Internet DRAFT - draft-fu-cats-muti-dp-solution
draft-fu-cats-muti-dp-solution
CATS H. Fu
Internet-Draft ZTE Corporation
Intended status: Standards Track B. Liu
Expires: 4 September 2024 Z. Li
China Mobile
D.H. Huang
D. Yuan
L. Ma
W. Duan
ZTE Corporation
3 March 2024
Analysis for Multiple Data Plane Solutions of Computing-Aware Traffic
Steering
draft-fu-cats-muti-dp-solution-00
Abstract
This document presents an overall framework for the data plane of
Computing-Aware Traffic Steering (CATS). In particular, it
illustrates several optional and possible data plane solutions,
compares their key features and main differences, and analyzes their
corresponding applicable scenarios.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 4 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Solution 1: Service ID carried in an anycast IP with
bidirectional address translation mode . . . . . . . . . 5
6. Solution 2: Service ID carried in the IPv6 EH with
unidirectional address translation mode . . . . . . . . . 7
7. Solution 3: Service ID carried in an anycast IP with TUNNEL/MAC
mode . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Solution Comparison Analysis . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . 12
12.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
As described in [I-D.ietf-cats-usecases-requirements], traffic
steering which takes computing resource conditions and metrics into
account would benefit computing-related services, including latency-
sensitive services which rely upon the use of augmented reality or
virtual reality (AR/VR) techniques.
Computing-Aware Traffic Steering (CATS) [I-D.ldbc-cats-framework]
aims to solve the problem that how the network edge can steer traffic
between clients of a service and sites offering the service. To
enable the computing- and network-aware traffic steering decisions,
awareness of computing information and network information are
fundamental premises. The CATS architecture is an overlay framework
for the selection of the most appropriate service contact instance
for placing a service request. However, the CATS framework does not
assume any specific data plane and control plane solutions.
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This document proposes several potential data plane solutions for the
realization of CATS, and compares their key features and main
application scenarios. These solutions use an anycast IP address or
digital identification as the Computing-aware Service ID (CS-ID)
associated with a service.
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
This document makes use of the terms defined in
[I-D.ldbc-cats-framework].
4. Overview
As illustrated in Figure 1, underlay network infrastructure and
devices are deployed between an ingress CATS-Router and service
contact instances, where corresponding CATS functionality is deployed
at the ingress CATS-Router 1 and egress CATS-Router 2/3. An egress
CAT-router connects to multiple service sites. At a specific service
site, single service contact instance or multiple service contact
instances are deployed.
CATS overlay encapsulation is established from the ingress CATS-
Router to the egress CATS-Router connected to the service site. For
ease of description in this document, it is assumed that a specific
tunnel between CATS-Routers is an SRv6 Policy[RFC8986].
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+--------+
| Client | <---------------------------
+----+---+
| Phase 1
+--------+-------+ <-----------------------
| C-TC |
+---------+------+
| | C-PS |
| +------+
+--------------+ CATS-Router 1 +--------------+
| +----------------+ |
| Underlay Infrastructure | Phase 2
| SRv6 Encap |
| +----------------+ +----------------+ |
+-+ CATS-Router 2 +--------+ CATS-Router 3 +-+
+----------------+ +----------------+
| C-SMA | | C-SMA |
+--------+-------+ +--------+-------+ <----------
| |
| |
+----+-----+ +---+------+ Phase 3
+--+--------+ | +--+--------+ |
| Service | | | Service | |
| instance +-+ | instance +-+
+-----------+ <------------+-----------+ <-------------
Edge site1 Edge site2
Figure 1: CATS Data Plane Workflow
Control plane: The ingress CATS-Router ("CATS-Router 1") receives
service routes from the egress CATS-Routers ("CATS-Router 2/3") ,
including network and computing indicators. The C-PS determines an
associated egress CATS-Router by selecting the most appropriate
service site and corresponding network forwarding path based on
routing strategies and policies, utilizing collected network and
computing metrics. The ingress CATS-Router generates the SRv6 tunnel
encapsulation from itself to the egress CATS router based on a
calculated and matched SR policy.
Data plane: From the client to the service contact instance, packet
processing and handling procedures are generally divided into at
least the following successive three phases:
* Phase I: A service request carrying a CATS Service ID (CS-ID)
needs to be routed to the ingress CATS-Router through the access
network. The CS-ID can be carried in multiple methods: 1) placing
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the CS-ID in the destination address field, where the destination
address would be encoded with the CS-ID as spcific anycast IPs; 2)
placing the CS-ID in an IPv6 extension header, and the destination
address would inherit the IP address of the ingress CATS-Router.
* Phase II: When packets of a service request are received by an
ingress CATS-Router, it is classified and determined by the C-TC
component. When a matching entry of service routes is found for
this request, the ingress CATS-Router encapsulates it and forwards
the packets to the C-PS selected egress CATS-Router via the
matching SR tunnel.
* Phase III: At egress CATS-Router, the packets are decapsulated and
successively forwarded according to local entries, and the packets
are sent to a corresponding selected service contact instance.
5. Solution 1: Service ID carried in an anycast IP with bidirectional
address translation mode
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+----+
+------+ +-------------------+ +-------------------+ |IP1 +-+
|Client| |Ingress CATS-Router| |Engress CATS-Router| +-+ IP2|
+------+ +-------------------+ +-------------------+ +----+
| | | |
| | +---------------+ | |
| | | DATA1 | | |
| | +---------------+ | |
| | | inner header | | |
| | | +-----------+ | | |
| | | |SA=clientIP| | | |
| +-------------+ | | +-----------+ | | |
| | DATA1 | | | | DA=Sid1 | | | |
| +-------------+ | | +-----------+ | | |
| | inner header| | +---------------+ | |
| |+-----------+| | | outer header | | +-------------+ |
| ||SA=clientIP|| | | +-----------+ | | | DATA1 | |
| |+-----------+| | | | SRH | | | +-------------+ |
| || DA=Sid1 || | | +-----------+ | | | inner header| |
| |+-----------+| | | | SA=C-R-I | | | |+-----------+| |
| +-------------+ | | +-----------+ | | ||SA=clientIP|| |
| | | | DA=C-R-E | | | |+-----------+| |
| | | +-----------+ | | || DA=IP1 || |
| | +---------------+ | |+-----------+| |
+---------------->| | +-------------+ |
| Phase 1 +--------------------->| |
| | Phase 2 +---------------->|
| | | Phase 3 |
| | | |
Figure 2: CATS Dataplane Workflow for solution 1
Figure 2 illustrates successive phases of workflow in Solution 1:
* Phase I: The packet of a service request carries a CS-ID in its
destination address field. The destination address is encoded as
an anycast IP address and would be routable within the access
network. This prerequisite requires that anycast prefix routes
are distributed throughout the access network. Service packets
can be forwarded to the ingress CATS-Router for processing in a
successive Phase II.
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* Phase II: The ingress CATS-Router looks up with the corresponding
service routing table indexed by the service ID in the packets’
destination address, determines appropriate service route entries
and routes the packet to the SR policy by encapsulating the SRH
tunnel header, and forwards the packet to the egress CATS-Router
for afterwards procedures in phase III.
* Phase III: The egress CATS-Router decapsulates the SRH tunnel
encapsulation of the packets. Since there might be multiple
service instances which provide the same service deployed under
the same CATS-Router, the packets carrying anycast IP addresses
cannot be directly routed to a corresponding service contact
instance. NAT (Network Address Translation) needs to be performed
for the packets, and the packets are forwarded to the
corresponding service contact instance by the lookup among service
routes entries and a corresponding translation of destination
address.
Anycast IP is used as the destination address of the end-to-end
session. Since the destination address of the user packet is
translated to the IP address of the service contact instance in phase
III. After the service contact instance receives the packet, the
service contact instance correspondingly utilizes the incoming source
address as the destination address of the response packet, and uses
the IP address of the service contact instance as the source address.
To eliminate influences on the host protocol stack for service
contact and session establishment, the source address of the response
packet must be translated to the corresponding upstream destination
address, for which an SNAT process should be performed for the
response packets in a downstream workflow.
6. Solution 2: Service ID carried in the IPv6 EH with unidirectional
address translation mode
Among up-to-date application scenarios, some newly introduced
transport protocols would support the change of connecting IP address
without interrupting the traffic flows and disconnecting the
connection session. In these cases, the CATS-Routers would modify
the destination address of the corresponding packets to the IP
address of the selected service contact instance when the client
sends its upstream packet, and establish a connection through the
downstream response packet from the service instance even the IP
address is modified. Corresponding capable transport protocols are
outside the scope of this document.
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+----+
+------+ +-------------------+ +-------------------+ |IP1 +-+
|Client| |Ingress CATS-Router| |Engress CATS-Router| +-+ IP2|
+------+ +-------------------+ +-------------------+ +----+
| | | |
| | +---------------+ | |
| | | DATA1 | | |
| | +---------------+ | |
| | | inner header | | |
| | | +-----------+ | | |
| | | |SA=clientIP| | | |
| +-------------+ | | +-----------+ | | |
| | DATA1 | | | | DA=Sid1 | | | |
| +-------------+ | | +-----------+ | | |
| | inner header| | +---------------+ | |
| |+-----------+| | | outer header | | +-------------+ |
| ||SA=clientIP|| | | +-----------+ | | | DATA1 | |
| |+-----------+| | | | SRH | | | +-------------+ |
| || DA=Sid1 || | | +-----------+ | | | inner header| |
| |+-----------+| | | | SA=C-R-I | | | |+-----------+| |
| +-------------+ | | +-----------+ | | ||SA=clientIP|| |
| | | | DA=C-R-E | | | |+-----------+| |
| | | +-----------+ | | || DA=IP1 || |
| | +---------------+ | |+-----------+| |
+---------------->| | +-------------+ |
| Phase 1 +--------------------->| |
| | Phase 2 +---------------->|
| | | Phase 3 |
| | | |
Figure 3: CATS Dataplane Workflow for solution 2
Figure 3 illustrates successive phases of workflow in Solution 2:
* Phase I: Forward packets to the ingress CATS-Router, the
destination address of the packet might be set to the ingress
CATS-Router's IP address, and the CS-ID is carried in the IPv6
extension header. The packet is then forwarded through the access
network to the ingress CATS-Router, at which it is processed in
phase II.
* Phase II: The ingress CATS-Router looks up with the corresponding
service routing table indexed by the service ID in the packets’
IPv6 extension header, determines appropriate service route
entries and routes the packet to the SR policy by encapsulating
the SRH tunnel header, and forwards the packet to the egress CATS-
Router for afterwards procedures in phase III.
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* Phase III: The egress CATS-Router decapsulates the SRH tunnel
encapsulation of the packets. The destination address in the
packet needs to be replaced with the IP address of the
corresponding service contact instance. The packet is then
forwarded to the corresponding service contact instance.
In order to adapt to the destination address modification on the
terminal and service host side, the protocol stack should be
correspondingly modified and upgraded. As a result, downstream
packets do not need SNAT translation. In the above condition, there
is only unidirectional address translation process in Solution 2. In
this case, the CATS-Router does not even need to maintain and
administer session status for traffic flows including unidirectional
translation entries, etc.
7. Solution 3: Service ID carried in an anycast IP with TUNNEL/MAC mode
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+----+
+------+ +-------------------+ +-------------------+ |IP1 +-+
|Client| |Ingress CATS-Router| |Engress CATS-Router| +-+--+2|
+--+---+ +----------+--------+ +--------+----------+ +--+-+
| | | |
| | | Option 1: |
| | +---------------+ | +---------------+ |
| | | DATA1 | | | DATA1 | |
| | +---------------+ | +---------------+ |
| | | inner header | | | inner header | |
| | | +-----------+ | | | +-----------+ | |
| | | |SA=clientIP| | | | |SA=clientIP| | |
| +---------------+ | | +-----------+ | | | +-----------+ | |
| | DATA1 | | | | DA=Sid1 | | | | | DA=Sid1 | | |
| +---------------+ | | +-----------+ | | | +-----------+ | |
| | inner header | | +---------------+ | +---------------+ |
| | +-----------+ | | | outer header | | | outer header | |
| | |SA=clientIP| | | | +-----------+ | | | +-----------+ | |
| | +-----------+ | | | | SRH | | | | | SRH | | |
| | | DA=Sid1 | | | | +-----------+ | | | +-----------+ | |
| | +-----------+ | | | | SA=C-R-I | | | | | SA=C-R-E | | |
| +---------------+ | | +-----------+ | | | +-----------+ | |
| | | | DA=C-R-E | | | | | DA=IP1 | | |
| | | +-----------+ | | | +-----------+ | |
| | +---------------+ | +---------------+ |
| | | |
| | | Option 2: |
| | | +--------------+ |
| | | | DATA1 | |
| | | +--------------+ |
| | | | inner header | |
| | | |+------------+| |
| | | ||SA=clientIP || |
| | | |+------------+| |
| | | || DA=Sid1 || |
| | | |+------------+| |
| | | ||DMAC=IP1-MAC|| |
| | | |+------------+| |
| | | +--------------+ |
+------------------>| | |
| Phase 1 +------------------>| |
| | Phase 2 +--------------------->|
| | | Phase 3 |
| | | |
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Figure 4: CATS Dataplane Workflow For solution 3
Figure 4 illustrates successive phases of workflow in Solution 3:
* Phase I: The packet of a service request carries a CS-ID in its
destination address field. The destination address is encoded as
an anycast IP address and would be routable within the access
network. This prerequisite requires that anycast prefix routes
are distributed throughout the access network. Service packets
can be forwarded to the ingress CATS-Router for processing in a
successive Phase II.
* Phase II: The ingress CATS-Router looks up with the corresponding
service routing table indexed by the service ID in the packets’
destination address, determines appropriate service route entries
and routes the packet to the SR policy byencapsulating the SRH
tunnel header, and forwards the packet to the egress CATS-Router
for afterwards procedures in phase III.
* Phase III: The egress CATS-Router decapsulates the SRH tunnel
encapsulation of the packets. Since there might be multiple
service instances which provide the same service deployed under
the same CATS-Router, the packets carrying anycast IP addresses
cannot be directly routed to a corresponding service contact
instance. Two optional methods can be applied to forward service
packets to the service contact instance: 1) Based on the IP
addresses of the CATS-Router and service instance, a bidirectional
tunnel (such as GRE and GIF) would be directly established between
them for forwarding packets to the service instance. This method
can be capable for both L2/L3 network;2) With the learned ARPs in
accordance with the service instance IP addresses, and utilizes
the corresponding ARP MAC as the destination MAC addresses of user
packets, and deliver the packets to the service instance through
layer-2 switching. This method can only be capable for the L2
network.
It should be noted that the client and service host stacks of this
solution are not modified, and there is no IP address translation
process in the above solution. However, the service instance needs
to support a mentioned tunneling model, and some protocol stacks
might not support the tunneling functionality.
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8. Solution Comparison Analysis
+==========================+============+============+============+
| | Solution 1 | Solution 2 | Solution 3 |
+==========================+============+============+============+
| CATS router requirement | High | Middle | Middle |
+--------------------------+------------+------------+------------+
| Client requirement | None | Middle | None |
+--------------------------+------------+------------+------------+
| Service host requirement | None | Middle | Low |
+--------------------------+------------+------------+------------+
| Forwarding Performance | Low | High | High |
+--------------------------+------------+------------+------------+
Table 1: CATS Dataplane Comprehensive Comparison of Solutions
As illustrated in Table 1, different solutions have disparate
requirements for clients, service hosts, and CATS-Routers, ultimately
resulting in different forwarding performances. Generally, solution
1 has the lowest requirements for terminals and service hosts, yet
its forwarding performance may be the worst. Solution 2 has the most
strict requirements for terminals and service hosts. In most cases,
protocol stack modification is applicable to new host protocol
stacks. Solution 3 requires the service host's anycast IP to be
configured and deployed, and a protocol stack to support tunnels.
Both solution 2 and solution 3 can provide satisfying forwarding
performance. Additionally, in solution 2 and 3, CATS-Routers are not
required to support the full and standard functionality of NAT.
To be added.
9. Security Considerations
TBD.
10. Acknowledgements
To be added upon contributions, comments and suggestions.
11. IANA Considerations
TBA
12. References
12.1. Normative References
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[I-D.ldbc-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-ldbc-
cats-framework-06, 8 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ldbc-cats-
framework-06>.
[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>.
[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>.
[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>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[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>.
12.2. Informative References
[I-D.huang-service-aware-network-framework]
Huang, D., Tan, B., and D. Yang, "Service Aware Network
Framework", Work in Progress, Internet-Draft, draft-huang-
service-aware-network-framework-01, 22 November 2022,
<https://datatracker.ietf.org/doc/html/draft-huang-
service-aware-network-framework-01>.
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[I-D.ietf-cats-usecases-requirements]
Yao, K., Trossen, D., Boucadair, M., Contreras, L. M.,
Shi, H., Li, Y., Zhang, S., and Q. An, "Computing-Aware
Traffic Steering (CATS) Problem Statement, Use Cases, and
Requirements", Work in Progress, Internet-Draft, draft-
ietf-cats-usecases-requirements-02, 1 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-cats-
usecases-requirements-02>.
[I-D.lbdd-cats-dp-sr]
Li, C., Boucadair, M., Du, Z., and J. Drake, "Computing-
Aware Traffic Steering (CATS) Using Segment Routing", Work
in Progress, Internet-Draft, draft-lbdd-cats-dp-sr-01, 11
January 2024, <https://datatracker.ietf.org/doc/html/
draft-lbdd-cats-dp-sr-01>.
[I-D.li-dyncast-architecture]
Li, Y., Iannone, L., Trossen, D., Liu, P., and C. Li,
"Dynamic-Anycast Architecture", Work in Progress,
Internet-Draft, draft-li-dyncast-architecture-08, 16
January 2023, <https://datatracker.ietf.org/doc/html/
draft-li-dyncast-architecture-08>.
[RFC1631] Egevang, K. and P. Francis, "The IP Network Address
Translator (NAT)", RFC 1631, DOI 10.17487/RFC1631, May
1994, <https://www.rfc-editor.org/info/rfc1631>.
[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>.
Authors' Addresses
Huakai Fu
ZTE Corporation
Wuhan
China
Email: fu.huakai@zte.com.cn
Bo Liu
China Mobile
Beijing
China
Email: liubo@chinamobile.com
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Zhenqiang Li
China Mobile
Beijing
China
Email: lizhenqiang@chinamobile.com
Daniel Huang
ZTE Corporation
Nanjing
China
Email: huang.guangping@zte.com.cn
Dongyu Yuan
ZTE Corporation
Nanjing
China
Email: yuan.dongyu@zte.com.cn
Liwei Ma
ZTE Corporation
Nanjing
China
Email: ma.liwei1@zte.com.cn
Wei Duan
ZTE Corporation
Nanjing
China
Email: duan.wei1@zte.com.cn
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