IDR Working Group J. Dong
Internet-Draft Z. Hu
Intended status: Standards Track Z. Li
Expires: August 26, 2021 Huawei Technologies
X. Tang
R. Pang
China Unicom
February 22, 2021
BGP-LS Extensions for Segment Routing based Enhanced VPN
draft-dong-idr-bgpls-sr-enhanced-vpn-03
Abstract
Enhanced VPN (VPN+) aims to provide enhanced VPN services to support
some applications' needs of enhanced isolation and stringent
performance requirements. VPN+ requires integration between the
overlay VPN connectivity and the characteristics provided by the
underlay network. A Virtual Transport Network (VTN) is a virtual
underlay network which consists of a customized network topology and
a set of network resource allocated from the physical network. A VTN
could be used as the underlay to support one or a group of VPN+
services.
This document specifies the BGP-LS mechanisms with necessary
extensions to advertise the information of Segment Routing (SR) based
VTNs to a centralized network controller. Each VTN can have a
customized topology and a set of network resources allocated.
Multiple VTNs may shared the same topology, and multiple VTNs may
share the same set of network resources on some network segments.
This allows flexible combination of network topology and network
resource attributes to build a large number of VTNs with a relatively
small number of logical topologies. The proposed mechanism is
applicable to both segment routing with MPLS data plane (SR-MPLS) and
segment routing with IPv6 data plane (SRv6).
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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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
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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 August 26, 2021.
Copyright Notice
Copyright (c) 2021 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Advertisement of VTN Definition . . . . . . . . . . . . . . . 4
3. Advertisement of VTN Topology Attribute . . . . . . . . . . . 5
3.1. Intra-domain Topology Advertisement . . . . . . . . . . . 5
3.1.1. MTR based Topology Advertisement . . . . . . . . . . 6
3.1.2. Flex-Algo based Topology Advertisement . . . . . . . 7
3.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 7
3.2.1. VTN ID TLV . . . . . . . . . . . . . . . . . . . . . 9
4. Advertisement of VTN Resource Attribute . . . . . . . . . . . 10
4.1. Link Attribute Flags TLV . . . . . . . . . . . . . . . . 10
5. Advertisement of VTN specific Data Plane Identifiers . . . . 11
5.1. VTN-specific SR-MPLS SIDs . . . . . . . . . . . . . . . . 11
5.1.1. VTN-specific Prefix-SID TLV . . . . . . . . . . . . . 11
5.1.2. VTN-specific Adj-SID TLV . . . . . . . . . . . . . . 12
5.2. VTN-specific SRv6 Locators . . . . . . . . . . . . . . . 13
5.3. Dedicated VTN ID in Data Plane . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
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9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Enhanced VPN (VPN+) is an enhancement to VPN services to support the
needs of new applications, particularly 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
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 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
underlay networks 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. Such a virtual underlay network is called Virtual
Transport Network (VTN) in [I-D.ietf-teas-enhanced-vpn].
[I-D.ietf-spring-resource-aware-segments] introduces resource-
awareness to Segment Routing (SR) [RFC8402] by associating existing
type of SIDs with network resource attributes (e.g. bandwidth,
processing or storage resources). These resource-aware SIDs retain
their original functionality, with the additional semantics of
identifying the set of network resources available for the packet
processing action. [I-D.ietf-spring-sr-for-enhanced-vpn] describes
the use of resource-aware segments to build SR based VTNs. 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 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.
This document describes BGP-LS [RFC7752] based mechanism with
necessary extensions to advertise the topology and resource attribute
of inter-area and inter-domain SR based VTNs. Each VTN can have a
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customized topology and a set of network resources allocated.
Multiple VTNs may shared the same topology, and multiple VTNs may
share the same set of network resources on some network segments.
This allows flexible combination of network topology and network
resource attributes to build a large number of VTNs with a relatively
small number of logical topologies. The definition of VTN is
advertised as a node attribute using BGP-LS. The associated network
topology and resources attributes of a VTN are advertised as link
attributes using BGP-LS.
2. Advertisement of VTN Definition
According to [I-D.ietf-teas-enhanced-vpn], a VTN has a customized
network topology and a set of dedicated or shared network resources.
Thus a VTN can be defined as the combination of a set of network
attributes, which include the topology attribute and other
attributes, such as the associated network resources.
The Virtual Transport Network Definition (VTND) TLV is a new TLV of
the optional BGP-LS Attribute which is associated with the node NLRI.
The format of VTND TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | Algorithm | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs |
~ ... ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: the length of the value field of the TLV. It is variable
dependent on the included Sub-TLVs.
o VTN ID: A global significant 32-bit identifier which is used to
identify a virtual transport network.
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o MT-ID: 16-bit identifier which indicates the multi-topology
identifier of the IGP topology.
o Algorithm: 8-bit identifier which indicates the algorithm which
applies to this virtual transport network. It can be either a
normal algorithm in [RFC8402] or a Flex-Algorithm
[I-D.ietf-lsr-flex-algo].
o Flags: 8-bit flags. Currently all the flags are reserved for
future use. They SHOULD be set to zero on transmission and MUST
be ignored on receipt.
o Sub-TLVs: optional sub-TLVs to specify the additional attributes
of a virtual transport network. Currently no sub-TLV is defined
in this document.
3. Advertisement of VTN Topology Attribute
[I-D.dong-lsr-sr-enhanced-vpn] describes the IGP mechanisms to
distribute the topology attributes of SR based VTNs. This section
describes the BGP-LS mechanism to distribute both the intra-domain
and inter-domain topology attributes of SR based VTNs.
3.1. Intra-domain Topology Advertisement
The intra-domain topology attribute of a VTN can be determined by the
MT-ID and/or the algorithm ID included in the VTN definition. In
practice, it could be described using two optional approaches.
The first approach is to use Multi-Topology Routing (MTR) [RFC4915]
[RFC5120] with the segment routing extensions to advertise the
topology associated with the SR based VTNs. Different algorithms MAY
be used to further specify the computation algorithm or the metric
type used for path computation within the topology. Multiple VTNs
can be associated with the same <topology, algorithm>, and the IGP
computation with the <topology, algorithm> tuple can be shared by
these VTNs.
The second approach is to use Flex-Algo [I-D.ietf-lsr-flex-algo] to
describe the topological constraints of SR based VTNs on a shared
network topology (e.g. the default topology). Multiple VTNs can be
associated with the same Flex-Algo, and the IGP computation with this
Flex-Algo can be shared.
This section describes the two optional approaches to advertise the
intra-domain topology of a VTN using BGP-LS.
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3.1.1. MTR based 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 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 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 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.
[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."
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
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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 will be elaborated in a future version.
3.1.2. Flex-Algo based Topology Advertisement
The Flex-Algo definition [I-D.ietf-lsr-flex-algo] can be used to
describe the calculation-type, the metric-type and the topological
constraints for path computation on a network topology. As specified
in [I-D.dong-lsr-sr-enhanced-vpn], the topology of a VTN can be
determined by applying Flex-Algo constraints on a particular
topology.
BGP-LS extensions for Flex-Algo [I-D.ietf-idr-bgp-ls-flex-algo]
provide the mechanisms to advertise the Flex-Algo definition
information. BGP-LS extensions for SR-MPLS
[I-D.ietf-idr-bgp-ls-segment-routing-ext] and SRv6
[I-D.ietf-idr-bgpls-srv6-ext] provide the mechanism to advertise the
algorithm-specific segment routing information.
In[I-D.ietf-idr-bgp-ls-segment-routing-ext], algorithm-specific
prefix-SIDs can be advertised in BGP-LS attribute associated with
Prefix NLRI. In [I-D.ietf-idr-bgpls-srv6-ext], algorithm-specific
SRv6 Locators can be advertised in BGP-LS Attribute associated with
the corresponding Prefix NLRI, and algorithm-specific End.X SID can
be advertised in BGP-LS Attribute associated with the corresponding
Link NLRI. Other types of SRv6 SIDs can also be algorithm-specific
and are advertised using the SRv6 SID NLRI.
3.2. Inter-Domain Topology Advertisement
In some network scenarios, a VTNs which span multiple areas or ASes
needs to be created. The multi-domain VTN 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.
[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
associated 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.
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Depending on the network scenarios and the requirement of inter-
domain VTNs, different mechanisms can be used to specify the inter-
domain connections of VTNs.
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.
In network scenarios where the MT-ID or Flex-Algo is used
consistently in multiple areas or ASes covered by a VTN. the
approaches to advertise topology-specific BGP peering SIDs are
described as below:
o Using MT-based mechanism, the topology-specific BGP peering SIDs
can be advertised with the MT-ID associated with the VTN carried
in the corresponding link NLRI. This can be supported with the
existing mechanisms defined in
[RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and
[I-D.ietf-idr-bgpls-srv6-ext].
o Using Flex-Algo based mechanism, the topology-specific BGP peering
SIDs can be advertised together with the Admin Group (color) of
the corresponding Flex-Algo in the BGP-LS attribute.
In network scenarios where consistent usage of MT-ID or Flex-Algo
among multiple ASes can not be expected, then the global-significant
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VTN-ID can be used to define the AS level topologies. Within each
domain, the MT or Flex-Algo based mechanism could still be used for
topology advertisement.
3.2.1. VTN ID TLV
A new VTN ID TLV is defined to describe the identifiers of one or
more VTNs an intra-domain or inter-domain link belongs to. It can be
carried in BGP-LS attribute which is associated with a Link NLRI, or
it could be carried as a sub-TLV in the L2 Bundle Member Attribute
TLV.
The format of VTN ID TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID-1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID-n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: The length of the value field of the sub-TLV. It is
variable dependent on the number of VTN IDs included.
o Flags: 16 bit flags. All the bits are reserved, which MUST be set
to 0 on transmission and ignored on receipt.
o Reserved: this field is reserved for future use. MUST be set to 0
on transmission and ignored on receipt.
o VTN IDs: One or more 32-bit identifiers to specify the VTNs this
link or member link belongs to.
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4. Advertisement of VTN Resource Attribute
[I-D.dong-lsr-sr-enhanced-vpn] specifies the mechanism to advertise
the resource information associated with each VTN. It is based on
the extensions to the advertisement of L2 bundle member links
information[RFC8668]. This section defines the corresponding BGP-LS
extensions. Two new TLVs are defined to carry the VTN ID and the
link attribute flags of either a Layer-3 link or the L2 bundle member
links. The VTN ID TLV is defined in section 3.2.1 of this document,
and a new Link Attribute Flags TLV is defined in this section. The
TE attributes of each Layer 3 link or the L2 bundle member link, such
as the bandwidth and the SR SIDs, can be advertised using the
mechanism as defined in [I-D.ietf-idr-bgp-ls-segment-routing-ext][I-D
.ietf-idr-bgpls-segment-routing-epe] and
[I-D.ietf-idr-bgpls-srv6-ext].
4.1. Link Attribute Flags TLV
A new Link attribute Flags TLV is defined to specify the
characteristics of a link. It can be carried in BGP-LS attribute
which is associated with a Link NLRI, or it could be carried as a
sub-TLV in the L2 Bundle Member Attribute TLV. The format of the
sub-TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD
Length: 4 octets.
Flags: 16-bit flags. This field is consistent with the Flag field
in IS-IS Link Attribute sub-TLV in [RFC5029]. In addition to the
flags defined in [RFC5029], A new Flag V is defined in this
document. When the V flag is set, it indicates this link is a
virtual link.
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5. Advertisement of VTN specific Data Plane Identifiers
In network scenarios where each VTN is associated with an independent
network topology or Flex-Algo, the topology or Flex-Algo specific
SIDs or Locators could be used as the identifier of the VTN in data
plane. In network scenarios where multiple VTNs share the same
topology or Flex-Algo, additional data plane identifiers would be
needed to identify different VTNs.
This section describes the mechanisms to advertise the VTN
identifiers with different data plane encapsulations.
5.1. VTN-specific SR-MPLS SIDs
With SR-MPLS data plane, the VTN identification information is
implicitly carried in the SR SIDs of the corresponding VTN. Each
node SHOULD allocate VTN-specific Prefix-SIDs for each VTN it
participates in. Similarly, VTN-specific Adj-SIDs MAY be allocated
for each link which participates in the VTN.
5.1.1. VTN-specific Prefix-SID TLV
A new VTN-specific Prefix-SID TLV is defined to advertise the prefix-
SID and its associated VTN. It is derived from VTN specific Prefix-
SID sub-TLV of IS-IS [I-D.dong-lsr-sr-enhanced-vpn]. The format of
the sub-TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label(Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: The length of the value field of the sub-TLV. It is
variable dependent on the length of the SID/Index/Label field.
o Flags: 16-bit flags. The high-order 8 bits are the same as in the
Prefix-SID sub-TLV defined in [RFC8667]. The lower-order 8 bits
are reserved for future use, which SHOULD be set to 0 on
transmission and MUST be ignored on receipt.
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o VTN ID: A 32-bit local identifier to identify the VTN this prefix-
SID associates with.
o SID/Index/Label: The same as defined in [RFC8667].
One or more of VTN-specific Prefix-SID TLVs MAY be carried in BGP-LS
attribute of the associated Prefix NLRI. The MT-ID in the Prefix
descriptors SHOULD be the same as the MT-ID in the definition of
these VTNs.
5.1.2. VTN-specific Adj-SID TLV
A new VTN-specific Adj-SID TLV is defined to advertise the Adj-SID
and its associated VTN. It is derived from VTN specific Adj-SID sub-
TLV of IS-IS [I-D.dong-lsr-sr-enhanced-vpn]. The format of the sub-
TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label(Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: The length of the value field of the sub-TLV. It is
variable dependent on the length of the SID/Index/Label field.
o Flags: 16-bit flags. The high-order 8 bits are the same as in the
Adj-SID sub-TLV defined in [RFC8667]. The lower-order 8 bits are
reserved for future use, which SHOULD be set to 0 on transmission
and MUST be ignored on receipt.
o VTN ID: A 32-bit local identifier to identify the VTN this Adj-SID
associates with.
o SID/Index/Label: The same as defined in [RFC8667].
Multiple VTN-specific Adj-SID TLVs MAY be carried in BGP-LS attribute
of the associated Link NLRI. The MT-ID in the Link descriptors
SHOULD be the same as the MT-ID in the definition of these VTNs.
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5.2. VTN-specific SRv6 Locators
With SRv6 data plane, the VTN identification information can be
implicitly or explicitly carried in the SRv6 Locator of the
corresponding VTN, this is to ensure that all network nodes
(including both the SRv6 End nodes and Transit nodes) can identify
the VTN to which a packet belongs to. Network nodes SHOULD allocate
VTN-specific Locators for each VTN it participates in. The VTN-
specific Locators are used as the covering prefix of VTN-specific
SRv6 End SIDs, End.X SIDs and other types of SIDs.
Each VTN-specific SRv6 Locator MAY be advertised in a separate Prefix
NLRI. If multiple VTNs share the same topology/algorithm, the
topology/algorithm specific Locator is the covering prefix of a group
of VTN-specific Locators. Then the advertisement of VTN-specific
locators can be optimized to reduce the amount of information
advertised in the control plane.
A new VTN locator-block sub-TLV under the SRv6 Locator TLV is defined
to advertise a set of sub-blocks which follows the topology/algorithm
specific Locator. Each VTN locator-block value is assigned to one of
the VTNs which share the same topology/algorithm.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of VTNs| Block Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Locator Block Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VTN ID #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Locator Block Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: The length of the value field of the sub-TLV. It is
variable dependent on the number of VTNs and the Block Length.
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o Number of VTNs: The number of VTNs which share the same topology/
algorithm specific Locator as the covering prefix.
o Block Length: The length of the VTN locator-block which follows
the length of the topology/algorithm specific Locator.
o VTN ID: A 32-bit identifier to identify the VTN the locator-block
is associates with.
o Block Value: The value of the VTN locator-block for each VTN.
With the VTN locator-block sub-TLV, the VTN-specific Locator can be
obtained by concatenating the topology/algorithm specific locator and
the locator-block value advertised for the VTN.
5.3. Dedicated VTN ID in Data Plane
As the number of VTNs increases, with the mechanism described in
[I-D.ietf-spring-sr-for-enhanced-vpn], the number of SR SIDs and SRv6
Locators allocated for different VTNs would also increase. In
network scenarios where the number of SIDs or Locators becomes a
concern, some data plane optimization may be needed to reduce the
amount of SR SIDs and Locators allocated. As described in
[I-D.dong-teas-enhanced-vpn-vtn-scalability], one approach is to
decouple the data plane identifiers used for topology based
forwarding and the identifiers used for the VTN-specific processing.
Thus a dedicated data plane VTN-ID could be introduced and
encapsulated in the packet. One possible encapsulation of VTN-ID in
IPv6 data plane is proposed in [I-D.dong-6man-enhanced-vpn-vtn-id].
One possible encapsulation of VTN-ID in MPLS data plane is proposed
in [I-D.li-mpls-enhanced-vpn-vtn-id].
In that case, the VTN ID encapsulated in data plane can be the same
value as the VTN ID in the control plane, so that the overhead of
advertising the mapping between the VTN IDs in the control plane and
the corresponding data plane identifiers could be saved.
6. 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.
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7. IANA Considerations
TBD
8. Acknowledgments
The authors would like to thank Shunwan Zhuang and Zhenbin Li for the
review and discussion of this document.
9. References
9.1. Normative References
[I-D.ietf-idr-bgp-ls-flex-algo]
Talaulikar, K., Psenak, P., Zandi, S., and G. Dawra,
"Flexible Algorithm Definition Advertisement with BGP
Link-State", draft-ietf-idr-bgp-ls-flex-algo-05 (work in
progress), November 2020.
[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.
[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-05 (work in progress), November 2020.
[I-D.ietf-idr-rfc7752bis]
Talaulikar, K., "Distribution of Link-State and Traffic
Engineering Information Using BGP", draft-ietf-idr-
rfc7752bis-05 (work in progress), November 2020.
[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", draft-ietf-spring-resource-aware-segments-01
(work in progress), January 2021.
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[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", February 2021,
<https://tools.ietf.org/html/draft-ietf-spring-sr-for-
enhanced-vpn>.
[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>.
9.2. Informative References
[I-D.dong-6man-enhanced-vpn-vtn-id]
Dong, J., Li, Z., Xie, C., and C. Ma, "Carrying Virtual
Transport Network Identifier in IPv6 Extension Header",
draft-dong-6man-enhanced-vpn-vtn-id-02 (work in progress),
November 2020.
[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.dong-teas-enhanced-vpn-vtn-scalability]
Dong, J., Li, Z., Qin, F., and G. Yang, "Scalability
Considerations for Enhanced VPN (VPN+)", draft-dong-teas-
enhanced-vpn-vtn-scalability-01 (work in progress),
November 2020.
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[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-13 (work in progress), October 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-11
(work in progress), October 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+)
Service", draft-ietf-teas-enhanced-vpn-06 (work in
progress), July 2020.
[I-D.li-mpls-enhanced-vpn-vtn-id]
Li, Z. and J. Dong, "Carrying Virtual Transport Network
Identifier in MPLS Packet", February 2021,
<https://tools.ietf.org/html/draft-li-mpls-enhanced-vpn-
vtn-id>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[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>.
[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>.
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Authors' Addresses
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
Zhibo Hu
Huawei Technologies
Email: huzhibo@huawei.com
Zhenbin Li
Huawei Technologies
Email: lizhenbin@huawei.com
Xiongyan Tang
China Unicom
Email: tangxy@chinaunicom.cn
Ran Pang
China Unicom
Email: pangran@chinaunicom.cn
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