Internet DRAFT - draft-xie-idr-bgpls-sr-vtn-mt
draft-xie-idr-bgpls-sr-vtn-mt
IDR Working Group C. Xie
Internet-Draft C. Li
Intended status: Informational China Telecom
Expires: 13 July 2022 J. Dong
Z. Li
Huawei Technologies
9 January 2022
BGP-LS with Multi-topology for Segment Routing based Virtual Transport
Networks
draft-xie-idr-bgpls-sr-vtn-mt-04
Abstract
Enhanced VPN (VPN+) aims to provide enhanced VPN service to support
some applications' 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 underlay network which consists of a subset of the
network topology and network resources allocated from the physical
network. A VTN could be used as the underlay for one or a group of
VPN+ services.
When Segment Routing is used as the data plane of VTNs, each VTN can
be allocated with a group of Segment Identifiers (SIDs) to identify
the topology and resource attributes of network segments in the VTN.
The association between the network topology, the network resource
attributes and the SR SIDs may need to be distributed to a
centralized network controller. For network scenarios where each VTN
can be associated with a unique logical network topology, this
document describes a 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.
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Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 13 July 2022.
Copyright Notice
Copyright (c) 2022 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Advertisement of SR VTN Topology Attribute . . . . . . . . . 4
2.1. Intra-domain Topology Advertisement . . . . . . . . . . . 4
2.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 5
3. Advertisement of SR VTN Resource Attribute . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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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. Thus these
properties require integration between the overlay connectivity and
the characteristics provided by the underlay 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 can be used for 5G
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 consists of a
subset of the underlay network topology and a subset of network
resources allocated from the underlay network to meet the requirement
of one or a group of VPN+ services.
[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 segments can be used to build SR based VTNs with the required
network topology and network resource attributes to support enhanced
VPN services.
To allow the network controller and network nodes to perform VTN-
specific explicit path computation and/or shortest path computation,
the group of resource-aware SIDs allocated by network nodes to each
VTN and the associated topology and resource attributes need to be
distributed in the control plane. When a centralized network
controller is used for VTN-specific path computation, especially 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 view of inter-area or inter-AS SR
VTNs.
In some network scenarios, each VTN can be associated with a unique
logical network topology, [I-D.ietf-lsr-isis-sr-vtn-mt] describes an
IGP mechanism to advertise the association between the topology,
resource attributes and the SR SIDs for each VTN. This document
describes a mechanism to distribute the information of SR based VTNs
to the network controller using BGP-LS with Multi-Topology.
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2. Advertisement of SR VTN Topology Attribute
[I-D.ietf-lsr-isis-sr-vtn-mt] describes the IS-IS Multi-topology
based 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 4.2.2.1 of [I-D.ietf-idr-rfc7752bis], 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.
[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 Multi-Topology 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 or 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 Multi-Topology 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.
[I-D.ietf-idr-rfc7752bis] 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 MUST be
generated where each NLRI contains a single unique MT-ID."
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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 needs to be advertised in multiple topologies, multiple NLRIs
needs to be generated to report all the topologies the link or prefix
participates in, together with the topology-specific segment routing
information and link attributes. This may increase the number of BGP
Updates needed for advertising MT-specific topology attributes, 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 needed for the reporting of multi-topology information and the
associated segment routing information in BGP-LS. Based on the WG's
opinion, this may be elaborated in a future version.
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 inter-domain topology information and the BGP
Egress 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 SR based VTNs, it is necessary to
advertise the topology and resource attribute of each VTN and the
associated BGP Peering SIDs on the inter-domain links.
Depending on the requirement of inter-domain VTNs, different
mechanism can be used on the inter-domain connection:
* 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. A VTN
is associated with one of the physical or virtual member links.
In both cases, different BGP Peer-Adj-SIDs or SRv6 End.X SID
SHOULD be allocated to each underlying physical or virtual member
link, the association between the BGP Peer Adj-SID/End.X SID and
the identifier of the VTN SHOULD be advertised by the ASBR.
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* 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 are advertised
using the mechanism in [I-D.ietf-idr-bgpls-segment-routing-epe]
and [I-D.ietf-idr-bgpls-srv6-ext], the association between the BGP
Peer Node SIDs and the identifier of the VTN SHOULD be advertised
by the ASBR.
* At the AS-level topology, different multi-domain VTNs may have
different inter-domain connectivity. Different BGP Peer Set SIDs
MAY 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-
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
domains can not be expected, a global-significant VTN-ID needs to be
introduced to define the inter-domain topologies. Within each
domain, the MT based mechanism could be reused for intra-domain
topology advertisement. The detailed mechanism is specified in
[I-D.dong-idr-bgpls-sr-enhanced-vpn].
3. Advertisement of SR VTN Resource Attribute
[I-D.ietf-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.
The information of the network resources associated with a VTN can be
specified by carrying the TE Link attribute TLVs in BGP-LS Attribute
[RFC7752], with the associated MT-ID carried in the corresponding
Link NLRI.
When Maximum Link Bandwidth sub-TLV is carried in the BGP-LS
attribute associated with the Link NLRI of a VTN, it indicates the
amount of link bandwidth resource allocated to the corresponding VTN
on the link. The bandwidth allocated to a VTN can be exclusive for
traffic in the corresponding VTN. The advertisement of other TE
attributes in BGP-LS for each VTN is for further study.
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4. Scalability Considerations
The mechanism described in this document requires that each VTN
mapped to an independent topology, and for the inter-domain VTNs, the
MT-IDs used in each involved domain need to be consistent. Reusing
MT-IDs as the identifier of VTN can avoid introducing new identifiers
in the control plane, while it also has some limitations. For
example, when multiple VTNs shares the same topology, each VTN still
need to be identified using different MT-IDs in the control plane,
thus independent path computation needs be executed for each VTN.
The number of VTNs supported in a network may be dependent on the
number of topologies supported, which is related to the control plane
overhead. The mechanism described in this document is applicable to
network scenarios where the number of required VTN is relatively
small. A detailed analysis about the VTN scalability and the
possible optimizations for supporting a large number of VTNs is
described in [I-D.dong-teas-enhanced-vpn-vtn-scalability].
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.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "Border Gateway Protocol - Link State (BGP-
LS) Extensions for Segment Routing", Work in Progress,
Internet-Draft, draft-ietf-idr-bgp-ls-segment-routing-ext-
18, 15 April 2021, <https://www.ietf.org/archive/id/draft-
ietf-idr-bgp-ls-segment-routing-ext-18.txt>.
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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, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing BGP Egress Peer
Engineering", Work in Progress, Internet-Draft, draft-
ietf-idr-bgpls-segment-routing-epe-19, 16 May 2019,
<https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-
segment-routing-epe-19.txt>.
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
Bernier, D., and B. Decraene, "BGP Link State Extensions
for SRv6", Work in Progress, Internet-Draft, draft-ietf-
idr-bgpls-srv6-ext-09, 10 November 2021,
<https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-
srv6-ext-09.txt>.
[I-D.ietf-idr-rfc7752bis]
Talaulikar, K., "Distribution of Link-State and Traffic
Engineering Information Using BGP", Work in Progress,
Internet-Draft, draft-ietf-idr-rfc7752bis-10, 10 November
2021, <https://www.ietf.org/archive/id/draft-ietf-idr-
rfc7752bis-10.txt>.
[I-D.ietf-spring-resource-aware-segments]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Introducing Resource Awareness to SR
Segments", Work in Progress, Internet-Draft, draft-ietf-
spring-resource-aware-segments-03, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-spring-
resource-aware-segments-03.txt>.
[I-D.ietf-spring-sr-for-enhanced-vpn]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Segment Routing based Virtual Transport
Network (VTN) for Enhanced VPN", Work in Progress,
Internet-Draft, draft-ietf-spring-sr-for-enhanced-vpn-01,
12 July 2021, <https://www.ietf.org/archive/id/draft-ietf-
spring-sr-for-enhanced-vpn-01.txt>.
[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>.
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[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., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS
Extensions for Segment Routing based Enhanced VPN", Work
in Progress, Internet-Draft, draft-dong-idr-bgpls-sr-
enhanced-vpn-03, 22 February 2021,
<https://www.ietf.org/archive/id/draft-dong-idr-bgpls-sr-
enhanced-vpn-03.txt>.
[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 Scalable Segment
Routing based Enhanced VPN", Work in Progress, Internet-
Draft, draft-dong-lsr-sr-enhanced-vpn-06, 11 July 2021,
<https://www.ietf.org/archive/id/draft-dong-lsr-sr-
enhanced-vpn-06.txt>.
[I-D.dong-teas-enhanced-vpn-vtn-scalability]
Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N.,
Mishra, G., and F. Qin, "Scalability Considerations for
Enhanced VPN (VPN+)", Work in Progress, Internet-Draft,
draft-dong-teas-enhanced-vpn-vtn-scalability-04, 25
October 2021, <https://www.ietf.org/archive/id/draft-dong-
teas-enhanced-vpn-vtn-scalability-04.txt>.
[I-D.ietf-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", Work in Progress, Internet-Draft, draft-ietf-
lsr-isis-sr-vtn-mt-01, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-lsr-isis-sr-
vtn-mt-01.txt>.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Segment Routing over
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IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
ietf-lsr-isis-srv6-extensions-18, 20 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-lsr-isis-srv6-
extensions-18.txt>.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Network (VPN+)
Services", Work in Progress, Internet-Draft, draft-ietf-
teas-enhanced-vpn-09, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-teas-enhanced-
vpn-09.txt>.
[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>.
[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>.
Authors' Addresses
Chongfeng Xie
China Telecom
China Telecom Beijing Information Science & Technology, Beiqijia
Beijing
102209
China
Email: xiechf@chinatelecom.cn
Cong Li
China Telecom
China Telecom Beijing Information Science & Technology, 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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