SRv6 Policy Selector
draft-yang-srv6ops-policy-selector-00
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draft-yang-srv6ops-policy-selector-00
srv6ops F. Yang
Internet-Draft China Mobile
Intended status: Informational C. Lin
Expires: 18 April 2026 New H3C Technologies
15 October 2025
SRv6 Policy Selector
draft-yang-srv6ops-policy-selector-00
Abstract
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. An SR Policy is associated with one or more candidate paths,
and each candidate path is either dynamic, explicit or composite.
This document describes a policy selection mechanism among the
candidate SRv6 Policies based on network quality in IPv6
environments.
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 18 April 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Problem and Requriements . . . . . . . . . . . . . . . . . . 3
5. SRv6 Policy Selector . . . . . . . . . . . . . . . . . . . . 5
5.1. Processing Model . . . . . . . . . . . . . . . . . . . . 5
5.2. Flow Classification . . . . . . . . . . . . . . . . . . . 6
5.3. Flow Steering . . . . . . . . . . . . . . . . . . . . . . 6
5.4. Policy Selector . . . . . . . . . . . . . . . . . . . . . 6
5.5. Network Quality Measurement . . . . . . . . . . . . . . . 8
5.6. Flow Forwarding . . . . . . . . . . . . . . . . . . . . . 8
6. Examples of Policy Selector . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. An SR Policy is associated with one or more candidate paths,
and each candidate path is either dynamic, explicit or composite.
The [I-D.ietf-idr-performance-routing] specification defines a
mechanism for disseminating path delay information across multiple
Autonomous Systems (ASes). This information is used for BGP route
computation.
An SRv6 Policy is associated with one or more candidate paths. A
composite candidate path acts as a container for grouping SRv6
Policies. As described in section 2.2 in [RFC9256], the composite
candidate path construct enables combination of SRv6 Policies, each
with explicit candidate paths and/or dynamic candidate paths with
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potentially different optimization objectives and constraints, for
load-balanced steering of packet flows over its constituent SRv6
Policies. For convenience, the composite candidate path formed by
the combination of SRv6 Policies is called parent SRv6 Policy in
[I-D.cheng-spring-sr-policy-group].
Different enterprise applications have varying network performance
requirements. For instance, voice is highly sensitive to packet loss
and jitter, while OA applications are not highly demanding in terms
of latency and packet loss.
This document describes a policy selection mechanism among the
candidate SRv6 Policies based on network quality in IPv6
environments.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
The definitions of the basic terms are identical to those found in
Segment Routing Policy Architecture [RFC9256]. Office Automation:
OA, which stands for "Office Automation," is a collaborative office
and internal management platform built using network and software
technologies. Parent SR Policy: Refer to
[I-D.cheng-spring-sr-policy-group]. A Parent SR Policy is the
composite candidate path that acts as a container for grouping SR
Policies which meet different service optimization objectives and
constraints and have the same destination endpoint.
4. Problem and Requriements
Take the networking shown in Figure 1 below as an example to
illustrate the current problems.
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CE1 and CE2 are the two access endpoints of the IP telecom network.
There are many service flows between CE1 and CE2 that have different
requirements for forwarding quality. E.g. OA and voice traffic have
different SLA requirement, and expected be carried by different SRv6
Policies. Generally, from CE1 to CE2, voice services with low
latency requirements are forwarded along the highly reliable path
PE1->PE2->CE2. The OA traffic is forwarded along the normal path
PE3->P5->P6->PE2->CE2. When failure or degradation happened in voice
traffic SRv6 Policy, there should be possible to assure basic
communication for voice traffic by using OA bandwidth.
In single SRv6 Policy, there are many mechanism provide failure/
degrade protection, such as TILFA, VPN FRR. However, it is not clear
how to handle failure or degradation between multiple SRv6 Policies
in a parent SR Policy.
+---------------+
| Controller |
+---------------+
+------+ +------+
+-----+ P1 +----+ P2 +-------+
| +---+--+ +---+--+ |
+---+--+ | \ / | |
+----+ PE1 | | \/ | |
| +---+--+ | /\ | |
| | | / \ | |
+--+--+ | +---+--+ +---+--+ +---+--+ +-----+
| CE1 | +-----+ P3 +----+ P4 +---+ PE2 +---+ CE2 |
+--+--+ +------+ +------+ +---+--+ +-----+
| |
| +------+ +------+ +------+ |
+----+ PE3 +----+ P5 +-----+ P6 +----+
+------+ +------+ +------+
Figure 1
Based on such scenarios, the following requirements are proposed:
1. Maximize failure/degradation protection
In case of failure or degradation detected on one SRv6 Policy, it
should be possible to do inter-policy protection.
2. Minimal impact after taking repairing action
Repair action can be done on flow level to minimize the ripple
effect cause by forwarding path switchover.
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3. Maximize bandwidth efficiency
For some critical applications, it should be possible to forward
the traffic over lower class policy in case of higher class SRv6
Policy degradation.
Refer to [I-D.cheng-spring-sr-policy-group], the services with
different forwarding quality requirements to the same destination
endpoint can be implemented through parent SRv6 Policy group.
This document proposes an SRv6 Policy selector for parent SRv6 Policy
based on network quality requirement. The head end node selects the
best constituent SRv6 Policy for the application according to the
quality of the constituent SRv6 Policy.
Take Figure 1 as an example, there is a parent SRv6 Policy between
CE1 to CE2, which has multiple constituent SRv6 Policies. A new SRv6
Policy Selector is defined for the application in the parent SRv6
Policy, which will select best constituent SRv6 Policy in the parent
SRv6 Policy. When the head node detects the quality degradation of
the active constituent SRv6 Policy, it will select another
constituent SRv6 Policy in the parent SRv6 Policy.
5. SRv6 Policy Selector
5.1. Processing Model
A new priority and a new quality threshold is created for each
constituent SRv6 Policy. The lower the priority number, the higher
the priority. That means avtive constituent SRv6 Policy will be the
one with higher priority and meeting the quality threshold. When the
network quality degradation is happened on the active constituent
SRv6 Policy, such as the packet loss rate exceeds the threshold,
switch to the next high priority constituent SRv6 Policy.
If the quality of the high priority forwarding constituent SRv6
Policy is restored and the specified quality threshold is met, the
traffic will be switched back to the high priority constituent SRv6
Policy after a period of wait-to-restore time.
According to the processing logic, the SRv6 Policy Policy Selector
model can be divided into five units, including Flow Classification,
Flow Steering, Policy Selector, Flow Forwarding, and Network Quality
Measurement, as shown in Figure 2 below.
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+----------------+ +----------+ +-------------+ +------------+
| Flow +->| Flow +->| SRv6 Policy +->| Flow |
| Classification | | Steering | | Selector | | Forwarding |
+----------------+ +----------+ +-------------+ +------------+
^
|
+---------+-------+
| Network Quality |
| Measurement |
+-----------------+
Figure 2
The functions of each unit are described below.
5.2. Flow Classification
After receiving the traffic, the head node first needs to label the
traffic with application type according to classification
configuration.
5.3. Flow Steering
According to the application type determined by the Flow
classification, the header node selects the parent SRv6 Policy for
traffic forwarding.
5.4. Policy Selector
SRv6 Policy Selector obtains the current quality of each constituent
SRv6 Policy from the Network Quality Measurement unit. Based on the
quality threshold and the priority, SRv6 Policy Selector selects the
active constituent SRv6 Policy.
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+---------------------------------------------------+
| Parent SRv6 Policy |
| +-----------------+ |
| | Constituent | |
| | SRv6 Policy | |
| | (high priority) | |
| | +-------------+ | |
| | |Active Policy| | |
| | +-------------+ | |
| +----------+ | +-------------+ | |
| | | | | Standby Path| | |
| | +->| +-------------+ | |
| +------------+ | SRv6 | +-------------+---+ |
| | Classified | | Policy | / |
| | +->| Selector |<-Measurement-+ |
| | Traffic | | | \ |
| +------------+ | | + ------------+---+ |
| | +->| +-------------+ | |
| | | | Active Path | | |
| +----------+ | +-------------+ | |
| | +-------------+ | |
| | | Standby Path| | |
| | +-------------+ | |
| | Constituent | |
| | SRv6 Policy | |
| | (lower priority)| |
| + ----------------+ |
+---------------------------------------------------+
Figure 3
Each parent SRv6 Policy contains multiple constituent SRv6 Policies.
Each constituent SRv6 Policy will include two new configuration
parameters, "priority" and "threshold". A lower priority value
indicates a higher precedence. The constituent SRv6 Policy with the
highest priority and qualified threshold will be active.
To avoid frequent path switching when the network quality is
unstable, a wait-to-restore timer is required. Only after automatic
restore is allowed and the wait-to-restore timer is timeout, the
forwarding path switch from the current constituent SRv6 Policy to
the one with higher priority.
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5.5. Network Quality Measurement
The Network Quality Measurement unit regularly monitors the quality
of all effective forwarding paths according to the measurement cycle,
records the current performance measurement data of the path, and
reports it to the SRv6 Policy Selector unit, which decides whether to
switch paths.
The following network quality parameters can be used:
* Jitter
* Latency
* Packet loss
* Available bandwidth
* Bandwidth utilization
* Current traffic statistics
* Other forwarding performance parameters
The quality parameters can be obtained through active or passive
performance measurement methods, such as iOAM, STAMP, TWAMP, SRv6
bandwidth measurement[I-D.liu-ippm-srv6-bandwidth-measurement], etc.
The network quality parameters can be calculated by the controller
and distributed to the head end node, or calculated by the head end
node according to the network measurement data. The measurement
method and quality parameter acquisition method are beyond the scope
of this document.
5.6. Flow Forwarding
The service flow is forwarded according to the path determined by the
Policy Selector unit.
When there are multiple paths with the same priority, the traffic
will share the load among these SRv6 Policy paths with the same
priority according to the weight value.
6. Examples of Policy Selector
The application of Policy Selector is described in detail in L3VPN
over TE scenario. The networking is shown in Figure 4 below.
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CE1 and CE2 belong to the same L3VPN and access the public network
through PE1, PE2 and PE3 respectively.
There are two services between CE1 and CE2: voice and OA. The
traffic from CE1 to CE2 can be forwarded through two paths: Path1
(PE1->PE2->CE2) and Path2 (PE3->P5->P6->PE2->CE2). Among them, the
reliability of path 1 is high and the transmission delay is low.
Path 2 has a large bandwidth.
The voice service traffic will be forwarded through Path1 first. The
OA service traffic will be forwarded through Path2 first. When the
transmission delay of Path1 exceeds the threshold value and Path2 can
meet the delay requirements, switch the voice service to Path2.
When the remaining bandwidth of Path2 is less than the bandwidth
guarantee threshold, if Path1 still has enough remaining bandwidth,
the OA traffic exceeding the bandwidth will be directed to Path1.
+------+ +------+
+------+ P1 +-----+ P2 +-------+
| +---+--+ +---+--+ |
+---+--+ | \ / | |
+-----+ PE1 | | \/ | |
| +---+--+ | /\ | |
+--+--+ | +---+--+/ \ +---+--+ +---+--+ +-----+
| CE1 | +------+ P3 +-----+ P4 +---+ PE2 +---+ CE2 |
+--+--+ +------+ +------+ +---+--+ +-----+
| |
| +------+ +------+ +------+ |
+-----+ PE3 +---+ P5 +-----+ P6 +-------+
+------+ +------+ +------+
Figure 4
The configuration on the head node CE1 includes the following three
parts. These configurations can be directly configured on the node
or distributed through the controller.
1. Define three Policy Selector policies, and specify the threshold
of network quality, path priority and the corresponding path
color value for routing.
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routing-policy-selector irp1
traffic-delay threshold 1000ms
priority 1 mapping-to color 100
priority default mapping-to color 200
routing-policy-selector irp2
remaining-bandwidth threshold 50M
priority 1 mapping-to color 200
priority default mapping-to color 100
2. Configure forwarding paths.
sr-policy policy-A (color 100, CE2_SID)
segment-list <SID_PE1, SID_PE2, SID_CE2>
sr-policy policy-B (color 200, CE2_SID)
segment-list <SID_PE3, SID_P5, SID_P6, SID_PE2, SID_CE2>
3. Configure corresponding Policy Selector policies for services
with specified characteristics in the parent SRv6 Policy group.
parent-sr-policy sr-policy-1(color 10, CE2_SID)
service voice use routing-policy-selector irp1
service oa use routing-policy-selector irp2
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
This document does not introduce any security considerations.
9. References
9.1. Normative References
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/rfc/rfc8402>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/rfc/rfc9256>.
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[RFC9830] Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
P., and D. Jain, "Advertising Segment Routing Policies in
BGP", RFC 9830, DOI 10.17487/RFC9830, September 2025,
<https://www.rfc-editor.org/rfc/rfc9830>.
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
9.2. Informative References
[I-D.ietf-idr-performance-routing]
Xu, X., Hegde, S., Talaulikar, K., Boucadair, M.,
Jacquenet, C., and J. Dong, "BGP Performance-aware Routing
Mechanism", Work in Progress, Internet-Draft, draft-ietf-
idr-performance-routing-05, 5 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
performance-routing-05>.
[I-D.cheng-spring-sr-policy-group]
Cheng, W., Wenying, J., Lin, C., Chen, R., Zhang, Y., and
Y. Liang, "SR Policy Group", Work in Progress, Internet-
Draft, draft-cheng-spring-sr-policy-group-08, 17 June
2025, <https://datatracker.ietf.org/doc/html/draft-cheng-
spring-sr-policy-group-08>.
[I-D.liu-ippm-srv6-bandwidth-measurement]
Liu, Y., Lin, C., Qiu, Y., Liu, Y., and Y. Liang,
"Measurement Method for Bandwidth of SRv6 Forwarding
Path", Work in Progress, Internet-Draft, draft-liu-ippm-
srv6-bandwidth-measurement-00, 26 November 2024,
<https://datatracker.ietf.org/doc/html/draft-liu-ippm-
srv6-bandwidth-measurement-00>.
Acknowledgements
The authors would like to thank the following for their valuable
contributions of this document.
TBD.
Authors' Addresses
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Feng Yang
China Mobile
Beijing
China
Email: yangfeng@chinamobile.com
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
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