A Framework for Enhanced Virtual Private Network (VPN+) Services
draft-ietf-teas-enhanced-vpn-08
The information below is for an old version of the document.
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| Authors | Jie Dong , Stewart Bryant , Zhenqiang Li , Takuya Miyasaka , Young Lee | ||
| Last updated | 2021-07-12 (Latest revision 2021-02-09) | ||
| Replaces | draft-dong-teas-enhanced-vpn | ||
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draft-ietf-teas-enhanced-vpn-08
TEAS Working Group J. Dong
Internet-Draft Huawei
Intended status: Informational S. Bryant
Expires: January 13, 2022 Futurewei
Z. Li
China Mobile
T. Miyasaka
KDDI Corporation
Y. Lee
Samsung
July 12, 2021
A Framework for Enhanced Virtual Private Network (VPN+) Services
draft-ietf-teas-enhanced-vpn-08
Abstract
This document describes the framework for Enhanced Virtual Private
Network (VPN+) services. The purpose of enhanced VPNs is to support
the needs of new applications, particularly applications that are
associated with 5G services, by utilizing an approach that is based
on existing VPN and Traffic Engineering (TE) technologies and adds
characteristics that specific services require over and above those
provided by traditional VPNs.
Typically, VPN+ will be used to underpin network slicing, but could
also be of use in its own right providing enhanced connectivity
services between customer sites.
It is envisaged that enhanced VPNs will be delivered using a
combination of existing, modified, and new networking technologies.
This document provides an overview of relevant technologies and
identifies some areas for potential new work.
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 January 13, 2022.
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
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of the Requirements . . . . . . . . . . . . . . . . 6
3.1. Performance Guarantees . . . . . . . . . . . . . . . . . 6
3.2. Isolation between Enhanced VPN Services . . . . . . . . . 8
3.2.1. A Pragmatic Approach to Isolation . . . . . . . . . . 10
3.3. Integration . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.1. Abstraction . . . . . . . . . . . . . . . . . . . . . 11
3.4. Dynamic Changes . . . . . . . . . . . . . . . . . . . . . 11
3.5. Customized Control . . . . . . . . . . . . . . . . . . . 12
3.6. Applicability . . . . . . . . . . . . . . . . . . . . . . 12
3.7. Inter-Domain and Inter-Layer Network . . . . . . . . . . 13
4. Architecture of Enhanced VPNs . . . . . . . . . . . . . . . . 13
4.1. Layered Architecture . . . . . . . . . . . . . . . . . . 15
4.2. Multi-Point to Multi-Point (MP2MP) Connectivity . . . . . 17
4.3. Application Specific Data Types . . . . . . . . . . . . . 17
4.4. Scaling Considerations . . . . . . . . . . . . . . . . . 18
5. Candidate Technologies . . . . . . . . . . . . . . . . . . . 18
5.1. Packet Forwarding Plane Technologies . . . . . . . . . . 19
5.1.1. Flexible Ethernet . . . . . . . . . . . . . . . . . . 19
5.1.2. Dedicated Queues . . . . . . . . . . . . . . . . . . 19
5.1.3. Time Sensitive Networking . . . . . . . . . . . . . . 20
5.2. Layer Three Data Plane . . . . . . . . . . . . . . . . . 20
5.2.1. Deterministic Networking . . . . . . . . . . . . . . 20
5.2.2. MPLS Traffic Engineering (MPLS-TE) . . . . . . . . . 21
5.2.3. Segment Routing . . . . . . . . . . . . . . . . . . . 21
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5.3. Non-Packet Data Plane . . . . . . . . . . . . . . . . . . 22
5.4. Control Plane . . . . . . . . . . . . . . . . . . . . . . 22
5.5. Management Plane . . . . . . . . . . . . . . . . . . . . 23
5.6. Applicability of Service Data Models to Enhanced VPN . . 24
5.6.1. An Example of Enhanced VPN Delivery . . . . . . . . . 25
6. Scalability Considerations . . . . . . . . . . . . . . . . . 25
6.1. Maximum Stack Depth of SR . . . . . . . . . . . . . . . . 26
6.2. RSVP-TE Scalability . . . . . . . . . . . . . . . . . . . 27
6.3. SDN Scaling . . . . . . . . . . . . . . . . . . . . . . . 27
7. OAM Considerations . . . . . . . . . . . . . . . . . . . . . 27
8. Telemetry Considerations . . . . . . . . . . . . . . . . . . 28
9. Enhanced Resiliency . . . . . . . . . . . . . . . . . . . . . 28
10. Operational Considerations . . . . . . . . . . . . . . . . . 29
11. Security Considerations . . . . . . . . . . . . . . . . . . . 29
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 30
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
15.1. Normative References . . . . . . . . . . . . . . . . . . 31
15.2. Informative References . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction
Virtual private networks (VPNs) have served the industry well as a
means of providing different groups of users with logically isolated
connectivity over a common network. The common or base network that
is used to provide the VPNs is often referred to as the underlay, and
the VPN is often called an overlay.
Customers of a network operator may request a connectivity services
with advanced characteristics such as low latency guarantees, bounded
jitter, or isolation from other services or customers so that changes
in some other service (such as changes in network load, or events
such as congestion or outages) have no or only acceptable effect on
the throughput or latency of the services provided to the customer.
These services are referred to as "enhanced VPNs" (known as VPN+) in
that they are similar to VPN services providing the customer with the
required connectivity, but in addition they have enhanced
characteristics.
The concept of network slicing has gained traction driven largely by
needs surfacing from 5G [NGMN-NS-Concept] [TS23501] [TS28530]
[BBF-SD406]. According to [TS28530], a 5G end-to-end network slice
consists of three major types of network segments: Radio Access
Network (RAN), Transport Network (TN), and Mobile Core Network (CN).
The transport network provides the connectivity between different
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entities in RAN and CN segments of a 5G end-to-end network slice,
with specific performance commitment.
An IETF network slice [I-D.ietf-teas-ietf-network-slices] is a
virtual (logical) network with its own network topology and a set of
shared or dedicated network resources, which are used to provide the
network slice customer with the required connectivity, appropriate
isolation, and a specific set of Service Level Objectives (SLOs) and
Service Level Expectations (SLEs). In this document (which is solely
about IETF technologies) we refer to an "IETF network slice" simply
as a "network slice": a network slice is considered one possible use
case of an enhanced VPN.
A network slice could span multiple technologies (such as IP or
Optical) and multiple administrative domains. Depending on the
customer's requirement, a network slice could be isolated from other
network slices in terms of data plane, control plane, and management
plane resources.
Network slicing builds on the concepts of resource management,
network virtualization, and abstraction to provide performance
assurance, flexibility, programmability, and modularity. It may use
techniques such as Software Defined Networking (SDN) [RFC7149],
network abstraction [RFC7926] and Network Function Virtualization
(NFV) [RFC8172] [RFC8568] to create multiple logical (virtual)
networks, each tailored for use by a set of services or by a
particular tenant or a group of tenants that share the same or
similar requirements. These logical networks are created on top of a
common underlay network. How the network slices are engineered can
be deployment-specific.
VPN+ can be used to instantiate a network slice, but the technique
can also be of use in general cases to provide enhanced connectivity
services between customer sites.
The requirements of enhanced VPN services cannot be met by simple
overlay networks, as these services require tighter coordination and
integration between the underlay and the overlay network. VPN+ is
built from a VPN overlay and an underlying Virtual Transport Network
(VTN) which has a customized network topology and a set of dedicated
or shared resources in the underlay network. The enhanced VPN may
also include a set of invoked service functions located within the
underlay network. Thus, an enhanced VPN can achieve greater
isolation with strict performance guarantees. These new properties,
which have general applicability, are also of interest as part of a
network slicing solution.
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It is not envisaged that VPN+ services will replace traditional VPN
services. Traditional VPN services will continue to be delivered
using pre-existing mechanisms and can co-exist with VPN+ services.
In fact, compared to traditional VPNs, it is not envisaged that large
numbers of VPN+ services will be deployed in a network. In other
words, it is not intended that all existing VPNs supported by a
network will use VPN+ techniques.
This document describes a framework for using existing, modified, and
potential new technologies as components to provide a VPN+ service.
Specifically, we are concerned with:
o The functional requirements and service characteristics of an
enhanced VPN.
o The design of the enhanced VPN data plane.
o The necessary control and management protocols in both the
underlay and the overlay of the enhanced VPN.
o The mechanisms to achieve integration between overlay and
underlay.
o The necessary Operation, Administration, and Management (OAM)
methods to instrument an enhanced VPN to make sure that the
required Service Level Agreement (SLA) between the customer and
the network operator is met, and to take any corrective action
(such as switching traffic to an alternate path) to avoid SLA
violation.
The required layered network structure to achieve this is shown in
Section 4.1.
2. Terminology
In this document, the relationship of the four terms "VPN", "VPN+",
"VTN", and "Network Slice" are as follows:
o A Virtual Private Network (VPN) refers to the overlay network
service that provides the connectivity between different customer
sites, and that maintains traffic separation between different
customers. IPVPN is defined in [RFC2764], L2VPN is defined in
[RFC4664], L3VPN is defined in [RFC4364], and EVPN is defined in
[RFC7209].
o An enhanced VPN (VPN+) is an evolution of the VPN service that
makes additional service-specific commitments. An enhanced VPN is
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made by integrating an overlay VPN with a set of network resources
allocated in the underlay network.
o A Virtual Transport Network (VTN) is a virtual underlay network
that provide the connection between the customer sites. The VTN
has the capability to deliver the performance characteristics
required by the VPN+ customers and to provide isolation between
separate VPN+ services.
o A network slice could be provided by building an enhanced VPN.
Other mechanisms for delivering network slices may exist but are
not in scope for this document.
The term "tenant" is used in this document to refer to the customers
and all of their associated enhanced VPNs.
The following terms are also used in this document. Some of them are
newly defined, some others reference existing definitions.
ACTN: Abstraction and Control of Traffic Engineered Networks
[RFC8453]
DetNet: Deterministic Networking. See [DETNET] and [RFC8655]
FlexE: Flexible Ethernet [FLEXE]
TSN: Time Sensitive Networking [TSN]
VN: Virtual Network [I-D.ietf-teas-actn-vn-yang]
VTP: Virtual Transport Path. A VTP is a path through the VTN which
provides the connection between two customer sites.
3. Overview of the Requirements
This section provides an overview of the requirements of an enhanced
VPN service.
3.1. Performance Guarantees
Performance guarantees are made by network operators to their
customers in relation to the services provided to the customers.
They are usually expressed in SLAs as a set of SLOs.
There are several kinds of performance guarantee, including
guaranteed maximum packet loss, guaranteed maximum delay, and
guaranteed delay variation. Note that these guarantees apply to
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conformance traffic, out-of-profile traffic will be handled according
to a separate agreement with the customer.
Guaranteed maximum packet loss is usually addressed by setting packet
priorities, queue size, and discard policy. However this becomes
more difficult when the requirement is combined with latency
requirements. The limiting case is zero congestion loss, and that is
the goal of DetNet [DETNET] and TSN [TSN]. In modern optical
networks, loss due to transmission errors already approaches zero,
but there is the possibility of failure of the interface or the fiber
itself. This type of fault can only be addressed by some form of
signal duplication and transmission over diverse paths.
Guaranteed maximum latency is required by a number of applications
particularly real-time control applications and some types of virtual
reality applications. DetNet [DETNET] is relevant, however
additional methods of enhancing the underlay to better support the
delay guarantees may be needed, and these methods will need to be
integrated with the overall service provisioning mechanisms.
Guaranteed maximum delay variation is a performance guarantee that
may also be needed. [RFC8578] calls up a number of cases that need
this guarantee, for example in electrical utilities. Time transfer
is an example service that needs a performance guarantee, although it
is in the nature of time that the service might be delivered by the
underlay as a shared service and not provided through different
enhanced VPNs. Alternatively, a dedicated enhanced VPN might be used
to provide this as a shared service.
This suggests that a spectrum of service guarantees need to be
considered when deploying an enhanced VPN. As a guide to
understanding the design requirements we can consider four types of
service:
o Best effort
o Assured bandwidth
o Guaranteed latency
o Enhanced delivery
The best effort service is the basic service as provided by current
VPNs.
An assured bandwidth service is one in which the bandwidth over some
period of time is assured. This can be achieved either simply based
on a best effort service with over-capacity provisioning, or it can
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be based on MPLS traffic engineered label switching paths (TE-LSPs)
with bandwidth reservations. Depending on the technique used,
however, the bandwidth is not necessarily assured at any instant.
Providing assured bandwidth to VPNs, for example by using per-VPN TE-
LSPs, is not widely deployed at least partially due to scalability
concerns. VPN+ aims to provide a more scalable approach for such
services.
A guaranteed latency service has an upper bound to edge-to-edge
latency. Assuring the upper bound is sometimes more important than
minimizing latency. There are several new technologies that provide
some assistance with this performance guarantee. Firstly, the IEEE
TSN project [TSN] introduces the concept of scheduling of delay- and
loss-sensitive packets. The DetNet work [DETNET] is also of
relevance in assuring an upper bound of end-to-end packet latency.
FlexE [FLEXE] is also useful to help provide these guarantees. The
use of such underlying technologies to deliver VPN+ services needs to
be considered.
An enhanced delivery service is one in which the underlay network (at
Layer 3) attempts to deliver the packet through multiple paths in the
hope of eliminating packet loss due to equipment or media failures.
Such a mechanism may need to be used for VPN+ service.
3.2. Isolation between Enhanced VPN Services
One element of the SLA demanded for an enhanced VPN may be a
guarantee that the service offered to the customer will not be
affected by any other traffic flows in the network. This is termed
"isolation" and a customer may express the requirement for isolation
as an SLE [I-D.ietf-teas-ietf-network-slices].
One way for a network operator to meet the requirement for isolation
is simply by setting and conforming to all the SLOs. For example,
traffic congestion (interference from other services) might impact on
the latency experienced by a VPN+ customer. Thus, in this example,
conformance to a latency SLO would be the primary requirement for
delivery of the VPN+ service, and isolation from other services might
be only a means to that end.
Another way for a service provider to meet this SLE is to control the
degree to which traffic from one service is isolated from other
services in the network.
There is a fine distinction between how isolation is requested by a
customer and how it is delivered by the service provider. In
general, the customer is interested in service performance and not
how it is delivered. Thus, for example, the customer wants specific
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quality guarantees and is not concerned about how the service
provider delivers them. However, it should be noted that some
aspects of isolation might be directly measurable by a customer if
they have information about the traffic patterns on a number services
supported by the same service provider. Furthermore, a customer may
be nervous about disruption caused by other services, contamination
by other traffic, or delivery of their traffic to the wrong
destinations. In this way, the customer may want to specify (and pay
for) the level of isolation provided by the service provider.
Isolation is achieved in the realization of a VPN+ through existing
technologies that may be supplemented by new mechanisms. The service
provider chooses which processes to use to meet this SLE just as they
choose how to meet all other SLOs and SLEs. Isolation may be
achieved in the network by various forms of resource partitioning
ranging from simple separation of service traffic on delivery
(ensuring that traffic is not delivered to the wrong customer),
through sharing of resources with some form of safeguards, to
dedicated allocation of resources for a specific enhanced VPN. For
example, interference avoidance may be achieved by network capacity
planning, allocating dedicated network resources, traffic policing or
shaping, prioritizing in using shared network resources, etc.
The terms hard and soft isolation are used to indicate different
levels of isolation. A service has soft isolation if the traffic of
one service cannot be received by the customers of another service.
The existing IP and MPLS VPNs are examples of services with soft
isolation: the network delivers the traffic only to the required
customer endpoints. However, with soft isolation, as the network
resources are shared, traffic from some services may congest the
network, resulting in packet loss and delay for other services. The
ability for a service or a group of services to be sheltered from
this effect is called hard isolation. Hard isolation may be needed
so that applications with exacting requirements can function
correctly, despite other demands (perhaps a burst of traffic in
another service) competing for the underlying resources. A customer
may request different degrees of isolation ranging from soft
isolation to hard isolation. In practice isolation may be delivered
on a spectrum between soft and hard, and in some cases soft and hard
isolation may be used in a hierarchical manner with one enhanced VPN
being built on another.
To provide the required level of isolation, resources may need to be
reserved in the data plane of the underlay network and dedicated to
traffic from a specific enhanced VPN or a specific group of enhanced
VPNs. This may introduce scalability concerns both in the
implementation (as each enhanced VPN would need to be tracked in the
network) and in how many resources need to be reserved and may be
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under-used (see Section 4.4). Thus, some trade-off needs to be
considered to provide the isolation between enhanced VPNs while still
allowing reasonable resource sharing.
An optical underlay can offer a high degree of isolation, at the cost
of allocating resources on a long-term and end-to-end basis. On the
other hand, where adequate isolation can be achieved at the packet
layer, this permits the resources to be shared amongst a group of
services and only dedicated to a service on a temporary basis.
The next section explores a pragmatic approach to isolation in packet
networks.
3.2.1. A Pragmatic Approach to Isolation
A key question is whether it is possible to achieve hard isolation in
packet networks that were designed to provide statistical
multiplexing through sharing of data plane resources, a significant
economic advantage when compared to a dedicated, or a Time Division
Multiplexing (TDM) network. Clearly, there is no need to provide
more isolation than is required by the applications, and an
approximation to full hard isolation is sufficient in most cases.
For example, pseudowires [RFC3985] emulate services that would have
had hard isolation in their native form.
O=================================================O
| \---------------v---------------/
Statistical Pragmatic Absolute
Multiplexing Isolation Isolation
(Traditional VPNs) (Enhanced VPN) (Dedicated Network)
Figure 1: The Spectrum of Isolation
Figure 1 shows a spectrum of isolation that may be delivered by a
network. At one end of the spectrum, we see statistical multiplexing
technologies that support traditional VPNs. This is a service type
that has served the industry well and will continue to do so. At the
opposite end of the spectrum, we have the absolute isolation provided
by dedicated transport networks. The goal of enhanced VPNs is
"pragmatic isolation". This is isolation that is better than what is
obtainable from pure statistical multiplexing, more cost effective
and flexible than a dedicated network, but is a practical solution
that is good enough for the majority of applications. Mechanisms for
both soft isolation and hard isolation are needed to meet different
levels of service requirement.
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3.3. Integration
The way to achieve the characteristics demanded by an enhanced VPN
(such as guaranteed or predictable performance) is by integrating the
overlay VPN with a particular set of resources in the underlay
network which are allocated to meet the service requirement. This
needs be done in a flexible and scalable way so that it can be widely
deployed in operators' networks to support a reasonable number of
enhanced VPN customers.
Taking mobile networks and in particular 5G into consideration, the
integration of the network with service functions is likely a
requirement. The IETF's work on service function chaining (SFC)
[SFC] provides a foundation for this. Service functions can be
considered as part of enhanced VPN services. The detailed mechanisms
about the integration between service functions and enhanced VPNs are
out of the scope of this document.
3.3.1. Abstraction
Integration of the overlay VPN and the underlay network resources
does not need to be a tight mapping. As described in [RFC7926],
abstraction is the process of applying policy to a set of information
about a traffic engineered (TE) network to produce selective
information that represents the potential ability to connect across
the network. The process of abstraction presents the connectivity
graph in a way that is independent of the underlying network
technologies, capabilities, and topology so that the graph can be
used to plan and deliver network services in a uniform way.
Virtual networks can be built on top of an abstracted topology that
represents the connectivity capabilities of the underlay network as
described in the framework for Abstraction and Control of TE Networks
(ACTN) [RFC8453] as discussed further in Section 5.5.
[I-D.king-teas-applicability-actn-slicing] describes the
applicability of ACTN to network slicing and is, therefore, relevant
to the consideration of using ACTN to enable enhanced VPNs.
3.4. Dynamic Changes
Enhanced VPNs need to be created, modified, and removed from the
network according to service demands. An enhanced VPN that requires
hard isolation (Section 3.2) must not be disrupted by the
instantiation or modification of another enhanced VPN. Determining
whether modification of an enhanced VPN can be disruptive to that
VPN, and whether the traffic in flight will be disrupted can be a
difficult problem.
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The data plane aspects of this problem are discussed further in
Section 5.1,Section 5.2, and Section 5.3.
The control plane aspects of this problem are discussed further in
Section 5.4.
The management plane aspects of this problem are discussed further in
Section 5.5.
Dynamic changes both to the enhanced VPN and to the underlay
transport network need to be managed to avoid disruption to services
that are sensitive to changes in network performance.
In addition to non-disruptively managing the network during changes
such as the inclusion of a new VPN endpoint or a change to a link,
VPN traffic might need to be moved because of changes to traffic
patterns and volumes.
3.5. Customized Control
In many cases the customers are delivered with enhanced VPN services
without knowing the information about the underlying VTNs. However,
depends on the agreement between the operator and the customer, in
some cases the customer may also be provided with some information
about the underlying VTNs. Such information can be filtered or
aggregated according to the operator's policy. This allows the
customer of the enhanced VPN to have some visibility and even control
over how the underlying topology and resources of the VTN are used.
For example, the customers may be able to specify the service paths
within the VTN for specific traffic flows of their enhanced VPNs.
Depending on the requirements, an enhanced VPN customer may have his
own network controller, which may be provided with an interface to
the control or management system run by the network operator. Note
that such control is within the scope of the customer's enhanced VPN,
any additional changes beyond this would require some intervention by
the network operator.
A description of the control plane aspects of this problem are
discussed further in Section 5.4. A description of the management
plane aspects of this feature can be found in Section 5.5.
3.6. Applicability
The concept of enhanced VPN can be applied to any existing and future
multi-tenancy overlay services including but not limited to :
o Layer-2 point-to-point services such as pseudowires [RFC3985]
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o Layer-2 VPNs [RFC4664]
o Ethernet VPNs [RFC7209]
o Layer-3 VPNs [RFC4364], [RFC2764]
Where such VPN service types need enhanced isolation and delivery
characteristics, the technologies described in Section 5 can be used
to provide an underlay with the required enhanced performance.
3.7. Inter-Domain and Inter-Layer Network
In some scenarios, an enhanced VPN service may span multiple network
domains. A domain is considered to be any collection of network
elements within a common realm of address space or path computation
responsibility [RFC5151] for example, an Autonomous System. In some
domains the network operator may manage a multi-layered network, for
example, a packet network over an optical network. When enhanced
VPNs are provisioned in such network scenarios, the technologies used
in different network planes (data plane, control plane, and
management plane) need to provide mechanisms to support multi-domain
and multi-layer coordination and integration, so as to provide the
required service characteristics for different enhanced VPNs, and
improve network efficiency and operational simplicity.
4. Architecture of Enhanced VPNs
A number of enhanced VPN services will typically be provided by a
common network infrastructure. Each enhanced VPN consists of both
the overlay and a VTN with a specific set of network resources and
service functions allocated in the underlay to satisfy the needs of
the VPN customer. One VTN may support one of more enhanced VPNs.
The integration between overlay and various underlay resources
ensures the required isolation between different enhanced VPNs, and
achieves the guaranteed performance for different services.
An enhanced VPN needs to be designed with consideration given to:
o An enhanced data plane.
o A control plane to create enhanced VPNs, making use of the data
plane isolation and performance guarantee techniques.
o A management plane for enhanced VPN service life-cycle management.
These topics are expanded below.
o The enhanced data plane:
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* Provides the required packet latency and jitter
characteristics.
* Provides the required packet loss characteristics.
* Provides the required resource isolation capability, e.g.,
bandwidth guarantee.
* Provides the mechanism to associate a packet with the set of
resources allocated to the enhanced VPN to which the packet
belongs.
o The control plane:
* Collects information about the underlying network topology and
available resources, and exports this to nodes in the network
and/or a centralized controller as required.
* Creates the required VTNs with the resources and properties
needed by the enhanced VPN services that are they support.
* Determines the risk of SLA violation and takes appropriate
avoiding action.
* Determines the right balance of per-packet and per-node state
according to the needs of the enhanced VPN services to scale to
the required size.
o The management plane:
* Provides an interface between the enhanced VPN provider (e.g.,
operator's network management system ) and the enhanced VPN
customer (e.g., an organization or a service with enhanced VPN
requirement) such that some of the operation requests can be
met without interfering with the enhanced VPN of other
customers.
* Provides an interface between the enhanced VPN provider and the
enhanced VPN customers to expose the network capability
information toward the enhanced VPN customer.
* Provides the service life-cycle management and operation of
enhanced VPNs (e.g., creation, modification, assurance/
monitoring, and decommissioning).
o Operations, Administration, and Maintenance (OAM)
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* Provides the tools to verify the connectivity and performance
of the enhanced VPN.
* Provides the tools to verify whether the underlay network
resources are correctly allocated and operating properly.
o Telemetry
* Provides the mechanisms to collect network information about
the operation of the data plane, control plane, and management
plane. More specifically, telemetry provides the mechanisms to
collect network data:
+ from the underlay network for overall performance evaluation
and for the planning enhanced VPN services.
+ from each enhanced VPN and for monitoring and analytics of
the characteristics and SLA fulfillment of the enhanced VPN
services.
4.1. Layered Architecture
The layered architecture of an enhanced VPN is shown in Figure 2.
Underpinning everything is the physical network infrastructure layer
which provide the underlying resources used to provision the
separated virtual transport networks (VTNs). This includes the
partitioning of link and/or node resources. Each subset of link or
node resource can be considered as a virtual link or virtual node
used to build the VTNs.
/\
||
+-------------------+ Centralized
| Network Controller| Control & Management
+-------------------+
||
\/
o---------------------------o VPN Service 1
/-------------o
o____________/______________o VPN Service 2
_________________o
_____/
o___/ \_________________o VPN Service 3
\_______________________o
...... ...
o-----------\ /-------------o
o____________X______________o VPN Service n
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__________________________
/ o----o-----o /
/ / / / VTN-1
/ o-----o-----o----o----o /
/_________________________/
__________________________
/ o----o /
/ / / \ / VTN-2
/ o-----o----o---o------o /
/_________________________/
...... ...
___________________________
/ o----o /
/ / / / VTN-m
/ o-----o----o----o-----o /
/__________________________/
++++ ++++ ++++
+--+===+--+===+--+
+--+===+--+===+--+
++++ +++\\ ++++
|| || \\ || Physical
|| || \\ || Network
++++ ++++ ++++ \\+++ ++++ Infrastructure
+--+===+--+===+--+===+--+===+--+
+--+===+--+===+--+===+--+===+--+
++++ ++++ ++++ ++++ ++++
o Virtual Node ++++
+--+ Physical Node with resource partition
-- Virtual Link +--+
++++
== Physical Link with resource partition
Figure 2: The Layered Architecture of VPN+
Various components and techniques discussed in Section 5 can be used
to enable resource partitioning, such as FlexE, TSN, DetNet,
dedicated queues, etc. These partitions may be physical or virtual
so long as the SLA required by the higher layers is met.
Based on the network resources provided by the physical network
infrastructure, multiple VTNs can be provisioned, each with
customized topology and other attributes to meet the requirements of
different enhanced VPNs or different groups of enhanced VPNs. To get
the required characteristics, each VTN needs to be mapped to a set of
network nodes and links in the network infrastructure. And on each
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node or link, the VTN is associated with a set of resources which are
allocated for the processing of traffic in the VTN. The VTN provides
the integration between the virtual network topology and the required
underlying network resources. The VTN is an essential scaling
technique, as it has the potential of eliminating per-path state from
the network. In addition, when a group of enhanced VPNs is supported
by a single VTN, there is need only to maintain network state for the
single VTN (see Section 4.4 for more information).
The centralized network controller is used to create the VTN, and to
instruct the network nodes to allocate the required resources to each
VTN and to provision the enhanced VPN services on the VTNs. A
distributed control plane may also be used for the distribution of
the VTN topology and attribute information between nodes within the
VTNs.
The process used to create VTNs and to allocate network resources for
use by VTNs needs to take a holistic view of the needs of all of its
customers and to partition the resources accordingly. However,
within a VTN these resources can, if required, be managed via a
dynamic control plane. This provides the required scalability and
isolation.
4.2. Multi-Point to Multi-Point (MP2MP) Connectivity
At the level of a overlay VPN service, the required connectivity for
an MP2MP service is usually full or partial mesh. To support such
VPN services, the corresponding VTN connectivity also needs to have
an abstracted MP2MP connectivity.
Other service requirements may be expressed at different
granularities, some of which can be applicable to the whole service,
while some others may only be applicable to some pairs of end points.
For example, when a particular level of performance guarantee is
required, the point-to-point path through the underlying VTN of the
enhanced VPN may need to be specifically engineered to meet the
required performance guarantee.
4.3. Application Specific Data Types
Although a lot of the traffic that will be carried over the enhanced
VPN will likely be IPv4 or IPv6, the design must be capable of
carrying other traffic types, in particular Ethernet traffic. This
is easily accomplished through the various pseudowire (PW) techniques
[RFC3985]. Where the underlay is MPLS, Ethernet can be carried over
the enhanced VPN encapsulated according to the method specified in
[RFC4448]. Where the underlay is IP, Layer Two Tunneling Protocol -
Version 3 (L2TPv3) [RFC3931] can be used with Ethernet traffic
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carried according to [RFC4719]. Encapsulations have been defined for
most of the common Layer-2 types for both PW over MPLS and for
L2TPv3.
4.4. Scaling Considerations
VPNs are instantiated as overlays on top of an operator's network and
offered as services to the operator's customers. An important
feature of overlays is that they can deliver services without placing
per-service state in the core of the underlay network.
Enhanced VPNs may need to install some additional state within the
network to achieve the features that they require. Solutions must
consider minimizing and controlling the scale of such state, and
deployment architectures should constrain the number of enhanced VPNs
that would exist where such services would place additional state in
the network. It is expected that the number of enhanced VPNs will be
small at the beginning, and even in future the number of enhanced
VPNs will be much fewer than traditional VPNs because pre-existing
VPN techniques are good enough to meet the needs of most existing
VPN-type services.
In general, it is not required that the state in the network be
maintained in a 1:1 relationship with the VPN+ services. It will
usually be possible to aggregate a set or group of VPN+ services so
that they share the same VTN and the same set of network resources
(much in the same way that current VPNs are aggregated over transport
tunnels) so that collections of enhanced VPNs that require the same
behavior from the network in terms of resource reservation, latency
bounds, resiliency, etc. can be grouped together. This is an
important feature to assist with the scaling characteristics of VPN+
deployments.
[I-D.dong-teas-enhanced-vpn-vtn-scalability] provides more details of
scalability considerations for enhanced VPNs, and Section 6 includes
a greater discussion of scalability considerations.
5. Candidate Technologies
A VPN is a network created by applying a demultiplexing technique to
the underlying network (the underlay) to distinguish the traffic of
one VPN from that of another. A VPN path that travels by other than
the shortest path through the underlay normally requires state in the
underlay to specify that path. State is normally applied to the
underlay through the use of the RSVP-TE signaling protocol, or
directly through the use of an SDN controller, although other
techniques may emerge as this problem is studied. This state gets
harder to manage as the number of VPN paths increases. Furthermore,
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as we increase the coupling between the underlay and the overlay to
support the enhanced VPN service, this state will increase further.
Thus, an enhanced VPN solution needs tighter coupling with the
underlay than is the case with existing VPN techniques. We cannot,
for example, share the network resource between enhanced VPNs which
require hard isolation.
In an enhanced VPN, different subsets of the underlay resources can
be dedicated to different enhanced VPNs or different groups of
enhanced VPNs through the use of VTNs.
5.1. Packet Forwarding Plane Technologies
Several candidate Layer 2 packet- or frame-based data plane solutions
which provide the required isolation and guarantees are described in
the following sections.
5.1.1. Flexible Ethernet
FlexE [FLEXE] provides the ability to multiplex channels over an
Ethernet link to create point-to-point fixed- bandwidth connections
in a way that provides hard isolation. FlexE also supports bonding
links to create larger links out of multiple low capacity links.
However, FlexE is only a link level technology. When packets are
received by the downstream node, they need to be processed in a way
that preserves that isolation in the downstream node. This in turn
requires a queuing and forwarding implementation that preserves the
end-to-end isolation.
If different FlexE channels are used for different services, then no
sharing is possible between the FlexE channels. This means that it
may be difficult to dynamically redistribute unused bandwidth to
lower priority services in another FlexE channel. If one FlexE
channel is used by one customer, the customer can use some methods to
manage the relative priority of their own traffic in the FlexE
channel.
5.1.2. Dedicated Queues
DiffServ based queuing systems are described in [RFC2475] and
[RFC4594]. This approach is not sufficient to provide isolation for
enhanced VPNs because DiffServ does not provide enough markers to
differentiate between traffic of a large number of enhanced VPNs.
Nor does DiffServ offer the range of service classes that each VPN
needs to provide to its tenants. This problem is particularly acute
with an MPLS underlay, because MPLS only provides eight traffic
classes.
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In addition, DiffServ, as currently implemented, mainly provides per-
hop priority-based scheduling, and it is difficult to use it to
achieve quantitative resource reservation.
To address these problems and to reduce the potential interference
between enhanced VPNs, it would be necessary to steer traffic to
dedicated input and output queues per enhanced VPN: some routers have
a large number of queues and sophisticated queuing systems which
could support this, while some routers may struggle to provide the
granularity and level of isolation required by the applications of
enhanced VPN.
5.1.3. Time Sensitive Networking
Time Sensitive Networking (TSN) [TSN] is an IEEE project to provide a
method of carrying time sensitive information over Ethernet. It
introduces the concept of packet scheduling where a packet stream may
be given a time slot guaranteeing that it experiences no queuing
delay or increase in latency beyond the very small scheduling delay.
The mechanisms defined in TSN can be used to meet the requirements of
time sensitive services of an enhanced VPN.
Ethernet can be emulated over a Layer 3 network using an IP or MPLS
pseudowire. However, a TSN Ethernet payload would be opaque to the
underlay and thus not treated specifically as time sensitive data.
The preferred method of carrying TSN over a Layer 3 network is
through the use of deterministic networking as explained in
Section 5.2.1.
5.2. Layer Three Data Plane
This section considers the problem of enhanced VPN differentiation
and resource representation in the network layer.
5.2.1. Deterministic Networking
Deterministic Networking (DetNet) [RFC8655] is a technique being
developed in the IETF to enhance the ability of Layer-3 networks to
deliver packets more reliably and with greater control over the
delay. The design cannot use re-transmission techniques such as TCP
since that can exceed the delay tolerated by the applications. Even
the delay improvements that are achieved with Stream Control
Transmission Protocol Partial Reliability Extension (SCTP-PR)
[RFC3758] may not meet the bounds set by application demands. DetNet
pre-emptively sends copies of the packet over various paths to
minimize the chance of all copies of a packet being lost. It also
seeks to set an upper bound on latency, but the goal is not to
minimize latency.
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5.2.2. MPLS Traffic Engineering (MPLS-TE)
MPLS-TE [RFC2702][RFC3209] introduces the concept of reserving end-
to-end bandwidth for a TE-LSP, which can be used to provide a point-
to-point Virtual Transport Path (VTP) across the underlay network to
support VPNs. VPN traffic can be carried over dedicated TE-LSPs to
provide reserved bandwidth for each specific connection in a VPN, and
VPNs with similar behavior requirements may be multiplexed onto the
same TE-LSPs. Some network operators have concerns about the
scalability and management overhead of MPLS-TE system especially with
regard to those systems that use an active control plane, and this
has lead them to consider other solutions for their networks.
5.2.3. Segment Routing
Segment Routing (SR) [RFC8402] is a method that prepends instructions
to packets at the head-end of a path. These instructions are used to
specify the nodes and links to be traversed, and allow the packets to
be routed on paths other than the shortest path. By encoding the
state in the packet, per-path state is transitioned out of the
network.
An SR traffic engineered path operates with a granularity of a link.
Hints about priority are provided using the Traffic Class (TC) or
Differentiated Services Code Point (DSCP) field in the header.
However, to achieve the latency and isolation characteristics that
are sought by enhanced VPN customers, it will be necessary to steer
packets through specific virtual links and/or queues on the same link
and direct them to use specific resources. With SR, it is possible
to introduce such fine-grained packet steering by specifying the
queues and resources through an SR instruction list.
Note that the concept of a queue is a useful abstraction for
different types of underlay mechanism that may be used to provide
enhanced isolation and latency support. How the queue satisfies the
requirement is implementation specific and is transparent to the
layer-3 data plane and control plane mechanisms used.
With Segment Routing, the SR instruction list could be used to build
a P2P path, and a group of SR SIDs could also be used to represent an
MP2MP network. Thus, the SR based mechanism could be used to provide
both a Virtual Transport Path (VTP) and a Virtual Transport Network
(VTN) for enhanced VPN services.
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5.3. Non-Packet Data Plane
Non-packet underlay data plane technologies often have TE properties
and behaviors, and meet many of the key requirements in particular
for bandwidth guarantees, traffic isolation (with physical isolation
often being an integral part of the technology), highly predictable
latency and jitter characteristics, measurable loss characteristics,
and ease of identification of flows. The cost is that the resources
are allocated on a long-term and end-to-end basis. Such an
arrangement means that the full cost of the resources has to be borne
by the service that is allocated with the resources.
5.4. Control Plane
An enhanced VPN would likely be based on a hybrid control mechanism
that takes advantage of a logically centralized controller for on-
demand provisioning and global optimization, whilst still relying on
a distributed control plane to provide scalability, high reliability,
fast reaction, automatic failure recovery, etc. Extension to and
optimization of the centralized and distributed control plane is
needed to support the enhanced properties of VPN+.
RSVP-TE [RFC3209] provides the signaling mechanism for establishing a
TE-LSP in an MPLS network with end-to-end resource reservation. This
can be seen as an approach of providing a Virtual Transport Path
(VTP) which could be used to bind the VPN to specific network
resources allocated within the underlay, but there remain scalability
concerns as mentioned in Section 5.2.2.
The control plane of SR [RFC8665] [RFC8667]
[I-D.ietf-idr-bgp-ls-segment-routing-ext] does not have the
capability of signaling resource reservations along the path. On the
other hand, the SR approach provides a potential way of binding the
underlay network resource and the enhanced VPN service without
requiring per-path state to be maintained in the network. A
centralized controller can perform resource planning and reservation
for enhanced VPNs, while it needs to ensure that resources are
correctly allocated in network nodes for the enhanced VPN service.
The controller could also compute the SR paths based on the planned
or collected network resource and other attributes, and provision the
SR paths based on the mechanism in
[I-D.ietf-spring-segment-routing-policy] to the ingress nodes of the
enhanced VPN services. The distributed control plane may be used to
advertise the network attributes associated with enhanced VPNs, and
compute the SR paths with specific constraints of enhanced VPN
services.
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5.5. Management Plane
The management plane provides the interface between the enhanced VPN
provider and the customers for life-cycle management of the service
(i.e., creation, modification, assurance/monitoring, and
decommissioning). It relies on a set of service data models for the
description of the information and operations needed on the
interface.
As an example, in the context of 5G end-to-end network slicing
[TS28530], the management of enhanced VPNs is considered as the
management of the transport network part of the 5G end-to-end network
slice. The 3GPP management system may provide the connectivity and
performance related parameters as requirements to the management
plane of the transport network. It may also require the transport
network to expose the capabilities and status of the network slice.
Thus, an interface between the enhanced VPN management plane and the
5G network slice management system, and relevant service data models
are needed for the coordination of 5G end-to-end network slice
management.
The management plane interface and data models for enhanced VPN can
be based on the service models described in Section 5.6.
It is important that the management life-cycle supports in-place
modification of enhanced VPNs. That is, it should be possible to add
and remove end points, as well as to change the requested
characteristics of the service that is delivered. The management
system needs to be able to assess the revised VPN+ requests and
determine whether they can be provided by the existing VTN or whether
changes must be made, and it will additionally need to determine
whether those changes to the VTN are possible. If not, then the
customer's modification request may be rejected.
When the modification of an enhanced VPN is possible, the management
system should make every effort to make the changes in a non-
disruptive way. That is, the modification of the enhanced VPN or the
underlying VTN should not perturbate traffic on the enhanced VPN in a
way that causes the service level to drop below the agreed levels.
Furthermore, in the spirit of isolation, changes to one enhanced VPN
should not cause disruption to other enhanced VPNs.
The network operator for the underlay network (i.e., the provider of
the enhanced VPN) may delegate some operational aspects of the
enhanced VPN to the customer. In this way, the VPN+ is presented to
the customer as a virtual network, and the customer can choose how to
use that network. The customer cannot exceed the capabilities of
virtual links and nodes, but can decide how to load traffic onto the
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network, for example, by assigning different metrics to the virtual
links so that the customer can control how traffic is routed through
the overlay. This approach requires a management system for the
overlay network, but does not necessarily require any coordination
between the underlay and overlay management systems, except that the
overlay management system might notice when the enhanced VPN network
is close to capacity or considerably under-used and automatically
request changes in the service provided by the underlay.
5.6. Applicability of Service Data Models to Enhanced VPN
This section describes the applicability of the existing and in-
progress service data models to enhanced VPN. New service models may
also be introduced for some of the required management functions.
The ACTN framework[RFC8453] supports operators in viewing and
controlling different domains and presenting virtualized networks to
their customers. It highlights how:
o Abstraction of the underlying network resources is provided to
higher-layer applications and customers.
o Underlying resources are virtualized and allocated for the
customer, application, or service.
o A virtualized environment is created allowing operators to view
and control multi-domain networks as a single virtualized network.
o Networks can be presented to customers as a virtual network via
open and programmable interfaces.
The type of network virtualization enabled by ACTN managed
infrastructure provides customers with the capability to utilize and
independently control allocated virtual network resources as if they
were physically their own resources. Service Data models are used to
represent, monitor, and manage the virtual networks and services
enabled by ACTN. The VPN customer service models (e.g., the layer 3
VPN service model (L3SM) [RFC8299], the layer 2 VPN service model
(L2SM) [RFC8466]), or the ACTN Virtual Network (VN) model
[I-D.ietf-teas-actn-vn-yang]) are a customer view of the ACTN managed
infrastructure, and is presented by the ACTN provider as a set of
abstracted services or resources. The layer 3 VPN network model
(L3NM) [I-D.ietf-opsawg-l3sm-l3nm] and layer 2 VPN network model
(L2NM) [I-D.ietf-opsawg-l2nm] provide network views of the ACTN
managed infrastructure presented by the ACTN provider as a set of
virtual networks and the associated resources. The VTN network model
[I-D.wd-teas-vtn-network-yang] further provides the management of the
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virtual underlay network topology and resources for the mapping of
the VPN network models.
[I-D.king-teas-applicability-actn-slicing] discusses the
applicability of the ACTN approach in the context of network slicing.
Since there is a strong correlation between network slices and
enhanced VPNs, that document can also give guidance on how ACTN can
be applied to enhanced VPNs.
5.6.1. An Example of Enhanced VPN Delivery
One typical use case of enhanced VPN is to instantiate a network
slice. In order to provide network slices to customers, a
technology-agnostic network slice Northbound Interface (NBI) data
model is needed for the customers to communicate the requirements and
operations of network slices (end points, connectivity, SLOs, and
SLEs). These requirements may then be realized using technology-
specific Southbound Interfaces (SBIs) to instruct the network to
instantiate an enhanced VPN service to meet the requirements of the
customer.
As per [RFC8453] and [I-D.ietf-teas-actn-yang], the CNC-MDSC
Interface (CMI) of ACTN can be used to convey the virtual network
service requirements, which is a generic interface to deliver various
TE based VN services. In the context of the network slice NBI, there
may be some gaps in the combination of the L3SM/L2SM and VN models.
The NBI is required to communicate the connectivity of the network
slice, along with the SLO parameters, SLEs, and traffic selection
rules, and provides a way to monitor the state of the network slice.
This can be described in a more abstract manner, so as to reduce the
association with specific technologies used to realize the network
slice, such as the VPN and TE technologies. The network slice NBI
model as defined in [I-D.wd-teas-ietf-network-slice-nbi-yang]
provides an abstract and generic approach to provide the network
slice NBI functions.
The MDSC-PNC Interface (MPI) models in the ACTN architecture can be
used for the realization of network slices, for example, in a TE
enabled network, and may also be used for cross-layer or cross-domain
implementation of network slice.
6. Scalability Considerations
An enhanced VPN provides performance guaranteed services in packet
networks, but with the potential cost of introducing additional state
into the network. There are at least three ways that this additional
state might be brought into the network:
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o Introduce the complete state into the packet, as is done in SR.
This allows the controller to specify the detailed series of
forwarding and processing instructions for the packet as it
transits the network. The cost of this is an increase in the
packet header size. The cost is also that systems will have
capabilities enabled in case they are called upon by a service.
This is a type of latent state, and increases as the path and
resources that need to be exclusively available to a VPN are
specified more precisely.
o Introduce the state to the network. This is normally done by
creating a path using signaling such as RSVP-TE. This could be
extended to include any element that needs to be specified along
the path, for example explicitly specifying queuing policy. It is
also possible to use other methods to introduce path state, such
as via an SDN controller, or possibly by modifying a routing
protocol. With this approach there is state per path: per-path
characteristic that needs to be maintained over the life of the
path. This is more network state than is needed using SR, but the
packets are usually shorter.
o Provide a hybrid approach. One example is based on using binding
SIDs [RFC8402] to create path fragments, and bind them together
with SR. Dynamic creation of a VPN service path using SR requires
less state maintenance in the network core at the expense of
larger packet headers. The packet size can be lower if a form of
loose source routing is used (using a few nodal SIDs), and it will
be lower if no specific functions or resources on the routers are
specified.
Reducing the state in the network is important to enhanced VPN, as it
requires the overlay to be more closely integrated with the underlay
than with traditional VPNs. This tighter coupling would normally
mean that more state needs to be created and maintained in the
network, as the state about fine granularity processing would need to
be loaded and maintained in the routers. However, an SR approach
allows much of this state to be spread amongst the network ingress
nodes, and transiently carried in the packets as SIDs.
Further discussion of the scalability considerations of enhanced VPNs
can be found in [I-D.dong-teas-enhanced-vpn-vtn-scalability].
6.1. Maximum Stack Depth of SR
One of the challenges with SR is the stack depth that nodes are able
to impose on packets [RFC8491]. This leads to a difficult balance
between adding state to the network and minimizing stack depth, or
minimizing state and increasing the stack depth.
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6.2. RSVP-TE Scalability
The traditional method of creating a resource allocated path through
an MPLS network is to use the RSVP-TE protocol. However, there have
been concerns that this requires significant continuous state
maintenance in the network. Work to improve the scalability of RSVP-
TE LSPs in the control plane can be found in [RFC8370].
There is also concern at the scalability of the forwarder footprint
of RSVP-TE as the number of paths through a label switching router
(LSR) grows. [RFC8577] addresses this by employing SR within a
tunnel established by RSVP-TE.
6.3. SDN Scaling
The centralized approach of SDN requires state to be stored in the
network, but does not have the overhead of also requiring control
plane state to be maintained. Each individual network node may need
to maintain a communication channel with the SDN controller, but that
compares favorably with the need for a control plane to maintain
communication with all neighbors.
However, SDN may transfer some of the scalability concerns from the
network to the centralized controller. In particular, there may be a
heavy processing burden at the controller, and a heavy load in the
network surrounding the controller. A centralized controller also
presents a single point of failure within the network.
7. OAM Considerations
The design of OAM for enhanced VPNs needs to consider the following
requirements:
o Instrumentation of the underlay so that the network operator can
be sure that the resources committed to a tenant are operating
correctly and delivering the required performance.
o Instrumentation of the overlay by the tenant. This is likely to
be transparent to the network operator and to use existing
methods. Particular consideration needs to be given to the need
to verify the isolation and the various committed performance
characteristics.
o Instrumentation of the overlay by the network provider to
proactively demonstrate that the committed performance is being
delivered. This needs to be done in a non-intrusive manner,
particularly when the tenant is deploying a performance sensitive
application.
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o Verification of the conformity of the path to the service
requirement. This may need to be done as part of a commissioning
test.
A study of OAM in SR networks has been documented in [RFC8403].
8. Telemetry Considerations
Network visibility is essential for network operation. Network
telemetry has been considered as an ideal means to gain sufficient
network visibility with better flexibility, scalability, accuracy,
coverage, and performance than conventional OAM technologies.
As defined in [I-D.ietf-opsawg-ntf], the objective of Network
Telemetry is to acquire network data remotely for network monitoring
and operation. It is a general term for a large set of network
visibility techniques and protocols. Network telemetry addresses the
current network operation issues and enables smooth evolution toward
intent-driven autonomous networks. Telemetry can be applied on the
forwarding plane, the control plane, and the management plane in a
network.
How the telemetry mechanisms could be used or extended for the
enhanced VPN service is out of the scope of this document.
9. Enhanced Resiliency
Each enhanced VPN has a life cycle, and may need modification during
deployment as the needs of its tenant change. This is discussed in
Section 5.5. Additionally, as the network evolves, there may need to
be garbage collection performed to consolidate resources into usable
quanta.
Systems in which the path is imposed, such as SR or some form of
explicit routing, tend to do well in these applications, because it
is possible to perform an atomic transition from one path to another.
That is, a single action by the head-end that changes the path
without the need for coordinated action by the routers along the
path. However, implementations and the monitoring protocols need to
make sure that the new path is operational and meets the required SLA
before traffic is transitioned to it. It is possible for deadlocks
to arise as a result of the network becoming fragmented over time,
such that it is impossible to create a new path or to modify an
existing path without impacting the SLA of other paths. Resolution
of this situation is as much a commercial issue as it is a technical
issue and is outside the scope of this document.
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There are, however, two manifestations of the latency problem that
are for further study in any of these approaches:
o The problem of packets overtaking one another if a path latency
reduces during a transition.
o The problem of transient variation in latency in either direction
as a path migrates.
There is also the matter of what happens during failure in the
underlay infrastructure. Fast reroute is one approach, but that
still produces a transient loss with a normal goal of rectifying this
within 50ms [RFC5654]. An alternative is some form of N+1 delivery
such as has been used for many years to support protection from
service disruption. This may be taken to a different level using the
techniques of DetNet with multiple in-network replication and the
culling of later packets [RFC8655].
In addition to the approach used to protect high priority packets,
consideration should be given to the impact of best effort traffic on
the high priority packets during a transition. Specifically, if a
conventional re-convergence process is used there will inevitably be
micro-loops and whilst some form of explicit routing will protect the
high priority traffic, lower priority traffic on best effort shortest
paths will micro-loop without the use of a loop prevention
technology. To provide the highest quality of service to high
priority traffic, either this traffic must be shielded from the
micro-loops, or micro-loops must be prevented completely.
10. Operational Considerations
It is likely that enhanced VPN services will be introduced in
networks which already have traditional VPN services deployed.
Depending on service requirements, the tenants or the operator may
choose to use a traditional VPN or an enhanced VPN to fulfill a
service requirement. The information and parameters to assist such a
decision needs to be reflected on the management interface between
the tenant and the operator.
11. Security Considerations
All types of virtual network require special consideration to be
given to the isolation of traffic belonging to different tenants.
That is, traffic belonging to one VPN must not be delivered to end
points outside that VPN. In this regard enhanced VPNs neither
introduce, nor experience a greater security risks than other VPNs.
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However, in an enhanced Virtual Private Network service the
additional service requirements need to be considered. For example,
if a service requires a specific upper bound to latency then it can
be damaged by simply delaying the packets through the activities of
another tenant, i.e., by introducing bursts of traffic for other
services. In some respects this makes the enhanced VPN more
susceptible to attacks since the SLA may be broken. But another view
is that the operator must, in any case, preform monitoring of the
enhanced VPN to ensure that the SLA is met, and this means that the
operator may be more likely to spot the early onset of a security
attack and be able to take pre-emptive protective action.
The measures to address these dynamic security risks must be
specified as part to the specific solution are form part of the
isolation requirements of a service.
While an enhanced VPN service may be sold as offering encryption and
other security features as part of the service, customers would be
well advised to take responsibility for their own security
requirements themselves possibly by encrypting traffic before handing
it off to the service provider.
The privacy of enhanced VPN service customers must be preserved. It
should not be possible for one customer to discover the existence of
another customer, nor should the sites that are members of an
enhanced VPN be externally visible.
12. IANA Considerations
There are no requested IANA actions.
13. Contributors
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Daniel King
Email: daniel@olddog.co.uk
Adrian Farrel
Email: adrian@olddog.co.uk
Jeff Tansura
Email: jefftant.ietf@gmail.com
Zhenbin Li
Email: lizhenbin@huawei.com
Qin Wu
Email: bill.wu@huawei.com
Bo Wu
Email: lana.wubo@huawei.com
Daniele Ceccarelli
Email: daniele.ceccarelli@ericsson.com
Mohamed Boucadair
Email: mohamed.boucadair@orange.com
Sergio Belotti
Email: sergio.belotti@nokia.com
Haomian Zheng
Email: zhenghaomian@huawei.com
14. Acknowledgements
The authors would like to thank Charlie Perkins, James N Guichard,
John E Drake, Shunsuke Homma, and Luis M. Contreras for their review
and valuable comments.
This work was supported in part by the European Commission funded
H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727).
15. References
15.1. Normative References
[RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
Malis, "A Framework for IP Based Virtual Private
Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000,
<https://www.rfc-editor.org/info/rfc2764>.
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[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<https://www.rfc-editor.org/info/rfc4664>.
15.2. Informative References
[BBF-SD406]
"BBF SD-406: End-to-End Network Slicing", 2016,
<https://wiki.broadband-forum.org/display/BBF/SD-406+End-
to-End+Network+Slicing>.
[DETNET] "Deterministic Networking", March ,
<https://datatracker.ietf.org/wg/detnet/about/>.
[FLEXE] "Flex Ethernet Implementation Agreement", March 2016,
<http://www.oiforum.com/wp-content/uploads/OIF-FLEXE-
01.0.pdf>.
[I-D.dong-teas-enhanced-vpn-vtn-scalability]
Dong, J., Li, Z., Qin, F., Yang, G., and J. N. Guichard,
"Scalability Considerations for Enhanced VPN (VPN+)",
draft-dong-teas-enhanced-vpn-vtn-scalability-02 (work in
progress), February 2021.
[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-18
(work in progress), April 2021.
[I-D.ietf-opsawg-l2nm]
Barguil, S., Dios, O. G. D., Boucadair, M., and L. A.
Munoz, "A Layer 2 VPN Network YANG Model", draft-ietf-
opsawg-l2nm-02 (work in progress), April 2021.
[I-D.ietf-opsawg-l3sm-l3nm]
Barguil, S., Dios, O. G. D., Boucadair, M., Munoz, L. A.,
and A. Aguado, "A Layer 3 VPN Network YANG Model", draft-
ietf-opsawg-l3sm-l3nm-08 (work in progress), April 2021.
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[I-D.ietf-opsawg-ntf]
Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and
A. Wang, "Network Telemetry Framework", draft-ietf-opsawg-
ntf-07 (work in progress), February 2021.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-11 (work in progress),
April 2021.
[I-D.ietf-teas-actn-vn-yang]
Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., and B. Y.
Yoon, "A YANG Data Model for VN Operation", draft-ietf-
teas-actn-vn-yang-11 (work in progress), February 2021.
[I-D.ietf-teas-actn-yang]
Lee, Y., Zheng, H., Ceccarelli, D., Yoon, B. Y., and S.
Belotti, "Applicability of YANG models for Abstraction and
Control of Traffic Engineered Networks", draft-ietf-teas-
actn-yang-07 (work in progress), February 2021.
[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", draft-ietf-teas-ietf-
network-slices-00 (work in progress), April 2021.
[I-D.king-teas-applicability-actn-slicing]
King, D., Drake, J., Zheng, H., and A. Farrel,
"Applicability of Abstraction and Control of Traffic
Engineered Networks (ACTN) to Network Slicing", draft-
king-teas-applicability-actn-slicing-10 (work in
progress), March 2021.
[I-D.wd-teas-ietf-network-slice-nbi-yang]
Wu, B., Dhody, D., Han, L., and R. Rokui, "A Yang Data
Model for IETF Network Slice NBI", draft-wd-teas-ietf-
network-slice-nbi-yang-02 (work in progress), February
2021.
[I-D.wd-teas-vtn-network-yang]
Wu, B. and D. Dhody, "A VTN Network YANG Module", draft-
wd-teas-vtn-network-yang-00 (work in progress), June 2021.
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[NGMN-NS-Concept]
"NGMN NS Concept", 2016, <https://www.ngmn.org/fileadmin/u
ser_upload/161010_NGMN_Network_Slicing_framework_v1.0.8.pd
f>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, DOI 10.17487/RFC2702, September 1999,
<https://www.rfc-editor.org/info/rfc2702>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758,
DOI 10.17487/RFC3758, May 2004,
<https://www.rfc-editor.org/info/rfc3758>.
[RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
RFC 3931, DOI 10.17487/RFC3931, March 2005,
<https://www.rfc-editor.org/info/rfc3931>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,
<https://www.rfc-editor.org/info/rfc4448>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>.
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[RFC4719] Aggarwal, R., Ed., Townsley, M., Ed., and M. Dos Santos,
Ed., "Transport of Ethernet Frames over Layer 2 Tunneling
Protocol Version 3 (L2TPv3)", RFC 4719,
DOI 10.17487/RFC4719, November 2006,
<https://www.rfc-editor.org/info/rfc4719>.
[RFC5151] Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
Domain MPLS and GMPLS Traffic Engineering -- Resource
Reservation Protocol-Traffic Engineering (RSVP-TE)
Extensions", RFC 5151, DOI 10.17487/RFC5151, February
2008, <https://www.rfc-editor.org/info/rfc5151>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/info/rfc5654>.
[RFC7149] Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
<https://www.rfc-editor.org/info/rfc7149>.
[RFC7209] Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
Henderickx, W., and A. Isaac, "Requirements for Ethernet
VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
<https://www.rfc-editor.org/info/rfc7209>.
[RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
Ceccarelli, D., and X. Zhang, "Problem Statement and
Architecture for Information Exchange between
Interconnected Traffic-Engineered Networks", BCP 206,
RFC 7926, DOI 10.17487/RFC7926, July 2016,
<https://www.rfc-editor.org/info/rfc7926>.
[RFC8172] Morton, A., "Considerations for Benchmarking Virtual
Network Functions and Their Infrastructure", RFC 8172,
DOI 10.17487/RFC8172, July 2017,
<https://www.rfc-editor.org/info/rfc8172>.
[RFC8299] Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
"YANG Data Model for L3VPN Service Delivery", RFC 8299,
DOI 10.17487/RFC8299, January 2018,
<https://www.rfc-editor.org/info/rfc8299>.
[RFC8370] Beeram, V., Ed., Minei, I., Shakir, R., Pacella, D., and
T. Saad, "Techniques to Improve the Scalability of RSVP-TE
Deployments", RFC 8370, DOI 10.17487/RFC8370, May 2018,
<https://www.rfc-editor.org/info/rfc8370>.
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[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>.
[RFC8403] Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
2018, <https://www.rfc-editor.org/info/rfc8403>.
[RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
Abstraction and Control of TE Networks (ACTN)", RFC 8453,
DOI 10.17487/RFC8453, August 2018,
<https://www.rfc-editor.org/info/rfc8453>.
[RFC8466] Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
Data Model for Layer 2 Virtual Private Network (L2VPN)
Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
2018, <https://www.rfc-editor.org/info/rfc8466>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
[RFC8568] Bernardos, CJ., Rahman, A., Zuniga, JC., Contreras, LM.,
Aranda, P., and P. Lynch, "Network Virtualization Research
Challenges", RFC 8568, DOI 10.17487/RFC8568, April 2019,
<https://www.rfc-editor.org/info/rfc8568>.
[RFC8577] Sitaraman, H., Beeram, V., Parikh, T., and T. Saad,
"Signaling RSVP-TE Tunnels on a Shared MPLS Forwarding
Plane", RFC 8577, DOI 10.17487/RFC8577, April 2019,
<https://www.rfc-editor.org/info/rfc8577>.
[RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
<https://www.rfc-editor.org/info/rfc8578>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
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[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[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>.
[SFC] "Service Function Chaining", March ,
<https://datatracker.ietf.org/wg/sfc/about>.
[TS23501] "3GPP TS23.501", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
[TS28530] "3GPP TS28.530", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3273>.
[TSN] "Time-Sensitive Networking", March ,
<https://1.ieee802.org/tsn/>.
Authors' Addresses
Jie Dong
Huawei
Email: jie.dong@huawei.com
Stewart Bryant
Futurewei
Email: stewart.bryant@gmail.com
Zhenqiang Li
China Mobile
Email: lizhenqiang@chinamobile.com
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Takuya Miyasaka
KDDI Corporation
Email: ta-miyasaka@kddi.com
Young Lee
Samsung
Email: younglee.tx@gmail.com
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