Data Model for Computing-Aware Traffic Steering (CATS)
draft-ietf-cats-data-model-00
| Document | Type | Active Internet-Draft (cats WG) | |
|---|---|---|---|
| Authors | Huijuan Yao , Changwang Lin , Zhenqiang Li , Quan Xiong , Luis M. Contreras | ||
| Last updated | 2026-09-23 | ||
| Replaces | draft-yl-cats-data-model | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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| Yang Validation | 0 errors, 0 warnings | ||
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draft-ietf-cats-data-model-00
CATS Working Group H. Yao
Internet-Draft China Mobile
Intended status: Standards Track C. Lin
Expires: 27 March 2027 New H3C Technologies
Z. Li
China Mobile
Q. Xiong
ZTE Corporation
L. M. Contreras
Telefonica
23 September 2026
Data Model for Computing-Aware Traffic Steering (CATS)
draft-ietf-cats-data-model-00
Abstract
This document defines a YANG data model for the management of
Computing-Aware Traffic Steering (CATS) systems.
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/.
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 27 March 2027.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Conventions Used in This Document . . . . . . . . . . . . 3
1.3. Tree Diagrams . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Prefixes in Data Node Names . . . . . . . . . . . . . . . 3
2. CATS System Overview . . . . . . . . . . . . . . . . . . . . 4
3. Design of CATS Data Model . . . . . . . . . . . . . . . . . . 5
3.1. Scope of Model . . . . . . . . . . . . . . . . . . . . . 5
3.2. Specification . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Model Structure . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. CATS Base . . . . . . . . . . . . . . . . . . . . . . 7
3.3.2. CATS Traffic-classifier . . . . . . . . . . . . . . . 8
3.3.3. CATS Service-metric . . . . . . . . . . . . . . . . . 9
3.3.4. CATS Notify . . . . . . . . . . . . . . . . . . . . . 10
4. CATS YANG Module . . . . . . . . . . . . . . . . . . . . . . 11
5. Operational Considerations . . . . . . . . . . . . . . . . . 23
5.1. Installation and Configuration . . . . . . . . . . . . . 23
5.2. Monitoring . . . . . . . . . . . . . . . . . . . . . . . 23
5.3. Migration Considerations . . . . . . . . . . . . . . . . 23
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. Normative References . . . . . . . . . . . . . . . . . . 26
8.2. Informative References . . . . . . . . . . . . . . . . . 27
Appendix A. Full Tree . . . . . . . . . . . . . . . . . . . . . 28
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
[I-D.ietf-cats-framework] introduces a framework for Computing-Aware
Traffic Steering (CATS). This document defines a YANG data model for
managing the CATS system. The model extends the "ietf-routing" YANG
model defined in [RFC8349], is agnostic to specific protocol
extensions, and conforms to the framework definition to serve as a
critical diagnostic or control mechanism.
1.1. Terminology
The following terms as defined in [I-D.ietf-cats-framework] are used:
* CS-ID: CATS Service ID.
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* CSCI-ID: CATS Service Contact Instance ID.
* C-SMA: CATS Service Metric Agent.
* C-NMA: CATS Network Metric Agent.
* C-PS: CATS Path Selector.
* C-TC: CATS Traffic Classifier.
The new defined terms:
* C-CIB: CATS Computing Information Base, as shown in Figure 1,
responsible for maintaining CATS network computing information.
Provides basic data for the C-SMA.
* C-NIB: CATS Network Information Base, as shown in Figure 1,
responsible for maintaining CATS network information. Provides
basic data for the C-NMA.
1.2. Conventions 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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.3. Tree Diagrams
Tree diagrams used in this document follow the notation defined in
[RFC8340].
1.4. Prefixes in Data Node Names
In this document, names of data nodes, actions, and other data model
objects are often used without a prefix, as long as it is clear from
the context in which YANG module each name is defined. Otherwise,
names are prefixed using the standard prefix associated with the
corresponding YANG module, as shown in Table 1.
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+========+=================+===========+
| Prefix | YANG module | Reference |
+========+=================+===========+
| ip | ietf-ip | [RFC8344] |
+--------+-----------------+-----------+
| rt | ietf-routing | [RFC8349] |
+--------+-----------------+-----------+
| cats | ietf-cats | Section 3 |
+--------+-----------------+-----------+
| yang | ietf-yang-types | [RFC9911] |
+--------+-----------------+-----------+
| inet | ietf-inet-types | [RFC9911] |
+--------+-----------------+-----------+
Table 1: Prefixes and Corresponding
YANG Modules
2. CATS System Overview
As defined in [I-D.ietf-cats-framework], the CATS framework structure
consists of the C-SMA (responsible for maintaining service metrics),
the C-NMA (responsible for maintaining network metrics), the C-PS
(responsible for maintaining forwarding table entries), and the C-TC
(responsible for traffic classification), as shown in Figure 1.
The C-CIB and C-NIB are defined in the management plane.
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+----------------------------------+ +-------+
| Management | | |
| Plane +------+----------+ |<=========>| C-SMA |
| | | | | | |
| | +--v---+ +--v---+ | +--+----+
| | |C-CIB | |C-NIB | | |
| | +---^--+ +--^---+ | |
| | | | | |
+---------|-------|---------|------+ |
| Control | +---v--+ +--v---+ | |
| Plane | |C-SMA | |C-NMA | | |
| | +------+ +------+ | |
| | | |
| | +-------+ | |
| +-->| C-PS | | |
| +-------+ | |
+----------------------------------+ |
/\ /\ |
|| || |
\/ \/ |
+----------------+ +-----------------------+ |
|CATS Forwarder1 | |CATS Forwarder2 | |
| +------+ | | +------+------+ | +--------+
| | C-TC | | | | C-TC | C-PS | |<=========>| +--------+
| +------+ | | +------+--+---+ | | |Service |
| | | | | | |Contact |
+----------------+ | | | +-|Instance|
| +---+---+ | +--------+
| | | | |
| +---+--+ +--+--+ | +--------+
| |C-SMA | |C-NMA| | | +--------+
| +------+ +-----+ | | |Service |
+-----------------------+ +-|Instance|
+--------+
Figure 1: CATS System Architecture
3. Design of CATS Data Model
3.1. Scope of Model
The model covers CATS systems as described in
[I-D.ietf-cats-framework]. This model can be used to manage CATS
systems.
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The operational state data and statistics can be retrieved by this
model. The subscription and push mechanism defined in [RFC8639] and
[RFC8641] can be implemented by the user to subscribe to
notifications on the data nodes in this model.
The model contains all the basic configuration parameters to operate
the CATS system. Depending on the implementation choices, some
systems might not allow some of the advanced parameters to be
configurable.
Occasionally-implemented parameters are modeled as optional features
in this model. This model can be extended, and it has been
structured in a way that such extensions can be conveniently made.
3.2. Specification
This model imports from and augments the "ietf-routing" YANG model
defined in [RFC8349]. Both configuration branch and state branch of
[RFC8349] are augmented. The configuration branch covers node base
and policy configuration. The container 'cats' is the top level
container in this data model. The operational state data is combined
with the associated configuration data in the same hierarchy
[RFC8407].
3.3. Model Structure
This document defines a YANG data model for the management of CATS
corresponding data. The data model is applicable to the CATS system
architecture in Figure 1.
The CATS YANG model includes basic CATS objects, traffic-classifier
objects, and service-metric objects. The model also includes YANG
notifications.
* The CATS base table provides interfaces for the functionality of
the C-PS component, which can be used for communication between
the Control Plane and the C-SMA, as well as for the interface
between the Control Plane and the CATS Forwarder.
* The CATS traffic-classifier table provides interfaces for the
functionality of the C-TC component, which can be used for
communication between the Control Plane and the CATS Forwarder.
The Control Plane can distribute directly CATS traffic-classifier
table to the CATS Forwarder, allowing the CATS Forwarder to
proactively select paths according to forwarding policies.
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* The CATS service-metric table provides interfaces for the C-SMA
component, which can be used for communication between the Control
Plane and the CATS Forwarder, as well as for transmitting service
metric information from the C-SMA to the Control Plane. It is
also used for forwarding service metric information from the
Control Plane to the CATS Forwarder.
* The CATS notification definitions are used by the management layer
component and can be utilized for the CATS Forwarder to report
events to the Control Plane.
The full tree diagram of the "ietf-cats" YANG module is provided in
Appendix A. And the Figure 2 is overall tree structure of the CATS
YANG module:
module: ietf-cats
augment /rt:routing:
+--rw cats
+--rw base
| ...
|
+--rw traffic-classifiers
| ...
|
+--rw service-metrics
| ...
|
+---n metric-limit-exceeded
| ...
+---n metric-limit-recovered
| ...
+---n flow-limit-exceeded
| ...
+---n flow-limit-recovered
...
Figure 2: Yang Organization and Hierarchy
3.3.1. CATS Base
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+--rw base
| +--rw enable? boolean
| +--rw update-interval? uint32
| +--rw metric-limits? uint32
| +--rw flow-limits? uint32
| +--rw flow-timeout? uint32
| +--rw notify-interval? uint32
| +--rw service-policy* [cs-id]
| +--rw cs-id cs-id
| +--rw policy-type? enumeration
Figure 3: Base Configuration Tree View
In the base shown in Figure 3, you can set the 'enable' attribute to
enable/disable CATS function on a per-device basis. When set to
false, the CATS function component is shut down.
You can set the 'update-interval' parameter to determine the interval
at which the C-SMA notifies the C-PS of metric changes. The default
value for this interval is 30 seconds.
You can set the maximum number of metric table entries by configuring
'metric-limits'.
You can set the maximum number of flow tables by configuring 'flow-
limits'.
When flow tables have been inactive for a long period of time, it is
necessary to age out the stale state entries. This can be achieved
by configuring 'flow-timeout' to control the aging time of flow
tables.
To prevent notification flooding when limits are reached and
unreached in quick succession (flapping), you can configure 'notify-
interval' to set the minimum time between consecutive notifications.
The default value is 10 seconds.
You can set the 'service-policy' table for traffic steering, which
includes affinity-based, service-metric-based, network-metric-based,
and combined service-metric and network-metric-based steering.
3.3.2. CATS Traffic-classifier
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+--rw traffic-classifiers
| +--rw traffic-classifier* [cs-id]
| +--rw cs-id cs-id
| +--rw description? string
| +--rw server-port? uint16
| +--rw protocol? uint8
| +--ro matched-packets? yang:zero-based-counter64
| +--ro matched-bytes? yang:zero-based-counter64
Figure 4: Traffic-classifier Tree View
The CATS traffic-classifier table is used to define the features of
the service and to classify the traffic, as shown in Figure 4.
The 'cs-id' is used to uniquely identify a CATS service, and the
'description' serves to document its content.
The 'server-port' defines the application port for a CATS service.
This port number matches the destination port in the IP packets of
data flows destined for the service.
The 'protocol' defines the application transport protocol for a CATS
service. This protocol number matches the protocol in the IP packets
of data flows destined for the service.
The 'matched-packets' and 'matched-bytes' indicate the statistics of
traffic matching the specified service.
3.3.3. CATS Service-metric
+--rw service-metrics
| +--rw service-metric* [cs-id csci-id source-type]
| +--rw cs-id cs-id
| +--rw csci-id csci-id
| +--rw source-type identityref
| +--rw priority? uint8
| +--rw affinity? uint8
| +--rw location? inet:ip-address
| +--rw metrics
| | +--rw metric* [metric-type]
| | +--rw metric-type identityref
| | +--rw metric-value? uint32
| +--ro forwarded-packets? yang:zero-based-counter64
| +--ro forwarded-bytes? yang:zero-based-counter64
Figure 5: Service-metric Tree View
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The CATS service-metric table is used to control the delivery service
metrics on the control plane, as shown in Figure 5, thereby
generating the forwarding table on the forwarding plane in
conjunction with network metrics.
The 'cs-id' is used to uniquely identify a CATS service, and the
'csci-id' is used to represent an instance of that service. The
'source-type' indicates the source protocol of this service metric
information, such as a static protocol.
The 'priority' indicates the priority of different service instances
of the same service, and the 'affinity' indicates the affinity
between this service and its service site.
The 'location' indicates the IP address of the service site where
this service instance resides. And the 'metrics' indicates different
types of service metric values.
The 'forwarded-packets' and 'forwarded-bytes' indicate the statistics
of traffic forwarded by the specified service metric entry.
3.3.4. CATS Notify
+---n metric-limit-exceeded
| +--ro timestamp yang:date-and-time
| +--ro message string
+---n metric-limit-recovered
| +--ro timestamp yang:date-and-time
| +--ro message string
+---n flow-limit-exceeded
| +--ro timestamp yang:date-and-time
| +--ro message string
+---n flow-limit-recovered
+--ro timestamp yang:date-and-time
+--ro message string
Figure 6: Notify Tree View
Four notifications are defined to alert operators when metric or flow
entry limits are exceeded or recovered:
* metric-limit-exceeded: Sent when the number of metric entries
exceeds the configured maximum.
* metric-limit-recovered: Sent when the number of metric entries
returns to or falls below the configured maximum.
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* flow-limit-exceeded: Sent when the number of flow entries exceeds
the configured maximum.
* flow-limit-recovered: Sent when the number of flow entries returns
to or falls below the configured maximum.
Each notification carries a timestamp indicating when the event
occurred and a human-readable message that includes the configured
maximum limit, as shown in Figure 6. Having separate notifications
for each event type allows operators to better parse and route
specific events. To prevent notification flooding caused by rapid
state changes (flapping), the 'notify-interval' parameter in the base
configuration can be used to set the minimum time between consecutive
notifications.
4. CATS YANG Module
<CODE BEGINS> file "ietf-cats@2026-06-25.yang"
module ietf-cats {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-cats";
prefix cats;
import ietf-routing {
prefix rt;
reference
"RFC 8349: A YANG Data Model for Routing
Management (NMDA Version)";
}
import ietf-inet-types {
prefix inet;
reference
"RFC 9911: Common YANG Data Types, Section 4";
}
import ietf-yang-types {
prefix yang;
reference
"RFC 9911: Common YANG Data Types, Section 3";
}
organization
"IETF Computing-Aware Traffic Steering (CATS) Working Group";
contact
"WG Web: https://datatracker.ietf.org/group/cats
WG List: CATS <mailto:cats@ietf.org>
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Editor: Huijuan Yao
<mailto:yaohuijuan@chinamobile.com>
Editor: Changwang Lin
<mailto:linchangwang.04414@h3c.com>
Editor: Zhenqiang Li
<mailto:lizhenqiang@chinamobile.com>
Editor: Quan Xiong
<mailto:xiong.quan@zte.com.cn>
Editor: Luis M. Contreras
<mailto:luismiguel.contrerasmurillo@telefonica.com>";
description
"This module describes a YANG model for managing the CATS
system.
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 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
Copyright (c) 2026 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Revised BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
All revisions of IETF and IANA published modules can be found
at the YANG Parameters registry group
(https://www.iana.org/assignments/yang-parameters).
This version of this YANG module is part of RFC XXXX; see the
RFC itself for full legal notices.";
revision 2026-06-25 {
description
"Initial Version";
reference
"RFC XXXX: YANG Data Model for CATS";
}
typedef cs-id {
type union {
type uint32;
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type inet:ipv4-address;
type inet:ipv6-address;
}
description
"This type defines the CATS Service ID (CS-ID),
which uniquely identifies a service.";
reference
"draft-ietf-cats-framework: A Framework for Computing-Aware
Traffic Steering (CATS)";
}
typedef csci-id {
type union {
type uint32;
type inet:ipv4-address;
type inet:ipv6-address;
}
description
"This type defines the CATS Service Contact Instance ID
(CSCI-ID), which uniquely identifies a service contact
instance.";
reference
"draft-ietf-cats-framework: A Framework for Computing-Aware
Traffic Steering (CATS)";
}
/*
* Identities for source-type
*/
identity source-type-base {
description
"Base identity for source types of service computing metrics.";
}
identity source-type-static {
base source-type-base;
description
"Static configuration. This identity is used when the
service metric information is configured statically
(not learned from a dynamic protocol).";
}
/*
* Identities for metric-type
*/
identity metric-type-base {
description
"Base identity for service metric types.";
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}
identity metric-delay {
base metric-type-base;
description
"Transmission delay metric. The metric value is the delay
time in milliseconds.";
}
identity metric-service-ratio {
base metric-type-base;
description
"Service capacity ratio metric. The metric value is the
current capacity percentage.";
}
identity metric-memory-ratio {
base metric-type-base;
description
"Memory utilization metric. The metric value is the current
memory utilization percentage.";
}
grouping service-policy-type {
description
"Service policy type";
leaf policy-type {
type enumeration {
enum base-on-affinity {
value 0;
description "Base on affinity";
}
enum base-on-sm-only {
value 1;
description "Base on service metric only";
}
enum base-on-nm-only {
value 2;
description "Base on network metric only";
}
enum base-on-sm-nm {
value 3;
description
"Base on the combination of service metric and network
metric";
}
}
description "Service policy type";
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}
}
augment "/rt:routing" {
description
"This augments the CATS configuration.";
container cats {
description
"Support for the CATS configuration.";
container base {
description
"CATS base configuration.";
leaf enable {
type boolean;
description
"Enable CATS";
}
leaf update-interval {
type uint32;
units "seconds";
default "30";
description
"Update interval of CATS metric. A value of 0
indicates that metrics are sent only when a
significant change occurs and not on a periodic
basis.";
}
leaf metric-limits {
type uint32;
description
"The maximum number of metric table entries that
can be maintained by the device. This limit prevents
resource exhaustion. The actual maximum value is
implementation-dependent and should be documented by the
vendor. A value of 0 indicates no configured limit
(subject to device capacity).";
}
leaf flow-limits {
type uint32;
description
"The maximum number of flow table entries that
can be maintained by the device. This limit prevents
resource exhaustion. The actual maximum value is
implementation-dependent and should be documented by the
vendor. A value of 0 indicates no configured limit
(subject to device capacity).";
}
leaf flow-timeout {
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type uint32;
units "seconds";
default "120";
description
"CATS flow timeout when no flow. A value of 0 means
that the flow does not time out due to inactivity
(i.e., infinite timeout), and must be terminated
explicitly (e.g., via signaling or administrative
action).";
}
leaf notify-interval {
type uint32;
units "seconds";
default "10";
description
"The minimum interval between consecutive notifications.
This is used to prevent notification flooding when
limits are reached and unreached in quick succession
(flapping). A value of 0 means notifications are
sent immediately without rate limiting.";
}
list service-policy {
key "cs-id";
description
"CATS service policy configuration for traffic steering.
Each entry defines the policy type for a specific
service identified by cs-id.";
leaf cs-id {
type cs-id;
description
"The CATS Service ID (CS-ID) that uniquely
identifies a service. This identifier is used
by clients to access the service.";
reference
"draft-ietf-cats-framework: A Framework for
Computing-Aware Traffic
Steering (CATS)";
}
uses service-policy-type;
}
}
container traffic-classifiers {
description
"CATS traffic-classifier entries for classifying
traffic by service. Each entry defines the matching
criteria for a specific service identified by cs-id.";
list traffic-classifier {
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key "cs-id";
description
"A traffic classifier entry for a specific service.
The cs-id uniquely identifies the service to be
classified.";
leaf cs-id {
type cs-id;
description
"The CATS Service ID (CS-ID) that uniquely
identifies a service.";
reference
"draft-ietf-cats-framework: A Framework for
Computing-Aware Traffic
Steering (CATS)";
}
leaf description {
type string {
length "0..255";
}
description
"A human-readable description of this service
(e.g., 'http', 'video-streaming'). The length
constraint provides a reasonable upper bound
for short descriptive text and avoids
unbounded-string risks. The value 255 follows
the historical SNMP SnmpAdminString convention
for management text. Note that length counts
Unicode characters, not UTF-8 octets.
Zero-length is permitted for empty descriptions.";
}
leaf server-port {
type uint16;
description
"Server-port of the service, matches the
destination port in the IP packets of data
flows destined for the service.";
}
leaf protocol {
type uint8;
description
"The IP protocol number of the service. This value
matches the protocol field in the IP header of data
flows destined for the service. Common values include:
6 (Transmission Control Protocol), 17 (User Datagram
Protocol), and 132 (Stream Control Transmission
Protocol).";
reference
"IANA: Protocol Numbers Registry
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<https://www.iana.org/assignments/
protocol-numbers/>";
}
leaf matched-packets {
type yang:zero-based-counter64;
config false;
description
"The number of packets matching the specified
service.";
}
leaf matched-bytes {
type yang:zero-based-counter64;
config false;
description
"The number of bytes in packets matching the specified
service.";
}
}
}
container service-metrics {
description
"CATS service metric entries for controlling
delivery of service metrics from the control plane
to the forwarding plane.";
list service-metric {
key "cs-id csci-id source-type";
description
"A service metric entry for a specific service
instance. The combination of cs-id, csci-id,
and source-type uniquely identifies a service
metric entry.";
leaf cs-id {
type cs-id;
description
"The CATS Service ID (CS-ID) that uniquely
identifies a service.";
reference
"draft-ietf-cats-framework: A Framework for
Computing-Aware Traffic
Steering (CATS)";
}
leaf csci-id {
type csci-id;
description
"The CATS Service Contact Instance ID (CSCI-ID)
that uniquely identifies a specific service contact
instance.";
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reference
"draft-ietf-cats-framework: A Framework for
Computing-Aware Traffic
Steering (CATS)";
}
leaf source-type {
type identityref {
base source-type-base;
}
description
"The source type of the service computing metric.
Indicates how the metric information was learned.
The base identity 'source-type-base' can be extended
by other modules to define additional source types.";
}
leaf priority {
type uint8;
description
"The server priority. The smaller the value,
the higher the priority (i.e., 0 is the highest
priority). This convention follows common practice
in networking protocols (e.g., IP precedence,
administrative distance).";
}
leaf affinity {
type uint8;
description
"The server affinity. The higher the value,
the higher the affinity (i.e., 0 is the lowest
affinity). This convention follows common practice
for affinity or weight metrics in load balancing.";
}
leaf location {
type inet:ip-address;
description
"The IPv4 or IPv6 address of the service site where
this service contact instance resides. This address
represents the logical location of the service in
the network topology. CATS-enabled routers use this
location information to compute network distances
and make steering decisions based on proximity to
the service instance.";
}
container metrics {
description
"Service metrics for the service contact instance.
Each metric entry carries a metric type and its
associated value.";
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list metric {
key "metric-type";
description "A service metric of a specific type.";
leaf metric-type {
type identityref {
base metric-type-base;
}
description
"The type of the service metric. The base identity
'metric-type-base' can be extended by other
modules to define additional metric types.";
reference
"draft-ietf-cats-metric-definition: CATS Metrics
Definition";
}
leaf metric-value {
type uint32;
description "The value of the service metric.";
}
}
}
leaf forwarded-packets {
type yang:zero-based-counter64;
config false;
description
"The number of packets forwarded by the specified
service";
}
leaf forwarded-bytes {
type yang:zero-based-counter64;
config false;
description
"The number of bytes in packets forwarded by the
specified service";
}
}
}
notification metric-limit-exceeded {
description
"Event notification sent when the number of metric
entries exceeds the configured maximum limit.";
leaf timestamp {
type yang:date-and-time;
mandatory true;
description
"The time when the metric limit was exceeded.";
}
leaf message {
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type string {
length "1..255";
}
mandatory true;
description
"A human-readable message describing the event,
including the configured maximum limit.
The length constraint provides a reasonable upper
bound for short event messages and avoids
unbounded-string risks. The value 255 follows the
historical SNMP SnmpAdminString convention for
management text. Note that length counts Unicode
characters, not UTF-8 octets. Zero-length is
disallowed since this notification always carries
content.";
}
}
notification metric-limit-recovered {
description
"Event notification sent when the number of metric
entries returns to or falls below the configured
maximum limit after having exceeded it.";
leaf timestamp {
type yang:date-and-time;
mandatory true;
description
"The time when the metric limit was recovered.";
}
leaf message {
type string {
length "1..255";
}
mandatory true;
description
"A human-readable message describing the event,
including the configured maximum limit.
The length constraint provides a reasonable upper
bound for short event messages and avoids
unbounded-string risks. The value 255 follows the
historical SNMP SnmpAdminString convention for
management text. Note that length counts Unicode
characters, not UTF-8 octets. Zero-length is
disallowed since this notification always carries
content.";
}
}
notification flow-limit-exceeded {
description
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"Event notification sent when the number of flow
entries exceeds the configured maximum limit.";
leaf timestamp {
type yang:date-and-time;
mandatory true;
description
"The time when the flow limit was exceeded.";
}
leaf message {
type string {
length "1..255";
}
mandatory true;
description
"A human-readable message describing the event,
including the configured maximum limit.
The length constraint provides a reasonable upper
bound for short event messages and avoids
unbounded-string risks. The value 255 follows the
historical SNMP SnmpAdminString convention for
management text. Note that length counts Unicode
characters, not UTF-8 octets. Zero-length is
disallowed since this notification always carries
content.";
}
}
notification flow-limit-recovered {
description
"Event notification sent when the number of flow
entries returns to or falls below the configured
maximum limit after having exceeded it.";
leaf timestamp {
type yang:date-and-time;
mandatory true;
description
"The time when the flow limit was recovered.";
}
leaf message {
type string {
length "1..255";
}
mandatory true;
description
"A human-readable message describing the event,
including the configured maximum limit.
The length constraint provides a reasonable upper
bound for short event messages and avoids
unbounded-string risks. The value 255 follows the
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historical SNMP SnmpAdminString convention for
management text. Note that length counts Unicode
characters, not UTF-8 octets. Zero-length is
disallowed since this notification always carries
content.";
}
}
}
}
}
<CODE ENDS>
5. Operational Considerations
This section provides operational considerations for implementing and
deploying the CATS YANG data model.
5.1. Installation and Configuration
When deploying the CATS YANG model, operators should configure the
'update-interval' parameter to balance responsiveness against control
plane load. The 'metric-limits' and 'flow-limits' parameters should
be set based on expected service scale and available device
resources.
5.2. Monitoring
The CATS YANG model provides read-only state data nodes for
monitoring: 'matched-packets' and 'matched-bytes' for traffic
classification statistics, and 'forwarded-packets' and 'forwarded-
bytes' for service forwarding statistics. The 'notify-interval'
parameter helps prevent notification flooding during unstable
conditions.
5.3. Migration Considerations
CATS can be incrementally deployed alongside traditional forwarding.
The CATS model augments the ietf-routing model without replacing it,
allowing for gradual migration.
6. Security Considerations
This section is modeled after the template described in Section 3.7.1
of [RFC9907].
The "ietf-cats" YANG module defines a data model that is designed to
be accessed via YANG-based management protocols, such as the Network
Configuration Protocol (NETCONF) [RFC6241] and RESTCONF [RFC8040].
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These YANG-based management protocols (1) have to use a secure
transport layer (e.g., Secure Shell (SSH) [RFC4252], TLS [RFC8446],
and QUIC [RFC9000]) and (2) have to use mutual authentication.
The Network Configuration Access Control Model (NACM) [RFC8341]
provides the means to restrict access for particular NETCONF or
RESTCONF users to a preconfigured subset of all available NETCONF or
RESTCONF protocol operations and content.
There are a number of data nodes defined in this YANG module that are
writable/creatable/deletable (i.e., "config true", which is the
default). All writable data nodes are likely to be sensitive or
vulnerable in some network environments. Write operations (e.g.,
edit-config) and delete operations to these data nodes without proper
protection or authentication can have a negative effect on network
operations. The following subtrees and data nodes have particular
sensitivities/vulnerabilities:
* /cats:base/cats:enable
* /cats:base/cats:update-interval
* /cats:base/cats:metric-limits
* /cats:base/cats:flow-limits
* /cats:base/cats:flow-timeout
* /cats:base/cats:service-policy/cats:cs-id
* /cats:base/cats:service-policy/cats:policy-type
* /cats:traffic-classifiers/cats:traffic-classifier/cats:cs-id
* /cats:traffic-classifiers/cats:traffic-classifier/cats:description
* /cats:traffic-classifiers/cats:traffic-classifier/cats:server-port
* /cats:traffic-classifiers/cats:traffic-classifier/cats:protocol
* /cats:service-metrics/cats:service-metric/cats:cs-id
* /cats:service-metrics/cats:service-metric/cats:csci-id
* /cats:service-metrics/cats:service-metric/cats:source-type
* /cats:service-metrics/cats:service-metric/cats:priority
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* /cats:service-metrics/cats:service-metric/cats:affinity
* /cats:service-metrics/cats:service-metric/cats:location
* /cats:service-metrics/cats:service-
metric/cats:metrics/cats:metric/cats:metric-type
* /cats:service-metrics/cats:service-
metric/cats:metrics/cats:metric/cats:metric-value
For these augmentations to ietf-routing.yang, the ability to delete,
add, and modify CATS base configuration, traffic classifier
configuration and service metric configuration would allow traffic to
be misrouted.
Some of the readable data nodes in this YANG module may be considered
sensitive or vulnerable in some network environments. It is thus
important to control read access (e.g., via get, get-config, or
notification) to these data nodes. Specifically, the following
subtrees and data nodes have particular sensitivities/
vulnerabilities:
* /cats:traffic-classifiers/cats:traffic-classifier/cats:matched-
packets
* /cats:traffic-classifiers/cats:traffic-classifier/cats:matched-
bytes
* /cats:service-metrics/cats:service-metric/cats:forwarded-packets
* /cats:service-metrics/cats:service-metric/cats:forwarded-bytes
* /cats:metric-limit-exceeded
* /cats:metric-limit-recovered
* /cats:flow-limit-exceeded
* /cats:flow-limit-recovered
Exposing the notification will expose the CATS table information of
the network device. This may be undesirable due to the fact that
such exposure may facilitate other attacks. Additionally, network
operators MAY consider their CATS table information to be sensitive
confidential data.
All the security considerations for writable and readable data nodes
defined in [RFC8349] apply to the augmentations described herein.
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There are no particularly sensitive RPC or action operations.
7. IANA Considerations
The IANA is requested to assign the following URI in the "IETF XML
Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-cats
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
This document registers the following YANG module in the "YANG Module
Names" registry [RFC6020]:
Name: ietf-cats
Maintained by IANA? N
Namespace: urn:ietf:params:xml:ns:yang:ietf-cats
Prefix: cats
Reference: RFC XXXX
8. References
8.1. Normative References
[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>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[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>.
[RFC8344] Bjorklund, M., "A YANG Data Model for IP Management",
RFC 8344, DOI 10.17487/RFC8344, March 2018,
<https://www.rfc-editor.org/info/rfc8344>.
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[RFC8349] Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
Routing Management (NMDA Version)", RFC 8349,
DOI 10.17487/RFC8349, March 2018,
<https://www.rfc-editor.org/info/rfc8349>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
[RFC8639] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Subscription to YANG Notifications",
RFC 8639, DOI 10.17487/RFC8639, September 2019,
<https://www.rfc-editor.org/info/rfc8639>.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/info/rfc8641>.
[RFC9911] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC
9911, DOI 10.17487/RFC9911, December 2025,
<https://www.rfc-editor.org/info/rfc9911>.
8.2. Informative References
[I-D.ietf-cats-framework]
Li, C., Du, Z., Boucadair, M., Contreras, L. M., and J.
Drake, "A Framework for Computing-Aware Traffic Steering
(CATS)", Work in Progress, Internet-Draft, draft-ietf-
cats-framework-24, 2 April 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-cats-
framework-24>.
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
January 2006, <https://www.rfc-editor.org/info/rfc4252>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
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[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9907] Bierman, A., Boucadair, M., Ed., and Q. Wu, "Guidelines
for Authors and Reviewers of Documents Containing YANG
Data Models", BCP 216, RFC 9907, DOI 10.17487/RFC9907,
March 2026, <https://www.rfc-editor.org/info/rfc9907>.
Appendix A. Full Tree
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module: ietf-cats
augment /rt:routing:
+--rw cats
+--rw base
| +--rw enable? boolean
| +--rw update-interval? uint32
| +--rw metric-limits? uint32
| +--rw flow-limits? uint32
| +--rw flow-timeout? uint32
| +--rw notify-interval? uint32
| +--rw service-policy* [cs-id]
| +--rw cs-id cs-id
| +--rw policy-type? enumeration
+--rw traffic-classifiers
| +--rw traffic-classifier* [cs-id]
| +--rw cs-id cs-id
| +--rw description? string
| +--rw server-port? uint16
| +--rw protocol? uint8
| +--ro matched-packets? yang:zero-based-counter64
| +--ro matched-bytes? yang:zero-based-counter64
+--rw service-metrics
| +--rw service-metric* [cs-id csci-id source-type]
| +--rw cs-id cs-id
| +--rw csci-id csci-id
| +--rw source-type identityref
| +--rw priority? uint8
| +--rw affinity? uint8
| +--rw location? inet:ip-address
| +--rw metrics
| | +--rw metric* [metric-type]
| | +--rw metric-type identityref
| | +--rw metric-value? uint32
| +--ro forwarded-packets? yang:zero-based-counter64
| +--ro forwarded-bytes? yang:zero-based-counter64
+---n metric-limit-exceeded
| +--ro timestamp yang:date-and-time
| +--ro message string
+---n metric-limit-recovered
| +--ro timestamp yang:date-and-time
| +--ro message string
+---n flow-limit-exceeded
| +--ro timestamp yang:date-and-time
| +--ro message string
+---n flow-limit-recovered
+--ro timestamp yang:date-and-time
+--ro message string
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Contributors
TBD
Authors' Addresses
Huijuan Yao
China Mobile
No.32 XuanWuMen West Street
Beijing
100053
China
Email: yaohuijuan@chinamobile.com
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
Zhenqiang Li
China Mobile
China
Email: lizhenqiang@chinamobile.com
Quan Xiong
ZTE Corporation
Email: xiong.quan@zte.com.cn
Luis M. Contreras
Telefonica
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
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