Internet DRAFT - draft-ietf-lsr-isis-sr-vtn-mt
draft-ietf-lsr-isis-sr-vtn-mt
LSR Working Group C. Xie
Internet-Draft C. Ma
Intended status: Informational China Telecom
Expires: 26 July 2024 J. Dong
Z. Li
Huawei Technologies
23 January 2024
Applicability of IS-IS Multi-Topology (MT) for Segment Routing based
Network Resource Partition (NRP)
draft-ietf-lsr-isis-sr-vtn-mt-07
Abstract
Enhanced VPNs aim to deliver VPN services with enhanced
characteristics, such as guaranteed resources, latency, jitter, etc.,
so as to support customers requirements for connectivity services
with these enhanced characteristics. Enhanced VPN requires
integration between the overlay VPN connectivity and the
characteristics provided by the underlay network. A Network Resource
Partition (NRP) is a subset of the network resources and associated
policies on each of a connected set of links in the underlay network.
An NRP could be used as the underlay to support one or a group of
enhanced VPN services.
In some network scenarios, each NRP can be associated with a unique
logical network topology. This document describes a mechanism to
build the SR-based NRPs using IS-IS Multi-Topology together with
other well-defined IS-IS extensions.
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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Drafts is at https://datatracker.ietf.org/drafts/current/.
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 26 July 2024.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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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. Advertisement of Topology Attribute for SR-based NRP . . . . 3
3. Advertisement of Resource Attribute for SR-based NRP . . . . 4
4. Forwarding Plane Operations . . . . . . . . . . . . . . . . . 5
5. Scalability Considerations . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Enhanced VPNs aim to deliver VPN services with enhanced
characteristics, such as guaranteed resources, latency, jitter, etc.,
so as to support customers requirements for connectivity services
with these enhanced characteristics. Enhanced VPN requires
integration between the overlay VPN connectivity and the
characteristics provided by the underlay network.
[I-D.ietf-teas-ietf-network-slices] discusses the general framework,
components, and interfaces for requesting and operating network
slices using IETF technologies. Network slice is considered as one
target use case of enhanced VPNs.
[I-D.ietf-teas-ietf-network-slices] also introduces the concept of
the Network Resource Partition (NRP), which is a subset of the
buffer/queuing/scheduling resources and associated policies on each
of a connected set of links in an underlay network. An NRP can be
associated with a logical network topology to select or specify the
set of links and nodes involved. [I-D.ietf-teas-enhanced-vpn]
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specifies the framework of NRP-based enhanced VPNs and describes the
candidate component technologies in different network planes and
network layers. An NRP could be used as the underlay to meet the
requirement of one or a group of enhanced VPN services. To meet the
requirement of enhanced VPN services, a number of NRPs can be
created, each with a subset of network resources allocated on network
nodes and links in a customized topology of the physical network.
[I-D.ietf-spring-resource-aware-segments] introduces resource
awareness to Segment Routing (SR) [RFC8402]. The resource-aware SIDs
have additional semantics to identify the set of network resources
available for the packet processing action associated with the SIDs.
As described in [I-D.ietf-spring-sr-for-enhanced-vpn], the resource-
aware SIDs can be used to build SR-based NRPs with the required
network topology and network resource attributes to support enhanced
VPN services. In an SR-based data plane, Segment Identifiers (SIDs)
can be used to represent both the topological instructions and a
subset of network resources on the network nodes and links which are
allocated to an NRP. The SR SIDs and the associated topology and
resource attributes of an NRP need to be distributed using a control
plane.
In some network scenarios, the required number of NRPs could be
small, and it can be assumed that each NRP is associated with an
independent topology and has a set of dedicated or shared network
resources. For such scenarios, this document describes a simplified
mechanism to build SR-based NRPs. It proposes to use IS-IS Multi-
Topology [RFC5120] with segment routing [RFC8667] to define the
independent network topology of each NRP. The network resources and
other TE attributes of an NRP can be advertised using IS-IS MT with
the Traffic Engineering (TE) extensions defined in [RFC5305] and
[RFC8570]. The resource-aware segments can be used with this
approach to provide resource-guaranteed SR-based NRPs, while the
normal SR segments may also be used to provide SR-based NRPs with
shared network resources in the forwarding plane.
Alternate enhancements will be proposed to provide a flexible
combination of the topology and resource attribute to build a
relatively large number of NRPs. The detailed mechanism is out of
the scope of this document.
2. Advertisement of Topology Attribute for SR-based NRP
As each SR-based NRP is associated with a network topology, the
topology attribute and SR SIDs of NRPs need to be advertised, so that
the SR shortest path could be calculated using the topology of the
corresponding NRP. In this document, IS-IS MT and IS-IS SR are
reused for advertising the topology and SR SIDs of NRPs.
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IS-IS Multi-Topology (MT) [RFC5120] has been defined to create
independent topologies in one network. In [RFC5120], MT-based TLVs
are introduced to advertise topology-specific link-state information.
The MT-specific Link or Prefix TLVs are defined by adding additional
two bytes, which includes 12-bit MT-ID field in front of the ISN TLV
and IP or IPv6 Reachability TLVs. This provides the capability of
specifying the customized attributes of each topology. When each NRP
is associated with an independent network topology, MT-ID could be
used as the identifier of NRP in the control plane.
IS-IS MT can be used with segment routing based data plane. Thus the
topology attribute of an SR based NRP could be advertised using MT
with segment routing. The IS-IS extensions to support the
advertisement of topology-specific MPLS SIDs are specified in
[RFC8667]. Topology-specific Prefix-SIDs can be advertised by
carrying the Prefix-SID sub-TLVs in the IS-IS TLV 235 (MT IP
Reachability) and TLV 237 (MT IPv6 IP Reachability). Topology-
specific Adj-SIDs can be advertised by carrying the Adj-SID sub-TLVs
in IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS Neighbor Attribute)
[RFC5311]. The topology-specific Prefix-SIDs and Adj-SIDs can be
resource-aware segments or normal SR segments.
The IS-IS extensions to support the advertisement of topology-
specific SRv6 Locators and SIDs are specified in [RFC9352]. The
topology-specific SRv6 locators are advertised using SRv6 Locator
TLV, and SRv6 End SIDs inherit the MT-ID from the parent locator.
The topology-specific End.X SID are advertised by carrying SRv6 End.X
SID sub-TLVs in the IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS
Neighbor Attribute). The topology-specific SRv6 locators can be
resource-aware locator or normal SRv6 locator, and accordingly the
topology-specific SRv6 SIDs can be resource-aware SRv6 segments or
normal SRv6 segments.
3. Advertisement of Resource Attribute for SR-based NRP
In order to perform constraint based path computation for each NRP on
the network controller or on the ingress nodes, the network resource
attributes and other attributes associated with each NRP need to be
advertised. In this document, IS-IS MT is reused to advertise
topology-specific TE attributes for different NRPs.
On each network link, the information of the network resources and
other attributes associated with an NRP can be specified by
advertising the TE attributes sub-TLVs [RFC5305] and [RFC8570] in the
IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS Neighbor Attribute)
[RFC5311] of the corresponding topology.
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When Maximum Link Bandwidth sub-TLV is advertised in the MT-ISN TLV
of a topology, it indicates the amount of link bandwidth allocated to
the corresponding NRP. The bandwidth allocated to an NRP can be
exclusive for services utilizing the corresponding NRP. The usage of
other TE attributes in topology-specific TLVs is out of the scope of
this document.
Editor's note: It is noted that advertising per-topology TE
attributes was considered as a possible feature in future when the
encoding of IS-IS multi-topology was defined in [RFC5120].
4. Forwarding Plane Operations
For SR-MPLS data planes, the Adj-SIDs and Prefix-SIDs associated with
the same NRP can be used together to build SR-MPLS paths with the
topological and resource constraints of the NRP taken into
consideration. A Prefix-SID is associated with the paths calculated
in the topology corresponding to the NRP. An outgoing interface is
determined for each path. In addition, the resource-aware prefix-SID
can steer the traffic to use the subset of network resources
allocated to the NRP on the outgoing interface for packet forwarding.
A forwarding entry is installed in the forwarding plane using the
MPLS label that corresponds to the Prefix-SID associated with the
topology corresponding to the NRP. A resource-aware Adj-SID is
associated with a subset of network resources allocated to the NRP on
the link it identifies, and can be used together with the prefix-SIDs
of the same NRP to build SR-MPLS TE paths using the NRP.
For SRv6 data planes, the SRv6 SIDs associated with the same NRP can
be used together to build SRv6 paths with the topological and
resource constraints of the NRP taken into consideration. An SRv6
Locator is a prefix which is associated with the paths calculated in
the topology corresponding to the NRP. An outgoing interface is
determined for each path. In addition, the resource-aware SRv6
Locator prefix also steers the traffic to use the subset of network
resources which are allocated to the NRP on the outgoing interface
for packet forwarding. A forwarding entry for the SRv6 Locator
prefix is installed in the forwarding plane for the topology
corresponding to the NRP. A resource-aware End.X SID is associated
with a subset of network resources allocated to the NRP on the link
it identifies, and can be used together with other types of SRv6 SIDs
of the same NRP to build SRv6 TE paths using the NRP.
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5. Scalability Considerations
The mechanism described in this document assumes that each NRP is
associated with a unique multi-topology, so that the MT-IDs can be
reused to identify the NRPs in the control plane. While this brings
the benefit of simplicity, it also has some limitations. For
example, it means that even if multiple NRPs share the same topology,
they would still need to be identified using different MT-IDs in the
control plane, then independent path computation needs to be executed
for each NRP. Thus the number of NRPs supported in a network may be
dependent on the number of topologies supported, which is related to
both the number of topologies supported in the protocol and the
control plane overhead which the network nodes could accomodate. The
mechanism described in this document is considered useful for network
scenarios in which the required number of NRPs is small, as no
control protocol extension is required. For network scenarios where
the number of required NRPs is large, more scalable solution would be
needed, which may require further protocol extensions and
enhancements. A detailed analysis about the NRP scalability and the
possible optimizations for supporting a large number of NRPs is
described in [I-D.ietf-teas-nrp-scalability].
6. Security Considerations
This document introduces no additional security vulnerabilities to
IS-IS.
The mechanism proposed in this document is subject to the same
vulnerabilities as any other protocol that relies on IGPs.
7. IANA Considerations
This document does not request any IANA actions.
8. Acknowledgments
The authors would like to thank Zhibo Hu, Dean Cheng, Les Ginsberg,
Peter Psenak, Daniele Ceccarelli, Jia He, Xuesong Geng and Acee
Lindem for the review and discussion of this document.
9. References
9.1. Normative References
[I-D.ietf-spring-resource-aware-segments]
Dong, J., Miyasaka, T., Zhu, Y., Qin, F., and Z. Li,
"Introducing Resource Awareness to SR Segments", Work in
Progress, Internet-Draft, draft-ietf-spring-resource-
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aware-segments-08, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
resource-aware-segments-08>.
[I-D.ietf-spring-sr-for-enhanced-vpn]
Dong, J., Miyasaka, T., Zhu, Y., Qin, F., and Z. Li,
"Segment Routing based Virtual Transport Network (VTN) for
Enhanced VPN", Work in Progress, Internet-Draft, draft-
ietf-spring-sr-for-enhanced-vpn-06, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-for-enhanced-vpn-06>.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for NRP-based Enhanced Virtual Private Network",
Work in Progress, Internet-Draft, draft-ietf-teas-
enhanced-vpn-17, 25 December 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
enhanced-vpn-17>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "A Framework for
Network Slices in Networks Built from IETF Technologies",
Work in Progress, Internet-Draft, draft-ietf-teas-ietf-
network-slices-25, 14 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
ietf-network-slices-25>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5311] McPherson, D., Ed., Ginsberg, L., Previdi, S., and M.
Shand, "Simplified Extension of Link State PDU (LSP) Space
for IS-IS", RFC 5311, DOI 10.17487/RFC5311, February 2009,
<https://www.rfc-editor.org/info/rfc5311>.
[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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[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
February 2023, <https://www.rfc-editor.org/info/rfc9352>.
9.2. Informative References
[I-D.ietf-teas-nrp-scalability]
Dong, J., Li, Z., Gong, L., Yang, G., Mishra, G. S., and
F. Qin, "Scalability Considerations for Network Resource
Partition", Work in Progress, Internet-Draft, draft-ietf-
teas-nrp-scalability-03, 21 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
nrp-scalability-03>.
Authors' Addresses
Chongfeng Xie
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing
102209
China
Email: chongfeng.xie@foxmail.com
Chenhao Ma
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing
102209
China
Email: chenhao.m@outlook.com
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Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: jie.dong@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: lizhenbin@huawei.com
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