Internet DRAFT - draft-yang-spring-sr-policy-intelligent-routing
draft-yang-spring-sr-policy-intelligent-routing
SPRING Working Group F. Yang
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: March 6, 2024 Y. Qiu
New H3C Technologies
September 6, 2023
Intelligent Routing Method of SR Policy
draft-yang-spring-sr-policy-intelligent-routing-00
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Abstract
Segment Routing 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 an intelligent routing method for SR Policy based
on network quality in MPLS and IPv6 environments.
Table of Contents
1. Introduction ................................................ 2
2. Terminology ................................................. 3
3. Background and Requriements ................................. 3
4. Intelligent Routing Method for SR Policy .................... 5
4.1. Processing Model ....................................... 5
4.2. Flow Classification .................................... 6
4.3. Flow Steering .......................................... 6
4.4. Intelligent Routing .................................... 6
4.5. Network Quality Measurement ............................ 8
4.6. Flow Forwarding......................................... 9
5. Examples of intelligent routing ............................. 9
6. IANA Considerations ........................................ 11
7. Security Considerations .................................... 11
8. References ................................................. 11
8.1. Normative References .................................. 11
8.2. Informative References ................................ 11
9. Acknowledgments ............................................ 12
Authors' Addresses ............................................ 13
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. The ingress node steers packets into a specific path according
to the Segment Routing Policy (SR Policy) as defined in [RFC9256].
In order to distribute SR policies to the headend, [I-D.ietf-idr-
segment-routing-te-policy] specifies a mechanism by using BGP.
An SR Policy is associated with one or more candidate paths. A
composite candidate path acts as a container for grouping SR
Policies. As described in section 2.2 in [RFC9256], the composite
candidate path construct enables combination of SR 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 SR
Policies. For convenience, the composite candidate path formed by
the combination of SR policies is called parent SR policy in [I-
D.jiang-spring-parent-sr-policy-use-cases].
This document describes an intelligent routing method for SR Policy
based on network quality in MPLS and IPv6 environments.
2. Terminology
The definitions of the basic terms are identical to those found in
Segment Routing Policy Architecture [RFC9256] and [I-D.jiang-spring-
parent-sr-policy-use-cases].
3. Background and Requriements
In single SR 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 SR
policies.
Take the networking shown in Figure 1 below as an example to
illustrate the current problems.
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 were carried by different SR 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 high bandwidth path PE3-
>P5->P6->PE2->CE2. When failure or degradation happened in OA
traffic SR policy, there should be possible to assure basic
communication for OA traffic by using voice bandwidth.
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+---------------+
| Controller |
+---------------+
+------+ +------+
+---------+ P1 +-----+ P2 +----------+
| +---+--+ +---+--+ |
+---+--+ | \ / | |
+-------+ PE1 | | \/ | |
| +---+--+ | /\ | |
+--+--+ | +---+--+/ \ +---+--+ +---+--+ +-----+
| CE1 | +---------+ P3 +-----+ P4 +------+ PE2 +---+ CE2 |
+--+--+ +------+ +------+ +---+--+ +-----+
| |
| +------+ +------+ +------+ |
+-------+ PE3 +------+ P5 +-----+ P6 +----------+
+------+ +------+ +------+
Figure 1
Based on such scenarios, the following requirements are proposed:
a) Maximize failure/degradation protection
In case of failure or degradation detected on one SR policy, it
should be possible to do inter-policy protection.
b) Minimal impact after taking repairing action
Repair action can be done on flow level to minimize the ripple
effect cause by bandwidth spillover.
c) Maximize bandwidth efficiency
For some critical applications, it should be possible to spillover
from high class to lower class policy in case of degradation.
In order to better meet these requirements, this document proposes
an intelligent routing method for SR policy based on network quality
requirement. The head end node selects the optimal path according to
the current network quality to improve the path switching speed and
forwarding performance.
Refer to [I-D.jiang-spring-sr-policy-group-use-cases], the services
with different forwarding quality requirements to the same
destination endpoint can be implemented through parent SR Policy
group.
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Define a parent SR Policy group for the above CE1 to CE2 services.
Specify the steering policies of services in the parent SR Policy
group. Different services can select different SR Policy paths in
the parent SR Policy group according to different quality
requirements. When the head node perceives that the quality of the
path of a service is deteriorating (such as bandwidth or delay
degradation), it searches for other path in the group that is
suboptimal and also meets its quality requirements.
4. Intelligent Routing Method for SR Policy
4.1. Processing Model
The path priority is assigned to the SR policy forwarding path
manually by the controller. Each path with quality requirement will
be assigned with a priority value. The lower the value, the higher
the priority. That is, when there is a group of qualified paths,
best path will be selected with higher priority.
Configure multiple SR policy paths for the service flows with
specified characteristics in the parent SR Policy group. Assign the
corresponding path priority to each path according to the priority
order of the path. If the traffic needs to be shared by multiple SR
policies, assign the same priority and sharing weight values to
these SR policies. If there is a backup path for the SR policies,
lower priority value should be used according to the quality
requirements.
After receiving the service packet with the specified
characteristics, when the network quality is good, the traffic is
forwarded through the path with high priority. When the network
quality degradation is happened on the high priority path, such as
the packet loss rate exceeds the acceptable range, switch to the
next high priority path of the service.
If the quality of the high priority forwarding path is restored and
the specified quality requirements are met, the traffic is switched
from the low priority forwarding path to the high priority
forwarding path.
When there are multiple paths with the same priority, the traffic
will share the bandwidth on these paths with the same priority
according to the weight value.
According to the processing logic, the SR policy intelligent routing
model can be divided into five units, including Flow Classification,
Flow Steering, Intelligent Routing, Flow Forwarding, and Network
Quality Measurement, as shown in Figure 2 below.
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+----------------+ +----------+ +-------------+ +------------+
| | | | | | | |
| Flow |->| Flow |->| Intelligent |->| Flow |
| Classification | | Steering | | Routing | | Forwarding |
| | | | | | | |
+----------------+ +----------+ +------+------+ +------------+
^
|
+-----------------+
| |
| Network Quality |
| Measurement |
| |
+-----------------+
Figure 2
The functions of each unit are described below.
4.2. Flow Classification
After receiving the traffic, the head node first needs to label the
traffic with forwarding class according to classification
configuration.
The head node can match flow characteristics in its ingress
interfaces (upon any field such as Ethernet
destination/source/VLAN/TOS or IP destination/source/DSCP or
transport ports or application attribute etc.) and color them with
an internal per-packet forwarding-class variable.
4.3. Flow Steering
According to the forwarding class variables determined by the Flow
classification, the header node selects the matching forwarding path,
that is, selects the SR policy or the parent SR policy representing
a group of policies.
If multiple SR policy forwarding paths are configured for the
traffic flow with the specified characteristics, all valid SR
policies will be retrieved and handed over to the Intelligent Routing
unit to select the optimal forwarding path.
4.4. Intelligent Routing
According to the SR policy(policies) provided by Flow Steering, the
Intelligent Routing unit obtains the current quality of each SR
policy path from the Network Quality Measurement unit. Based on the
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mapping between the quality and the priority of intelligent routing,
it selects the forwarding path with the highest priority and the
best quality requirements for the traffic flow.
+------------------------------------------------------+
| +-----------------------+ |
| | SR Policy | |
| +-----------------+ | (high priority) | |
| | +-----------+ | | +-------------+ | |
| | | Normal +----->+ | Active Path | | |
| | | Flows | | | +-------------+ | |
| | +-----------+ | | +-------------+ | |
+--------+ | | | | | Standby Path| | |
| | | | | | +-------------+ | |
|Grouping| | | | +-------------------+---+ |
| SR +--->+ | Policy | / |
| Policy | | | Decision +<---Measurement Data -+ |
| | | | | \ |
| | | | | +-------------------+---+ |
+--------+ | | | | +-------------+ | |
| | +-----------+ | | | Active Path | | |
| | | Spillover +----->+ +-------------+ | |
| | | Flows | | | +-------------+ | |
| | +-----------+ | | | Standby Path| | |
| +-----------------+ | +-------------+ | |
| | SR Policy | |
| | (lower priority) | |
| +-----------------------+ |
+------------------------------------------------------+
Figure 3
When the network quality is good, the traffic is forwarded by the
policy with high priority. When the network quality of the high
priority SR policy degrades, such as the remaining bandwidth is
insufficient, switch to the secondary high priority SR policy path
with enough remaining bandwidth. Similarly, when the next higher
priority SR policy forwarding path cannot meet the forwarding
quality requirements, switch to the lower priority SR policy path.
If the quality of the high priority forwarding path gets better and
meets the specified quality requirements, the traffic can be
recovered from the low priority forwarding path to the high priority
SR policy forwarding path.
If multiple SR policies in the parent SR policy have the same
priority, when the traffic flow selects the path of this priority,
the traffic flow will share the load on these SR policy paths
according to the weight value.
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In order to better control the switchover process of SR policies
between different priorities, the quality threshold and switchover
waiting time can be specified. If the value of network quality
degradation consistently exceeds the switchover threshold during the
waiting time, select the SR policy with the next highest priority
from the highest priority to the lowest. In contrast, if the network
quality continues to improve, after exceeding the failback waiting
time, the forwarding path can be switched to a high priority SR
policy that meets the current network quality requirements.
To avoid frequent path switching when the network quality is
unstable, if the current path can meet the forwarding quality
requirements, the head node can choose not to automatically switch
back to the higher priority path in case of the quality of the
higher priority path is restored. The device can provide a
configuration for automatic failback, and add a restore waiting
timer. Only after automatic restore is allowed and the restore
waiting timer is timeout, the forwarding path switch from the
current path that meets the quality requirements to the path with
higher priority.
4.5. 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 Intelligent Routing unit, which decides whether to
switch paths.
The following network quality parameters of forwarding path can be
used for path scheduling:
* Jitter
* Latency
* Packet loss
* Available bandwidth
* Bandwidth utilization
* Current traffic statistics
* Other forwarding performance parameters
The quality parameters of network forwarding path can be obtained
through active or passive performance measurement methods, such as
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iOAM, STAMP, TWAMP, 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.
4.6. Flow Forwarding
The service flow is forwarded according to the path determined by
the Intelligent Routing unit.
When there are multiple paths with the same priority, the traffic
will share the load among these SR policy paths with the same
priority according to the weight value.
5. Examples of intelligent routing
The application of intelligent routing is described in detail in
L3VPN over TE scenario. The networking is shown in Figure 4 below.
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.
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+------+ +------+
+---------+ 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 intelligent routing policies, and specify the
threshold of network quality, path priority and the corresponding
path color value for routing.
intelligent-routing-policy irp1
traffic-delay threshold 1000ms
priority 1 mapping-to color 100
priority default mapping-to color 200
intelligent-routing-policy 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>
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3. Configure corresponding intelligent routing policies for services
with specified characteristics in the parent SR Policy group.
parent-sr-policy sr-policy-1(color 10, CE2_SID)
service voice use intelligent-routing-policy irp1
service oa use intelligent-routing-policy irp2
6. IANA Considerations
This document has no IANA actions.
7. Security Considerations
This document does not introduce any security considerations.
8. References
8.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C.,
Talaulikar, K., Mattes, P., Rosen, E., Jain, D., and S.
Lin, "Advertising Segment Routing Policies in BGP", draft-
ietf-idr-segment-routing-te-policy-20 (work in progress),
July 2022.
[I-D.jiang-spring-parent-sr-policy-use-cases] Jiang, W., Cheng, W.,
Lin, C. and Qiu, Y., "Use Cases for Parent SR Policy",
draft-jiang-spring-parent-sr-policy-use-cases-01 (work in
progress), January 2023.
[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/info/rfc8402>.
[RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", RFC 9256,
DOI 10.17487/RFC9256, July 2022, <https://www.rfc-
editor.org/info/rfc9256>.
8.2. Informative References
TBD
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9. Acknowledgments
The authors would like to thank the following for their valuable
contributions of this document:
TBD
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Authors' Addresses
Feng Yang
China Mobile
Beijing
China
Email: yangfeng@chinamobile.com
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
Yuanxiang Qiu
New H3C Technologies
Email: qiuyuanxiang@h3c.com
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