Internet DRAFT - draft-lbdd-cats-dp-sr
draft-lbdd-cats-dp-sr
CATS C. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track M. Boucadair
Expires: 14 July 2024 Orange
Z. peng
China Mobile
J. Drake
Juniper Networks, Inc.
11 January 2024
Computing-Aware Traffic Steering (CATS) Using Segment Routing
draft-lbdd-cats-dp-sr-01
Abstract
This document describes a solution that adheres to the Computing-
Aware Traffic Steering (CATS) framework. The solution uses anycast
IP addresses as the CATS service identifier and Segment Routing (SR)
as the data plane encapsulation to achieve computing-aware traffic
steering among multiple services instances.
Status of This Memo
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This Internet-Draft will expire on 14 July 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Realization of CATS Framework Components . . . . . . . . 3
3.1.1. CATS Identifiers . . . . . . . . . . . . . . . . . . 3
3.1.2. CATS Components . . . . . . . . . . . . . . . . . . . 3
3.2. Realization of the CATS Framework Workflow . . . . . . . 4
3.2.1. Service Announcement . . . . . . . . . . . . . . . . 4
3.2.2. Metrics Distribution . . . . . . . . . . . . . . . . 4
3.2.3. Service Demand Processing . . . . . . . . . . . . . . 5
3.2.4. Service Instance Affinity . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
As described in [I-D.yao-cats-ps-usecases], traffic steering that
takes into account computing resource metrics would benefit several
services, e.g., latency-sensitive service like immersive services
that rely upon the use of augmented reality or virtual reality (AR/
VR) techniques.
[I-D.ldbc-cats-framework] defines a framework for Computing-Aware
Traffic Steering (CATS). Such a framework defines an approach for
making compute- and network-aware traffic steering decisions in
networking environments where services are deployed in many
locations.
The CATS framework is an overlay framework for the selection of the
suitable service contact instance for placing a service request. The
exact characterization of 'suitable' will be determined by a
combination of networking and computing metrics. The CATS framework
does not assume any specific data plane and control plane solutions.
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This document proposes a data plane solution for the realization of
CATS. The solution uses an anycast IP address as the Computing-aware
Service ID (CS-ID) associated with a service. Also, the solution
uses Segment Routing (SR) as the data plane encapsulation from an
Ingress CATS-Router to an Egress CATS-Router.
2. Terminology
This document makes use of the terms defined in
[I-D.ldbc-cats-framework].
Note: Terms such as CATS Instance Selector ID (CIS-ID) may be updated
to echo what will be agreed in the CATS framework
[I-D.ldbc-cats-framework].
3. Solution Overview
This section describes the details of realizing CATS identifiers,
CATS components, and workflow.
3.1. Realization of CATS Framework Components
3.1.1. CATS Identifiers
A CATS Service ID (CS-ID) is an anycast IPv4 or IPv6 address. Such
an IP address is associated with a specific service that is reachable
via one or multiple service contact instances.
The CATS overlay encapsulation is established from an Ingress CATS-
Router to an Egress CATS-Router connected to a service contact
instance. The service contact instance is typically hosted in a
service site.
Depending on the deployment requirements, CIS-IDs may be needed to
indicate where to forward the packet to a specific interface pointing
to a specific site in the case that multiple sites connect to the
same Egress CATS-Router.
3.1.2. CATS Components
In the context of this document, CATS-Routers are required to support
SR encapsulation, including SR-MPLS [RFC8660] and SRv6 [RFC8986].
The CATS Traffic Classifier (C-TC) is assumed to be running on
Ingress CATS-Routers.
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For each service site, one or multiple C-SMAs and C-NMAs can be
implemented within the site to collect the metrics of the service
instances.
3.2. Realization of the CATS Framework Workflow
3.2.1. Service Announcement
The service anycast IP address may announced using a rendezvous
service (DNS, for example). Clients can obtain the CS-ID of the
service from the rendezvous service used by the application (e.g.,
DNS). It is out of scope of this document to provide a comprehensive
list of all candidate rendezvous services.
3.2.2. Metrics Distribution
As per the CATS framework, CS-ID routes with metrics are distributed
among the overlay CATS Routers. The detailed control plane solutions
of metrics distribution are out of the scope of this document.
However, a sample procedure is provided for the readers convenience.
For example, BGP can be used to distribute CS-ID routes with metrics.
In the case of the C-SMA running as stand alone outside an Egress
CATS-Router, the C-SMA collects the metrics of computing resource
within a service site and distributes the CS-ID routes with the
collected metrics to the Egress CATS-Router. Egress CATS-Routers
will generate the new metrics combined with network metrics and
computing-related metrics, and redistribute the CS-ID route to
Ingress CATS-Routers. In the case of the C-SMA running as a logic
entity on an Egress CATS-Router, the same process will be performed
inside the Egress CATS-Router.
As described in Section 3.4 of [I-D.ldbc-cats-framework], CATS can be
deployed in a distributed model, centralized model, or a hybrid
model. In a centralized model or hybrid model, the routes with
metrics may be collected by centralized controllers. BGP-LS may be a
candidate solution to collect the route with metrics from CATS-
Routers to controllers; the use of BGP-LS is however out of the scope
of this document.
A centralized controller may also install the forwarding policy on
Ingress CATS-Routers to steer the traffic; how these policies are
communicated to the routers is out of the scope of this document.
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3.2.3. Service Demand Processing
Two SR [RFC8402] data plane approaches are supported: SRv6 [RFC8986]
and SR-MPLS [RFC8660]. This section introduces a solution based upon
SRv6 and SR-MPLS as data planes for CATS purposes.
An Ingress CATS-Router generates SRv6/SR-MPLS encapsulations from
itself to Egress CATS-Routers according to the SR policy received
from a controller. An Ingress CATS-Router receives service routes
with network and computing-related metrics from Egress CATS-Routers.
An C-PS will select the best service site according to the received
service routes and routing policies. Once the best service site is
selected, the associated Egress CATS-Router can be determined and the
appropriate SR encapsulation from an Ingress CATS-Router to the C-PS-
computed Egress CATS-Router can be selected.
When a service demand is received by an Ingress CATS-Router, it is
classified by the C-TC component. When a matching classification
entry is found for this demand, the Ingress CATS-Router encapsulates
and forwards it to the C-PS selected Egress CATS-Router via the
matching SR tunnel.
3.2.3.1. SRv6
As shown in Figure 1, SRv6 tunnels are established from Ingress CATS-
Routers to Egress CATS-Routers.
There may be multiple encapsulations from a single Ingress CATS-
Router to different Egress CATS-Routers so that the ingress can
choose the best Egress CATS-Router connected to the target site.
Furthermore, there may be multiple tunnels from a single Ingress
CATS-Router to a single Egress CATS-Router, e.g., to provide
different connectivity performance guarantees.
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+------+
|Client|
+------+
|
+-------------+
| C-TC |
|-------------|
| | C-PS |
......................| +-------|....................
: |CATS-Router 2| :
: +-------------+ :
: :
: Underlay :
: Infrastructure :
: SRv6 Encap 1 SRv6 Encap 2 :
: :
: +-------------+ +-------------+ :
: |CATS-Router 1| |CATS-Router 3| :
:...| |................| |......:
+-------------+ +-------------+
| C-SMA | | C-SMA |
+-------------+ +-------------+
| END.DX SID1 | | END.DX SID2
| | |
+-----------+ +----------+ +-----------+
+-----------+ | +----------+ | +----------+ |
| Service | | | Service | | | Service | |
| instance |-+ | instance |-+ | instance |-+
+-----------+ +----------+ +----------+
Edge site 1 Edge site 2 Edge site 3
Figure 1: Using SRv6 in CATS
In some cases, multiple service sites may be connected to a single
Egress CATS-Router. To demux these sites, a specific attachment
circuit must be provided to indicate the specific target service. In
order to explicitly indicate the interface towards a site, an END.DX
[RFC8986] is encoded as the last segment in the SRv6 encapsulation.
The associated END.DX is learned from the control plane.
When the traffic reaches the Egress CATS-Router, the SRv6 packet is
decapsulated and the traffic is forwarded to the service contact
instance. How the packet is handled beyond that point is out of the
scope.
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3.2.3.2. SR-MPLS
Similarly, SR-MPLS can be used as the overlay CATS encapsulation.
The forwarding path is encoded as an MPLS label stack, and a
potential VPN label can be included as the last label to indicate to
steer the traffic through a specific interface to a target service
contact instance in the case multiple service sites connect to the
same Egress CATS-Router.
3.2.4. Service Instance Affinity
As per [I-D.ldbc-cats-framework], different services may have
different notions of what constitutes a 'flow' and may thus identify
a flow differently. Typically, a flow is identified by the 5-tuple
transport coordinates (source and destination addresses, source and
destination port numbers, and protocol).
Note: This section will be updated to reflect the discussion in
the WG about affinity.
4. Security Considerations
This document specifies a CATS solution using anycast IP addresses as
CS-IDs and SR as data plane. It does not introduce further security
threats considering to the existing ones in [RFC8402], [RFC8660],
[RFC8986] and [I-D.ldbc-cats-framework].
Anycast-related security considerations are discussed in Section 4.4
of [RFC7094].
5. IANA Considerations
This document makes no requests for IANA action.
6. Acknowledgements
TBD
7. References
7.1. Normative References
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[I-D.ldbc-cats-framework]
Li, C., Du, Z., Boucadair, M., Contreras, L. M., Drake,
J., Huang, D., and G. S. Mishra, "A Framework for
Computing-Aware Traffic Steering (CATS)", Work in
Progress, Internet-Draft, draft-ldbc-cats-framework-05, 2
January 2024, <https://datatracker.ietf.org/doc/html/
draft-ldbc-cats-framework-05>.
[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>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
7.2. Informative References
[I-D.yao-cats-ps-usecases]
Yao, K., Trossen, D., Boucadair, M., Contreras, L. M.,
Shi, H., Li, Y., and S. Zhang, "Computing-Aware Traffic
Steering (CATS) Problem Statement, Use Cases, and
Requirements", Work in Progress, Internet-Draft, draft-
yao-cats-ps-usecases-03, 30 June 2023,
<https://datatracker.ietf.org/doc/html/draft-yao-cats-ps-
usecases-03>.
[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
Contributors
Dirk Trossen
Huawei Technologies
Email: dirk.trossen@huawei.com
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Luigi Iannone
Huawei Technologies
Email: luigi.iannone@huawei.com
Yizhou Li
Huawei Technologies
Email: liyizhou@huawei.com
Hang Shi
Huawei Technologies
Email: shihang9@huawei.com
Authors' Addresses
Cheng Li
Huawei Technologies
China
Email: c.l@huawei.com
Mohamed Boucadair
Orange
France
Email: mohamed.boucadair@orange.com
Zongpeng Du
China Mobile
China
Email: duzongpeng@chinamobile.com
John E Drake
Juniper Networks, Inc.
United States of America
Email: jdrake@juniper.net
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