LSR Working Group C. Xie
Internet-Draft C. Ma
Intended status: Standards Track China Telecom
Expires: January 14, 2021 J. Dong
Z. Li
Huawei Technologies
July 13, 2020
Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual
Transport Network
draft-xie-lsr-isis-sr-vtn-mt-01
Abstract
Enhanced VPN (VPN+) as defined in I-D.ietf-teas-enhanced-vpn aims to
provide enhanced VPN service to support some application's needs of
enhanced isolation and stringent performance requirements. VPN+
requires integration between the overlay VPN and the underlay
network. A Virtual Transport Network (VTN) is a virtual network
which consists of a subset of the network topology and network
resources allocated from the underlay network. A VTN could be used
as the underlay for one or a group of VPN+ services.
I-D.dong-lsr-sr-enhanced-vpn defines the IGP extensions to build a
set of Segment Routing (SR) based VTNs. This document describes a
simplified mechanism to build the SR based VTNs using IGP multi-
topology together with other well-defined IS-IS extensions.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
working documents as Internet-Drafts. The list of current Internet-
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
Xie, et al. Expires January 14, 2021 [Page 1]
Internet-Draft IS-IS MT for SR VTN July 2020
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 January 14, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Advertisement of SR VTN Topology Attribute . . . . . . . . . 3
3. Advertisement of SR VTN Resource Attribute . . . . . . . . . 4
3.1. Advertising Topology-specific TE attributes . . . . . . . 4
4. Scalability Considerations . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Enhanced VPN (VPN+) is an enhancement to VPN services to support the
needs of new applications, particularly including the applications
that are associated with 5G services. These applications require
enhanced isolation and have more stringent performance requirements
than that can be provided with traditional overlay VPNs. These
properties cannot be met with pure overlay networks, as they require
integration between the underlay and the overlay networks.
[I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN
and describes the candidate component technologies in different
network planes and layers. An enhanced VPN may be used for 5G
Xie, et al. Expires January 14, 2021 [Page 2]
Internet-Draft IS-IS MT for SR VTN July 2020
transport network slicing, and will also be of use in other generic
scenarios.
To meet the requirement of enhanced VPN services, a number of virtual
transport networks (VTN) need to be created, each with a subset of
the underlay network topology and a set of network resources
allocated to meet the requirement of a specific VPN+ service or a
group of VPN+ services. Another existing approach is to build a set
of point-to-point paths, each with a set of network resource reserved
along the path, such paths is called Virtual Transport Path (VTP).
Although using a set of dedicated VTPs can provide similar
characteristics, it has some scalability issues in large networks.
[I-D.dong-spring-sr-for-enhanced-vpn] specifies how segment routing
(SR) [RFC8402] can be used to build virtual transport networks (VTNs)
with the required network topology and network resource attributes to
support enhanced VPN services. With segment routing based data
plane, Segment Identifiers (SIDs) can be used to represent the
topology and the set of network resources allocated by network nodes
to a virtual network. The SIDs of each VTN and the associated
topology and resource attributes need to be distributed using control
plane.
[I-D.dong-lsr-sr-enhanced-vpn] defines the IGP mechanisms with
necessary extensions to build a set of Segment Routing (SR) based
VTNs. The VTNs could be used as the underlay of the enhanced VPN
service. The mechanism described in [I-D.dong-lsr-sr-enhanced-vpn]
allows flexible combination of the topology and resource attribute to
build customized VTNs. In some network scenarios, it is assumed that
each VTN has an independent topology and a set of dedicated network
resources. This document describes a simplified mechanism to build
the SR based VTNs in those scenarios.
The approach is to use IS-IS Multi-Topology [RFC5120] with segment
routing [RFC8667] to define the independent network topologies of
each VTN. The information of network resources allocated to a VTN
can be advertised by using IS-IS MT with the Traffic Engineering (TE)
extensions defined in [RFC5305].
2. Advertisement of SR VTN Topology Attribute
Multi-Topology Routing (MTR) [RFC5120] has been defined to create
independent topologies in one network. It also has the capability of
specifying the customized attributes of each topology. MTR can be
used with segment routing based data plane. The IS-IS extensions to
support the advertisement of topology-specific MPLS SIDs are
specified in [RFC8667]. Topology-specific Prefix-SIDs are advertised
by carrying the Prefix-SID sub-TLVs in the IS-IS TLV 235 (MT IP
Xie, et al. Expires January 14, 2021 [Page 3]
Internet-Draft IS-IS MT for SR VTN July 2020
Reachability) and TLV 237 (MT IPv6 IP Reachability). Topology-
specific Adj-SIDs are advertised by carrying the Adj-SID sub-TLVs in
IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS Neighbor Attribute).
The IS-IS extensions to support the advertisement of topology-
specific SRv6 Locators and SIDs are specified in
[I-D.ietf-lsr-isis-srv6-extensions]. 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).
When each VTN has an independent network topology, the MT-ID could be
used as the identifier of VTN in control plane. Thus the topology
attribute of a VTN could be advertised using MTR with segment
routing.
3. Advertisement of SR VTN Resource Attribute
In order to perform constraint based path computation for each VTN on
the network controller or on the ingress nodes, the network resource
attribute associated with each VTN needs to be advertised.
3.1. Advertising Topology-specific TE attributes
On each network link, the information of the network resources
associated with a VTN can be specified by carrying the TE attributes
sub-TLVs [RFC5305] in the IS-IS TLV 222 (MT-ISN) and TLV 223 (MT IS
Neighbor Attribute) of the corresponding topology.
When Maximum Link Bandwidth sub-TLV is carried in the MT-ISN TLV, it
indicates the amount of link bandwidth allocated to the corresponding
VTN. The bandwidth allocated to a VTN can be exclusive for services
carried in the corresponding VTN. The usage of other TE attributes
in topology-specific TLVs is for further study.
Editor's note1: It is noted that carrying per-topology TE attributes
was considered as a possible feature in future when the encoding of
IS-IS multi-topology was defined [RFC5120].
4. Scalability Considerations
The mechanism described in this document requires that each VTN has
an independent topology. Even if multiple VTNs may have the same
topology attribute, they would still need to be identified using
different MT-IDs in the control plane. This requires that for each
VTN, independent path computation would be executed. The number of
Xie, et al. Expires January 14, 2021 [Page 4]
Internet-Draft IS-IS MT for SR VTN July 2020
VTNs supported in a network may be dependent on the control plane
computation overhead.
5. 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.
6. IANA Considerations
This document does not request any IANA actions.
7. Acknowledgments
The authors would like to thank Zhibo Hu, Dean Cheng, Les Ginsberg
and Peter Psenak for the review and discussion of this document.
8. References
8.1. Normative References
[I-D.dong-spring-sr-for-enhanced-vpn]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., and
Z. Li, "Segment Routing for Resource Guaranteed Virtual
Networks", draft-dong-spring-sr-for-enhanced-vpn-08 (work
in progress), June 2020.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08
(work in progress), April 2020.
[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>.
[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>.
Xie, et al. Expires January 14, 2021 [Page 5]
Internet-Draft IS-IS MT for SR VTN July 2020
[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>.
[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>.
[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>.
8.2. Informative References
[I-D.dong-lsr-sr-enhanced-vpn]
Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L.,
and S. Bryant, "IGP Extensions for Segment Routing based
Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-04 (work in
progress), June 2020.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-16 (work in
progress), June 2020.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Networks (VPN+)
Services", draft-ietf-teas-enhanced-vpn-05 (work in
progress), February 2020.
Authors' Addresses
Chongfeng Xie
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing 102209
China
Email: xiechf@chinatelecom.cn
Xie, et al. Expires January 14, 2021 [Page 6]
Internet-Draft IS-IS MT for SR VTN July 2020
Chenhao Ma
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing 102209
China
Email: machh@chinatelecom.cn
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
Xie, et al. Expires January 14, 2021 [Page 7]