IDR Working Group C. Xie
Internet-Draft C. Li
Intended status: Standards Track China Telecom
Expires: September 10, 2020 J. Dong
Z. Li
Huawei Technologies
March 9, 2020
BGP-LS with Multi-topology for Segment Routing based Virtual Transport
Networks
draft-xie-idr-bgpls-sr-vtn-mt-00
Abstract
Enhanced VPN (VPN+) as defined in I-D.ietf-teas-enhanced-vpn aims to
provide enhanced VPN service to support applications's needs of
enhanced isolation and stringent performance requirements. VPN+
requries 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 toplogy 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-idr-bgpls-sr-enhanced-vpn defines the BGP-LS extensions to
distribute the information of Segment Routing (SR) based VTNs to
external entities, such as the network controllers. This document
describes a simplified mechanism to distribute the information of SR
based VTNs using BGP-LS with Multi-Topology.
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
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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 September 10, 2020.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Advertisement of SR VTN Topology . . . . . . . . . . . . . . 3
2.1. Intra-domain Topology Advertisement . . . . . . . . . . . 3
2.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 5
3. Advertisement of VTN Resource Attribute . . . . . . . . . . . 6
3.1. Advertising Topology specific TE attributes . . . . . . . 6
3.2. Associating VTNs with L2 Bundle Member Links . . . . . . 6
4. Scalability Considerations . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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
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and describes the candidate component technologies in different
network planes and layers. An enhanced VPN can be used for 5G
transport network slicing, and will also be of use in more generic
scenarios.
To meet the requirement of enhanced VPN services, a number of Virtual
Transport Networks (VTNs) 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.
[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 resources, which could
be used as the underlay of enhanced VPN services.
[I-D.dong-lsr-sr-enhanced-vpn] and [I-D.xie-lsr-isis-sr-vtn-mt]
specifies the IGP mechanism and extensions to build a set of SR based
VTNs. When a VTN spans multiple IGP areas or multiple Autonomous
Systems (ASes), BGP-LS is needed to advertise the VTN information in
each IGP area or AS to the network controller, so that the controller
could use the collected information to build the inter-area or inter-
AS SR VTNs.
[I-D.dong-idr-bgpls-sr-enhanced-vpn] defines the BGP-LS extensions to
distribute the information of Segment Routing (SR) based VTNs to
external entities, such as the network controllers, which allows
flexible combination of the topology and resource attribute to build
customized VTNs. While in some network scenarios, it is assumed that
each VTN has an independent topology and a set of dedicated network
resources. For such scenarios, this document describes a simplified
mechanism to distribute the information of SR based VTNs using BGP-LS
with Multi-Topology.
2. Advertisement of SR VTN Topology
[I-D.xie-lsr-isis-sr-vtn-mt] describes the ISIS Multi-topology
mechanisms to distribute the topology attributes of SR based VTNs.
This section describes the corresponding BGP-LS mechanism to
distribute both the intra-domain and inter-domain topology attributes
of SR based VTNs.
2.1. Intra-domain Topology Advertisement
In section 3.2.1.5 of [RFC7752], Multi-Topology Identifier (MT-ID)
TLV is defined, which can contain one or more IS-IS or OSPF Multi-
Topology IDs. The MT-ID TLV MAY be present in a Link Descriptor, a
Prefix Descriptor, or the BGP-LS Attribute of a Node NLRI.
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[I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS
extensions to carry the segment routing information using TLVs of
BGP-LS Attribute. When MTR is used with SR-MPLS data plane,
topology-specific prefix-SIDs and topology-specific Adj-SIDs can be
carried in the BGP-LS Attribute associated with the prefix NLRI and
link NLRI respectively, the MT-ID TLV is carried in the prefix
descriptor and link descriptor to identify the corresponding topology
of the SIDs.
[I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to
advertise SRv6 segments along with their functions and attributes.
When MTR is used with SRv6 data plane, the SRv6 Locator TLV is
carried in the BGP-LS Attribute associated with the prefix-NLRI, the
MT-ID TLV can be carried in the prefix descriptor to identify the
corresponding topology of the SRv6 Locator. The SRv6 End.X SIDs are
carried in the BGP-LS Attribute associated with the link NLRI, the
MT-ID TLV can be carried in the link descriptor to identify the
corresponding topology of the End.X SIDs. The SRv6 SID NLRI is
defined to advertise other types of SRv6 SIDs, in which the SRv6 SID
Descriptors can include the MT-ID TLV so as to advertise topology-
specific SRv6 SIDs.
[RFC7752] also defines the rules of the usage of MT-ID TLV:
"In a Link or Prefix Descriptor, only a single MT-ID TLV containing
the MT-ID of the topology where the link or the prefix is reachable
is allowed. In case one wants to advertise multiple topologies for a
given Link Descriptor or Prefix Descriptor, multiple NLRIs need to be
generated where each NLRI contains an unique MT-ID. In the BGP-LS
attribute of a Node NLRI, one MT-ID TLV containing the array of MT-
IDs of all topologies where the node is reachable is allowed."
Editor's note: the above rules indicates that only one MT-ID is
allowed to be carried the Link or Prefix descriptors. When a link or
prefix participates in multiple topologies, multiple NLRIs needs to
be generated to report all the topologies a link or prefix
participates in, together with the topology-specific segment routing
information. This would increase the number of BGP Updates and may
introduce additional processing burden to both the sending BGP
speaker and the receiving network controller. When the number of
topologies in a network is not a small number, some optimization may
be introduced for the reporting of multi-topology information and the
associated segment routing information in BGP-LS. Based on the WG's
This will be elaborated in a future version.
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2.2. Inter-Domain Topology Advertisement
[I-D.ietf-idr-bgpls-segment-routing-epe] and
[I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions for
advertisement of BGP topology information between ASes and the BGP
Peering Segment Identifiers. Such information could be used by a
network controller for the computation and instantiation of inter-AS
traffic engineering SR paths.
In some network scenarios, there are needs to create VTNs which span
multiple ASes. The inter-domain VTNs could have different inter-
domain connectivity, and may be associated with different set of
network resources in each domain and also on the inter-domain links.
In order to build the multi-domain VTNs using segment routing, it is
necessary to advertise the topology and resource attribute of VTN on
the inter-domain links and the associated BGP Peering SIDs.
Depending on the requirement of inter-domain VTNs, different
mechanism can be used on the inter-domain connection:
o One EBGP session between two ASes can be established over multiple
underlying links. In this case, different underlying links can be
used for different inter-domain VTNs which requires link isolation
between each other. In another similar case, the EBGP session is
established over a single link, while the network resource (e.g.
bandwidth) on this link can be partitioned into several pieces,
each of which can be considered as a virtual member link. In both
cases, different BGP Peer-Adj-SIDs SHOULD be allocated to each
underlying physical or virtual member link, and ASBRs SHOULD
advertise the VTN identifier associated with each BGP Peer-Adj-
SID.
o For inter-domain connection between two ASes, multiple EBGP
sessions can be established between different set of peering
ASBRs. It is possible that some of these BGP sessions are used
for one multi-domain VTN, while some other BGP sessions are used
for another multi-domain VTN. In this case, different BGP peer-
node-SIDs are allocated to each BGP session, and ASBRs SHOULD
advertise the VTN identifier associated with each BGP Peer-node-
SIDs.
o At the AS-level topology, different multi-domain VTNs may have
different inter-domain connectivity. Different BGP Peer-Set-SIDs
can be allocated to represent the groups of BGP peers which can be
used for load-balancing in each multi-domain VTN.
When MT-ID is used consistently in multiple ASes covered by a VTN,
the topology-specific BGP peering SIDs can be advertised with the MT-
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ID carried in the corresponding Link NLRI. This can be achieved with
the existing mechanisms as defined in
[RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and
[I-D.ietf-idr-bgpls-srv6-ext].
In network scenarios where consistent usage of MT-ID among multiple
ASes can not be expected, then a global-significant VTN ID needs to
be introduced to define the AS level topologies. Within each domain,
the MT based mechanism could be used for intra-domain topology
advertisement. The detailed mechanism is specified in
[I-D.dong-idr-bgpls-sr-enhanced-vpn].
3. Advertisement of VTN Resource Attribute
[I-D.xie-lsr-isis-sr-vtn-mt] specifies the mechanism to advertise the
resource information associated with each VTN. This section
describes the corresponding BGP-LS mechanisms. Two optional
approaches are described in the following sections.
3.1. Advertising Topology specific TE attributes
The information of the network resources associated with a VTN can be
specified by carrying the Link TE attribute TLVs [RFC7752] in BGP-LS
Attribute, with the associated MT-ID carried in the corresponding
Link NLRI.
For example, the Maximum Link Bandwidth TLV associated with a MT-ID
could be used to specify the link bandwidth allocated to the
corresponding VTN on a link.
3.2. Associating VTNs with L2 Bundle Member Links
In some network scenarios, the network resources allocated to
different VTNs are instantiated using different physical or virtual
members links of a Layer 3 interface. The TE attributes of each
member link can be advertised using the mechanism described in
[I-D.ietf-idr-bgp-ls-segment-routing-ext] and
[I-D.ietf-idr-bgpls-srv6-ext]. In order to further describe the
association of each VTN with the corresponding Layer 2 member link,
the MT-ID TLV as defined in [RFC7752] SHOULD be carried as a sub-TLV
in the L2 Bundle Member Attribute TLV. In each L2 Bundle member
Attribute TLV, the MT-ID TLV contains only one MT-ID, which describes
the association of a VTN with the corresponding Bundle Member Link
Local Identifier.
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4. Scalability Considerations
The mechanism described in this document requires that each VTN has
an independent topology, and for inter-domain VTNs, the MT-ID used in
each involved domain is consistent. While this brings the benefits
of simplicity, it also has some limitations. For example, it means
that 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 VTNs supported in a
network may be dependent on the number of topologies supported, which
is related to the control plane computation overhead.
5. Security Considerations
This document introduces no additional security vulnerabilities to
BGP-LS.
The mechanism proposed in this document is subject to the same
vulnerabilities as any other protocol that relies on BGP-LS.
6. IANA Considerations
This document does not request any IANA actions.
7. Acknowledgments
The authors would like to thank Shunwan Zhuang 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 Partitioned Virtual
Networks", draft-dong-spring-sr-for-enhanced-vpn-06 (work
in progress), December 2019.
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
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[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link
State Extensions for SRv6", draft-ietf-idr-bgpls-
srv6-ext-02 (work in progress), January 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>.
[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
September 2007, <https://www.rfc-editor.org/info/rfc5029>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[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>.
8.2. Informative References
[I-D.dong-idr-bgpls-sr-enhanced-vpn]
Dong, J. and Z. Hu, "BGP-LS Extensions for Segment Routing
based Enhanced VPN", draft-dong-idr-bgpls-sr-enhanced-
vpn-00 (work in progress), November 2019.
[I-D.dong-lsr-sr-enhanced-vpn]
Dong, J., Hu, Z., and S. Bryant, "IGP Extensions for
Segment Routing based Enhanced VPN", draft-dong-lsr-sr-
enhanced-vpn-02 (work in progress), November 2019.
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[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-06
(work in progress), March 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.
[I-D.xie-lsr-isis-sr-vtn-mt]
Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi-
Topology (MT) for Segment Routing based Virtual Transport
Network", March 2020, <https://tools.ietf.org/html/draft-
xie-lsr-isis-sr-vtn-mt>.
[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>.
[RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
M., and E. Aries, "Advertising Layer 2 Bundle Member Link
Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
December 2019, <https://www.rfc-editor.org/info/rfc8668>.
Authors' Addresses
Chongfeng Xie
China Telecom
China Telecom Beijing Information Science & Technology, Innovation park, Beiqijia
Beijing 102209
China
Email: xiechf@chinatelecom.cn
Cong Li
China Telecom
China Telecom Beijing Information Science & Technology, Innovation park, Beiqijia
Beijing 102209
China
Email: licong@chinatelecom.cn
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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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