A Framework for Computing-Aware Traffic Steering (CATS)
draft-ietf-cats-framework-04
| Document | Type | Active Internet-Draft (cats WG) | |
|---|---|---|---|
| Authors | Cheng Li , Zongpeng Du , Mohamed Boucadair , Luis M. Contreras , John Drake | ||
| Last updated | 2024-10-25 (Latest revision 2024-10-17) | ||
| Replaces | draft-ldbc-cats-framework | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-cats-framework-04
cats C. Li, Ed.
Internet-Draft Huawei Technologies
Intended status: Informational Z. Du
Expires: 20 April 2025 China Mobile
M. Boucadair, Ed.
Orange
L. M. Contreras
Telefonica
J. Drake
Juniper Networks, Inc.
17 October 2024
A Framework for Computing-Aware Traffic Steering (CATS)
draft-ietf-cats-framework-04
Abstract
This document describes a framework for Computing-Aware Traffic
Steering (CATS). Particularly, the document identifies a set of CATS
components, describes their interactions, and exemplifies the
workflow of the control and data planes.
Status of This Memo
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This Internet-Draft will expire on 20 April 2025.
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Copyright (c) 2024 IETF Trust and the persons identified as the
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CATS Framework and Components . . . . . . . . . . . . . . . . 6
3.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. CATS Identifiers . . . . . . . . . . . . . . . . . . . . 7
3.3. Framework Overview . . . . . . . . . . . . . . . . . . . 7
3.4. CATS Functional Components . . . . . . . . . . . . . . . 8
3.4.1. Service Sites, Services Instances, and Service Contact
Instances . . . . . . . . . . . . . . . . . . . . . . 9
3.4.2. CATS Service Metric Agent (C-SMA) . . . . . . . . . . 10
3.4.3. CATS Network Metric Agent (C-NMA) . . . . . . . . . . 10
3.4.4. CATS Path Selector (C-PS) . . . . . . . . . . . . . . 10
3.4.5. CATS Traffic Classifier (C-TC) . . . . . . . . . . . 11
3.4.6. Overlay CATS-Forwarders . . . . . . . . . . . . . . . 11
3.4.7. Underlay Infrastructure . . . . . . . . . . . . . . . 12
3.5. Deployment Considerations . . . . . . . . . . . . . . . . 12
4. CATS Framework Workflow . . . . . . . . . . . . . . . . . . . 13
4.1. Provisioning of CATS Components . . . . . . . . . . . . . 13
4.2. Service Announcement . . . . . . . . . . . . . . . . . . 13
4.3. Metrics Distribution . . . . . . . . . . . . . . . . . . 13
4.4. Service Access Processing . . . . . . . . . . . . . . . . 19
4.5. Service Contact Instance Affinity . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 20
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Informative References . . . . . . . . . . . . . . . . . . . 21
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Computing service architectures have been expanding from single
service site to multiple, sometimes collaborative, service sites to
address various issues (e.g., long response times or suboptimal
service and network resource usage).
The underlying networking infrastructures that include computing
resources usually provide relatively static service dispatching (that
is, the selection of the service instances that will be invoked for a
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request). In such infrastructures, service-specific traffic is often
directed to the closest service site from a routing perspective
without considering the actual network state (e.g., traffic
congestion conditions) or the service site state.
As described in [I-D.ietf-cats-usecases-requirements], traffic
steering that takes into account computing resource metrics would
benefit several services, including latency-sensitive services like
immersive services that rely upon the use of augmented reality or
virtual reality (AR/VR) techniques. This document provides an
architectural framework that aims at facilitating the making of
compute- and network-aware traffic steering decisions in networking
environments where computing service resources are deployed.
The Computing-Aware Traffic Steering (CATS) framework assumes that
there might be multiple service instances that are providing one
given service. Each of these service instances can be accessed via a
service contact instance. A single service site may have limited
computing resources available at a given time, whereas the various
service sites may experience different resource availability issues
over time. A single service site may host one or multiple service
contact instances.
Steering in CATS is about selecting the appropriate service contact
instance that will service a request according to a set of network
and computing metrics. That selection may not necessarily reveal the
actual service instance that will be invoked, e.g., in hierarchical
or recursive contexts. Therefore, the metrics of the service contact
instance may be the aggregated metrics from multiple service
instances.
The CATS framework is an overlay framework for the selection of the
suitable service contact instance(s) from a set of candidates. The
exact characterization of 'suitable' is determined by a combination
of networking and computing metrics.
Also, this document describes a workflow of the main CATS procedures
that are executed in both the control and data planes.
2. Terminology
This document makes use of the following terms:
Client: An endpoint that is connected to a service provider network.
Computing-Aware Traffic Steering (CATS): A traffic engineering
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approach [I-D.ietf-teas-rfc3272bis] that takes into account the
dynamic nature of computing resources and network state to
optimize service-specific traffic forwarding towards a given
service contact instance. Various relevant metrics may be used to
enforce such computing-aware traffic steering policies.
Metric: An information that provides suitable input information to a
selection mechanism to determine a CATS egress node.
Service: An offering that is made available by a provider by
orchestrating a set of resources (networking, compute, storage,
etc.).
Which and how these resources are solicited is part of the service
logic which is internal to the provider. For example, these
resources may be:
* Exposed by one or multiple processes.
* Provided by virtual instances, physical, or a combination
thereof.
* Hosted within the same or distinct nodes.
* Hosted within the same or multiple service sites.
* Chained to provide a service using a variety of means.
How a service is structured is out of the scope of CATS.
The same service can be provided in many locations; each of them
constitutes a service instance.
Computing Service: An offering is made available by a provider by
orchestrating a set of computing resources.
CATS Service ID (CS-ID): An identifier representing a service, which
the clients use to access it. See Section 3.2.
Service instance: An instance of running resources according to a
given service logic.
Many such instances can be enabled by a provider. Instances that
adhere to the same service logic provide the same service.
An instance is typically running in a service site. Clients'
requests are serviced by one of these instances.
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Service site: A location that hosts the resources that are required
to offer a service.
A service site may be a node or a set of nodes.
A CATS-serviced site is a service site that is connected to a
CATS-Forwarder.
Service contact instance: A client-facing service function instance
that is responsible for receiving requests in the context of a
given service.
A service contact instance can handle one or more service
instances.
Steering beyond a service contact instance is hidden to both
clients and CATS components.
A service request is processed according to the service logic
(e.g., handle locally or solicit backend resources).
A service contact instance is reachable via at least one Egress
CATS Forwarder.
A service can be accessed via multiple service contact instances
running at the same or different locations (service sites).
A service contact instance may dispatch service requests to one or
more service instances (e.g., a service contact instance that
behaves as a service load-balancer).
CATS Service Contact Instance ID (CSCI-ID): An identifier of a
specific service contact instance. See Section 3.2.
Computing-aware forwarding (or steering, computing): A forwarding
(or steering, computing) scheme which takes a set of metrics that
reflect the capabilities and state of computing resources as
input.
Service request: A request to access or invoke a specific service.
Such a request is steered to a service contact instance via CATS-
Forwarders.
A service request is placed using service-specific protocols.
Service requests are not explicitly sent by clients to CATS-
Forwarders.
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CATS-Forwarder: A network entity that steers traffic specific to a
service request towards a corresponding yet selected service
contact instance according to provisioned forwarding decisions.
These decisions are supplied by a C-PS, which may or may not be on
the CATS-Forwarder.
A CATS-Forwarder may behave as Ingress or Egress CATS-Forwarder.
Ingress CATS-Forwarder: An entity that steers service-specific
traffic along a CATS-computed path that leads to an Egress CATS-
Forwarder that connects to the most suitable service site that
host the service contact instance selected to satisfy the initial
service request.
Egress CATS-Forwarder: An entity that is located at the end of a
CATS-computed path and which connects to a CATS-serviced site.
CATS Path Selector (C-PS): A functional entity that selects paths
towards service locations and instances and which accommodates the
requirements of service requests. Such a path selection engine
takes into account the service and network status information.
See Section 3.4.4.
CATS Service Metric Agent (C-SMA): A functional entity that is
responsible for collecting service capabilities and status, and
for reporting them to a CATS Path Selector (C-PS). See
Section 3.4.2.
CATS Network Metric Agent (C-NMA): A functional entity that is
responsible for collecting network capabilities and status, and
for reporting them to a C-PS. See Section 3.4.3.
CATS Traffic Classifier (C-TC): A functional entity that is
responsible for determining which packets belong to a traffic flow
for a particular service request. It is also responsible for
forwarding such packets along a C-PS computed path that leads to
the relevant service contact instance. See Section 3.4.5.
3. CATS Framework and Components
3.1. Assumptions
CATS assumes that there are multiple service instances running on
different service sites, and which provide a given service that is
represented by the same service identifier (see Section 3.2).
However, CATS does not make any assumption about these instances
other than they are reachable via one or multiple service contact
instances.
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3.2. CATS Identifiers
CATS uses the following identifiers:
CATS Service ID (CS-ID): An identifier representing a service, which
the clients use to access it. Such an ID identifies all the
instances of a given service, regardless of their location.
The CS-ID is independent of which service contact instance serves
the service request.
Service requests are spread over the service contact instances
that can accommodate them, considering the location of the
initiator of the service request and the availability (in terms of
resource/traffic load, for example) of the service instances
resource-wise among other considerations like traffic congestion
conditions.
CATS Service Contact Instance ID (CSCI-ID): An identifier of a
specific service contact instance.
3.3. Framework Overview
A high-level view of the CATS framework, without expanding the
functional entities in the network, is illustrated in Figure 1.
+----------------------------------+ | +--------+
| Management Plane | | | |
+----------------------------------+ |<=======>| C-SMA |
| Control Plane | | | |
+----------------------------------+ | +---+----+
/\ | |
|| | |
\/ | |
+----------------------------------+ | +--------+
| Data Plane | | | +--------+
+----------------------------------+ |<=======>| |Service |
| +-|Contact |
| |Instance|
| +--------+
Network Domain Computing Domain
Figure 1: Main CATS Interactions
The following planes are defined:
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* CATS Management Plane: Responsible for monitoring, configuring,
and maintaining CATS network devices.
* CATS Control Plane: Responsible for scheduling services based on
computing and network information. It is also responsible for
making decisions about how packets should be forwarded by involved
forwarding nodes and communicating such decisions to the CATS Data
Plane for execution.
* CATS Data Plane: Responsible for computing-aware routing,
including handling packets in the data path, such as packet
forwarding.
Depending on implementation and deployment, these planes may consist
of several functional elements/components, and the details will be
described in the following sections.
3.4. CATS Functional Components
CATS nodes make forwarding decisions for a given service request that
has been received from a client according to the capabilities and
status information of both service contact instances and network.
The main CATS functional elements and their interactions are shown in
Figure 2.
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+-----+ +------+ +------+
+------+| +------+ | +------+ |
|client|+ |client|-+ |client|-+
+---+--+ +---+--+ +---+--+
| | |
| +----------------+ | +-----+----------+
+-+ C-TC#1 +-+ +-----+ C-TC#2 |
|----------------| | |----------------|
| |C-PS#1 | +------+ |CATS-Forwarder 4|
......| +----------|....|C-PS#2|..| |...
: |CATS-Forwarder 2| | | | | .
: +----------------+ +------+ +----------------+ :
: :
: +-------+ :
: Underlay | C-NMA | :
: Infrastructure +-------+ :
: :
: :
: +----------------+ +----------------+ :
: |CATS-Forwarder 1| +-------+ |CATS-Forwarder 3| :
:.| |..|C-SMA#1|.... | |....:
+---------+------+ +-------+ +----------------+
| | | C-SMA#2 |
| | +-------+--------+
| | |
| | |
+------------+ +------------+
+------------+ | +------------+ |
| Service | | | Service | |
| Contact | | | Contact | |
| Instance |-+ | Instance |-+
+------------+ +------------+
Service Site 1 Service Site 2
Figure 2: CATS Functional Components
3.4.1. Service Sites, Services Instances, and Service Contact Instances
As service instances are accessed via a service contact instance, a
client will not see the service instances but only the service
contact instance.
Service sites are locations that host resources (including computing
resources) that are required to offer a service. As mentioned in
Section 3.2, a compute service (e.g., for face recognition purposes
or a game server) is uniquely identified by a CATS Service IDentifier
(CS-ID). The CS-ID does not need to be globally unique, though.
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A single service can be represented and accessed via several contact
instances that run in same or different regions of a network.
Figure 2 shows two CATS nodes ("CATS-Forwarder 1" and "CATS-Forwarder
3") that provide access to service contact instances. These nodes
behave as Egress CATS-Forwarders (Section 3.4.6).
Note: "Egress" is used here in reference to the direction of the
service request placement. The directionality is called to
explicitly identify the exit node of the CATS infrastructure.
3.4.2. CATS Service Metric Agent (C-SMA)
The CATS Service Metric Agent (C-SMA) is a functional component that
gathers information about service sites and server resources, as well
as the status of the different service instances. The C-SMAs may be
located adjacent to the service contact instances, co-located with
service contact instances, hosted by the Egress CATS-Forwarders
(Section 3.4.6), etc.
Figure 2 shows one C-SMA embedded in "CATS-Forwarder 3", and another
C-SMA that is adjacent to "CATS-Forwarder 1".
3.4.3. CATS Network Metric Agent (C-NMA)
The CATS Network Metric Agent (C-NMA) is a functional component that
gathers information about the state of the underlay network. The
C-NMAs may be implemented as standalone components or may be hosted
by other components, such as CATS-Forwarders or CATS Path Selectors
(C-PS) (Section 3.4.4).
C-NMA is likely to leverage existing techniques (e.g., [RFC7471],
[RFC8570], and [RFC8571]).
Figure 2 shows a single, standalone C-NMA within the underlay
network. There may be one or more C-NMAs for an underlay network.
3.4.4. CATS Path Selector (C-PS)
The C-SMAs and C-NMAs share the collected information with CATS Path
Selectors (C-PSes) that use such information to select the Egress
CATS-Forwarders (and potentially the service contact instances) where
to forward traffic for a given service request. C-PSes also
determine the best paths (possibly using tunnels) to forward traffic,
according to various criteria that include network state and traffic
congestion conditions. The collected information is encoded into one
or more metrics that feed the C-PS path selection logic. Such an
information also includes CS-ID and possibly CSCI-IDs.
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There might be one or more C-PSes used to select CATS paths in a CATS
infrastructure.
A C-PS can be integrated into CATS-Forwarders (e.g., "C-PS#1" in
Figure 2) or may be deployed as a standalone component (e.g.,
"C-PS#2" in Figure 2). Generally, a standalone C-PS can be a
functional component of a centralized controller (e.g., a Path
Computation Element (PCE) [RFC4655]).
3.4.5. CATS Traffic Classifier (C-TC)
CATS Traffic Classifier (C-TC) is a functional component that is
responsible for associating incoming packets from clients with
existing service requests. CATS classifiers also ensure that packets
that are bound to a specific service contact instance are all
forwarded towards that same service contact instance, as instructed
by a C-PS.
CATS classifiers are typically hosted in CATS-Forwarders.
3.4.6. Overlay CATS-Forwarders
Egress CATS-Forwarders are the endpoints that behave as an overlay
egress for service requests that are forwarded over a CATS
infrastructure. A service site that hosts service instances may be
connected to one or more Egress CATS-Forwarders (e.g., multi-homing
design). If a C-PS has selected a specific service contact instance
and the C-TC has marked the traffic with the CIS-ID related
information, the Egress CATS-Forwarder then forwards traffic to the
relevant service contact instance accordingly. In some cases, the
choice of the service contact instance may be left open to the Egress
CATS-Forwarder (i.e., traffic is marked only with the CS-ID). In
such cases, the Egress CATS-Forwarder selects a service contact
instance using its knowledge of service and network capabilities as
well as the current load as observed by the CATS-Forwarder, among
other considerations. Absent explicit policy, an Egress CATS-
Forwarder must make sure to forward all packets that pertain to a
given service request towards the same service contact instance.
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Note that, depending on the design considerations and service
requirements, per-service contact instance computing-related metrics
or aggregated per-site computing related metrics (and a combination
thereof) can be used by a C-PS. Using aggregated per-site computing
related metrics appears as a preferred option scalability-wise, but
relies on Egress CATS-Forwarders that connect to various service
contact instances to select the proper service contact instance. An
Egress CATS-Forwarder may choose to aggregate the metrics from
different sites as well. In this case, the Egress CATS-Forwarder
will choose the best site by itself when the packets arrive at it.
3.4.7. Underlay Infrastructure
The "underlay infrastructure" in Figure 2 indicates an IP and/or MPLS
network that is not necessarily CATS-aware. The CATS paths that are
computed by a C-PS will be distributed among the CATS-Forwarders
(Section 3.4.6), and will not affect the underlay nodes. Underlay
nodes are typically P routers (Section 5.3.1 of [RFC4026]).
3.5. Deployment Considerations
This document does not make any assumption about how the various CATS
functional elements are implemented and deployed. Concretely,
whether a CATS deployment follows a fully distributed design or
relies upon a mix of centralized (e.g., a C-PS) and distributed CATS
functions (e.g., CATS traffic classifiers) is deployment-specific and
may reflect the savoir-faire of the (CATS) service provider.
For example, in a Centralized design, both the computing related
metrics from the C-SMAs and the network metrics are collected by a
(logically) centralized path computation logic (e.g., a PCE). In
this case, the CATS computation logic may process incoming service
requests to compute paths to service contact instances. More
generally, the paths might be computed before the service request
comes. Based on the metrics and computed paths, the C-PS can select
the most appropriate path and then synchronize with CATS traffic
classifiers (C-TCs).
According to the method of distributing and collecting the computing
related metrics, three deployment models can be considered for the
deployment of the CATS framework:
Distributed model: Computing metrics are distributed among network
devices directly using distributed protocols without interactions
with a centralized control plane. Service scheduling function is
performed by the CATS forwarders in the distribution model,
Therefore, the C-PS is integrated into an Ingress CATS-Forwarder.
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Centralized model: Computing metrics are collected by a centralized
control plane, and then the centralized control plane computes the
forwarding path for service requests and syncs up with the Ingress
CATS-Forwarder. In this model, C-PS is implemented in the
centralized control plane.
Hybrid model: Is a combination of distribution and centralized
models.
A part of computing metrics are distributed among involved network
devices, and others may be collected by a centralized control
plane. For example, some static information (e.g., capabilities
information) can be distributed among network devices since they
are quite stable. Frequent changing information (e.g., resource
utilization) can be collected by a centralized control plane to
avoid frequent flooding in the distributed control plane. Service
scheduling function can be performed by a centralized control
plane and/or the CATS forwarder. The entire or partial C-PS
function may be implemented in the centralized control plane,
depending on the specific implementation and deployment.
4. CATS Framework Workflow
The following subsections provide an overview of how the CATS
workflow operates.
4.1. Provisioning of CATS Components
TBC: --detail required provisioning at CAST elements (booptsrapping,
credentials of peer CAST nodes, services, optimization metrics per
service, etc.)--
4.2. Service Announcement
A service is associated with a unique identifier called a CS-ID. A
CS-ID may be a network identifier, such as an IP address. The
mapping of CS-IDs to network identifiers may be learned through a
name resolution service, such as DNS [RFC1034].
4.3. Metrics Distribution
As described in Section 3.4, a C-SMA collects both service-related
capabilities and metrics, and associates them with a CS-ID that
identifies the service. The C-SMA may aggregate the metrics for
multiple service contact instances, or maintain them separately or
both.
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The C-SMA then advertises CS-IDs along with metrics to related C-PSes
in the network. Depending on deployment choice, CS-IDs with metrics
may be distributed in different ways.
For example, in a distributed model, CS-IDs with metrics can be
distributed from the C-SMA to an Egress CATS Forwarder firstly and
then be redistributed by the Egress CATS Forwarder to related C-PSes
that are integrated into Ingress CATS Forwarders.
In the centralized model, CS-IDs with metrics can be distributed from
the C-SMA to a centralized control plane, for instance, a standalone
C-PS.
In the hybrid model, the metrics can be distributed to C-PSes in
combination of distributed and centralized ways. The specific
combination of metric distribution is an implementation choice, which
is determined by the requirements of specific services.
The service metrics include computing-related metrics and potentially
other service-specific metrics like the number of end-users who
access the service contact instance at any given time, their
location, etc.
Computing metrics may change very frequently (see
[I-D.ietf-cats-usecases-requirements] for a discussion). How
frequently such information is distributed is to be determined as
part of the specification of any communication protocol (including
routing protocols) that may be used to distribute the information.
Various options can be considered, such as (but not limited to)
interval-based updates, threshold-triggered updates, or policy-based
updates.
Additionally, the C-NMA collects network-related capabilities and
metrics. These may be collected and distributed by existing
measurement protocols and/or routing protocols, although extensions
to such protocols may be required to carry additional information
(e.g., link latency). The C-NMA distributes the network metrics to
the C-PSes so that they can use the combination of service and
network metrics to determine the best Egress CATS-Forwarder to
provide access to a service contact instance and invoke the compute
function required by a service request. Similar to service-related
metrics, the network-related metrics can be distributed using
distributed, centralized, or hybrid schemes. This document does not
describe such details since this is a deployment-specific.
Network metrics may also change over time. Dynamic routing protocols
may take advantage of some information or capabilities to prevent the
network from being flooded with state change information (e.g.,
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Partial Route Computation (PRC) of OSPFv3 [RFC5340]). C-NMAs should
also be configured or instructed like C-SMAs to determine when and
how often updates should be notified to the C-PSes.
Figure 3 shows an example of how CATS metrics can be disseminated in
the distributed model. There is a client attached to the network via
"CATS-Forwarder 1". There are three instances of the service with
CS-ID "1": two are located at "Service Site 2" attached via "CATS-
Forwarder 2" and have CSCI-IDs "1" and "2"; the third service contact
instance is located at "Service Site 3" attached via "CATS-Forwarder
3" and with CSCI-ID "3". There is also a second service with CS-ID
"2" with only one service contact instance located at "Service Site
2".
In Figure 3, the C-SMA collocated with "CATS-Forwarder 2" distributes
the service metrics for both service contact instances (i.e., (CS-ID
1, CSCI-ID 1) and (CS-ID 1, CSCI-ID 2)). Note that this information
may be aggregated into a single advertisement, but in this case, the
metrics for each service contact instance are indicated separately.
Similarly, the C-SMA agent located at "Service Site 3" advertises the
service metrics for the two services hosted by "Service Site 3".
The service metric advertisements are processed by the C-PS hosted by
"CATS-Forwarder 1". The C-PS also processes network metric
advertisements sent by the C-NMA. All metrics are used by the C-PS
to compute and select the most relevant path that leads to the Egress
CATS-Forwarder according to the initial client's service request, the
service that is requested ("CS-ID 1" or "CS-ID 2"), the state of the
service contact instances as reported by the metrics, and the state
of the network.
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Service CS-ID 1, contact instance CSCI-ID 1 <metrics>
Service CS-ID 1, contact instance CSCI-ID 2 <metrics>
:<----------------------:
: : +---------+
: : |CS-ID 1 |
: : +--|CSCI-ID 1|
: +----------------+ | +---------+
: | C-SMA |----| Service Site 2
: +----------------+ | +---------+
: |CATS-Forwarder 2| +--|CS-ID 1 |
: +----------------+ |CSCI-ID 2|
+--------+ : | +---------+
| Client | : Network +----------------------+
+--------+ : metrics | +-------+ |
| : :<---------| C-NMA | |
| : : | +-------+ |
+---------------------+ | |
|CATS-Forwarder 1|C-PS|----| |
+---------------------+ | Underlay |
: | Infrastructure | +---------+
: | | |CS-ID 1 |
: +----------------------+ +---|CSCI-ID 3|
: | | +---------+
: +----------------+ +-------+
: |CATS-Forwarder 3|--| C-SMA | Service Site 3
: +----------------+ +-------+
: : | +-------+
: : +---|CS-ID 2|
: : +-------+
:<-------------------------------:
Service CS-ID 1, contact instance CSCI-ID 3 <metrics>
Service CS-ID 2, <metrics>
Figure 3: An Example of CATS Metric Dessimination in a
Distributed Model
The example in Figure 3 mainly describes a per-instance computing-
related metric distribution. In the case of distributing aggregated
per-site computing-related metrics, the per-instance CSCI-ID
information will not be included in the advertisement. Instead, a
per-site CSCI-ID may be used in case multiple sites are connected to
the Egress CATS-Forwarder to explicitly indicate the site from where
the aggregated metrics come.
If the CATS framework is implemented using a centralized model, the
metric can be, e.g., distributed as illustrated in Figure 4.
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Service CS-ID 1, instance CSCI-ID 1 <metrics>
Service CS-ID 1, instance CSCI-ID 2 <metrics>
Service CS-ID 1, instance CSCI-ID 3 <metrics>
Service CS-ID 2, <metrics>
: +------+
:<------| C-PS |<-----------------------------------+
: +------+ <------+ +---------+ |
: ^ | +--|CS-ID 1 | |
: | | | |CSCI-ID 1| |
: | +----------------+ | +---------+ |
: | | C-SMA |---|Service Site 2 |
: | +----------------+ | +---------+ |
: | |CATS-Forwarder 2| +--|CS-ID 1 | |
: | +----------------+ |CSCI-ID 2| |
+--------+ : | | +---------+ |
| Client | : Network | +----------------------+ |
+--------+ : metrics | | +-------+ | |
| : +-----| C-NMA | | +-----+
| : | | +-------+ | |C-SMA|<-+
+----------------+ <---+ | | +-----+ |
|CATS-Forwarder 1|---------| | ^ |
+----------------+ | Underlay | | |
: | Infrastructure | +---------+|
: | | |CS-ID 1 ||
: +----------------------+ +-|CSCI-ID 3||
: | | +---------+|
: +----------------+------------+ |
: |CATS-Forwarder 3| Service Site 3 |
: +----------------+ |
: | : +-------+ |
: +-------:------|CS-ID 2|-----+
: : +-------+
:<-------------------------------:
Service CS-ID 1, contact instance CSCI-ID 3
Service CS-ID 2
Figure 4: An Example of CATS Metric Distribution in a Centralized
Model
If the CATS framework is implemented using an hybrid model, the
metric can be distributed, e.g., as illustrated in the Figure 5. For
example, the metrics 1,2,3 associated with the CS-ID1 are collected
by the centralized C-PS, and the metrics 4 and 5 are distributed via
distributed protocols to the ingress CATS-Forwarder directly. For a
service with CS-ID2, all the metrics are collected by the centralized
C-PS. The CATS-computed path result will be distributed to the
Ingress CATS-Forwarders from the C-PS by considering both the metrics
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from the C-SMA and C-NMA. Furthermore, the Ingress CATS-Forwarder
may also have some ability to compute the path for the subsequent
service accessing packets.
Service CS-ID 1, instance CSCI-ID 1 <metric 1,2,3>
Service CS-ID 1, instance CSCI-ID 2 <metric 1,2,3>
Service CS-ID 1, instance CSCI-ID 3 <metric 1,2,3>
Service CS-ID 2, <metrics>
: +------+
:<------| C-PS |<-----------------------------------+
: +------+ <------+ +---------+ |
: ^ | +--|CS-ID 1 | |
: | | | |CSCI-ID 1| |
: | +----------------+ | +---------+ |
: | | C-SMA |---|Service Site 2 |
: | +----------------+ | +---------+ |
: | |CATS-Forwarder 2| +--|CS-ID 1 | |
: | +----------------+ |CSCI-ID 2| |
+--------+ : | | +---------+ |
| Client | : Network | +----------------------+ |
+--------+ : metrics | | +-------+ | |
| : +-----| C-NMA | | +-----+
| : | | +-------+ | |C-SMA|<-+
+----------------+ <---+ | | +-----+ |
|CATS-Forwarder 1|---------| | ^ |
|----------------+ | Underlay | | |
|C-PS| : | Infrastructure | +---------+|
+----+ : | | |CS-ID 1 ||
: +----------------------+ +-|CSCI-ID 3||
: | | +---------+|
: +----------------+------------+ |
: |CATS-Forwarder 3| Service Site 3 |
: +----------------+ |
: | : +-------+ |
: +-------:------|CS-ID 2|-----+
: : +-------+
:<-------------------------------:
Service CS-ID 1, contact instance CSCI-ID 3, <metric 4,5>
Service CS-ID 2
Figure 5: An Example of CATS Metric Distribution in Hybrid Model
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4.4. Service Access Processing
A C-PS selects paths that lead to Egress CATS-Forwarders according to
both service and network metrics that were advertised. A C-PS may be
collocated with an Ingress CATS-Forwarder (as shown in Figure 3) or
logically centralized (in a centralized model or hybrid model).
This document does not specify any particular algorithm for path
selection purposes to be supported by C-PSes in order to not
constrain the CATS framework to one possible selection only.
Instead, it is expected that a service request or local policy may
feed the C-PS with appropriate information on that selection logic
that takes the suitable metric information as input and the selected
service contact instance as output. Such "appropriate information"
may be utilized to differentiate selection mechanisms to enable
service-specific selections.
In the example shown in Figure 3, the client sends a service access
via the network through the "CATS-Forwarder 1", which is an Ingress
CATS-Forwarder. Note that, a service access may consist of one or
more service packets (e.g., Session Initiation Protocol (SIP)
[RFC3261], HTTP [RFC9112], IPv6 [RFC8200], SRv6 [RFC8754] or Real-
Time Streaming Protocol (RTSP) [RFC7826]) that carry the CS-ID and
potential parameters. The Ingress CATS-Forwarder classifies the
packets using the information provided by the CATS classifier (C-TC).
When a matching classification entry is found for the packets, the
Ingress CATS-Forwarder encapsulates and forwards them to the C-PS
selected Egress CATS-Forwarder. When these packets reach the Egress
CATS-Forwarder, the outer header of the possible overlay
encapsulation will be removed and the inner packets will be sent to
the relevant service contact instance.
Note that multi-homed clients may be connected to multiple CATS
infrastructures that may be operated by the same or distinct
service providers. This version of the framework does not cover
multihoming specifics.
4.5. Service Contact Instance Affinity
Instance affinity means that packets that belong to a flow associated
with a service should always be sent to the same service contact
instance. Furthermore, packets of a given flow should be forwarded
along the same path to avoid mis-ordering and to prevent the
introduction of unpredictable latency variations. Specifically, the
same Egress CATS-Forwarder may be solicited to forward the packets.
The affinity is configured on the C-PS when the service is deployed,
or is determined at the time of newly formulated service requests.
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Note that different services may have different notions of what
constitutes a 'flow' and may, thus, identify a flow differently.
Typically, a flow is identified by the 5-tuple transport coordinates
(source and destination addresses, source and destination port
numbers, and protocol). However, for instance, an RTP video stream
may use different port numbers for video and audio channels: in that
case, affinity may be identified as a combination of the two 5-tuple
flow identifiers so that both flows are addressed to the same service
contact instance.
Hence, when specifying a protocol to communicate information about
service contact instance affinity, a certain level of flexibility for
identifying flows should be supported. Or, from a more general
perspective, there should be a flexible mechanism to specify and
identify the set of packets that are subject to a service contact
instance affinity.
More importantly, the means for identifying a flow for the purpose of
ensuring instance affinity should be application-independent to avoid
the need for service-specific instance affinity methods. However,
service contact instance affinity information may be configurable on
a per-service basis. For each service, the information can include
the flow/packets identification type and means, affinity timeout
value, etc.
This document does not define any mechanism for defining or enforcing
service contact instance affinity.
5. Security Considerations
The computing resource information changes over time very frequently,
especially with the creation and termination of service contact
instances. When such an information is carried in a routing
protocol, too many updates may affect network stability. This issue
could be exploited by an attacker (e.g., by spawning and deleting
service contact instances very rapidly). CATS solutions must support
guards against such misbehaviors. For example, these solutions
should support aggregation techniques, dampening mechanisms, and
threshold-triggered distribution updates.
The information distributed by the C-SMA and C-NMA agents may be
sensitive. Such information could indeed disclose intel about the
network and the location of compute resources hosted in service
sites. This information may be used by an attacker to identify weak
spots in an operator's network. Furthermore, such information may be
modified by an attacker resulting in disrupted service delivery for
the clients, up to and including misdirection of traffic to an
attacker's service implementation. CATS solutions must support
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authentication and integrity-protection mechanisms between C-SMAs/
C-NMAs and C-PSes, and between C-PSes and Ingress CATS-Forwarders.
Also, C-SMA agents need to support a mechanism to authenticate the
services for which they provide information to C-PS computation
logics, among other CATS functions.
6. Privacy Considerations
Means to prevent that on-path nodes in the underlay infrastructure to
fingerprint and track clients (e.g., determine which client accesses
which service) must be supported by CATS solutions. More generally,
personal data must not be exposed to external parties by CATS beyond
what is carried in the packet that was originally issued by the
client.
In some cases, the service will need to know about applications,
clients, and even user identity. This information is sensitive and
should be encrypted. To prevent the information leaking, if the
client/service communication is not already encrypted, the the C-PS
computed path information should be encrypted.
For more discussion about privacy, refer to [RFC6462] and [RFC6973].
7. IANA Considerations
This document makes no requests for IANA action.
8. Informative References
[I-D.ietf-cats-usecases-requirements]
Yao, K., Trossen, D., Contreras, L. M., Shi, H., Li, Y.,
Zhang, S., and Q. An, "Computing-Aware Traffic Steering
(CATS) Problem Statement, Use Cases, and Requirements",
Work in Progress, Internet-Draft, draft-ietf-cats-
usecases-requirements-03, 3 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-cats-
usecases-requirements-03>.
[I-D.ietf-teas-rfc3272bis]
Farrel, A., "Overview and Principles of Internet Traffic
Engineering", Work in Progress, Internet-Draft, draft-
ietf-teas-rfc3272bis-27, 12 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
rfc3272bis-27>.
[I-D.yao-cats-awareness-architecture]
Yao, H., wang, X., Li, Z., Huang, D., and C. Lin,
"Computing and Network Information Awareness (CNIA) system
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architecture for CATS", Work in Progress, Internet-Draft,
draft-yao-cats-awareness-architecture-02, 22 October 2023,
<https://datatracker.ietf.org/doc/html/draft-yao-cats-
awareness-architecture-02>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/rfc/rfc1034>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/rfc/rfc3261>.
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual
Private Network (VPN) Terminology", RFC 4026,
DOI 10.17487/RFC4026, March 2005,
<https://www.rfc-editor.org/rfc/rfc4026>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/rfc/rfc4655>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/rfc/rfc5340>.
[RFC6462] Cooper, A., "Report from the Internet Privacy Workshop",
RFC 6462, DOI 10.17487/RFC6462, January 2012,
<https://www.rfc-editor.org/rfc/rfc6462>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/rfc/rfc6973>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<https://www.rfc-editor.org/rfc/rfc7471>.
[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, Ed., "Real-Time Streaming Protocol
Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
2016, <https://www.rfc-editor.org/rfc/rfc7826>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/rfc/rfc8200>.
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/rfc/rfc8570>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/rfc/rfc8571>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/rfc/rfc8754>.
[RFC9112] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.
Appendix A. Acknowledgements
The authors would like to thank Joel Halpern, John Scudder, Dino
Farinacci, Adrian Farrel, Cullen Jennings, Linda Dunbar, Jeffrey
Zhang, Peng Liu, Fang Gao, Aijun Wang, Cong Li, Xinxin Yi, Jari
Arkko, Mingyu Wu, Haibo Wang, Xia Chen, Jianwei Mao, Guofeng Qian,
Zhenbin Li, Xinyue Zhang, Weier Li, and Nagendra Kumar for their
comments and suggestions.
Some text about various deployment models was originally documented
in [I-D.yao-cats-awareness-architecture].
Contributors
Guangping Huang
ZTE
Email: huang.guangping@zte.com.cn
Gyan Mishra
Verizon Inc.
Email: hayabusagsm@gmail.com
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Huijuan Yao
China Mobile
Email: yaohuijuan@chinamobile.com
Yizhou Li
Huawei Technologies
Email: liyizhou@huawei.com
Dirk Trossen
Huawei Technologies
Email: dirk.trossen@huawei.com
Luigi Iannone
Huawei Technologies
Email: luigi.iannone@huawei.com
Hang Shi
Huawei Technologies
Email: shihang9@huawei.com
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Xueshun Wang
CICT
Email: xswang@fiberhome.com
Xuewei Wang
Ruijie Networks
Email: wangxuewei1@ruijie.com.cn
Christian Jacquenet
Orange
Email: christian.jacquenet@orange.com
Authors' Addresses
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Cheng Li (editor)
Huawei Technologies
China
Email: c.l@huawei.com
Zongpeng Du
China Mobile
China
Email: duzongpeng@chinamobile.com
Mohamed Boucadair (editor)
Orange
France
Email: mohamed.boucadair@orange.com
Luis M. Contreras
Telefonica
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
John E Drake
Juniper Networks, Inc.
United States of America
Email: je_drake@yahoo.com
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