Internet DRAFT - draft-dong-teas-enhanced-vpn-vtn-scalability
draft-dong-teas-enhanced-vpn-vtn-scalability
TEAS Working Group J. Dong
Internet-Draft Z. Li
Intended status: Informational Huawei Technologies
Expires: 28 April 2022 L. Gong
China Mobile
G. Yang
China Telecom
J. Guichard
Futurewei Technologies
G. Mishra
Verizon Inc.
F. Qin
China Mobile
25 October 2021
Scalability Considerations for Enhanced VPN (VPN+)
draft-dong-teas-enhanced-vpn-vtn-scalability-04
Abstract
Enhanced VPN (VPN+) aims to meet the needs of some customers or
applications, including the customers and applications that are
associated with 5G, which requires connectivity services with
advanced characteristics, such as the assurance of some Service Level
Objectives (SLOs) and specific Service Level Expectations (SLEs).
VPN+ could be used for network slice realization both in the context
of 5G and in more generic scenarios, such as enterprise services
which have requirement on the performance assurance. With the demand
for VPN+ services increases, scalability would become an important
factor for the large scale deployment of VPN+. This document
describes the scalability considerations about the network control
plane and data plane in enabling VPN+ services, some optimization
mechanisms are also proposed.
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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working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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This Internet-Draft will expire on 28 April 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. VPN+ Scalability Requirements . . . . . . . . . . . . . . . . 4
3. VTN Scalability Considerations . . . . . . . . . . . . . . . 5
3.1. Control Plane Scalability . . . . . . . . . . . . . . . . 6
3.1.1. Distributed Control Plane . . . . . . . . . . . . . . 6
3.1.2. Centralized Control Plane . . . . . . . . . . . . . . 6
3.2. Data Plane Scalability . . . . . . . . . . . . . . . . . 7
3.3. Gap Analysis of Existing Mechanisms . . . . . . . . . . . 8
4. Proposed Scalability Optimizations . . . . . . . . . . . . . 8
4.1. Control Plane Optimizations . . . . . . . . . . . . . . . 9
4.2. Data Plane Optimizations . . . . . . . . . . . . . . . . 11
5. Solution Evolution for Improved Scalability . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
Virtual Private Networks (VPNs) have served the industry well as a
means of providing different customers with logically separated
connectivity services over a common network infrastructure. The
common or base network that is used to provide the VPNs is often
referred to as the underlay, and the VPNs are often called the
overlay. The underlay network is responsible for establishing the
network connectivity and managing the network resources to meet
specific service requirement. The overlay network is used to
distribute the membership and reachability information of the
customers, and provide logical separation in terms of service
delivery between different customers in the shared network.
Enhanced VPN (VPN+) aims to meet the needs of some customers or
applications, including the applications that are associated with 5G,
which requires connectivity services with advanced characteristics,
such as the assurance of Service Level Objectives (SLOs) and specific
Service Level Expectations (SLEs).
[I-D.ietf-teas-ietf-network-slices] defines the terminologies and the
general framework of IETF network slices. VPN+ could be used for
IETF network slice realization both in the context of 5G and in more
generic scenarios, such as enterprise services which have requirement
on the performance assurance.
[I-D.ietf-teas-enhanced-vpn] describes the framework for delivering
VPN+ services. To meet the requirement of some VPN+ services, a
Virtual Transport Networks (VTNs) need to be created, which has a
subset of network resources allocated from the physical network and
is associated with a logical network topology to meet the
requirements of one or a group of VPN+ services. VPN+ services can
be delivered by mapping one or a group of overlay VPNs to the
appropriate VTNs as the virtual underlay.
Section 6 of [I-D.ietf-teas-enhanced-vpn] provides some general
analysis of the scalability of VPN+. This document gives further
analysis of the scalability considerations when a large number of
VPN+ services needs to be provided. Since the scalability of the
overlay is usually not the major bottleneck, this document mainly
focuses on the scalability of the VTNs in the underlay .
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2. VPN+ Scalability Requirements
As described in [I-D.ietf-teas-enhanced-vpn], VPN+ services may
require additional state to be introduced into the network to take
advantage of the enhanced functionality. This may introduces some
concerns about the network scalability. This section gives some
analysis of the number of VPN+ services and the VTNs that might be
needed in different network scenarios.
Since the typical use case of VPN+ is to deliver IETF network slice
[I-D.ietf-teas-ietf-network-slices] for customers and services in 5G
and other scenarios, the number of IETF network slices required could
reflect the number of VPN+ needed in the network. With the
development and evolution of 5G and other services, it is expected
that an increasing number of IETF network slices will be deployed.
The number of network slices required depends on how IETF network
slices will be used, and the progress of network slicing for the
vertical industrial services. The potential number of VPN+ services
and VTNs is analyzed by classifying the network slice deployment into
three typical scenarios:
1. IETF network slices can be used by a network operator for
different types of services. For example, in a converged multi-
service network, different IETF network slices can be created to
carry mobile transport service, fixed broadband service and
enterprise services respectively, each type of service could be
managed by a separate department or management team. Some
service types, such as multicast service may also be deployed in
a dedicated network slice. In this case, a separate VTN may need
to be created for each service type. It is also possible that a
network infrastructure operator provides IETF network slices to
other network operators as a wholesale service, and a VTN may
also be needed for each wholesale service customer. In this
scenario, the number of VTNs in a network could be relatively
small, such as in the order of 10 or so. This could be one of
the typical cases in the beginning of IETF network slice
deployment.
2. IETF network slices can be requested by customers in vertical
industries, where the assurance of SLOs and the fulfilment of
SLEs are quite important. At the early stage of the vertical
industrial services, a few top customers in some industries will
begin to use IETF network slices to provide performance assurance
to their business, such as smart grid, manufacturing, public
safety, on-line gaming, etc. The realization of such IETF
network slices typically requires to provide different VTNs for
different industries, and some top customers can require
dedicated VTNs for strict service performance guarantee.
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Considering the number of vertical industries, and the number of
top customers in each industry, the number of VTNs needed may be
in the order of 100.
3. With the evolution of 5G and cloud networks, IETF network slices
could be widely used by various vertical industrial customers and
enterprise customers who require guaranteed or predictable
service performance. The total amount of IETF network slices may
increase to thousands or more, although it is expected that the
number of IETF network slices would still be less than the number
of traditional VPN services in the network. Accordingly, the
number of VTNs needed may be in the order of 1000.
As defined by 3GPP [TS23501], a 5G network slice is identified using
the Single Network Slice Selection Assistance Information (S-NSSAI),
which is a 32-bit identifier comprised of 8-bit Slice/Service Type
(SST) and 24-bit Slice Differentiator (SD). This allows the mobile
networks (the RAN and mobile core networks) to support a large number
of 5G network slices. Although it is likely that multiple 5G network
slices are mapped to the same IETF network slice, in some cases the
number of IETF network slices may still be comparable to the number
of 5G network slices.
8-bit 24-bit
+------------+-------------------------+
| SST | Slice Differentiator |
+------------+-------------------------+
Figure 1. Format of S-NSSAI in 3GPP
Thus solution of VPN+ and VTN needs to meet the scalability
requirement of IETF network slices in different scenarios. The
increased number of VPN+ services will introduce additional
complexity and overhead both to the control plane and the data plane,
especially in the aspects related to the underlay VTNs. Although in
many cases multiple VPN+ services can be mapped to the same VTN as
the underlay, there still can be scalability challenges with the
increased number of VTNs.
3. VTN Scalability Considerations
In this section, the scalability of VTN in the control plane and data
plane is analyzed to understand the possible gaps in meeting the
scalability requirement of VPN+ and VTN.
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3.1. Control Plane Scalability
As described in [I-D.ietf-teas-enhanced-vpn], the control plane of
VPN+ could be based on the hybrid of a centralized controller and the
distributed control plane.
3.1.1. Distributed Control Plane
At part of the delivery of VPN+ services, it is necessary to create
multiple VTNs, each of which is allocated with a set of dedicated or
shared network resources, and is associated with a customized logical
topology. The topological and resource attributes and the state
information of each VTN may need to be exchanged among the network
nodes. The scalability of the distributed control plane used for the
distribution of VTN information needs to be considered in the
following aspects:
* The number of control protocol instances maintained on each node
* The number of protocol sessions maintained on each link
* The number of routes advertised by each node
* The amount of attributes associated with each route
* The number of route computation (i.e. SPF computation) executed
by each node
As the number of VTNs increases, it is expected that in some of the
above aspects, the overhead in the control plane may increase
dramatically. For example, the overhead of maintaining separated
control protocol instances (e.g. IGP instances) for different VTNs
is considered higher than maintaining the information of separated
VTNs in the same control protocol instance with appropriate
separation, and the overhead of maintaining separate protocol
sessions for different VTNs is considered higher than using a shared
protocol session for the information exchange of multiple VTNs. To
meet the requirement of the increasing number of VTNs, It is
suggested to choose the control plane mechanisms which could improve
the scalability while still provide the required functionality.
3.1.2. Centralized Control Plane
By introducing the centralized network controller, the SDN approach
can reduce the amount of control plane overhead in the distributed
control plane, while it may also transfer some of the scalability
concerns from network nodes to the centralized controller, thus the
scalability of the controller also needs to be considered.
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To provide global optimization for the Traffic Engineered (TE) paths
in different VTNs, the controller needs to keep the topology and
resource information of all the VTNs up-to-date. To achieve this,
the controller may need to maintain a communication channel with each
network node in the network. When there is significant change in the
network, or multiple VTNs requires global optimization concurrently,
there may be a heavy processing burden at the controller, and a heavy
load in the network surrounding the controller for the distribution
of the updated network state and the TE paths.
3.2. Data Plane Scalability
To provide different VPN+ services with the required SLOs and SLEs,
it is necessary to allocate different subsets of network resources to
different VTNs to avoid or reduce unexpected interruption. As the
number of VTNs increases, it is required that the underlying network
can provide fine-granular network resource partitioning, which means
the amount of state about the partitioned network resources to be
maintained on the network nodes will also increase.
In packet forwarding, VPN+ service traffic needs to be processed
separately according to the topology and resource attributes of the
VTN it mapped to, this means that some fields in the data packet
needs to be used to identify the VTN topology and resources either
directly or implicitly. Different approaches of encapsulating the
VTN information in data packet can have different scalability
implications.
One practical approach is to reuse some of the existing fields in the
data packet to additionally identify the VTN the packet belongs to.
For example, the destination IP addresses or the MPLS forwarding
labels may be reused to further identify a VTN. This can avoid the
cost of introducing new fields in the data packet, while since it
introduces additional semantics to the existing fields, the
processing of the existing fields in packet forwarding may need to be
changed. Moreover, introducing VTN semantics to existing identifiers
in the packet (e.g. IP addresses, MPLS forwarding labels, etc.) may
result in the increase of the amount of the existing IDs in
proportion to the number of the VTNs, which may cause scalability
problem in networks where a relatively large number of VTNs is
needed.
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An alternative approach is to introduce a new dedicated field in the
data packet for VTN identification. This could avoid the impacts to
the existing fields in the packet. And if this new field carries a
global-significant VTN identifier, it could be used together with the
existing fields to determine the VTN-specific packet forwarding. The
potential issue with this approach is the difficulty in introducing a
new field in some of the data plane technologies.
In addition, the introduction of per VTN packet forwarding has impact
on the scalability of the forwarding entries on network nodes, as a
network node may need to maintain separate forwarding entries for
each VTN it participates in.
3.3. Gap Analysis of Existing Mechanisms
One candidate mechanism to build VTN is to use VTN-specific Segment
Routing (either SR-MPLS or SRv6) Identifiers in the data plane as
described in [I-D.ietf-spring-sr-for-enhanced-vpn], and define and
distribute the associated topology and resource attribute of each VTN
based on either Multi-topology [I-D.ietf-lsr-isis-sr-vtn-mt], Flex-
Algo [I-D.zhu-lsr-isis-sr-vtn-flexalgo] or the combination of these
mechanisms in the control plane. This mechanism is suitable for
networks where a small number of VTNs is needed. As the number of
VTNs increases, there may be several scalability challenges with this
approach:
1. The number of SR SIDs needed will increase in proportion to the
number of VTNs in the network, which will bring challenges both
to the distribution of SIDs and the related information in the
control plane, and to the installation of forwarding entries for
VTN-specific SIDs in the data plane.
2. The number of route computation (e.g. SPF computation) will
increase in proportion to the number of VTNs in the network,
which may introduce significant overhead to the control plane of
network nodes.
3. The maximum number of logical topologies supported by OSPF is
128, and the maximum number of Flex-Algo is 128, which may not
meet the required number of VTNs in some network scenarios.
4. Proposed Scalability Optimizations
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4.1. Control Plane Optimizations
For the distributed control plane, several optimizations can be
considered to reduce the control plane overhead and improve the
control plane scalability.
The first optimization mechanism is to reduce the amount of control
plane sessions used for the establishment and maintenance of the
VTNs. For multiple VTNs which have the same peering relationship
between two adjacent network nodes, it is proposed that one single
control protocol session is used for the establishment of multiple
VTNs. The information of different VTNs can be exchanged over the
same session, with necessary identification information to
distinguish the VTNs in the control messages. This could reduce the
overhead of maintaining a large number of control protocol sessions
for different VTNs, and could also reduce the amount of control plane
messages flooded in the network.
The second optimization mechanism is to decompose the attributes of a
VTN into different groups, so that different types of VTN attribute
can be advertised and processed separately in control plane. There
are two basic types of attributes associated with a VTN: the topology
attribute and the network resource attribute. In a network, it is
possible that multiple VTNs share the same topology, and multiple
VTNs may share the same set of network resources on particular
network nodes and links. Then it is more efficient if only one copy
of the topology information is advertised, and multiple VTNs sharing
the same topology could refer to this topology information. More
importantly, with this approach, the result of topology-based route
computation could be shared by multiple VTNs, so that the overhead of
per-VTN route computation could also be reduced . Similarly,
information of a subset of network resources reserved on a particular
network node or link could be advertised once and be referred to by
multiple VTNs which share the same set of resources. This
methodology could also apply to other attributes of VTN which may be
introduced later and can be processed independently.
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O#####O#####O O*****O*****O
# # # * * *
# # # * * *
O#####O#####O O*****O*****O
VTN-1 VTN-2
O-----O-----O
| | |
| | |
O-----O-----O
Shared Network Topology
Legend
O Virtual node
### Virtual links with a set of reserved resources
*** Virtual links with another set of reserved resources
Figure 2. Topology Sharing between VTNs
Figure 1: FIG-2
Figure 2 gives an example of two VTNs which share the same logical
topology. As shown in the figure, VTN-1 and VTN-2 are associated
with the same topology, while the resource attributes of each VTN are
different. In this case, only one copy of the network topology
information needs to be advertised, and the topology-based route
computation result can be shared by the two VTNs to generate the
corresponding routing and forwarding tables.
O#####O#####O O----O#####O
# # # \/ # #
# # # /\ # #
O#####O#####O O----O#####O
VTN-1 VTN-2
Legend
O Virtual node
### Virtual links with a set of reserved resource
--- Virtual links with another set of reserved resource
Figure 3. Resource Sharing between VTNs
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Figure 3 gives another example of two VTNs which share the same set
of network resources on some of the links. In this case, information
about the resources allocated on each link only needs to be
advertised once, then both VTN-1 and VTN-2 could refer to the
reserved link resource for constraint based path computation.
For the optimization of the centralized control plane, it is
suggested that the centralized controller is used as a complementary
mechanism to the distributed control plane rather than a replacement,
so that the workload for VTN specific path computation in control
plane could be shared by both the centralized controller and the
network nodes, and the scalability of both systems could be improved.
4.2. Data Plane Optimizations
To support more VPN+ services while keeping the amount of data plane
state at a reasonable scale, one typical approach is to classify a
set of VPN+ services which have similar service characteristics and
performance requirements into a group, and such group of VPN+
services are mapped to one VTN, which is allocated with an aggregated
set of network resources and the union of the required logical
topologies to meet the service requirement of the whole group of VPN+
services. Different groups of VPN+ services can be mapped to
different VTNs with different set of network resources allocated.
With appropriate grouping of VPN+ services, a reasonable number of
VTNs with network resources reservation and aggregation could still
meet the service requirements.
Another optimization in the data plane is to decouple the identifiers
used for topology-based forwarding and the identifier used for the
resource-specific processing introduced by VTN. One possible
mechanism is to introduce a dedicated VTN Resource identifier in the
packet header to uniquely identify the set of local network resources
allocated to a VTN on each network node for the processing and
forwarding of the received packets. Then the existing identifiers in
the packet header used for topology based forwarding (e.g. the
destination IP address, MPLS forwarding labels) are kept unchanged.
The benefit is the amount of the existing topology-specific
identifiers will not be impacted by the increasing number of VTNs.
Since this new VTN Resource ID field will be used together with other
existing fields to determine the VTN-specific packet forwarding, this
may require network nodes to support a hierarchical forwarding table
in data plane. Figure 4 shows the concept of using different data
plane identifiers for topology-specific and resource-specific packet
forwarding and processing in a VTN respectively.
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+--------------------------+
| Packet Header |
| |
| +----------------------+ |
| | Topology-specific IDs| |
| +----------------------+ |
| |
| +----------------------+ |
| | VTN Resource ID | |
| +----------------------+ |
+--------------------------+
Figure 4. Decoupled Data Plane Topology and Resource Identifiers
In an IPv6 [RFC8200] based network, this could be achieved by
introducing a dedicated field in either the IPv6 fixed header or the
extension headers to carry the VTN resource identifier for the
resource-specific forwarding, while keeping the destination IP
address field used for routing towards the destination prefix in the
corresponding topology. Note that the VTN resource ID needs to be
parsed by every node along the path which is capable of VTN-specific
forwarding. [I-D.dong-6man-enhanced-vpn-vtn-id] introduces the
mechanism of carrying the VTN resource ID in IPv6 Hop-by-Hop
extension header.
In an MPLS [RFC3032] based network, this may be achieved by
introducing a dedicated VTN resource ID either in the MPLS label
stack or following the MPLS label stack. This way, the existing MPLS
forwarding labels could be used for topology-specific packet
forwarding towards the destination node, and the VTN resource ID is
used to determine the set of network resources for packet processing.
This requires that both the forwarding label and the VTN Resource ID
be parsed by nodes along the forwarding path of the packet, and the
forwarding behavior may depend on the position of the VTN resource ID
in the packet. The detailed extensions in MPLS data plane are out of
the scope of this document.
5. Solution Evolution for Improved Scalability
Based on the analysis in this document, the control plane and data
plane for VPN+ and VTN needs to evolve to support the increasing
number of VPN+ services and the increasing number of VTNs in the
network.
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At the first step, by introducing resource-awareness to segment
routing SIDs [I-D.ietf-spring-resource-aware-segments], and using
Multi-Topology or Flex-Algo as the control plane, it could provide a
solution for building a limited number of VTNs in the network to meet
the requirement of a relatively small number of VPN+ services in the
network. This mechanism is considered as the basic SR VTN.
As the required number of VPN+ services increases, more VTNs may be
needed, then the control plane scalability could be improved by
decoupling the topology attribute from the resource attribute and
other attributes of VTN, so that multiple VTNs could share the same
topology or resource attribute to reduce the control plane and data
plane overhead. This mechanism is considered as the scalable SR VTN.
Both the basic and the scalable SR VTN mechanisms are described in
[I-D.ietf-spring-sr-for-enhanced-vpn].
If the data plane scalability becomes a concern, a dedicated VTN
resource ID can be introduced in the data packet to decouple the
topology-specific identifiers from the VTN resource identifiers in
the data plane, this could help to reduce the number of SR SIDs
needed to support a large number of VTNs. This mechanism is
considered as the Resource-Independent (RI) VTN.
6. Security Considerations
This document describes the scalability considerations about the
network control plane and data plane in enabling VPN+ services and
the VTNs, and proposes several scalability optimization mechanisms.
The security considerations in [I-D.ietf-teas-enhanced-vpn] applies
to this document.
7. IANA Considerations
This document makes no request of IANA.
8. Contributors
Zhibo Hu
Email: huzhibo@huawei.com
Hongjie Yang
Email: hongjie.yang@huawei.com
9. Acknowledgments
The authors would like to thank Adrian Farrel for the review and
discussion of this document.
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10. References
10.1. Normative References
[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-08, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-teas-enhanced-
vpn-08.txt>.
10.2. Informative References
[I-D.dong-6man-enhanced-vpn-vtn-id]
Dong, J., Li, Z., Xie, C., Ma, C., and G. Mishra,
"Carrying Virtual Transport Network Identifier in IPv6
Extension Header", Work in Progress, Internet-Draft,
draft-dong-6man-enhanced-vpn-vtn-id-05, 8 September 2021,
<https://www.ietf.org/archive/id/draft-dong-6man-enhanced-
vpn-vtn-id-05.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.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-17, 6 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-lsr-flex-algo-
17.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-spring-resource-aware-segments]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Introducing Resource Awareness to SR
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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>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L. M., and J. Tantsura,
"Framework for IETF Network Slices", Work in Progress,
Internet-Draft, draft-ietf-teas-ietf-network-slices-04, 23
August 2021, <https://www.ietf.org/archive/id/draft-ietf-
teas-ietf-network-slices-04.txt>.
[I-D.zhu-lsr-isis-sr-vtn-flexalgo]
Zhu, Y., Dong, J., and Z. Hu, "Using Flex-Algo for Segment
Routing based VTN", Work in Progress, Internet-Draft,
draft-zhu-lsr-isis-sr-vtn-flexalgo-03, 11 July 2021,
<https://www.ietf.org/archive/id/draft-zhu-lsr-isis-sr-
vtn-flexalgo-03.txt>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
Dong, et al. Expires 28 April 2022 [Page 15]
Internet-Draft VPN+ Scalability October 2021
[TS23501] "3GPP TS23.501", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
Authors' Addresses
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
Liyan Gong
China Mobile
No. 32 Xuanwumenxi Ave., Xicheng District
Beijing
China
Email: gongliyan@chinamobile.com
Guangming Yang
China Telecom
No.109 West Zhongshan Ave., Tianhe District
Guangzhou
China
Email: yangguangm@chinatelecom.cn
Dong, et al. Expires 28 April 2022 [Page 16]
Internet-Draft VPN+ Scalability October 2021
James N Guichard
Futurewei Technologies
2330 Central Express Way
Santa Clara,
United States of America
Email: james.n.guichard@futurewei.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Fengwei Qin
China Mobile
No. 32 Xuanwumenxi Ave., Xicheng District
Beijing
China
Email: qinfengwei@chinamobile.com
Dong, et al. Expires 28 April 2022 [Page 17]
