SR Policy Group
draft-cheng-spring-sr-policy-group-01
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| Authors | Weiqiang Cheng , Liyan Gong , Changwang Lin , Yuanxiang Qiu , Yawei Zhang , Ran Chen , Yanrong Liang | ||
| Last updated | 2023-04-17 (Latest revision 2022-10-24) | ||
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draft-cheng-spring-sr-policy-group-01
SPRING Working Group W. Cheng
Internet Draft L. Gong
Intended status: Standards Track China Mobile
Expires: October 18, 2023 C. Lin
Y. Qiu
New H3C
Y.Wei
Huawei
Ran.Chen
ZTE
R. Liang
Ruijie Networks
April 18, 2023
SR Policy Group
draft-cheng-spring-sr-policy-group-01
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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 SR policy Group in MPLS and IPv6 environments.
Table of Contents
1. Introduction ................................................ 2
2. Terminology ................................................. 3
3. SR Policy Group ............................................. 4
3.1. Identification of SR Policy Group ...................... 4
3.2. Constituent Parent SR policy ........................... 5
3.3. Steering into SR Policy Group .......................... 6
3.4. Summary ................................................ 7
4. SR Policy Group Use Cases ................................... 9
4.1. SR Policy Group in L3VPN over TE Scenarios ............. 9
5. IANA Considerations ........................................ 12
6. Security Considerations .................................... 12
7. References ................................................. 12
7.1. Normative References .................................. 12
7.2. Informative References ................................ 13
8. Acknowledgments ............................................ 13
Authors' Addresses ............................................ 14
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.
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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 [RFC9256], the composite candidate path
construct enables combination of SR Policies, each with explicit
candidate paths and or dynamic candidate paths with 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 SR Policy Group in MPLS and IPv6
environments.
2. Terminology
The definitions of the basic terms are identical to those found in
Segment Routing Architecture [RFC8402], Segment Routing Policy
Architecture [RFC9256].
SR policy As described in [RFC9256], the general concept of SR
Policy provides a framework that enables the instantiation of an
ordered list of segments on a node for implementing a source routing
policy for the steering of traffic for a specific purpose (e.g., for
a specific Service Level Agreement (SLA)) from that node. An SR
Policy is a forwarding path that meets the specified forwarding
requirements.
Parent SR Policy A Parent SR Policy represents a composite candidate
path, which is a group of SR policies that meet different service
objectives and have the same destination endpoint address. As
described in [RFC9256],the following criteria apply for inclusion of
constituent SR Policies using a composite candidatepath under a
parent SR Policy:
* The endpoints of the constituent SR Policies and the parent SR
Policy MUST be identical.
* The colors of each of the constituent SR Policies and the parent
SR Policy MUST be different.
* The constituent SR Policies MUST NOT use composite candidate
paths.
Different flows(match flows in its ingress interfaces (upon any
field such as Ethernet destination/source/VLAN/TOS or IP
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destination/source/Differentiated Services Code Point (DSCP), or
transport ports etc.) bound to the same endpoint, and color them
with an internal per-packet forwarding-class variable, which are
steered on different constituent SR Policies.
SR Policy Group: An SR policy Group represents a set of paths with
different forwarding requirements. It is composited by different
parent SR policies which have the same color but different
destiontion endpoints. It establish the mapping relationship between
the flow characteristics and the color value of the SR Policy, and
guide the flows with different SLA requirements to the SR Policy
with different colors.
3. SR Policy Group
SR Policy Group provides a framework that enables the instantiation
of a set of paths to different destination endpoints with the same
service forwarding model.It implements a source routing policy to
steer the service traffic from different source endpoints for a
specific purpose (e.g., for a specific SLA).
Referring to RFC9256 and [I-D.jiang-spring-parent-sr-policy-use-
cases], the Parent SR policy represents a composite candidate path,
which is a group of SR policies with the same destination endpoint
address. The Ingress node specifies the service characteristics and
maps different services to different colors. In the Parent SR policy,
configure multiple constituent SR policies. The services with
different characteristics are forwarded through the constituent SR
policies of different colors. Based on the Parent SR policy, a SR
Policy Group can be built using Parent SR Policy.
This section defines the key aspects and constituents of an SR
Policy Group.
3.1. Identification of SR Policy Group
An SR Policy Group MUST be identified through a color attribute.
According to the service quality requirements, a unified service
forwarding model is planned for nodes to determine the forwarding
path of service flow. The traffic with the same service forwarding
model from different source endpoints to different destination
endpoints uses the same SR Policy Group.
The color is an unsigned non-zero 32-bit integer value that
associates the SR Policy Group with a service forwarding model (e.g.,
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A set of SLA attributes). Different service qualities use different
Color values.
The color value identifying the SR Policy Group corresponds to the
Color attribute of the BGP route published by the endpoint. The
destination endpoint publishes the BGP route and indicates which SR
Policy Group path the header node should use to send packets to it
through the Color attribute in the route.
In the Policy Group, establish the mapping relationship between the
flow characteristics and the color value of the SR Policy path, and
guide the business flows with different SLA requirements to the SR
Policy path with different colors.
3.2. Constituent Parent SR policy
An SR Policy Group is associated with one or more constituent Parent
SR Policies. Referring to RFC9256, the Parent SR policy is a group
of SR policies with the same destination endpoint address.
The hierarchical relationship between SR policy group, Parent SR
policy and SR policy is shown in the figure below.
Service forwarding
Service model to specified Path of
forwarding model destination endpoint specified service
+-----------------+ +------------------+ +-------------------+
| | | | | |
| SR Policy Group |--->| Parent SR Policy |---->| SR policy |
| (Color) | |(Color, Endpoint) | | (Service path's |
| | | | | Color, Endpoint) |
+-----------------+ +------------------+ +-------------------+
Figure 1
The parent SR policy can be generated through static configuration,
or dynamically generated when the destination endpoint accesses
based on the service forwarding requirements specified by the SR
policy group.
The following criteria apply for inclusion of constituent Parent SR
Policies under a SR Policy Group:
A SR Policy Group contains one or more Parent SR policies.
The colors of SR Policy group and its each constituent Parent SR
Policy MUST be identical.
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The colors of SR Policy group and its each constituent SR Policy
of echo constituent Parent SR Policies MUST be different.
The destination endpoint addresses of the Parent SR policy in the
SR policy group can be the same or different.
There can only be one Parent SR Policy with the same source end
and the same destination end in the SR Policy group.
3.3. Steering into SR Policy Group
The process of guiding traffic forwarding through the SR Policy
Group is as follows:
The destination endpoint publishes a BGP route with the specified
Color extended community attribute.
Get the color extended community attribute in the received BGP
route.
Match the color attribute value of the received BGP route with the
SR Policy Group.
Searches for a SR Policy Group with color matching the color
extended community attribute.
Searches for a Parent SR Policy with endpoint address matching the
next hop in the BGP route, and recurses the BGP route to the
parent SR policy.
The Ingress 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. According to the
forwarding-class variable the ingress node selects a matching SR
policy in the Parent SR policy.
An SR Policy Group can be instantiated with SR Policies which are
associated with different set of network resources (i.e. NRPs),
based on SR policy group, it is also a network slice deployment
scheme for single user and multiple services. When different
services are forwarded through different SR policy paths, different
network resources can be used. After associating the SR policy with
the network slice, different network slices can be used for
forwarding different traffic of the same user.
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3.4. Summary
In summary, the information model is the following:
SR Policy Group PG-1 <Color = 1>
Parent SR Policy PP-1<Color = 1, Endpoint = E1>
Service Service-1 mapping-to color 100
Service Service-2 mapping-to color 200
Service Service-3 mapping-to color 300
SR Policy POL1 <Headend = H1, Color = 100, Endpoint = E1>
Candidate Path CP1 <Protocol-Origin = 20, Originator =
64511:192.0.2.1, Discriminator = 1>
Preference 200
Priority 10
Segment List 1 <SID11...SID1i>
SR Policy POL2 <Headend = H1, Color = 200, Endpoint = E1>
Candidate Path CP1 <Protocol-Origin = 20, Originator =
64511:192.0.2.1, Discriminator = 2>
Preference 200
Priority 10
Segment List 1 <SID21...SID2i>
SR Policy POL3 <Headend = H1, Color = 300, Endpoint = E1>
Candidate Path CP1 <Protocol-Origin = 20, Originator =
64511:192.0.2.1, Discriminator = 3>
Preference 200
Priority 10
Segment List 1 <SID31...SID3i>
Parent SR Policy PP-2<Color = 1, Endpoint = E2>
Service Service-1 mapping-to color 100
Service Service-2 mapping-to color 200
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Service Service-3 mapping-to color 300
SR Policy POL4 <Headend = H1, Color = 100, Endpoint = E2>
Candidate Path CP1 <Protocol-Origin = 20, Originator =
64511:192.0.2.1, Discriminator = 4>
Preference 200
Priority 10
Segment List 1 <SID41...SID4i>
SR Policy POL5 <Headend = H1, Color = 200, Endpoint = E2>
Candidate Path CP1 <Protocol-Origin = 20, Originator =
64511:192.0.2.1, Discriminator = 5>
Preference 200
Priority 10
Segment List 1 <SID51...SID5i>
SR Policy POL6 <Headend = H1, Color = 300, Endpoint = E1>
Candidate Path CP1 <Protocol-Origin = 20, Originator =
64511:192.0.2.1, Discriminator = 6>
Preference 200
Priority 10
Segment List 1 <SID61...SID6i>
The SR Policy Group PG-1 is identified by color. It has two
constituent Parent SR Policies: PP-1 and PP-2. Each is identified
by a tuple <Headend, Color, Endpoint>.
The SR Parent Policy PP-1 is identified by the tuple <Headend = H1,
Color = 1, Endpoint = E1>. It has three constituent SR Policies: SR
Policy POL1 SR Policy POL2 and SR Policy POL3.
The SR Policy POL1 is identified by the tuple <Headend = H1,Color =
100, Endpoint = E1>. It has one candidate paths: CP1.
The SR Policy POL2 is identified by the tuple <Headend = H1,Color =
200, Endpoint = E1>. It has one candidate paths: CP1.
The SR Policy POL3 is identified by the tuple <Headend = H1,Color =
300, Endpoint = E1>. It has one candidate paths: CP1.
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The SR Parent Policy PP-2 is identified by the tuple <Headend = H1,
Color = 1, Endpoint = E2>. It has three constituent SR Policies: SR
Policy POL4 SR Policy POL5 and SR Policy POL6.
The SR Policy POL4 is identified by the tuple <Headend = H1,Color =
100, Endpoint = E2>. It has one candidate paths: CP1.
The SR Policy POL2 is identified by the tuple <Headend = H1,Color =
200, Endpoint = E2>. It has one candidate paths: CP1.
The SR Policy POL6 is identified by the tuple <Headend = H1,Color =
300, Endpoint = E2>. It has one candidate paths: CP1.
According to the service forwarding quality requirements, three
forwarding paths, Color 100, Color 200 and Color 300, are planned in
advance.
The service forwarding model of PP-1 is adopted for the destination
endpoint E1. According to service characteristics. Services to E1
are divided into three categories: service-1, service-2 and service-
3. The service-1 service is forwarded according to the SR Policy
POL1 path of Color 100. The service-2 service is forwarded according
to the SR Policy POL2 path of Color 200. The services of service-3
are forwarded according to the SR Policy POL3 path of Color 300.
The destination endpoint E2 also uses the same service forwarding
model. The traffic to E1 is differentiated in the same way, and the
traffic is sent to E2 according to the SR policy path of Color 100,
200, and 300.
4. SR Policy Group Use Cases
4.1. SR Policy Group in L3VPN over TE Scenarios
In the L3VPN over TE application scenario shown in Figure 2, VPN
users are connected to the SRv6 network. Controller defines SR
Policy Group for each VPN tenant. Different VPNs use different SR
Policy Groups with different colors. The Ingress node generates
different Parent SRv6 policies as required according to the
destination endpoint address dynamically. Since user's traffic of
different services between two endpoints has different requirements
for forwarding quality, identify the service type according to the
DSCP of the packet, and steer the flow to the corresponding SR
Policy, which is forwarded through different network slices. The
path constituting the SR Policy is calculated by the controller and
distributed to the Ingress node.
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+------------+
| Controller |
+------------+
/ \
/ \
.----. / \ .----.
( VPN1 )\ / \ /( VPN1 )
'----' \ +---+ +---+ +---+ +---+ / '----'
+ A +-----+ B +-----+ C +-----+ D +
/+-+-+ +-+-+ +-+-+ +-+-+
.----. / | | | |
( VPN2 )/ | | | | .----.
'----' | | | | /( VPN1 )
+-+-+ +-+-+ +-+-+ +-+-+ / '----'
+ E |-----+ F +-----+ G +-----+ H +
.----. / +---+ +---+ +-+-+ +---+ \ .----.
( VPN1 )/ \( VPN2 )
'----' '----'
Figure 2 L3VPN over TE application scenario
VPN1 uses SR Policy group 1 identified by Color 100. Plan the
forwarding path for VPN1 traffic, and allocate different sets of
network resources for network slices as blow:
Slice 1: Voice service of VIP users. Low delay forwarding is
required, and the DSCP range of the packet is 1~10. The controller
calculates the low delay path for the voice traffic of VIP users,
and maps the DSCP 1~10 to Color 500. The voice traffic of VIP
users is forwarded through the constituent SR policy (Color 500)
of the Parent SRv6 Policy (Color 100) corresponding to VPN1.
Slice 2: Other services of VIP users. The DSCP range of the packet
is 11~20, and low delay is not required. However, compared with
the packet of ordinary users, the traffic of VIP users should be
forwarded first. The controller calculates the SR Policy path and
maps the DSCP 11~20 to Color 501. Other traffic of VIP users are
forwarded along the constituent SR policy (Color 501) of the
Parent SRv6 policy (color 100) corresponding to VPN1.
Slice 3: Services of ordinary users. Low latency forwarding and
priority forwarding are not required. The controller calculates
the SR Policy path and maps all DSCP values outside the range of 1
to 20 to Color 502. The service traffic of ordinary users are
forwarded along the constituent SR policy (Color 502) of the
Parent SRv6 policy (color 100) corresponding to VPN1.
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SRv6 Network
.-------------------.
.-------. | | .-------.
/ \ <==|======Slice-1======|==> / \
( VPN1 )<==|======Slice-2======|==> ( VPN1 )
\ / <==|======Slice-3======|==> \ /
'-------' | | '-------'
| SR Policy Group 1 |
| (Color 100) |
'-------------------'
Figure 4 SR Policy Group for VPN1
The traffic of VPN1 from A to D of Slice 1 will be forwarded based
on the SR policy (Headend=A, Color=500, Endpoint=D) of Parent SR
policy (Color=100, Endpoint=D) of SR Policy Group1.
Similarly the traffic of VPN1 from A to H of Slice 1 will be
forwarded based on the SR policy (Headend=A, Color=500, Endpoint=H)
of Parent SR policy (Color=100, Endpoint=H) of SR Policy Group1.
VPN2 uses SR Policy Group 2 identified by Color 101. Plan the
forwarding path for VPN2 traffic. Different sets of network resources
are further allocated for the network slices as blow:
Slice 4: Voice service. Low latency forwarding is required. The
DSCP range of the packet is 1 to 10. The controller calculates the
low delay path for voice service and maps the DSCP 1~10 to Color
600. The voice traffic is forwarded through the constituent SR
policy (Color 600) of the Parent SRv6 Policy (color 101)
corresponding to VPN2.
Slice 5: Non voice services. No special forwarding quality
requirements. The controller calculates the SR Policy path and
maps all DSCP values outside the range of 1 to 10 to Color 601.
Non voice service messages are forwarded along the constituent SR
policy (Color 601) of the Parent SR policy (color 101)
corresponding to VPN2.
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SRv6 Network
.-------------------.
.-------. | | .-------.
/ \ <==|======Slice-4======|==> / \
( VPN2 ) | | ( VPN2 )
\ / <==|======Slice-5======|==> \ /
'-------' | | '-------'
| SR Policy Group 2 |
| (Color 101) |
'-------------------'
Figure 5 SR Policy Group for VPN2
The traffic of VPN2 from A to H of Slice 4 will be forwarded based
on the SR policy (Headend=A, Color=600, Endpoint=H) of Parent SR
policy (Color=101, Endpoint=H) of SR Policy Group2.
Because there are many access endpoints and each endpoint may act as
an entry node, compared with the traditional method of distributing
service forwarding policies on each Ingress node, the above SR
Policy Group can greatly simplify the configuration of VPN access
endpoints and effectively improve the efficiency of network
deployment and operation and maintenance.
5. IANA Considerations
This document has no IANA actions.
6. Security Considerations
This document presents use cases to be considered by the deployment
of SR Policy. It does not introduce any security considerations.
7. References
7.1. Normative References
[RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", RFC9256,
DOI 10.17487/RFC9256, July 2022, <https://www.rfc-
editor.org/info/rfc9256>.
[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>.
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[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-18 (work in progress),
June 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-00 (work in
progress), July 2022.
7.2. Informative References
TBD
8. Acknowledgments
The authors would like to thank the following for their valuable
contributions of this document:
TBD
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Authors' Addresses
Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
Liyan Gong
China Mobile
Email: gongliyan@chinamobile.com
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Yuanxiang Qiu
New H3C Technologies
Email: qiuyuanxiang@h3c.com
YaWei Zhang
Huawei Technologies
Email: zhangyawei@huawei.com
Ran Chen
ZTE Corporation
Email: chen.ran@zte.com.cn
Yanrong Liang
Ruijie Networks
Email: liangyanrong@ruijie.com.cn
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