| Internet-Draft | Metadata Path | July 2024 |
| Dunbar, et al. | Expires 23 January 2025 | [Page] |
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).¶
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.¶
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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This Internet-Draft will expire on 23 January 2025.¶
Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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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 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.¶
The extension is targeted for a single domain with RR controlling the propagation of the BGP UPDATE. The edge service Metadata Path Attribute is only attached to the low latency services (routes) hosted in the 5G edge cloud sites, which are only a small subset of services initiated from UEs, not for UEs accessing many internet sites.¶
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.¶
The following conventions are used in this document.¶
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.¶
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 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 CATS WG. This document illustrates a few examples of Sub-TLVs of the metrics under the edge service Metadata Path Attribute:¶
This section specifies how those Metadata impact the ingress node's path selections.¶
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.¶
When the ingress router receives a packet and does a lookup on the route in the FIB, it gets the destination prefix's whole path. It encapsulates the packet destined towards the optimal egress node.¶
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. Keeping packets from one flow to the same egress router, a.k.a. Flow Affinity, is supported by many commercial routers. Most registered EC services have relatively short flows.¶
How Flow Affinity is implemented is out of the scope for this document.¶
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 Next Hop for this route. The detailed algorithm is out of the scope of this document.¶
The Metadata Path Attribute is an optional non-transitive BGP Path attribute to carry metrics and metadata about the edge services attached to the egress router. The Metadata Path Attribute, to be assigned by IANA [RFC2042], consists of a set of Sub-TLVs, and each Sub-TLV contains information for specific metrics of the edge services.¶
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], etc.¶
The metadata Path Attribute has the following characteristics:¶
The metrics Sub-TLVs included in the Metadata Path Attribute apply to all the address families carried in the NLRI field of the BGP UPDATE message [RFC4271]. For a multi-protocol BGP UPDATE message [RFC4760] [RFC7606], the metrics Sub-TLVs included in the Metadata Path Attribute apply to all the AFIs/SAFIs address families carried by the MP_REACH_NLRI.¶
A BGP speaker that advertises a path received from one of its neighbors SHOULD advertise the BGP Metadata Path attribute received with the path without modification as long as the BGP Metadata Path attribute was acceptable. If the path did not come with a BGP Metadata Path attribute, the speaker MAY attach a BGP Metadata Attribute to the path if configured to do so.¶
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.¶
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.¶
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 the configuration. When a BGP Speaker does not recognize some of the Sub-TLVs within one Metadata Path Attribute in a BGP UPDATE message, the BGP Speaker should forward the received BGP UPDATE message without any change if the transitive bit is set to 1 [RFC4271]. 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 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.¶
The metrics Sub-TLVs included in the Metadata Path Attribute apply to all the address families carried in the NLRI field of the BGP UPDATE message [RFC4271]. For a multi-protocol BGP UPDATE message [RFC4760] [RFC7606], the metrics Sub-TLVs included in the Metadata Path Attribute apply to all the AFIs/SAFIs address families carried by the MP_REACH_NLRI.¶
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|AttFlag|Reserve|MetaDataPathAtt|Length(1 Octet)| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value (multiple Metadata Sub-TLVs) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All values in the Sub-TLVs are unsigned 32 bits integers.¶
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 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference Index value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 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. Depending on deployment, 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, such as fiber cut connecting to the site or among pods, cooling failures, insufficient backup power, cyber threats attacks, too many changes outside of the maintenance window, etc. Fiber-cut is not uncommon within a Cloud site or between sites.¶
When those failure events happen, the edge (egress) router is running fine. Therefore, the ingress routers with paths to the egress router can't use BFD to detect the failures.¶
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 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 |I| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Site-ID (2 octets) | Site Availability Percentage | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
Upon receiving a BGP update message from Router-X, containing the Metadata Path Attribute with the Site Physical Availability Index Sub-TLV, the next-hop should be the loopback of Router-X. The local BGP peer uses local policy to evaluate the route (prefix and path attributes). When the local policy processes the Metadata Attribute with the Site Physical availability, it will use the site availability index to efficiently reduce or increase the preference for all BGP routes with the Router-X next-hop (loopback).¶
The BGP UPDATE with a standalone Site Availability Index is NOT intended for resolving NextHop.¶
It is desirable for an ingress router to select a site with the shortest processing time for an ultra-low latency service. But it is not easy to predict which site has "the fastest processing time" or "the shortest processing delay" for an incoming service request because:¶
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.¶
The remaining available resource at a site is a more reasonable indication of process delay for future service requests.¶
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 Metadata Path Attribute of the BGP Route UPDATE message to the ingress routers.¶
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ServiceDelayPredict Sub-Type | Length |F|L|Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Delay Predication Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When ingress routers have embedded analytics tool relying on the raw measurements, it is useful for the egress router to send the raw measurement.¶
Raw Measurement Sub-TLV has the following format:¶
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Raw-Measurement Sub-Type | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Raw-Measurement Sub-Type =4 (specified in this document): Raw measurements metadata from the edge service address.¶
- Length: specifies the total length in octets of the value field, i.e., not including the Sub-Type, the Length fields.¶
- Reserved: Reserved for future use.¶
- Value: The value fileds can contain multiple types of sub-TLVs, which are used to describe the raw metadata.¶
A typical raw mesurement metadata sub-TLV is defined below.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Type | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Measurement Period | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of packets to the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of packets from the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of bytes to the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of bytes from the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Sub-Type =4 (specified in this document): Type = 0, Raw measurements of packets/bytes to/from the edge service address.¶
- Length: specifies the total length in octets of the value field, i.e., not including the Sub-Type, the Length fields. The value is 22.¶
- Reserved: Reserved for future use.¶
- Measurement Period: BGP Update period in Seconds or user-specified period.¶
- Total number of pakcets and bytes: 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 node and preconfigured algorithms.¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.¶
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 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.¶
In addition, the Service Metadata propagation can be further constrained to a set of ingress nodes that are specifically interested in the services. For example, for each registered low-latency Service, BGP RT Constrained Distribution [RFC4684] can be used to form a Group interested in the Service. The "Service ID", an IP address prefix, is the Route Target. When an ingress router receives the first packet of a flow destined to a Service ID (i.e., IP prefix), the ingress router sends a BGP UPDATE that advertises the Route Target membership NLRI per [RFC4684]. The ingress router must assign a Timer for the Service ID, as the UE that uses the Service ID might move away. Upon receiving a packet destined for the Service ID, the ingress router must refresh the Timer. The ingress router must send a BGP Withdraw UPDATE for the Service ID upon expiration of the Timer.¶
[RFC4684]specifies SAFI=132 for the Route Target membership NLRI Advertisements.¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 MUST drop the BGP UPDATE message containing the AS-Scope Sub-TLV.¶
- Forwarding Rules: The AS-Scope Sub-TLV ensures that the Metadata Path Attribute is only propagated within the intended ASes, thereby preventing unauthorized dissemination of sensitive metadata.¶
- Non-Transitive: The AS-Scope Sub-TLV is marked as non-transitive to ensure it is not forwarded beyond the intended scope.¶
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.¶
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.¶
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.¶
Furthermore, operators should implement robust route damping and filtering policies to control the propagation of changes and minimize the impact on dependent routes. By acknowledging and planning for these broader impacts, the mechanism can be deployed more effectively, ensuring optimal performance without compromising network stability.¶
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, the load metrics change rate can be in the magnitude of hours or days.¶
In addition to the Error Handling procedure described in [RFC7606], a BGP speaker should ignore the Metadata Path Attribute if more than one Metadata Path Attribute is within one BGP Update message.¶
The Metadata Path Attribute contains a sequence of Sub-TLVs. The Metadata Path Attribute's length minus 1 determines the total number of octets for all the Sub-TLVs under the Metadata Path Attribute. The sum of the lengths from all the Sub-TLVs under the Metadata Path Attribute plus 1 should equal the length of the Metadata Path Attribute. If this is not the case, the TLV should be considered malformed, and the "Treat-as-withdraw" procedure of [RFC7606] is applied.¶
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.¶
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.¶
The proposed edge service Metadata are advertised within the trusted domain of 5G LDN's ingress and egress routers. The ingress routers should not propagate the edge service Metadata to any nodes that are not within the trusted domain.¶
To prevent the BGP UPDATE receivers (a.k.a. ingress routers in this document) from leaking the Metadata Path Attribute by accident to nodes outside the trusted domain [ATTRIBUTE-ESCAPE], the following practice should be enforced:¶
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:¶
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] |
+-------+--------------------------------------+-----------------+
¶
IANA is requested to create a new sub-registry under the Metadata Path Attribute registry as follows:¶
+========+==========================+=================+ |Sub-Type| Description | Reference | +========+==========================+=================+ | 0 | reserved | [this document] | +--------+--------------------------+-----------------+ | 1 | Site Preference Index | [this document] | +--------+--------------------------+-----------------+ | 2 | Site Availability Index | [this document] | +--------+--------------------------+-----------------+ | 3 | Service Delay Predication| [this document] | +--------+--------------------------+-----------------+ | 4 | Raw Load Measurement | [this document] | +--------+--------------------------+-----------------+ | 5 | Service-Oriented | | | | Capability | [this document] | +--------+--------------------------+-----------------+ | 6 | Service-Oriented | | | | Utilization | [this document] | +--------+--------------------------+-----------------+ | 7 | AS-Scope | [this document] | +--------+--------------------------+-----------------+ | 8-254 | unassigned | [this document] | +--------+--------------------------+-----------------+ | 255 | reserved | [this document] | +--------+--------------------------+-----------------+¶
Changwang Lin¶
New H3C Technologies¶
China¶
Email: linchangwang.04414@h3c.com¶
Acknowledgements to Jeff Hass, 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.¶
When data centers detailed running status are not exposed to the network operator, historic traffic patterns through the egress nodes 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:¶
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.¶
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 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).¶
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
¶
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.¶
When an ingress router receives BGP updates for the same IP address from multiple egress routers, all those egress routers are considered as the next hops for the IP address. For the selected services configured to be influenced by the edge service Metadata, the ingress router BGP Decision process [IDR-CUSTOM-DECISION] would trigger the edge service Management function to compute the weight to be applied to the route's next hop in the forwarding plane. The decision process is influenced by the edge service Metadata associated with the client routes, such as Capacity Availability Index, Site Preference, and Service Delay Prediction Index, in addition to the traditional BGP multipath computation algorithm, such as the Weight, Local preference, Origin, MED, etc., shown below:¶
BGP ANYCAST Update
+--------+ with Metadata +---------------+
| BGP |----------------->| EdgeServiceMgn|
|Decision|< - - - - - - - - | |
+---^-|--+ +-------|-------+
| | BGP ANYCAST | Update Anycast
| | Route | Route Nexthops
| | Multi-path NH install | with weight
+---|-V--+ |
| RIB | |
+----+---+ |
| |
+---V------------------------------V-------+
| Forwarding Plane |
| |
+------------------------------------------+
When any of those metadata value goes to 0, the effect is the same as the routes becoming ineligible via the egress router who originates the metadata UPDATE. But when any of those metadata just degrade, there is possibility, even though smaller, for the egress router to continue as the optimal next hop.¶
Suppose a destination address for aa08::4450 can be reached by three next hops (R1, R2, R3). Further, suppose the local BGP's Decision Process based on the traditional network layer policies and metrics identifies the R1 as the optimal next hop for this destination (aa08::4450). If the edge service Metadata results in R2 as the optimal next hop for the prefix, the Forwarding Plane will have R2 as the next-hop for the destination address of aa08::4450.¶
The edge service Metadata influencing next hop selection is different from the metric (or weight) to the next hop. The metric to a next hop can impact many (sometimes, tens of thousands) routes that have the node as their next hop. while as the edge service Metadata only impact the optimal next hop selection for a subset of client routes that are identified as the edge services.¶
When the BGP custom decision [idr-custom-decision] is used, the edge service Management function would have algorithm to combine the edge service Metadata attributes with the custom decision to derive the optimal next hop for the Edge service routes.¶
Note: For a BGP UPDATE message that includes the edge service Metadata Path Attribute with the RouteFlag-I=0 and the egress router's loopback prefix as the NLRI, the Site Capacity Availability Index value is applied to all the routes associated with the Site-ID.¶