Internet Engineering Task Force T. Mizrahi
Internet-Draft HUAWEI
Intended status: Informational E. Grossman, Ed.
Expires: February 15, 2021 DOLBY
August 14, 2020

Deterministic Networking (DetNet) Security Considerations


A DetNet (deterministic network) provides specific performance guarantees to its data flows, such as extremely low data loss rates and bounded latency. As a result, securing a DetNet requires that in addition to the best practice security measures taken for any mission-critical network, additional security measures may be needed to secure the intended operation of these novel service properties.

This document addresses DetNet-specific security considerations from the perspectives of both the DetNet system-level designer and component designer. System considerations include a threat model, taxonomy of relevant attacks, and associations of threats versus use cases and service properties. Component-level considerations include ingress filtering and packet arrival time violation detection. This document also addresses DetNet security considerations specific to the IP and MPLS data plane technologies thereby complementing the Security Considerations sections of the various DetNet Data Plane (and other) DetNet documents.

Status of This Memo

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Table of Contents

1. Introduction

A deterministic network is one that can carry data flows for real-time applications with extremely low data loss rates and bounded latency. Deterministic networks have been successfully deployed in real-time Operational Technology (OT) applications for some years. However, such networks are typically isolated from external access, and thus the security threat from external attackers is low. IETF Deterministic Networking (DetNet, [RFC8655]) specifies a set of technologies that enable creation of deterministic networks on IP-based networks of potentially wide area (on the scale of a corporate network) potentially bringing the OT network into contact with Information Technology (IT) traffic and security threats that lie outside of a tightly controlled and bounded area (such as the internals of an aircraft).

These DetNet technologies have not previously been deployed together on a wide area IP-based network, and thus can present security considerations that may be new to IP-based wide area network designers; this document provides insight into such system-level security considerations. In addition, designers of DetNet components (such as routers) face new security-related challenges in providing DetNet services, for example maintaining reliable isolation between traffic flows in an environment where IT traffic co-mingles with critical reserved-bandwidth OT traffic; this document also examines security implications internal to DetNet components.

Security is of particularly high importance in DetNet networks because many of the use cases which are enabled by DetNet [RFC8578] include control of physical devices (power grid components, industrial controls, building controls) which can have high operational costs for failure, and present potentially attractive targets for cyber-attackers.

This situation is even more acute given that one of the goals of DetNet is to provide a "converged network", i.e. one that includes both IT traffic and OT traffic, thus exposing potentially sensitive OT devices to attack in ways that were not previously common (usually because they were under a separate control system or otherwise isolated from the IT network, for example [ARINC664P7]). Security considerations for OT networks are not a new area, and there are many OT networks today that are connected to wide area networks or the Internet; this document focuses on the issues that are specific to the DetNet technologies and use cases.

Given the above considerations, securing a DetNet starts with a scrupulously well-designed and well-managed engineered network following industry best practices for security at both the data plane and controller plane; this is the assumed starting point for the considerations discussed herein. Such assumptions also depend on the network components themselves upholding the security-related properties that are to be assumed by DetNet system-level designers; for example, the assumption that network traffic associated with a given flow can never affect traffic associated with a different flow is only true if the underlying components make it so. Such properties, which may represent new challenges to component designers, are also considered herein.

In this context we view the network design and management aspects of network security as being primarily concerned with denial-of service prevention by ensuring that DetNet traffic goes where it's supposed to and that an external attacker can't inject traffic that disrupts the DetNet's delivery timing assurance. The time-specific aspects of DetNet security presented here take up where the design and management aspects leave off.

The exact security requirements for any given DetNet network are necessarily specific to the use cases handled by that network. Thus the reader is assumed to be familiar with the specific security requirements of their use cases, for example those outlined in the DetNet Use Cases [RFC8578] and the Security Considerations sections of the DetNet documents applicable to the network technologies in use, for example [I-D.ietf-detnet-ip]). A general introduction to the DetNet architecture can be found in [RFC8655] and it is also recommended to be familiar with the DetNet Data Plane [I-D.ietf-detnet-data-plane-framework] and Flow Information Model [I-D.ietf-detnet-flow-information-model].

The DetNet technologies include ways to:

This document includes sections considering DetNet component design as well as system design. The latter includes threat modeling and analysis, threat impact and mitigation, and the association of attacks with use cases (based on the Use Case Common Themes section of the DetNet Use Cases [RFC8578]).

The structure of the threat model and threat analysis sections were originally derived from [RFC7384], which also considers time-related security considerations in IP networks.

2. Abbreviations and Terminology

IT         Information Technology (the application of computers to store, study, retrieve, transmit, and manipulate data or information, often in the context of a business or other enterprise - [IT_DEF]).

OT         Operational Technology (the hardware and software dedicated to detecting or causing changes in physical processes through direct monitoring and/or control of physical devices such as valves, pumps, etc. - [OT_DEF])

MITM       Man in the Middle

Component       A component of a DetNet system - used here to refer to any hardware or software element of a DetNet network which implements DetNet-specific functionality, for example all or part of a router, switch, or end system.

Resource Segmentation       Used as a more general form for Network Segmentation (the act or practice of splitting a computer network into subnetworks, each being a network segment - [RS_DEF])

3. Security Considerations for DetNet Component Design

As noted above, DetNet provides resource allocation, explicit routes and redundant path support. Each of these has associated security implications, which are discussed in this section, in the context of component design. Detection, reporting and appropriate action in the case of packet arrival time violations are also discussed.

3.1. Resource Allocation

A DetNet system security designer relies on the premise that any resources allocated to a resource-reserved (OT-type) flow are inviolable, in other words there is no physical possibility within a DetNet component that resources allocated to a given flow can be compromised by any type of traffic in the network; this includes both malicious traffic as well as inadvertent traffic such as might be produced by a malfunctioning component, for example one made by a different manufacturer. From a security standpoint, this is a critical assumption, for example when designing against DOS attacks. It is the responsibility of the component designer to ensure that this condition is met; this implies protection against excess traffic from adjacent flows, and against compromises to the resource allocation/deallocation process.

3.2. Explicit Routes

The DetNet-specific purpose for constraining the network's ability to re-route OT traffic is to maintain the specified service parameters (such as upper and lower latency boundaries) for a given flow. For example if the network were to re-route a flow (or some part of a flow) based exclusively on statistical path usage metrics, or due to malicious activity, it is possible that the new path would have a latency that is outside the required latency bounds which were designed into the original TE-designed path, thereby violating the quality of service for the affected flow (or part of that flow).

However, it is acceptable for the network to re-route OT traffic in such a way as to maintain the specified latency bounds (and any other specified service properties) for any reason, for example in response to a runtime component or path failure. From a security standpoint, the system designer relies on the premise that the packets will be delivered with the specified latency boundaries; thus any component that is involved in controlling or implementing any change of the initially TE-configured flow routes needs to prevent malicious or accidental re-routing of OT flows that might adversely affect delivering the traffic within the specified service parameters.

3.3. Redundant Path Support

The DetNet provision for redundant paths (PREOF) (as defined in the DetNet Architecture [RFC8655]) provides the foundation for high reliablity of a DetNet, by virtually eliminating packet loss (i.e. to a degree which is implementation-dependent) through hitless redundant packet delivery. (Note that PREOF is not defined for a DetNet IP data plane).

It is the responsibility of the system designer to determine the level of reliability required by their use case, and to specify redundant paths sufficient to provide the desired level of reliability (in as much as that reliability can be provided through the use of redundant paths). It is the responsibility of the component designer to ensure that the relevant PREOF operations are executed reliably and securely. (However, note that not all PREOF operations are necessarily implemented in every network; for example a packet re-ordering function may not be necessary if the packets are either not required to be in order, or if the ordering is performed in some other part of the network.)

As noted in Section 7.2, Integrity Protection, there is a trust relationship between the pair of devices that replicate and remove packets, so it is the responsibility of the system designer to define these relationships with the appropriate security considerations, and the components must each uphold the security rights implied by these relationships.

Ideally a redundant path could be specified from end to end of the flow's path, however given that this is not always possible (as described in [RFC8655]) the system designer will need to consider the resulting end-to-end reliability and security resulting from any given arrangment of network segments along the path, each of which provides its individual PREOF implementation and thus its individual level of reliabiilty and security.

At the data plane the implementation of PREOF depends on the correct assignment and interpretation of packet sequence numbers, as well as the actions taken based on them, such as elimination. Thus the integrity of these values must be maintained by the component as they are assigned by the DetNet Data Plane's Service sub-layer, and transported by the Forwarding sub-layer.

3.4. Timing (or other) Violation Reporting

Another fundamental assumption of a secure DetNet is that in any case in which an incoming packet arrives with any timing or bandwidth violation, something can be done about it which doesn't cause damage to the system. For example having the network shut down a link if a packet arrives outside of its prescribed time window may serve the attacker better than it serves the network. That means that the component's data plane must be able to detect and act on a variety of such violations, at least alerting the controller plane. Any action apart from that needs to be carefully considered in the context of the specific system. Some possible violations that warrant detection include cases where a packet arrives:

Logging of such issues is unlikely to be adequate, since a delay in response to the situation could result in material damage, for example to mechanical devices controlled by the network. Given that the data plane component probably has no knowledge of the use case of the network, or its applications and end systems, it would seem useful for a data plane component to allow the system designer to configure its actions in the face of such violations.

Possible direct actions that may be taken at the data plane include dropping the packet and/or shutting down the link; however if any such actions are configured to be taken, the system designer must ensure that such actions do not compromise the continued safe operation of the system. For example, the controller plane should mitigate in a timely fashion any potential adverse effect on mechanical devices controlled by the network.

4. DetNet Security Considerations Compared With DiffServ Security Considerations

DetNet is designed to be compatible with DiffServ [RFC2474] as applied to IT traffic in the DetNet. DetNet also incorporates the use of the 6-bit value of the DSCP field of the TOS field of the IP header for flow identification for OT traffic, however the DetNet interpretation of the DSCP value for OT traffic is not equivalent to the PHB selection behavior as defined by DiffServ.

Thus security consideration for DetNet have some aspects in common with DiffServ, in fact overlapping 100% with respect to IP IT traffic. Security considerations for these aspects are part of the existing literature on IP network security, specifically the Security sections of [RFC2474] and [RFC2475]. However DetNet also introduces timing and other considerations which are not present in DiffServ, so the DiffServ security considerations are necessary but not sufficient for DetNet.

In the case of DetNet OT traffic, the DSCP value, although interpreted differently than in DiffServ, does contribute to determination of the service provided to the packet. Thus in DetNet there are similar consequences to DiffServ for lack of detection of, or incorrect handling of, packets with mismarked DSCP values, and thus many of the points made in the DiffServ draft Security discussions are also relevant to DetNet OT traffic, though perhaps in modified form. For example, in DetNet the effect of an undetected or incorrectly handled maliciously mismarked DSCP field in an OT packet is not identical to affecting that packet's PHB, since DetNet does not use the PHB concept for OT traffic, but nonetheless the service provided to the packet could be affected, so mitigation measures analogous to those prescribed by DiffServ would be appropriate for DetNet. For example, mismarked DSCP values should not cause failure of network nodes, and any internal link that cannot be adequately secured against modification of DSCP values should be treated as a boundary link (and hence any arriving traffic on that link is treated as if it were entering the domain at an ingress node). The remarks in [RFC2474] regarding IPsec and Tunnelling Interactions are also relevant (though this is not to say that other sections are less relevant).

5. Security Threats

This section presents a threat model, and analyzes the possible threats in a DetNet-enabled network. The threats considered in this section are independent of any specific technologies used to implement the DetNet; Section 9) considers attacks that are associated with the DetNet technologies encompassed by [I-D.ietf-detnet-data-plane-framework].

We distinguish controller plane threats from data plane threats. The attack surface may be the same, but the types of attacks as well as the motivation behind them, are different. For example, a delay attack is more relevant to data plane than to controller plane. There is also a difference in terms of security solutions: the way you secure the data plane is often different than the way you secure the controller plane.

5.1. Threat Model

The threat model used in this memo is based on the threat model of Section 3.1 of [RFC7384]. This model classifies attackers based on two criteria:

Care has also been taken to adhere to Section 5 of [RFC3552], both with respect to which attacks are considered out-of-scope for this document, but also which are considered to be the most common threats (explored further in Section 5.2, Threat Analysis). Most of the direct threats to DetNet are active attacks, but it is highly suggested that DetNet application developers take appropriate measures to protect the content of the DetNet flows from passive attacks.

DetNet-Service, one of the service scenarios described in [I-D.varga-detnet-service-model], is the case where a service connects DetNet networking islands, i.e. two or more otherwise independent DetNet network domains are connected via a link that is not intrinsically part of either network. This implies that there could be DetNet traffic flowing over a non-DetNet link, which may provide an attacker with an advantageous opportunity to tamper with DetNet traffic. The security properties of non-DetNet links are outside of the scope of DetNet Security, but it should be noted that use of non-DetNet services to interconnect DetNet networks merits security analysis to ensure the integrity of the DetNet networks involved.

5.2. Threat Analysis

5.2.1. Delay

An attacker can maliciously delay DetNet data flow traffic. By delaying the traffic, the attacker can compromise the service of applications that are sensitive to high delays or to high delay variation. The delay may be constant or modulated.

5.2.2. DetNet Flow Modification or Spoofing

An attacker can modify some header fields of en route packets in a way that causes the DetNet flow identification mechanisms to misclassify the flow. Alternatively, the attacker can inject traffic that is tailored to appear as if it belongs to a legitimate DetNet flow. The potential consequence is that the DetNet flow resource allocation cannot guarantee the performance that is expected when the flow identification works correctly.

5.2.3. Resource Segmentation (Inter-segment Attack)

An attacker can inject traffic that will consume network resources such that it affects DetNet flows. This can be performed using non-DetNet traffic that indirectly affects DetNet traffic (hardware resource exhaustion), or by using DetNet traffic from one DetNet flow that directly affects traffic from different DetNet flows.

5.2.4. Packet Replication and Elimination Replication: Increased Attack Surface

Redundancy is intended to increase the robustness and survivability of DetNet flows, and replication over multiple paths can potentially mitigate an attack that is limited to a single path. However, the fact that packets are replicated over multiple paths increases the attack surface of the network, i.e., there are more points in the network that may be subject to attacks. Replication-related Header Manipulation

An attacker can manipulate the replication-related header fields. This capability opens the door for various types of attacks. For example:

5.2.5. Path Choice Path Manipulation

An attacker can maliciously change, add, or remove a path, thereby affecting the corresponding DetNet flows that use the path. Path Choice: Increased Attack Surface

One of the possible consequences of a path manipulation attack is an increased attack surface. Thus, when the attack described in the previous subsection is implemented, it may increase the potential of other attacks to be performed.

5.2.6. Controller Plane Control or Signaling Packet Modification

An attacker can maliciously modify en route control packets in order to disrupt or manipulate the DetNet path/resource allocation. Control or Signaling Packet Injection

An attacker can maliciously inject control packets in order to disrupt or manipulate the DetNet path/resource allocation.

5.2.7. Scheduling or Shaping Reconnaissance

A passive eavesdropper can identify DetNet flows and then gather information about en route DetNet flows, e.g., the number of DetNet flows, their bandwidths, their schedules, or other temporal properties. The gathered information can later be used to invoke other attacks on some or all of the flows.

Note that in some cases DetNet flows may be identified based on an explicit DetNet header, but in some cases the flow identification may be based on fields from the L3/L4 headers. If L3/L4 headers are involved, for the purposes of this document we assume they are encrypted and/or integrity-protected from external attackers.

5.2.8. Time Synchronization Mechanisms

An attacker can use any of the attacks described in [RFC7384] to attack the synchronization protocol, thus affecting the DetNet service.

5.3. Threat Summary

A summary of the attacks that were discussed in this section is presented in Figure 1. For each attack, the table specifies the type of attackers that may invoke the attack. In the context of this summary, the distinction between internal and external attacks is under the assumption that a corresponding security mechanism is being used, and that the corresponding network equipment takes part in this mechanism.

| Attack                                  |   Attacker Type   |
|                                         +---------+---------+
|                                         |Internal |External |
|                                         |MITM|Inj.|MITM|Inj.|
|Delay attack                             | +  | +  | +  | +  |
|DetNet Flow Modification or Spoofing     | +  | +  |    |    |
|Inter-segment Attack                     | +  | +  |    |    |
|Replication: Increased Attack Surface    | +  | +  | +  | +  |
|Replication-related Header Manipulation  | +  |    |    |    |
|Path Manipulation                        | +  | +  |    |    |
|Path Choice: Increased Attack Surface    | +  | +  | +  | +  |
|Control or Signaling Packet Modification | +  |    |    |    |
|Control or Signaling Packet Injection    |    | +  |    |    |
|Reconnaissance                           | +  |    | +  |    |
|Attacks on Time Sync Mechanisms          | +  | +  | +  | +  |

Figure 1: Threat Analysis Summary

6. Security Threat Impacts

This section describes and rates the impact of the attacks described in Section 5, Security Threats. In this section, the impacts as described assume that the associated mitigation is not present or has failed. Mitigations are discussed in Section 7, Security Threat Mitigation.

In computer security, the impact (or consequence) of an incident can be measured in loss of confidentiality, integrity or availability of information. In the case of time sensitive networks, the impact of a network exploit can also include failure or malfunction of mechanical and/or other OT systems.

DetNet raises these stakes significantly for OT applications, particularly those which may have been designed to run in an OT-only environment and thus may not have been designed for security in an IT environment with its associated devices, services and protocols.

The severity of various components of the impact of a successful vulnerability exploit to use cases by industry is available in more detail in the DetNet Use Cases [RFC8578]. Each of these use cases is represented in the table below, including Pro Audio, Electrical Utilities, Industrial M2M (split into two areas, M2M Data Gathering and M2M Control Loop), and others.

Components of Impact (left column) include Criticality of Failure, Effects of Failure, Recovery, and DetNet Functional Dependence. Criticality of failure summarizes the seriousness of the impact. The impact of a resulting failure can affect many different metrics that vary greatly in scope and severity. In order to reduce the number of variables, only the following were included: Financial, Health and Safety, People well being (People WB), Affect on a single organization, and affect on multiple organizations. Recovery outlines how long it would take for an affected use case to get back to its pre-failure state (Recovery time objective, RTO), and how much of the original service would be lost in between the time of service failure and recovery to original state (Recovery Point Objective, RPO). DetNet dependence maps how much the following DetNet service objectives contribute to impact of failure: Time dependency, data integrity, source node integrity, availability, latency/jitter.

The scale of the Impact mappings is low, medium, and high. In some use cases there may be a multitude of specific applications in which DetNet is used. For simplicity this section attempts to average the varied impacts of different applications. This section does not address the overall risk of a certain impact which would require the likelihood of a failure happening.

In practice any such ratings will vary from case to case; the ratings shown here are given as examples.

Table, Part One (of Two)
|                  | Pro A | Util | Bldg |Wire- | Cell |M2M  |M2M  |
|                  |       |      |      | less |      |Data |Ctrl |
| Criticality      | Med   | Hi   | Low  | Med  | Med  | Med | Med |
| Effects
|  Financial       | Med   | Hi   | Med  | Med  | Low  | Med | Med |
|  Health/Safety   | Med   | Hi   | Hi   | Med  | Med  | Med | Med |
|  People WB       | Med   | Hi   | Hi   | Low  | Hi   | Low | Low |
|  Effect 1 org    | Hi    | Hi   | Med  | Hi   | Med  | Med | Med |
|  Effect >1 org   | Med   | Hi   | Low  | Med  | Med  | Med | Med |
|  Recov Time Obj  | Med   | Hi   | Med  | Hi   | Hi   | Hi  | Hi  |
|  Recov Point Obj | Med   | Hi   | Low  | Med  | Low  | Hi  | Hi  |
|DetNet Dependence
|  Time Dependency | Hi    | Hi   | Low  | Hi   | Med  | Low | Hi  |
|  Latency/Jitter  | Hi    | Hi   | Med  | Med  | Low  | Low | Hi  |
|  Data Integrity  | Hi    | Hi   | Med  | Hi   | Low  | Hi  | Low |
|  Src Node Integ  | Hi    | Hi   | Med  | Hi   | Med  | Hi  | Hi  |
|  Availability    | Hi    | Hi   | Med  | Hi   | Low  | Hi  | Hi  |

Table, Part Two (of Two)
|                  | Mining | Block | Network |
|                  |        | Chain | Slicing |
| Criticality      | Hi     | Med   | Hi      |
| Effects
|  Financial       | Hi     | Hi    | Hi      |
|  Health/Safety   | Hi     | Low   | Med     |
|  People WB       | Hi     | Low   | Med     |
|  Effect 1 org    | Hi     | Hi    | Hi      |
|  Effect >1 org   | Hi     | Low   | Hi      |
|  Recov Time Obj  | Hi     | Low   | Hi      |
|  Recov Point Obj | Hi     | Low   | Hi      |
|DetNet Dependence
|  Time Dependency | Hi     | Low   | Hi      |
|  Latency/Jitter  | Hi     | Low   | Hi      |
|  Data Integrity  | Hi     | Hi    | Hi      |
|  Src Node Integ  | Hi     | Hi    | Hi      |
|  Availability    | Hi     | Hi    | Hi      |

Figure 2: Impact of Attacks by Use Case Industry

The rest of this section will cover impact of the different groups in more detail.

6.1. Delay-Attacks

6.1.1. Data Plane Delay Attacks

Note that 'delay attack' also includes the possibility of a 'negative delay' or early arrival of a packet, or possibly adversely changing the timestamp value.

Delayed messages in a DetNet link can result in the same behavior as dropped messages in ordinary networks as the services attached to the DetNet flow have strict deterministic requirements.

For a single path scenario, disruption is a real possibility, whereas in a multipath scenario, large delays or instabilities in one DetNet flow can lead to increased buffer and processor resources at the eliminating router.

A data-plane delay attack on a system controlling substantial moving devices, for example in industrial automation, can cause physical damage. For example, if the network promises a bounded latency of 2ms for a flow, yet the machine receives it with 5ms latency, the machine's control loop can become unstable.

6.1.2. Controller Plane Delay Attacks

In and of itself, this is not directly a threat to the DetNet service, but the effects of delaying control messages can have quite adverse effects later.

6.2. Flow Modification and Spoofing

6.2.1. Flow Modification

If the contents of a packet header or body can be modified by the attacker, this can cause the packet to be routed incorrectly or dropped, or the payload to be corrupted or subtly modified.

6.2.2. Spoofing Dataplane Spoofing

Spoofing dataplane messages can result in increased resource consumptions on the routers throughout the network as it will increase buffer usage and processor utilization. This can lead to resource exhaustion and/or increased delay.

If the attacker manages to create valid headers, the false messages can be forwarded through the network, using part of the allocated bandwidth. This in turn can cause legitimate messages to be dropped when the resource budget has been exhausted.

Finally, the endpoint will have to deal with invalid messages being delivered to the endpoint instead of (or in addition to) a valid message. Controller Plane Spoofing

A successful controller plane spoofing-attack will potentionally have adverse effects. It can do virtually anything from:

6.3. Segmentation Attacks (injection)

6.3.1. Data Plane Segmentation

Injection of false messages in a DetNet flow could lead to exhaustion of the available bandwidth for that flow if the routers attribute these false messages to that flow's budget.

In a multipath scenario, injected messages will cause increased processor utilization in elimination routers. If enough paths are subject to malicious injection, the legitimate messages can be dropped. Likewise it can cause an increase in buffer usage. In total, it will consume more resources in the routers than normal, giving rise to a resource exhaustion attack on the routers.

If a DetNet flow is interrupted, the end application will be affected by what is now a non-deterministic flow.

6.3.2. Controller Plane Segmentation

In a successful controller plane segmentation attack, control messages are acted on by nodes in the network, unbeknownst to the central controller or the network engineer. This has the potential to:

6.4. Replication and Elimination

The Replication and Elimination is relevant only to data plane messages as controller plane messages are not subject to multipath routing.

6.4.1. Increased Attack Surface

Covered briefly in Section 6.3, Segmentation Attacks.

6.4.2. Header Manipulation at Elimination Routers

Covered briefly in Section 6.3, Segmentation Attacks.

6.5. Control or Signaling Packet Modification

If control packets are subject to manipulation undetected, the network can be severely compromised.

6.6. Control or Signaling Packet Injection

If an attacker can inject control packets undetected, the network can be severely compromised.

6.7. Reconnaissance

Of all the attacks, this is one of the most difficult to detect and counter. Often, an attacker will start out by observing the traffic going through the network and use the knowledge gathered in this phase to mount future attacks.

The attacker can, at their leisure, observe over time all aspects of the messaging and signalling, learning the intent and purpose of all traffic flows. At some later date, possibly at an important time in an operational context, the attacker can launch a multi-faceted attack, possibly in conjunction with some demand for ransom.

The flow-id in the header of the data plane messages gives an attacker a very reliable identifier for DetNet traffic, and this traffic has a high probability of going to lucrative targets.

Applications which are ported from a private OT network to the higher visibility DetNet environment may need to be adapted to limit distinctive flow properties that could make them susceptible to reconnaissance.

6.8. Attacks on Time Sync Mechanisms

Attacks on time sync mechanisms are addressed in [RFC7384].

6.9. Attacks on Path Choice

This is covered in part in Section 6.3, Segmentation Attacks, and as with Replication and Elimination (Section 6.4), this is relevant for DataPlane messages.

7. Security Threat Mitigation

This section describes a set of measures that can be taken to mitigate the attacks described in Section 5, Security Threats. These mitigations should be viewed as a toolset that includes several different and diverse tools. Each application or system will typically use a subset of these tools, based on a system-specific threat analysis.

7.1. Path Redundancy


Related attacks

7.2. Integrity Protection


Packet Sequence Number Integrity Considerations

Related attacks

7.3. DetNet Node Authentication


Related attacks

7.4. Dummy Traffic Insertion


Related attacks

7.5. Encryption


Related attacks

7.5.1. Encryption Considerations for DetNet

Any compute time which is required for encryption and decryption processing ('crypto') must be included in the flow latency calculations. Thus, crypto algorithms used in a DetNet must have bounded worst-case execution times, and these values must be used in the latency calculations.

Some crypto algorithms are symmetric in encode/decode time (such as AES) and others are asymmetric (such as public key algorithms). There are advantages and disadvantages to the use of either type in a given DetNet context. The discussion in this document relates to the timing implications of crypto for DetNet; it is assumed that integrity considerations are covered elsewhere in the literature.

Asymmetrical crypto is typically not used in networks on a packet-by-packet basis due to its computational cost. For example, if only endpoint checks or checks at a small number of intermediate points are required, asymmetric crypto can be used to authenticate distribution or exchange of a secret symmetric crypto key; a successful check based on that key will provide traffic origin verification, as long as the key is kept secret by the participants. TLS and IKE (for IPsec) are examples of this for endpoint checks.

However, if secret symmetrical keys are used for this purpose the key must be given to all relays, which increases the probability of a secret key being leaked. Also, if any relay is compromised or misbehaving it may inject traffic into the flow.

Alternatively, asymmetric crypto can provide traffic origin verification at every intermediate node. For example, a DetNet flow can be associated with an (asymmetric) keypair, such that the private key is available to the source of the flow and the public key is distributed with the flow information, allowing verification at every node for every packet. However, this is more computationally expensive.

In either case, origin verification also requires replay detection as part of the security protocol to prevent an attacker from recording and resending traffic, e.g., as a denial of service attack on flow forwarding resources.

If crypto keys are to be regenerated over the duration of the flow then the time required to accomplish this must be accounted for in the latency calculations.

7.6. Control and Signaling Message Protection


Related attacks

7.7. Dynamic Performance Analytics


Related attacks

7.8. Mitigation Summary

The following table maps the attacks of Section 5, Security Threats, to the impacts of Section 6, Security Threat Impacts, and to the mitigations of the current section. Each row specifies an attack, the impact of this attack if it is successfully implemented, and possible mitigation methods.

| Attack               |      Impact         |     Mitigations     |
|Delay Attack          |-Non-deterministic   |-Path redundancy     |
|                      | delay               |-Performance         |
|                      |-Data disruption     | analytics           |
|                      |-Increased resource  |                     |
|                      | consumption         |                     |
|Reconnaissance        |-Enabler for other   |-Encryption          |
|                      | attacks             |-Dummy traffic       |
|                      |                     |           insertion |
|DetNet Flow Modificat-|-Increased resource  |-Path redundancy     |
|ion or Spoofing       | consumption         |-Integrity protection|
|                      |-Data disruption     |-DetNet Node         |
|                      |                     | authentication      |
|Inter-Segment Attack  |-Increased resource  |-Path redundancy     |
|                      | consumption         |-Performance         |
|                      |-Data disruption     | analytics           |
|Replication: Increased|-All impacts of other|-Integrity protection|
|attack surface        | attacks             |-DetNet Node         |
|                      |                     | authentication      |
|Replication-related   |-Non-deterministic   |-Integrity protection|
|Header Manipulation   | delay               |-DetNet Node         |
|                      |-Data disruption     | authentication      |
|Path Manipulation     |-Enabler for other   |-Control message     |
|                      | attacks             | protection          |
|Path Choice: Increased|-All impacts of other|-Control message     |
|Attack Surface        | attacks             | protection          |
|Control or Signaling  |-Increased resource  |-Control message     |
|Packet Modification   | consumption         | protection          |
|                      |-Non-deterministic   |                     |
|                      | delay               |                     |
|                      |-Data disruption     |                     |
|Control or Signaling  |-Increased resource  |-Control message     |
|Packet Injection      | consumption         | protection          |
|                      |-Non-deterministic   |                     |
|                      | delay               |                     |
|                      |-Data disruption     |                     |
|Attacks on Time Sync  |-Non-deterministic   |-Path redundancy     |
|Mechanisms            | delay               |-Control message     |
|                      |-Increased resource  | protection          |
|                      | consumption         |-Performance         |
|                      |-Data disruption     | analytics           |

Figure 3: Mapping Attacks to Impact and Mitigations

8. Association of Attacks to Use Cases

Different attacks can have different impact and/or mitigation depending on the use case, so we would like to make this association in our analysis. However since there is a potentially unbounded list of use cases, we categorize the attacks with respect to the common themes of the use cases as identified in the Use Case Common Themes section of the DetNet Use Cases [RFC8578].

See also Figure 2 for a mapping of the impact of attacks per use case by industry.

8.1. Association of Attacks to Use Case Common Themes

In this section we review each theme and discuss the attacks that are applicable to that theme, as well as anything specific about the impact and mitigations for that attack with respect to that theme. The table Figure 5, Mapping Between Themes and Attacks, then provides a summary of the attacks that are applicable to each theme.

8.1.1. Sub-Network Layer

DetNet is expected to run over various transmission mediums, with Ethernet being the first identified. Attacks such as Delay or Reconnaissance might be implemented differently on a different transmission medium, however the impact on the DetNet as a whole would be essentially the same. We thus conclude that all attacks and impacts that would be applicable to DetNet over Ethernet (i.e. all those named in this document) would also be applicable to DetNet over other transmission mediums.

With respect to mitigations, some methods are specific to the Ethernet medium, for example time-aware scheduling using 802.1Qbv [IEEE802.1Qbv-2015] can protect against excessive use of bandwidth at the ingress - for other mediums, other mitigations would have to be implemented to provide analogous protection.

8.1.2. Central Administration

A DetNet network can be controlled by a centralized network configuration and control system. Such a system may be in a single central location, or it may be distributed across multiple control entities that function together as a unified control system for the network.

In this document we distinguish between attacks on the DetNet Controller plane vs. Data Plane. But is an attack affecting controller plane packets synonymous with an attack on the controller plane itself? For the purposes of this document let us consider an attack on the control system itself to be out of scope, and consider all attacks named in this document which are relevant to controller plane packets to be relevant to this theme, including Path Manipulation, Path Choice, Control Packet Modification or Injection, Reconaissance and Attacks on Time Sync Mechanisms.

8.1.3. Hot Swap

A DetNet network is not expected to be "plug and play" - it is expected that there is some centralized network configuration and control system. However, the ability to "hot swap" components (e.g. due to malfunction) is similar enough to "plug and play" that this kind of behavior may be expected in DetNet networks, depending on the implementation.

An attack surface related to Hot Swap is that the DetNet network must at least consider input at runtime from devices that were not part of the initial configuration of the network. Even a "perfect" (or "hitless") replacement of a device at runtime would not necessarily be ideal, since presumably one would want to distinguish it from the original for OAM purposes (e.g. to report hot swap of a failed device).

This implies that an attack such as Flow Modification, Spoofing or Inter-segment (which could introduce packets from a "new" device (i.e. one heretofore unknown on the network) could be used to exploit the need to consider such packets (as opposed to rejecting them out of hand as one would do if one did not have to consider introduction of a new device).

Similarly if the network was designed to support runtime replacement of a clock device, then presence (or apparent presence) and thus consideration of packets from a new such device could affect the network, or the time sync of the network, for example by initiating a new Best Master Clock selection process. Thus attacks on time sync should be considered when designing hot swap type functionality (see [RFC7384]).

8.1.4. Data Flow Information Models

Data Flow YANG models specific to DetNet networks are specified by DetNet, and thus are 'new' and thus potentially present a new attack surface.

8.1.5. L2 and L3 Integration

A DetNet network integrates Layer 2 (bridged) networks (e.g. AVB/TSN LAN) and Layer 3 (routed) networks via the use of well-known protocols such as IP, MPLS Pseudowire, and Ethernet.

There are no specific entries in the mapping table Figure 4, however that does not imply that there could be no relevant attacks related to L2-L3 integration.

8.1.6. End-to-End Delivery

Packets sent over DetNet are not to be dropped by the network due to congestion. (Packets may however intentionally be dropped for intended reasons, e.g. per security measures).

A data plane attack may force packets to be dropped, for example a "long" Delay or Replication/Elimination or Flow Modification attack.

The same result might be obtained by a controller plane attack, e.g. Path Manipulation or Signaling Packet Modification.

It may be that such attacks are limited to Internal MITM attackers, but other possibilities should be considered.

An attack may also cause packets that should not be delivered to be delivered, such as by forcing packets from one (e.g. replicated) path to be preferred over another path when they should not be (Replication attack), or by Flow Modification, or by Path Choice or Packet Injection. A Time Sync attack could cause a system that was expecting certain packets at certain times to accept unintended packets based on compromised system time or time windowing in the scheduler.

8.1.7. Replacement for Proprietary Fieldbuses and Ethernet-based Networks

There are many proprietary "field buses" used in today's industrial and other industries, as well as proprietary non-interoperable deterministic Ethernet-based networks. DetNet is intended to provide an open-standards-based alternative to such buses/networks. In cases where a DetNet intersects with such fieldbuses/networks or their protocols, such as by protocol emulation or access via a gateway, new attack surfaces can be opened.

For example an Inter-Segment or Controller plane attack such as Path Manipulation, Path Choice or Control Packet Modification/Injection could be used to exploit commands specific to such a protocol, or that are interpreted differently by the different protocols or gateway.

8.1.8. Deterministic vs Best-Effort Traffic

Most of the themes described in this document address OT (reserved) DetNet flows - this item is intended to address issues related to IT traffic on a DetNet.

DetNet is intended to support coexistence of time-sensitive operational (OT, deterministic) traffic and information (IT, "best effort") traffic on the same ("unified") network.

With DetNet, this coexistance will become more common, and mitigations will need to be established. The fact that the IT traffic on a DetNet is limited to a corporate controlled network makes this a less difficult problem compared to being exposed to the open Internet, however this aspect of DetNet security should not be underestimated.

An Inter-segment attack can flood the network with IT-type traffic with the intent of disrupting handling of IT traffic, and/or the goal of interfering with OT traffic. Presumably if the DetNet flow reservation and isolation of the DetNet is well-designed (better-designed than the attack) then interference with OT traffic should not result from an attack that floods the network with IT traffic.

However the DetNet's handling of IT traffic may not (by design) be as resilient to DOS attack, and thus designers must be otherwise prepared to mitigate DOS attacks on IT traffic in a DetNet.

8.1.9. Deterministic Flows

Reserved bandwidth data flows (deterministic flows) must provide the allocated bandwidth, and must be isolated from each other.

A Spoofing or Inter-segment attack which adds packet traffic to a bandwidth-reserved DetNet flow could cause that flow to occupy more bandwidth than it was allocated, resulting in interference with other DetNet flows.

A Flow Modification or Spoofing or Header Manipulation or Control Packet Modification attack could cause packets from one flow to be directed to another flow, thus breaching isolation between the flows.

8.1.10. Unused Reserved Bandwidth

If bandwidth reservations are made for a DetNet flow but the associated bandwidth is not used at any point in time, that bandwidth is made available on the network for best-effort traffic. However, note that security considerations for best-effort traffic on a DetNet network is out of scope of the present document, provided that such an attack does not affect performance for DetNet OT traffic.

8.1.11. Interoperability

The DetNet network specifications are intended to enable an ecosystem in which multiple vendors can create interoperable products, thus promoting device diversity and potentially higher numbers of each device manufactured.

Given that the DetNet specifications are unambiguously written and that the implementations are accurate, then this should not in and of itself cause a security concern; however, in the real world, it could be. The network operator can mitigate this through sufficient interoperability testing.

8.1.12. Cost Reductions

The DetNet network specifications are intended to enable an ecosystem in which multiple vendors can create interoperable products, thus promoting higher numbers of each device manufactured, promoting cost reduction and cost competition among vendors.

This envisioned breadth of DetNet-enabled products is in general a positive factor, however implementation flaws in any individual component can present an attack surface. In addition, implementation differences between components from different vendors can result in attack surfaces (resulting from their interaction) which may not exist in any individual component.

Network operators can mitigate such concerns through sufficient product and interoperability testing.

8.1.13. Insufficiently Secure Devices

The DetNet network specifications are intended to enable an ecosystem in which multiple vendors can create interoperable products, thus promoting device diversity and potentially higher numbers of each device manufactured. However this raises the possibility that a vendor might repurpose for DetNet applications a hardware or software component that was originally designed for operation in an isolated OT network, and thus may not have been designed to be sufficiently secure, or secure at all. Deployment of such a device on a DetNet network that is intended to be highly secure may present an attack surface.

The DetNet network operator may need to take specific actions to protect such devices, such as implementing a dedicated security layer around the device.

8.1.14. DetNet Network Size

DetNet networks range in size from very small, e.g. inside a single industrial machine, to very large, for example a Utility Grid network spanning a whole country.

The size of the network might be related to how the attack is introduced into the network, for example if the entire network is local, there is a threat that power can be cut to the entire network. If the network is large, perhaps only a part of the network is attacked.

A Delay attack might be as relevant to a small network as to a large network, although the amount of delay might be different.

Attacks sourced from IT traffic might be more likely in large networks, since more people might have access to the network, presenting a larger attack surface. Similarly Path Manipulation, Path Choice and Time Sync attacks seem more likely relevant to large networks.

8.1.15. Multiple Hops

Large DetNet networks (e.g. a Utility Grid network) may involve many "hops" over various kinds of links for example radio repeaters, microwave links, fiber optic links, etc.

An attack that takes advantage of flaws (or even normal operation) in the device drivers for the various links (through internal knowledge of how the individual driver or firmware operates) could take proportionately greater advantage of this topology.

It is also possible that this DetNet topology will not be in as common use as other more homogeneous topologies so there may be more opportunity for attackers to exploit software and/or protocol flaws in the implementations which have not been tested through extensive use, particularly in the case of early adopters.

Of the attacks we have defined, the ones identified in Section 8.1.14 as germane to large networks are the most relevant.

8.1.16. Level of Service

A DetNet is expected to provide means to configure the network that include querying network path latency, requesting bounded latency for a given DetNet flow, requesting worst case maximum and/or minimum latency for a given path or DetNet flow, and so on. It is an expected case that the network cannot provide a given requested service level. In such cases the network control system should reply that the requested service level is not available (as opposed to accepting the parameter but then not delivering the desired behavior).

Controller plane attacks such as Signaling Packet Modification and Injection could be used to modify or create control traffic that could interfere with the process of a user requesting a level of service and/or the network's reply.

Reconnaissance could be used to characterize flows and perhaps target specific flows for attack via the controller plane as noted in Section 6.7.

8.1.17. Bounded Latency

DetNet provides the expectation of guaranteed bounded latency.

Delay attacks can cause packets to miss their agreed-upon latency boundaries.

Time Sync attacks can corrupt the system's time reference, resulting in missed latency deadlines (with respect to the "correct" time reference).

8.1.18. Low Latency

Applications may require "extremely low latency" however depending on the application these may mean very different latency values; for example "low latency" across a Utility grid network is on a different time scale than "low latency" in a motor control loop in a small machine. The intent is that the mechanisms for specifying desired latency include wide ranges, and that architecturally there is nothing to prevent arbitrarily low latencies from being implemented in a given network.

Attacks on the controller plane (as described in the Level of Service theme Section 8.1.16) and Delay and Time attacks (as described in the Bounded Latency theme Section 8.1.17) both apply here.

8.1.19. Bounded Jitter (Latency Variation)

DetNet is expected to provide bounded jitter (packet to packet latency variation).

Delay attacks can cause packets to vary in their arrival times, resulting in packet to packet latency variation, thereby violating the jitter specification.

8.1.20. Symmetrical Path Delays

Some applications would like to specify that the transit delay time values be equal for both the transmit and return paths.

Delay attacks can cause path delays to materially differ between paths.

Time Sync attacks can corrupt the system's time reference, resulting in path delays that may be perceived to be different (with respect to the "correct" time reference) even if they are not materially different.

8.1.21. Reliability and Availability

DetNet based systems are expected to be implemented with essentially arbitrarily high availability (for example 99.9999% up time, or even 12 nines). The intent is that the DetNet designs should not make any assumptions about the level of reliability and availability that may be required of a given system, and should define parameters for communicating these kinds of metrics within the network.

Any attack on the system, of any type, can affect its overall reliability and availability, thus in the mapping table Figure 4 we have marked every attack. Since every DetNet depends to a greater or lesser degree on reliability and availability, this essentially means that all networks have to mitigate all attacks, which to a greater or lesser degree defeats the purpose of associating attacks with use cases. It also underscores the difficulty of designing "extremely high reliability" networks.

8.1.22. Redundant Paths

DetNet based systems are expected to be implemented with essentially arbitrarily high reliability/availability. A strategy used by DetNet for providing such extraordinarily high levels of reliability is to provide redundant paths that can be seamlessly switched between, all the while maintaining the required performance of that system.

Replication-related attacks are by definition applicable here. Controller plane attacks can also interfere with the configuration of redundant paths.

8.1.23. Security Measures

A DetNet network must be made secure against devices failures, attackers, misbehaving devices, and so on. Does the threat affect such security measures themselves, e.g. by attacking SW designed to protect against device failure?

This is TBD, thus there are no specific entries in the mapping table Figure 4, however that does not imply that there could be no relevant attacks.

8.2. Summary of Attack Types per Use Case Common Theme

The List of Attacks table Figure 4 lists the attacks of Section 5, Security Threats, assigning a number to each type of attack. That number is then used as a short form identifier for the attack in Figure 5, Mapping Between Themes and Attacks.

|  | Attack                                 |       Section        |
| 1|Delay Attack                            |  Section 3.2.1       |
| 2|DetNet Flow Modification or Spoofing    |  Section 3.2.2       |
| 3|Inter-Segment Attack                    |  Section 3.2.3       |
| 4|Replication: Increased attack surface   |  Section     |
| 5|Replication-related Header Manipulation |  Section     |
| 6|Path Manipulation                       |  Section     |
| 7|Path Choice: Increased Attack Surface   |  Section     |
| 8|Control or Signaling Packet Modification|  Section     |
| 9|Control or Signaling Packet Injection   |  Section     |
|10|Reconnaissance                          |  Section 3.2.7       |
|11|Attacks on Time Sync Mechanisms         |  Section 3.2.8       |

Figure 4: List of Attacks

The Mapping Between Themes and Attacks table Figure 5 maps the use case themes of [RFC8578] (as also enumerated in this document) to the attacks of Figure 4. Each row specifies a theme, and the attacks relevant to this theme are marked with a '+'.

| Theme                      |             Attack             |
|                            +--+--+--+--+--+--+--+--+--+--+--+
|                            | 1| 2| 3| 4| 5| 6| 7| 8| 9|10|11|
|Network Layer - AVB/TSN Eth.| +| +| +| +| +| +| +| +| +| +| +|
|Central Administration      |  |  |  |  |  | +| +| +| +| +| +|
|Hot Swap                    |  | +| +|  |  |  |  |  |  |  | +|
|Data Flow Information Models|  |  |  |  |  |  |  |  |  |  |  |
|L2 and L3 Integration       |  |  |  |  |  |  |  |  |  |  |  |
|End-to-end Delivery         | +| +| +| +| +| +| +| +| +|  | +|
|Proprietary Deterministic   |  |  | +|  |  | +| +| +| +|  |  |
|Ethernet Networks           |  |  |  |  |  |  |  |  |  |  |  |
|Replacement for Proprietary |  |  | +|  |  | +| +| +| +|  |  |
|Fieldbuses                  |  |  |  |  |  |  |  |  |  |  |  |
|Deterministic vs. Best-     |  |  | +|  |  |  |  |  |  |  |  |
|Effort Traffic              |  |  |  |  |  |  |  |  |  |  |  |
|Deterministic Flows         |  | +| +|  | +| +|  | +|  |  |  |
|Unused Reserved Bandwidth   |  | +| +|  |  |  |  | +| +|  |  |
|Interoperability            |  |  |  |  |  |  |  |  |  |  |  |
|Cost Reductions             |  |  |  |  |  |  |  |  |  |  |  |
|Insufficiently Secure       |  |  |  |  |  |  |  |  |  |  |  |
|Devices                     |  |  |  |  |  |  |  |  |  |  |  |
|DetNet Network Size         | +|  |  |  |  | +| +|  |  |  | +|
|Multiple Hops               | +| +|  |  |  | +| +|  |  |  | +|
|Level of Service            |  |  |  |  |  |  |  | +| +| +|  |
|Bounded Latency             | +|  |  |  |  |  |  |  |  |  | +|
|Low Latency                 | +|  |  |  |  |  |  | +| +| +| +|
|Bounded Jitter              | +|  |  |  |  |  |  |  |  |  |  |
|Symmetric Path Delays       | +|  |  |  |  |  |  |  |  |  | +|
|Reliability and Availability| +| +| +| +| +| +| +| +| +| +| +|
|Redundant Paths             |  |  |  | +| +|  |  | +| +|  |  |
|Security Measures           |  |  |  |  |  |  |  |  |  |  |  |

Figure 5: Mapping Between Themes and Attacks

8.3. Security Considerations for OAM Traffic

This section considers DetNet-specific security considerations for packet traffic that is generated and transmitted over a DetNet as part of OAM (Operations, Administration, and Maintenance). For the purposes of this discussion, OAM traffic falls into one of two basic types:

Thus OAM traffic presents no additional (i.e. OAM-specific) DetNet security considerations.

9. DetNet Technology-Specific Threats

Section 5, Security Threats, described threats which are independent of a DetNet implementation. This section considers threats specifically related to the IP- and MPLS-specific aspects of DetNet implementations.

The primary security considerations for the data plane specifically are to maintain the integrity of the data and the delivery of the associated DetNet service traversing the DetNet network.

The primary relevant differences between IP and MPLS implementations are in flow identification and OAM methodologies.

As noted in [RFC8655], DetNet operates at the IP layer ([I-D.ietf-detnet-ip]) and delivers service over sub-layer technologies such as MPLS ([I-D.ietf-detnet-mpls]) and IEEE 802.1 Time-Sensitive Networking (TSN) ([I-D.ietf-detnet-ip-over-tsn]). Application flows can be protected through whatever means are provided by the layer and sub-layer technologies. For example, technology-specific encryption may be used, such as that provided by IPSec [RFC4301] for IP flows and/or by an underlying sub-net using MACSec [IEEE802.1AE-2018] for IP over Ethernet (Layer-2) flows.

However, if the DetNet nodes cannot decrypt IPsec traffic, IPSec may not be a valid option; this is because the DetNet IP Data Plane identifies flows via a 6-tuple that consists of two IP addresses, the transport protocol ID, two transport protocol port numbers and the DSCP in the IP header. When IPsec is used, the transport header is encrypted and the next protocol ID is an IPsec protocol, usually ESP, and not a transport protocol (e.g., neither TCP nor UDP, etc.) leaving only three components of the 6-tuple, which are the two IP addresses and the DSCP, which are in general not sufficient to identify a DetNet flow.

Sections below discuss threats specific to IP and MPLS in more detail.

9.1. IP

The IP protocol has a long history of security considerations and architectural protection mechanisms. From a data plane perspective DetNet does not add or modify any IP header information, so the carriage of DetNet traffic over an IP data plane does not introduce any new security issues that were not there before, apart from those already described in the data-plane-independent threats section Section 5, Security Threats.

Thus the security considerations for a DetNet based on an IP data plane are purely inherited from the rich IP Security literature and code/application base, and the data-plane-independent section of this document.

Maintaining security for IP segments of a DetNet may be more challenging than for the MPLS segments of the network, given that the IP segments of the network may reach the edges of the network, which are more likely to involve interaction with potentially malevolent outside actors. Conversely MPLS is inherently more secure than IP since it is internal to routers and it is well-known how to protect it from outside influence.

Another way to look at DetNet IP security is to consider it in the light of VPN security; as an industry we have a lot of experience with VPNs running through networks with other VPNs, it is well known how to secure the network for that. However for a DetNet we have the additional subtlety that any possible interaction of one packet with another can have a potentially deleterious effect on the time properties of the flows. So the network must provide sufficient isolation between flows, for example by protecting the forwarding bandwidth and related resources so that they are available to detnet traffic, by whatever means are appropriate for that network's data plane.

In a VPN, bandwidth is generally guaranteed over a period of time, whereas in DetNet it is not aggregated over time. This implies that any VPN-type protection mechanism must also maintain the DetNet timing constraints.

9.2. MPLS

An MPLS network carrying DetNet traffic is expected to be a "well-managed" network. Given that this is the case, it is difficult for an attacker to pass a raw MPLS encoded packet into a network because operators have considerable experience at excluding such packets at the network boundaries, as well as excluding MPLS packets being inserted through the use of a tunnel.

MPLS security is discussed extensively in [RFC5920] ("Security Framework for MPLS and GMPLS Networks") to which the reader is referred.

[RFC6941] builds on [RFC5920] by providing additional security considerations that are applicable to the MPLS-TP extensions appropriate to the MPLS Transport Profile [RFC5921], and thus to the operation of DetNet over some types of MPLS network.

[RFC5921] introduces to MPLS new Operations, Administration, and Maintenance (OAM) capabilities, a transport-oriented path protection mechanism, and strong emphasis on static provisioning supported by network management systems.

The operation of DetNet over an MPLS network is modeled on the operation of multi-segment pseudowires (MS-PW). Thus for guidance on securing the DetNet elements of DetNet over MPLS the reader is referred to the MS-PW security mechanisms as defined in [RFC4447], [RFC3931], [RFC3985], [RFC6073], and [RFC6478].

Having attended to the conventional aspects of network security it is necessary to attend to the dynamic aspects. The closest experience that the IETF has with securing protocols that are sensitive to manipulation of delay are the two way time transfer protocols (TWTT), which are NTP [RFC5905] and Precision Time Protocol [IEEE1588]. The security requirements for these are described in [RFC7384].

One particular problem that has been observed in operational tests of TWTT protocols is the ability for two closely but not completely synchronized flows to beat and cause a sudden phase hit to one of the flows. This can be mitigated by the careful use of a scheduling system in the underlying packet transport.

Further consideration of protection against dynamic attacks is work in progress.

10. IANA Considerations

This memo includes no requests from IANA.

11. Security Considerations

The security considerations of DetNet networks are presented throughout this document.

12. Contributors

The Editor would like to recognize the contributions of the following individuals to this draft.

    Andrew J. Hacker (MistIQ Technologies, Inc)
    Harrisburg, PA, USA

    Subir Das (Applied Communication Sciences)
    150 Mount Airy Road, Basking Ridge
    New Jersey, 07920, USA

    John Dowdell (Airbus Defence and Space)
    Celtic Springs, Newport, NP10 8FZ, United Kingdom
    Henrik Austad (SINTEF Digital)
    Klaebuveien 153, Trondheim, 7037, Norway

    Norman Finn
    Stewart Bryant
    Futurewei Technologies

    David Black
    Dell EMC
    176 South Street, Hopkinton, MA  01748, USA

    Carsten Bormann

13. Informative References

[ARINC664P7] ARINC, "ARINC 664 Aircraft Data Network, Part 7, Avionics Full-Duplex Switched Ethernet Network", 2009.
[I-D.ietf-detnet-data-plane-framework] Varga, B., Farkas, J., Berger, L., Malis, A. and S. Bryant, "DetNet Data Plane Framework", Internet-Draft draft-ietf-detnet-data-plane-framework-06, May 2020.
[I-D.ietf-detnet-flow-information-model] Varga, B., Farkas, J., Cummings, R., Jiang, Y. and D. Fedyk, "DetNet Flow Information Model", Internet-Draft draft-ietf-detnet-flow-information-model-10, May 2020.
[I-D.ietf-detnet-ip] Varga, B., Farkas, J., Berger, L., Fedyk, D. and S. Bryant, "DetNet Data Plane: IP", Internet-Draft draft-ietf-detnet-ip-07, July 2020.
[I-D.ietf-detnet-ip-over-tsn] Varga, B., Farkas, J., Malis, A. and S. Bryant, "DetNet Data Plane: IP over IEEE 802.1 Time Sensitive Networking (TSN)", Internet-Draft draft-ietf-detnet-ip-over-tsn-03, June 2020.
[I-D.ietf-detnet-mpls] Varga, B., Farkas, J., Berger, L., Malis, A., Bryant, S. and J. Korhonen, "DetNet Data Plane: MPLS", Internet-Draft draft-ietf-detnet-mpls-10, July 2020.
[I-D.varga-detnet-service-model] Varga, B. and J. Farkas, "DetNet Service Model", Internet-Draft draft-varga-detnet-service-model-02, May 2017.
[IEEE1588] IEEE, "IEEE 1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems Version 2", 2008.
[IEEE802.1AE-2018] IEEE Standards Association, "IEEE Std 802.1AE-2018 MAC Security (MACsec)", 2018.
[IEEE802.1Qbv-2015] IEEE Standards Association, "IEEE Standard for Local and metropolitan area networks -- Bridges and Bridged Networks - Amendment 25: Enhancements for Scheduled Traffic", 2015.
[IEEE802.1Qch-2017] IEEE Standards Association, "IEEE Standard for Local and metropolitan area networks--Bridges and Bridged Networks--Amendment 29: Cyclic Queuing and Forwarding", 2017.
[IT_DEF] Wikipedia, "IT Definition", 2020.
[OT_DEF] Wikipedia, "OT Definition", 2020.
[RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 10.17487/RFC2474, December 1998.
[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.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, DOI 10.17487/RFC3552, July 2003.
[RFC3931] Lau, J., Townsley, M. and I. Goyret, "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, DOI 10.17487/RFC3931, March 2005.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, DOI 10.17487/RFC3985, March 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T. and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, DOI 10.17487/RFC4447, April 2006.
[RFC5905] Mills, D., Martin, J., Burbank, J. and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010.
[RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L. and L. Berger, "A Framework for MPLS in Transport Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M. and M. Aissaoui, "Segmented Pseudowire", RFC 6073, DOI 10.17487/RFC6073, January 2011.
[RFC6478] Martini, L., Swallow, G., Heron, G. and M. Bocci, "Pseudowire Status for Static Pseudowires", RFC 6478, DOI 10.17487/RFC6478, May 2012.
[RFC6941] Fang, L., Niven-Jenkins, B., Mansfield, S. and R. Graveman, "MPLS Transport Profile (MPLS-TP) Security Framework", RFC 6941, DOI 10.17487/RFC6941, April 2013.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, October 2014.
[RFC8578] Grossman, E., "Deterministic Networking Use Cases", RFC 8578, DOI 10.17487/RFC8578, May 2019.
[RFC8655] Finn, N., Thubert, P., Varga, B. and J. Farkas, "Deterministic Networking Architecture", RFC 8655, DOI 10.17487/RFC8655, October 2019.
[RS_DEF] Wikipedia, "RS Definition", 2020.

Authors' Addresses

Tal Mizrahi Huawei Network.IO Innovation Lab EMail:
Ethan Grossman (editor) Dolby Laboratories, Inc. 1275 Market Street San Francisco, CA 94103 USA Phone: +1 415 645 4726 EMail: URI: