attribute do not forward the packet to
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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
4.1. Metadata Path Attribute
The 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 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 Metadata Path Attribute should
indicate this by signaling the 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 Metadata Path Attributes forms a
limited domain, either within a single AS or within a group of ASes
under a single Administrative Authority.
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The fields within the 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. Metadata Path Attribute Characteristics
Only a small subset of BGP UPDATE messages include the Metadata Path
Attribute. The choice of which prefix to carry the Metadata Path
Attribute is determined by local policies. The 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 Metadata Path Attribute has the following characteristics:
- Non-transitive
- Boundary node filtering SHOULD be deployed to remove the BGP
Metadata Path Attribute at the administrative boundary to prevent
the distribution of the BGP 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 Metadata Sub-TLV. Multiple Metadata
Sub-TLVs can be included in a Metadata Path Attribute in one BGP
UPDATE message. The choice of the Sub-TLVs present in the BGP
Metadata Path Attribute is determined by the local policies.
Multiple Sub-TLVs may be carried by a single BGP Metadata Path
Attribute.
4.1.2. Metadata Path Attribute Processing
A BGP speaker that advertises a BGP UPDATE message received from one
of its neighbors SHOULD advertise the BGP Metadata Path Attribute
received with the UPDATE message without modification only when
forwarding to peers within the same domain. Otherwise, the Metadata
Path Attribute should be removed. If the UPDATE message did not come
with a BGP Metadata Path Attribute, the speaker MAY attach a BGP
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.
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A BGP Peer receiving a BGP 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 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 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 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 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 Metadata Path Attribute of the
received BGP UPDATE message.
To ensure consistent route selection, a deployment specific algorithm
should be configured across all ingress nodes to factor in the
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 Metadata.
4.1.4. Metadata Path Attribute Handling Procedure
The Metadata Path Attribute MUST contain at least one Metadata Sub-
TLV. Multiple Metadata Sub-TLVs can be included in a Metadata Path
Attribute in one BGP UPDATE message. The content of the Sub-TLVs
present in the BGP Metadata Path Attribute is determined by
configuration. The domain ingress nodes should process the
recognized Sub-TLVs carried by the Metadata Path Attribute and ignore
the unrecognized Sub-TLVs. By default, a BGP speaker does not report
any unrecognized Sub-TLVs within a 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 Metadata Path
Attribute of the received BGP UPDATE message.
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4.1.5. 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 Metadata Path Attribute, a new Metadata
Processing Capability code (TBD2) is defined. This capability allows
a BGP speaker to communicate its ability to process the Metadata Path
Attribute for specified AFI and SAFI pairs.
The Value Field of the 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: Metadata Capability Value Field
Where:
- A Flag(1 bit): Set to 1 indicates that the Metadata attribute can
be attached to any AFI/SAFI. Set to 0 indicates that the 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 Metadata Processing Capability
in its BGP OPEN message for a specific BGP session, or if it does not
receive the Metadata Processing Capability from its peer on that
session, it MUST NOT send any BGP UPDATE message on that session that
bind the Metadata Path Attribute to any prefix.
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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 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).
- 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..
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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.
If the access network attached to the egress router doesn't support
BFD, it can be challenging for the egress router to directly notify
ingress routers about failures within the access network. However,
if BFD is implemented on the access network, concatenated path down
mechanisms can be employed to propagate failure information more
effectively.
When there is a failure occurring at an edge site (or a pod), many
instances can be impacted. In addition, the routes (i.e., the IP
addresses) in the site might not be aggregated nicely. Instead of
many BGP UPDATE messages to the ingress routers for all the
instances, i.e. routes, impacted, the egress router can send one
single BGP UPDATE to indicate the capacity availability of the site.
The ingress routers can switch all or a portion of the instances
associated with the site depending on how much the site is degraded.
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
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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
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
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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 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 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:
- 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
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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.
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 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 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.
- 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 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.
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 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.
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 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.
- 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 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 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 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 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 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 Metadata Path Attribute originator sets the attribute
as Non-transitive when sending the BGP UPDATE message to its
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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 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 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 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 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. This flexibility ensures that service specific
requirements are accounted for while maintaining network-wide
consistency.
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.
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). This ensures that
the reflected route already aligns with service specific
requirements.
- At the Ingress Node:
When the RR reflects multiple routes (e.g., using Add Paths), the
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:
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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.
- 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.
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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 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 Metadata Path Attributes into BGP route
selection based on their specific operational goals and requirements,
while maintaining compatibility with traditional BGP operations.
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.
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.
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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.
8. Validation and Error Handling
The 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 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 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 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.
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To prevent the BGP UPDATE receivers (a.k.a. ingress routers in this
document) from leaking the Metadata Path Attribute by accident to
nodes outside the trusted domain [ATTRIBUTE-ESCAPE], the following
practice should be enforced:
- The 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
to the BGP UPDATE message with Metadata Path Attribute when
forwarding to the ingress routers. By doing so, the Route
Reflector signals to ingress nodes that the routes with the
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.
BGP Route Filtering or BGP Route Policies [RFC5291] can also be used
to ensure that BGP UPDATE messages with 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 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.
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11. IANA Considerations
11.1. Metadata Path Attribute
IANA is requested to assign a new path attribute from the "BGP Path
Attributes" registry. The symbolic name of the attribute is
"Metadata", and the reference is [This Document].
+=======+======================================+=================+
| Value | Description | Reference |
+=======+======================================+=================+
| TBD1 | Metadata Path Attribute | [this document] |
+-------+--------------------------------------+-----------------+
| TBD2 | Metadata Capability in BGP OPEN | [This document] |
+-------+--------------------------------------+-----------------+
11.2. Metadata Path Attribute Sub-Types
IANA is requested to create a new sub-registry under the Metadata
Path Attribute registry as follows:
Name: Sub-TLVs under the "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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[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>.
[RFC2042] Manning, B., "Registering New BGP Attribute Types",
RFC 2042, DOI 10.17487/RFC2042, January 1997,
<https://www.rfc-editor.org/info/rfc2042>.
[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
[RFC 4271], 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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