Routing Area Working Group S. Bryant Internet-Draft J. Dong Intended status: Informational Huawei Expires: May 3, 2018 October 30, 2017 Enhanced Virtual Private Networks (VPN+) draft-bryant-rtgwg-enhanced-vpn-01 Abstract This draft describes a number of enhancements that need to be made to virtual private networks (VPNs) to support the needs of new applications, particularly applications that are associated with 5G services. A network enhanced with these properties may form the underpin of network slicing, but will also be of use in its own right. 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 http://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 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 May 3, 2018. Copyright Notice Copyright (c) 2017 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Bryant & Dong Expires May 3, 2018 [Page 1] Internet-Draft VPN+ October 2017 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. Overview of the Requirements . . . . . . . . . . . . . . . . 3 3.1. Isolation between VPNs . . . . . . . . . . . . . . . . . 4 3.2. Guaranteed Performance . . . . . . . . . . . . . . . . . 5 3.3. Integration . . . . . . . . . . . . . . . . . . . . . . . 6 3.4. Dynamic Configuration . . . . . . . . . . . . . . . . . . 6 3.5. Customized Control Plane . . . . . . . . . . . . . . . . 7 4. Architecture and Components of VPN+ . . . . . . . . . . . . . 7 4.1. Data-Plane . . . . . . . . . . . . . . . . . . . . . . . 7 4.1.1. Data-plane Layering . . . . . . . . . . . . . . . . . 8 4.1.2. Use of Segment Routing Constructs . . . . . . . . . . 8 4.1.3. Segment Routing and Isolation . . . . . . . . . . . . 8 4.2. Stateful and Stateless Virtual Networks . . . . . . . . . 9 4.3. Latency Support . . . . . . . . . . . . . . . . . . . . . 10 4.4. Integrating Service Function Chains and VPNs . . . . . . 11 4.5. Application Specific Network Types . . . . . . . . . . . 11 4.6. Control Plane Considerations . . . . . . . . . . . . . . 12 5. Scalability Considerations . . . . . . . . . . . . . . . . . 12 5.1. Maximum Stack Depth . . . . . . . . . . . . . . . . . . . 13 5.2. RSVP scalability . . . . . . . . . . . . . . . . . . . . 13 6. OAM and Instrumentation . . . . . . . . . . . . . . . . . . . 14 7. Service Disruption During Change . . . . . . . . . . . . . . 14 8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction Virtual networks, often referred to as virtual private networks (VPNs) have served the industry well as a means of providing different groups of users with logically isolated access to 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. Driven largely by needs surfacing from 5G, the concept of network slicing has gained traction. There is a need to create a VPN with enhanced characteristics. Specifically there is a need for a transport network supporting a set of virtual networks each of which Bryant & Dong Expires May 3, 2018 [Page 2] Internet-Draft VPN+ October 2017 provides the client with dedicated (private) networking, computing and storage resources drawn from a shared pool. The tenant of such a network can require a degree of isolation and performance that previously could only be satisfied by dedicated networks. Additionally the tenant may ask for some level of control of their virtual network e.g. to customize the service paths in the network slice. These properties cannot be met with pure overlay networks, as they require tighter coordination and integration between the underlay and the overlay network. This document introduces a new network service called enhanced VPN (VPN+). VPN+ refers to a virtual network which has dedicated network resources allocated from the underlay network, and can achieve a greater isolation and lower latency than traditional VPN. These new network layer properties, which have general applicability, may also be of interest as part of a network slicing solution [I-D.geng-netslices-architecture] In this draft we identify the new and modified components that need to be provided in the network layer and their associated control and monitoring of an enhanced VPN (VPN+). Specifically we are concerned with the technology needed to be provided by the enhanced VPN underlay, the enhanced VPN data-plane and the necessary protocols in both the underlay and the overlay of enhanced VPN. One use for enhanced VPNs is to create network slices with different isolation requirements. Such slices may be used to provide different tenants of vertical industrial markets with their own virtual network with the explicit characteristics required. These slices may be "hard" slices providing a high degree of confidence that the VPN+ characteristics will be maintained over the slice life cycle, of they may be "soft" slices in which case some degree of interaction may be experienced. 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Overview of the Requirements In this section we provide an overview of the requirements of an enhanced VPN. Bryant & Dong Expires May 3, 2018 [Page 3] Internet-Draft VPN+ October 2017 3.1. Isolation between VPNs The requirement is to provide both hard and soft isolation between the tenants/applications using one enhanced VPN and the tenants/ applications using another enhanced VPN. Hard isolation is needed so that applications with exacting requirements can function correctly despite a flash demand being created on another VPN competing for the underlying resources. An example might be a network supporting both emergency services and public broadband multi-media services. During a major incident the VPNs supporting these services would both be expected to experience high data volumes, and it is important that both make progress in the transmission of their data. In these circumstances the VPNs would require an appropriate degree of isolation to be able to continue to operate acceptably. We introduce the terms hard (static) and soft (dynamic) isolation to cover cases such as the above. A VPN has soft isolation if the traffic of one VPN cannot be inspected by the traffic of another. Both IP and MPLS VPNs are examples of soft isolated VPNs because the network delivers the traffic only to the required VPN endpoints. However the traffic from one or more VPNs and regular network traffic may congest the network resulting in delays for other VPNs operating normally. The ability for a VPN to be sheltered from this effect is called hard isolation, and this property is required by some critical applications. Although these isolation requirements are triggered by the needs of 5G networks, they have general utility. It is of course possible to achieve high degrees of isolation in the optical layer. However this is done at the cost of allocating resources on a long term basis and end-to-end basis. Such an arrangement means that the full cost of the resources must be borne by the service that is allocated the resources. On the other hand, isolation at the packet layer allows the resources to be shared among-st many services and only dedicated to a service on a temporary basis. This allows greater statistical multiplexing of network resources and amortizes the cost over many services, leading to better economy. However, the degree of isolation required by network slicing cannot easily be met with MPLS-TE packet LSPs. Thus some trade-off between the two approaches needs to be considered to provide the required isolation between virtual networks while still allows reasonable sharing inside each VPN. The work of the IEEE project on Time Sensitive Networking is introducing the concept of packet scheduling where a high priority packet stream may be given a scheduled time slot thereby guaranteeing that it experiences no queuing delay and hence a reduced latency. However where no Bryant & Dong Expires May 3, 2018 [Page 4] Internet-Draft VPN+ October 2017 scheduled packet arrives its reserved time-slot is handed over to best effort traffic, thereby improving the economics of the network. One of the key areas in which isolation needs to be provided is at the interfaces. If nothing is done the system falls back to the router queuing system in which the ingress places it on a selected output queue. Modern routers have quite sophisticated output queuing systems, but normally these do not provide the type of scheduling system needed to support the levels of isolation needed for the applications that are the target of VPN+ networks. One alternative approach is to employ a true time domain multiplexing system with fixed time elements allocated to a number of sub-interfaces. This is the approach that FlexE uses. As noted elsewhere this produces hard isolation but at the cost of making the reclamation of unused bandwidth harder. Another approach, pursued in the Time Sensitive Networking (TSN) space, is to time schedule the transmission of one, or a small number of packets from a queue dedicated to a time-slot. Such an approach appears to offer greater flexibility for the reclamation of unused bandwidth, thereby improving the economics of the system. These approaches can usefully be used in tandem. It is possible to use FlexE to provide tenant isolation, and then to use the TSN approach over FlexE to provide service performance guarantee inside the a slice/tenant VPN. 3.2. Guaranteed Performance There are several aspects to guaranteed performance, guaranteed maximum packet loss, guaranteed maximum delay and guaranteed delay variation. Guaranteed maximum packet loss is a common parameter, and is usually addressed by setting the packet priorities, queue size and discard policy. However this becomes more difficult when the requirement is combine with the latency requirement. The limiting case is zero congestion loss, and than is the goal of the Deterministic Networking work that the IETF and IEEE are pursuing. In modern optical networks loss due to transmission errors is already asymptotic to zero due, but there is always the possibility of failure of the interface and the fiber itself. This can only be addressed by some form of packet duplication and transmission over diverse paths. Guaranteed maximum latency is required in a number of applications particularly real-time control applications and some types of virtual reality applications. The work of the IETF Deterministic Networking (DetNet) Working Group is relevant, however the scope needs to be Bryant & Dong Expires May 3, 2018 [Page 5] Internet-Draft VPN+ October 2017 extended to methods of enhancing the underlay to better support the delay guarantee, and to integrate these enhancements with the overall service provision. Guaranteed maximum delay variation is a service that may also be needed. Time transfer is one example of a service that needs this, although the fungible nature of time means that it might be delivered by the underlay as a shared service and not provided through different virtual networks. Alternatively a dedicated virtual network may be used to provide this as a shared service. The need for guaranteed maximum delay variation as a general requirement is for further study. A useful mechanism to provide these guarantees is to use Flex Ethernet [FLEXE] as the underlay. This is a method of bonding Ethernets together and of providing time-slot based channelization over an Ethernet bearer. Such channels are fully isolated from other channels running over the same Ethernet bearer. 3.3. Integration A solution to the enhanced VPN problem will need to provide seamless integration of both physical and virtual network. Given the targeting of both this technology and service function chaining at mobile networks and in particular 5G the co-integration of service functions is a likely requirement. 3.4. Dynamic Configuration It is necessary that new enhanced VPNs can be introduced to the network, modified, and removed from the network. In doing so due regard must be given to the impact of other enhanced VPNs that are operational. An enhanced VPN that requires hard isolation must not be disrupted by the installation or modification of another enhanced VPN. Whether modification of an enhanced VPN can be disruptive to that VPN, and in particular the traffic in flight is to be determined, but is likely to be a difficult problem to address. The data-plane aspect of this are discussed further in Section 7. The control-plane aspects of this, particularly the garbage collection are likely to be challenging and are for further study. Bryant & Dong Expires May 3, 2018 [Page 6] Internet-Draft VPN+ October 2017 3.5. Customized Control Plane In some cases it is desirable that an enhanced VPN has a custom control plane, so that the tenant of the enhanced VPN can have some control to the resources and functions partitioned for this VPN. Each enhanced VPN may have its own dedicated controller, or be provided with an interface to the control plane of the underlay. Further detail on this requirement will be provided in a future version of the draft. 4. Architecture and Components of VPN+ VPN+ runs over a substrate or underlay that it draws on to provide the resources and features needed to provide enhanced VPN services to its tenants. The assumption is that a number of such enhanced VPNs are layered on this underlay, each drawing the resources that they need to satisfy the needs of their tenants. Thus each enhanced VPN is bound to a specific set of resources allocated from the underlay, with different subsets of the underlay resources dedicated to different enhanced VPNs. The consequence of this is that any VPN+ solution needs tighter coupling to underlay that is the case with classical VPNs. An enhanced VPN needs to be designed with consideration given to: o The layering of the VPN+ data-plane onto the substrate. o The amount of static and dynamic state. o The ammount of state in the packet vs the am-mount of state in the control plane. o How sufficient isolation is achieved between VPN+ instances and between VPN+ instances and the best effort traffic. o How the required latency demands are achieved. o Support of the required integration between network functions and service functions. o The design of the control plane. 4.1. Data-Plane The data-plane is required to provide each VPN+ with paths through the specific resources allocated to it. This requires a finer granularity of packet steering than is normally provided in networks. Bryant & Dong Expires May 3, 2018 [Page 7] Internet-Draft VPN+ October 2017 One of the candidate approaches is to use segment routing. This is discussed Section 4.1.2. 4.1.1. Data-plane Layering An enhanced VPN needs to run on a substrate or underlay that can draw on to provide the resources and features it needs. In order to meet the isolation requirement, network resources in the underlay need to split into different subsets, which are dedicated to different VPNs. For VPNs which require hard isolation, at least the underlay tunnels cannot be shared. In a scalable solution we need to layer a number of VPNs on the underlay, and for each enhanced VPN to draws on the resources provided by the underlay to deliver a service with the required properties. Different subsets of the underlay resources are dedicated to different VPNs. The VPN+ solution needs tighter coupling with underlay. We cannot for example share the tunnel between enhanced VPNs which require hard isolation. 4.1.2. Use of Segment Routing Constructs Clearly we can use traditional constructs to create a VPN, but there are advantages to the use of other constructs such as Segment Routing (SR) in the creation of virtual networks with enhanced properties. Segment Routing [I-D.ietf-spring-segment-routing] is a method that prepends instructions to packets at entry and sometimes at various points as it passes though the network. These instructions allow packets to be routed on paths other than the shortest path for various traffic engineering reasons. These paths can be strict or loose paths, depending on the compactness required of the instruction list and the degree of autonomy granted to the network (for example to support ECMP). With SR, a path needs to be dynamically created through a set of resources by simply specifying the Segment IDs (SIDs), i.e. instructions rooted at a particular point in the network. Thus if a path is to be provisioned from some ingress point A to some egress point B in the underlay, A is provided with the A..B SID list and instructions on how to identify the packets to which the SID list is to be prepended. 4.1.3. Segment Routing and Isolation With current segment routing, the instructions are used to specify the nodes and links to be traversed. However, in order to achieve the required isolation between different services, new instructions Bryant & Dong Expires May 3, 2018 [Page 8] Internet-Draft VPN+ October 2017 can be created which can be prepended to a packet to steer it through specific dedicated network resources and functions, e.g. links, queues, processors, services etc. 4.2. Stateful and Stateless Virtual Networks A VPN is a network created by applying a multiplexing technique to the underlying network (the underlay) in order 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 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, as we increase the coupling between the underlay and the overlay to support the VPN which requires enhanced VPN service, this state will increase further. By encoding the state in the packet, as is done in Segment Routing, state is transitioned out of the network. A-------B-----E | | | | | | C-------D-----+ Figure 1: An SR Network Fragment Consider the network fragment shown in Figure 1. To send a packet from A to E via B, D & E: Node A prepends the ordered list of SIDs:D, E to the packet and pushes the packet to B. SID list {B, D, E} can be used as a VPN path. Thus, to create a VPN, a set of SID Lists is created and provided to each ingress node of the VPN together with packet selection criteria. In this way it is possible to create a VPN with no state in the core. However this is at the expense of creating a larger packet with possible MTU and hardware restriction limits that need to be overcome. Note in the above if A and E support multiple VPN an additional VPN identifier will need to be added to the packet, but this is omitted from this text for simplicity. Bryant & Dong Expires May 3, 2018 [Page 9] Internet-Draft VPN+ October 2017 A---P---B---S---E | | | | Q | | | | C---R---D-------+ Figure 2: Another SR Network Fragment Consider a further network fragment shown in Figure 2, and further consider VPN A+D+E. A has lists: {P, B, Q, D}, {P, B, S, E} D has lists: {Q, B, P, A}, {E} E has lists: {S, B, P, A}, {D} To create a new VPN C+D+B the following list are introduced: C lists: {R, D}, {A, P, B} D lists: {R, C}, {Q, B} B lists: {Q, D}, {P, A, C} Thus VPN C+D+B was created without touching the settings of the core routers, indeed it is possible to add endpoints to the VPNs, and move the paths around simply by providing new lists to the affected endpoints. When SR is extended to support isolation finer granularity state needs to be added to the core in anticipation of its use. We therefore need to evaluate the balance between this additional state and the performance delivered by the network. 4.3. Latency Support The IETF has ongoing work on support for a latency ceiling [I-D.ietf-detnet-architecture]. The provision of a latency ceiling is a requirement of the application seeking the use of enhanced virtual networks. The current design of DetNet assumes the design of the underlay network is unchanged. In this document we look at some changes that could be used to assist in achieving low latency ceiling across the wide area. Traditionally a traffic engineered path operates with a granularity of a link with hints about priority provided through the use of the traffic class field in the header. However to achieve the latency and isolation characteristics that are sought by VPN+ users, steering packets through specific queues resources will likely be required. The extent to which these needs can be satisfied through existing QoS mechanisms is to be determined. What is clear is that a fine control Bryant & Dong Expires May 3, 2018 [Page 10] Internet-Draft VPN+ October 2017 of which services wait for which, with a fine granularity of queue management policy is needed. Note that the concept of a queue is a useful abstraction for many types of underlay mechanism that may be used to provide enhanced latency support. From the perspective of the control plane and from the perspective of the segment routing the method of steering a packet to a queue that provides the required properties is a universal construct. How the queue satisfies the requirement is outside the scope of these aspect of the enhanced VPN system. Thus for example a FlexE channel, or time sensitive networking packet scheduling slot are abstracted to the same concept and bound to the data plane in a common manner. We can introduce the specification of finer, deterministic, granularity to path selection through extensions to traditional path construction techniques such as RSVP-TE and MPLS-TP. We can also introduce it by specifying the queue through an SR instruction list. Thus new SR instructions may be created to specify not only which resources are traversed, but in some cases how they are traversed. For example, it may be possible to specify not only the queue to be used but the policy to be applied when enqueuing and dequeuing. This concept can be further generalized, since as well as queuing to the output port of a router, it is possible to queue to any resource, for example: o A network processor unit (NPU) o A Central Processing Unit (CPU) Core o A Look-up engine such as TCAM 4.4. Integrating Service Function Chains and VPNs There is a significant overlap between the problem of routing a packet though a set of network resources and the problem of routing a packet through a set of compute resources. Service Function Chain technology is designed to forward a packet through a set of compute resources. A future version of this document will discuss this further. 4.5. Application Specific Network Types Although the transport service that underpins the extended VPN is likely MPLS/IP based, it needs to be able to carry application Bryant & Dong Expires May 3, 2018 [Page 11] Internet-Draft VPN+ October 2017 specific non-MPLS/IP traffic. This can be accommodated through the use of pseudowires (PWs). 4.6. Control Plane Considerations It is expected that VPN+ would be based on a hybrid control mechanism, which takes advantage of the logically centralized controller for on-demand provisioning and global optimization, whilst still relies on distributed control plane to provide scalability, high reliability, fast reaction, automatic failure recovery etc. Extension and optimization to the distributed control plane is needed to support the enhanced properties of VPN+. Where SR is used as a the data-plane construct it needs to be noted that it does not have the capability of reserving resources along the path nor do its currently specified distributed control plane (the link state routing protocols). An SDN controller can clearly do this, from the controllers point of view, and no resource reservation is done on the device. Thus if a distributed control plane is needed either in place of an SDN controller or as an assistant to it there is a risk of resource conflict. This needs further study. On the other hand an advantage of using an SR approach is that it provides a way of efficiently binding the network underlay and the enhanced VPN overlay. With a technology such as RSVP-TE LSPs, each virtual path in the VPN is bound to the underlay with a dedicated TE- LSP. RSVP-TE could be enhanced to bind the VPN to specific resources within the underlay, but as noted elsewhere in this document there are concerns as to the scalability of this approach. With an SR- based approach to resource reservation (per-slice reservation), it is straightforward to create dedicated SR network slices, and the VPN can be bound to a particular SR network slice. 5. Scalability Considerations For a packet to transit a network, other than on a best effort, shortest path basis, it is necessary to introduce additional state, either in the packet, or in the network of some combination of both. There are at least three ways of doing this: o Introduce the complete state into the packet. That is how SR does this, and this allows the controller to specify the precise series of forwarding and processing instructions that will happen to 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 Bryant & Dong Expires May 3, 2018 [Page 12] Internet-Draft VPN+ October 2017 service. This is a type of latent state, and increases as we more precisely specify the path and resources that need to be exclusively available to a VPN. o Introduce the state to the network. This is normally done by creating a path using RSVP-TE, which can be extended to introduce any element that needs to be specified along the path, for example explicitly specifying queuing policy. It is of course possible to use other methods to introduce path state, such as via a Software Defined Network (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 its life- cycle. This is more state than is needed using SR, but the packet are shorter. o Provide a hybrid approach based on using binding SIDs to create path fragments, and bind them together with SR. Dynamic creation of a VPN path using SR requires less state maintenance in the network core at the expense of larger VPN headers on the packet. The scaling properties will reduce roughly from a function of (N/2)^2 to a function of N, where N is the VPN path length in intervention points (hops plus network functions). Reducing the state in the network is important to VPN+, as VPN+ requires the overlay to be more closely integrated with the underlay than with traditional VPNs. This tighter coupling would normally mean that significant state needed to be created and maintained in the core. However, a segment routed approach allows much of this state to be spread amongst the network ingress nodes, and transiently carried in the packets as SIDs. These approaches are for further study. 5.1. Maximum Stack Depth One of the challenges with SR is the stack depth that nodes are able to impose on packets. This leads to a difficult balance between adding state to the network and minimizing stack depth, or minimizing state and increasing the stack depth. 5.2. RSVP scalability The traditional method of creating a resource allocated path through an MPLS network is to use the RSVP protocol. However there have been concerns that this requires significant continuous state maintenance in the network. There are ongoing works to improve the scalability of RSVP-TE LSPs in the control plane Bryant & Dong Expires May 3, 2018 [Page 13] Internet-Draft VPN+ October 2017 [I-D.ietf-teas-rsvp-te-scaling-rec]. This will be considered further in a future version of this document. There is also concern at the scalability of the forwarder footprint of RSVP as the number of paths through an LSR grows [I-D.sitaraman-mpls-rsvp-shared-labels] proposes to address this by employing SR within a tunnel established by RSVP-TE. This work will be considered in a future version of this document. 6. OAM and Instrumentation This will be discussed in a future version of this draft. A discussion should include o Instrumentation of the underlay. o Instrumentation of the overlay by both customer and provider. o Verification of the conformity of the path to the service requirement. 7. Service Disruption During Change Each enhanced VPN, of necessity, has a life-cycle, and needs modification during deployment as the needs of its user change. Additionally as the network as a whole evolves there will 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. However implementations and the monitoring protocols need to make sure that the new path is up before traffic is transitioned to it. 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 and other if a path latency reduces during a transition. o The problem of the latency transient 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. An alternative is some form of N+1 delivery such as has Bryant & Dong Expires May 3, 2018 [Page 14] Internet-Draft VPN+ October 2017 been used for many years to support protection from service disruption. This may be taken to a different level using the techniques proposed by the IETF deterministic network work with multiple in-network replication and the culling of later packets. In addition to the approach used to protect high priority packets, consideration has to be given to the impact of best effort traffic on the high priority packets during a transient. 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. 8. Security Considerations All types of virtual network require special consideration to be given to the isolation between the tenants. However in an enhanced virtual network service hard isolation needs to be considered. If a service requires a specific latency then it can be damaged by simply delaying the packet through the activities of another tenant. In a network with virtual functions, depriving a function used by another tenant of compute resources can be just as damaging as delaying transmission of a packet in the network. 9. IANA Considerations There are no requested IANA actions. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . 10.2. Informative References [FLEXE] "Flex Ethernet Implementation Agreement", March 2016, . Bryant & Dong Expires May 3, 2018 [Page 15] Internet-Draft VPN+ October 2017 [I-D.geng-netslices-architecture] 67, 4., Dong, J., Bryant, S., kiran.makhijani@huawei.com, k., Galis, A., Foy, X., and S. Kuklinski, "Network Slicing Architecture", draft-geng-netslices-architecture-02 (work in progress), July 2017. [I-D.ietf-detnet-architecture] Finn, N., Thubert, P., Varga, B., and J. Farkas, "Deterministic Networking Architecture", draft-ietf- detnet-architecture-03 (work in progress), August 2017. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf-spring-segment-routing-13 (work in progress), October 2017. [I-D.ietf-teas-rsvp-te-scaling-rec] Beeram, V., Minei, I., Shakir, R., Pacella, D., and T. Saad, "Techniques to Improve the Scalability of RSVP Traffic Engineering Deployments", draft-ietf-teas-rsvp-te- scaling-rec-07 (work in progress), September 2017. [I-D.sitaraman-mpls-rsvp-shared-labels] Sitaraman, H., Beeram, V., Parikh, T., and T. Saad, "Signaling RSVP-TE tunnels on a shared MPLS forwarding plane", draft-sitaraman-mpls-rsvp-shared-labels-02 (work in progress), September 2017. Authors' Addresses Stewart Bryant Huawei Email: stewart.bryant@gmail.com Jie Dong Huawei Email: jie.dong@huawei.com Bryant & Dong Expires May 3, 2018 [Page 16]