text:
Deterministic Networking (DetNet) Security Considerations
draft-ietf-detnet-security-13
Active Internet-Draft (detnet WG)
Ethan Grossman , Tal Mizrahi , Andrew Hacker
draft-sdt-detnet-security
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Internet Engineering Task Force                         E. Grossman, Ed.
Internet-Draft                                                     DOLBY
Intended status: Informational                                T. Mizrahi
Expires: June 14, 2021                                            HUAWEI
A. Hacker
MISTIQ
A DetNet (deterministic network) provides specific performance
guarantees to its data flows, such as extremely low data loss rates
and bounded latency (including bounded latency variation, i.e.
"jitter").  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 security considerations specific to the
IP and MPLS data plane technologies, thereby complementing the
Security Considerations sections of those documents.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
Grossman, et al.          Expires June 14, 2021                 [Page 1]
Internet-Draft               DetNet Security               December 2020
This Internet-Draft will expire on June 14, 2021.
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1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
2.  Abbreviations and Terminology . . . . . . . . . . . . . . . .   6
3.  Security Considerations for DetNet Component Design . . . . .   7
3.1.  Resource Allocation . . . . . . . . . . . . . . . . . . .   7
3.2.  Explicit Routes . . . . . . . . . . . . . . . . . . . . .   8
3.3.  Redundant Path Support  . . . . . . . . . . . . . . . . .   8
3.4.  Timing (or other) Violation Reporting . . . . . . . . . .   9
4.  DetNet Security Considerations Compared With DiffServ
Security Considerations . . . . . . . . . . . . . . . . . . .  10
5.  Security Threats  . . . . . . . . . . . . . . . . . . . . . .  11
5.1.  Threat Model  . . . . . . . . . . . . . . . . . . . . . .  11
5.2.  Threat Analysis . . . . . . . . . . . . . . . . . . . . .  12
5.2.1.  Delay . . . . . . . . . . . . . . . . . . . . . . . .  12
5.2.2.  DetNet Flow Modification or Spoofing  . . . . . . . .  12
5.2.3.  Resource Segmentation (Inter-segment Attack)  . . . .  12
5.2.4.  Packet Replication and Elimination  . . . . . . . . .  13
5.2.4.1.  Replication: Increased Attack Surface . . . . . .  13
5.2.4.2.  Replication-related Header Manipulation . . . . .  13
5.2.5.  Controller Plane  . . . . . . . . . . . . . . . . . .  14
5.2.5.1.  Path Choice Manipulation  . . . . . . . . . . . .  14
5.2.5.2.  Compromised Controller  . . . . . . . . . . . . .  14
5.2.6.  Reconnaissance  . . . . . . . . . . . . . . . . . . .  14
5.2.7.  Time Synchronization Mechanisms . . . . . . . . . . .  15
5.3.  Threat Summary  . . . . . . . . . . . . . . . . . . . . .  15
6.  Security Threat Impacts . . . . . . . . . . . . . . . . . . .  16
6.1.  Delay-Attacks . . . . . . . . . . . . . . . . . . . . . .  19
6.1.1.  Data Plane Delay Attacks  . . . . . . . . . . . . . .  19
6.1.2.  Controller Plane Delay Attacks  . . . . . . . . . . .  20
6.2.  Flow Modification and Spoofing  . . . . . . . . . . . . .  20
6.2.1.  Flow Modification . . . . . . . . . . . . . . . . . .  20
6.2.2.  Spoofing  . . . . . . . . . . . . . . . . . . . . . .  20
6.2.2.1.  Dataplane Spoofing  . . . . . . . . . . . . . . .  20
6.2.2.2.  Controller Plane Spoofing . . . . . . . . . . . .  21
6.3.  Segmentation Attacks (injection)  . . . . . . . . . . . .  21
6.3.1.  Data Plane Segmentation . . . . . . . . . . . . . . .  21
6.3.2.  Controller Plane Segmentation . . . . . . . . . . . .  21
6.4.  Replication and Elimination . . . . . . . . . . . . . . .  22
6.4.1.  Increased Attack Surface  . . . . . . . . . . . . . .  22
6.4.2.  Header Manipulation at Elimination Routers  . . . . .  22
6.5.  Control or Signaling Packet Modification  . . . . . . . .  22
6.6.  Control or Signaling Packet Injection . . . . . . . . . .  22
6.7.  Reconnaissance  . . . . . . . . . . . . . . . . . . . . .  22
6.8.  Attacks on Time Synchronization Mechanisms  . . . . . . .  23
6.9.  Attacks on Path Choice  . . . . . . . . . . . . . . . . .  23
7.  Security Threat Mitigation  . . . . . . . . . . . . . . . . .  23
7.1.  Path Redundancy . . . . . . . . . . . . . . . . . . . . .  23
7.2.  Integrity Protection  . . . . . . . . . . . . . . . . . .  24
7.3.  DetNet Node Authentication  . . . . . . . . . . . . . . .  25
7.4.  Dummy Traffic Insertion . . . . . . . . . . . . . . . . .  26
7.5.  Encryption  . . . . . . . . . . . . . . . . . . . . . . .  26
7.5.1.  Encryption Considerations for DetNet  . . . . . . . .  27
7.6.  Control and Signaling Message Protection  . . . . . . . .  28
7.7.  Dynamic Performance Analytics . . . . . . . . . . . . . .  28
7.8.  Mitigation Summary  . . . . . . . . . . . . . . . . . . .  30
8.  Association of Attacks to Use Cases . . . . . . . . . . . . .  32
8.1.  Association of Attacks to Use Case Common Themes  . . . .  32
8.1.1.  Sub-Network Layer . . . . . . . . . . . . . . . . . .  32
8.1.2.  Central Administration  . . . . . . . . . . . . . . .  33
8.1.3.  Hot Swap  . . . . . . . . . . . . . . . . . . . . . .  33
8.1.4.  Data Flow Information Models  . . . . . . . . . . . .  34
8.1.5.  L2 and L3 Integration . . . . . . . . . . . . . . . .  34
8.1.6.  End-to-End Delivery . . . . . . . . . . . . . . . . .  34
8.1.7.  Replacement for Proprietary Fieldbuses and Ethernet-
based Networks  . . . . . . . . . . . . . . . . . . .  35
8.1.8.  Deterministic vs Best-Effort Traffic  . . . . . . . .  35
8.1.9.  Deterministic Flows . . . . . . . . . . . . . . . . .  36
8.1.10. Unused Reserved Bandwidth . . . . . . . . . . . . . .  36
8.1.11. Interoperability  . . . . . . . . . . . . . . . . . .  36
8.1.12. Cost Reductions . . . . . . . . . . . . . . . . . . .  37
8.1.13. Insufficiently Secure Components  . . . . . . . . . .  37
8.1.14. DetNet Network Size . . . . . . . . . . . . . . . . .  37
8.1.15. Multiple Hops . . . . . . . . . . . . . . . . . . . .  38
8.1.16. Level of Service  . . . . . . . . . . . . . . . . . .  38
8.1.17. Bounded Latency . . . . . . . . . . . . . . . . . . .  39
8.1.18. Low Latency . . . . . . . . . . . . . . . . . . . . .  39
8.1.19. Bounded Jitter (Latency Variation)  . . . . . . . . .  39
8.1.20. Symmetrical Path Delays . . . . . . . . . . . . . . .  39
8.1.21. Reliability and Availability  . . . . . . . . . . . .  40
8.1.22. Redundant Paths . . . . . . . . . . . . . . . . . . .  40
8.1.23. Security Measures . . . . . . . . . . . . . . . . . .  40
8.2.  Summary of Attack Types per Use Case Common Theme . . . .  41
8.3.  Security Considerations for OAM Traffic . . . . . . . . .  43
9.  DetNet Technology-Specific Threats  . . . . . . . . . . . . .  43
9.1.  IP  . . . . . . . . . . . . . . . . . . . . . . . . . . .  44
9.2.  MPLS  . . . . . . . . . . . . . . . . . . . . . . . . . .  45
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  46
11. Security Considerations . . . . . . . . . . . . . . . . . . .  46
12. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  46
13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  46
14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  47
14.1.  Normative References . . . . . . . . . . . . . . . . . .  47
14.2.  Informative References . . . . . . . . . . . . . . . . .  48
Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  52
1.  Introduction
A DetNet is one that can carry data flows for real-time applications
with extremely low data loss rates and bounded latency.  The bounds
on latency defined by DetNet
([I-D.ietf-detnet-flow-information-model]) include both worst case
latency (Maximum Latency, Section 5.9.2) and worst case jitter
(Maximum Latency Variation, Section 5.9.3).  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 flows 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 (OT-type) technologies may not have previously been
deployed on a wide area IP-based network that also carries IT
traffic, 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 because many of
the use cases which are enabled by DetNet [RFC8578] include control
of physical devices (power grid devices, 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 "traditional" (i.e. non-time-sensitive)
network design and management aspects of network security as being
primarily concerned with denial-of service prevention, i.e. they must
ensure that DetNet traffic goes where it's supposed to and that an
external attacker can't inject traffic that disrupts the delivery
timing assurance of the DetNet.  The time-specific aspects of DetNet
security presented here take up where those "traditional" design and
management aspects leave off.
However note that "traditional" methods for mitigating (among all the
others) denial-of service attack (such as throttling) can only be
effectively used in a DetNet when their use does not compromise the
required time-sensitive or behavioral properties required for the OT
flows on the network.  For example, a "retry" protocol is typically
not going to be compatible with a low-latency (worst-case maximum
latency) requirement, however if in a specific use case and
implementation such a retry protocol is able to meet the timing
constraints, then it may well be used in that context.  Similarly if
common security protocols such as TLS/DTLS or IPsec are to be used,
it must be verified that their implementations are able to meet the
timing and behavioral requirements of the time-sensitive network as
implemented for the given use case.  An example of "behavioral
properties" might be that dropping of more than a specific number of
packets in a row is not acceptable according to the service level
The exact security requirements for any given DetNet 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
[RFC8939]).  Readers can find a general introduction to the DetNet
Architecture in [RFC8655], the DetNet Data Plane in [RFC8938], and
the Flow Information Model in
[I-D.ietf-detnet-flow-information-model].
The DetNet technologies include ways to:
o  Assign data plane resources for DetNet flows in some or all of the
intermediate nodes (routers) along the path of the flow
o  Provide explicit routes for DetNet flows that do not dynamically
change with the network topology in ways that affect the quality
of service received by the affected flow(s)
o  Distribute data from DetNet flow packets over time and/or space to
ensure delivery of the data in each packet in spite of the loss of
a path.
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])
Component: A component of a DetNet system - used here to refer to any
hardware or software element of a DetNet which implements DetNet-
specific functionality, for example all or part of a router, switch,
or end system.
Device: Used here to refer to a physical entity controlled by the
DetNet, for example a motor.
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, for example through the use of
traffic shaping and policing.
As an example, consider the implementation of Flow Aggregation for
DetNet flows (as discussed in [RFC8938]).  In this example say there
are N flows that are to be aggregated, thus the bandwidth resources
of the aggregate flow must be sufficient to contain the sum of the
bandwidth reservation for the N flows.  However if one of those flows
were to consume more than its individually allocated bandwidth, this
could cause starvation of the other flows.  Thus simply providing and
enforcing the calculated aggregate bandwidth may not be a complete
solution - the bandwidth for each individual flow must still be
guaranteed, for example via ingress policing of each flow (i.e.
before it is aggregated).  Alternatively, if by some other means each
flow to be aggregated can be trusted not to exceed its allocated
bandwidth, the same goal can be achieved.
3.2.  Explicit Routes
The DetNet-specific purpose for constraining the ability of the
DetNet 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, to avoid potentially catastrophic
situations for the operational technology relying on them.
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.
Ideally a redundant path for a flow could be specified from end to
end, 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 (including
elimination of packets with spurious sequence numbers).  Thus the
integrity of these values must be maintained by the component as they
are assigned by the DetNet Data Plane Service sub-layer, and
transported by the Forwarding sub-layer.  This is no different than
the integrity of the values in any header used by the DetNet (or any
other) data plane, and is not unique to redundant paths.  The
integrity protection of header values is technology-dependent; for
example, in Layer 2 networks the integrity of the header fields can
be protected by using MACsec [IEEE802.1AE-2018].  Similary, from the
sequence number injection perspective, it is no different from any
other protocols that use sequence numbers.
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 data
plane of the component 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:
o  Outside of its prescribed time window
o  Within its time window but with a compromised time stamp that
makes it appear that it is not within its window
o  Exceeding the reserved flow bandwidth
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.
Some possible direct actions that may be taken at the data plane
include traffic policing and shaping functions (e.g., those described
in [RFC2475]), separating flows into per-flow rate-limited queues,
and potentially applying active queue management [RFC7567].  However
if those (or any other) actions are to be taken, the system designer
must ensure that the results of such actions do not compromise the
continued safe operation of the system.  For example, the network
(i.e. the controller plane and data plane working together) must
mitigate in a timely fashion any potential adverse effect on
mechanical devices controlled by the network.
4.  DetNet Security Considerations Compared With DiffServ Security
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
Considerations 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 is interpreted
differently than in DiffServ and contribute to determination of the
service provided to the packet.  In DetNet, there are similar
consequences to DiffServ for lack of detection of, or incorrect
handling of, packets with mismarked DSCP values, and many of the
Grossman, et al.          Expires June 14, 2021                [Page 10]
points made in the DiffServ Security discussions ([RFC2475] Sec. 6.1
, [RFC2474] Sec. 7 and [RFC6274] Sec 3.3.2.1) 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
the PHB of that packet, 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.  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 [RFC8938].
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 document employs organizational
elements of the threat models of [RFC7384] and [RFC7835].  This model
classifies attackers based on two criteria:
o  Internal vs. external: internal attackers either have access to a
trusted segment of the network or possess the encryption or
authentication keys.  External attackers, on the other hand, do
not have the keys and have access only to the encrypted or
authenticated traffic.
o  On-path vs. off-path: on-path attackers are located in a position
that allows interception and modification of in-flight protocol
packets, whereas off-path attackers can only attack by generating
protocol packets.
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 (i.e. attacks that modify
DetNet traffic), but it is highly suggested that DetNet application
developers take appropriate measures to protect the content of the
DetNet flows from passive attacks (i.e. attacks that observe but do
not modify DetNet traffic) for example through the use of TLS or
DTLS.
DetNet-Service, one of the service scenarios described in
[I-D.varga-detnet-service-model], is the case where a service
connects DetNet islands, i.e. two or more otherwise independent
DetNets 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 DetNets merits security analysis to ensure the integrity
of the 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
5.2.4.1.  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.
5.2.4.2.  Replication-related Header Manipulation
An attacker can manipulate the replication-related header fields.
This capability opens the door for various types of attacks.  For
o  Forward both replicas - malicious change of a packet SN (Sequence
Number) can cause both replicas of the packet to be forwarded.
Note that this attack has a similar outcome to a replay attack.
o  Eliminate both replicas - SN manipulation can be used to cause
both replicas to be eliminated.  In this case an attacker that has
access to a single path can cause packets from other paths to be
dropped, thus compromising some of the advantage of path
redundancy.
o  Flow hijacking - an attacker can hijack a DetNet flow with access
to a single path by systematically replacing the SNs on the given
path with higher SN values.  For example, an attacker can replace
every SN value S with a higher value S+C, where C is a constant
integer.  Thus, the attacker creates a false illusion that the
attacked path has the lowest delay, causing all packets from other
paths to be eliminated in favor of the attacked path.  Once the
flow from the compromised path is favored by the elminating
bridge, the flow is hijacked by the attacker.  It is now posible
to either replace en route packets with malicious packets, or
simply injecting errors, causing the packets to be dropped at
their destination.
o  Amplification - an attacker who injects packets into a flow that
is to be replicated will have their attack amplified through the
replication process.  This is no different than any attacker who
injects packets that are delivered through multicast, broadcast,
or other point-to-multi-point mechanisms.
5.2.5.  Controller Plane
5.2.5.1.  Path Choice Manipulation
5.2.5.1.1.  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.
5.2.5.1.2.  Control or Signaling Packet Injection
An attacker can maliciously inject control packets in order to
disrupt or manipulate the DetNet path/resource allocation.
5.2.5.1.3.  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.
5.2.5.2.  Compromised Controller
An attacker can subvert a controller, or enable a compromised
controller to falsely represent itself as a controller so that the
network nodes believe it to be authorized to instruct them.
Presence of compromised nodes in a DetNet is not a new threat that
arises as a result of determinism or time sensitivity; the same
techniques used to prevent or mitigate against compromised nodes in
any network are equally applicable in the DetNet case.  However this
underscores the requirement for careful system security design in a
DetNet, given that the effects of even one bad actor on the network
can be potentially catastrophic.
Security concerns specific to any given controller plane technology
used in DetNet will be addressed by the DetNet documents associated
with that technology.
5.2.6.  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.
DetNet flows are typically uniquely identified by their 6-tuple, i.e.
fields within the IP header, however in some implementations the flow
ID may also be augmented by additional per-flow attributes known to
the system, e.g. above the IP-layer.  For the purpose of this
document we assume any such additional fields used for flow ID are
encrypted and/or integrity-protected from external attackers.
5.2.7.  Time Synchronization Mechanisms
An attacker can use any of the attacks described in [RFC7384] to
attack the synchronization protocol, thus affecting the DetNet
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
+-------------------------------------------+----+-----+----+-----+
| Attack                                    |    Attacker Type    |
|                                           +----------+----------+
|                                           | Internal | External |
|                                           |On-P|Off-P|On-P|Off-P|
|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 Synchronization 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
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 components, services and protocols.
The extent of impact of a successful vulnerability exploit varies
considerably by use case and by industry; additional insights
regarding the individual use cases is available from [RFC8578],
DetNet Use Cases.  Each of those use cases is represented in
Figure 2, including Pro Audio, Electrical Utilities, Industrial M2M
(split into two areas, M2M Data Gathering and M2M Control Loop), and
Aspects 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 |
|Recovery
|  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      |
|  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      |
|  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, control
loop of the machine 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.
o  Delayed tear-down can lead to resource leakage, which in turn can
result in failure to allocate new DetNet flows, finally giving
rise to a denial of service attack.
o  Failure to deliver, or severely delaying, controller plane
messages adding an endpoint to a multicast-group will prevent the
new endpoint from receiving expected frames thus disrupting
expected behavior.
o  Delaying messages removing an endpoint from a group can lead to
loss of privacy as the endpoint will continue to receive messages
even after it is supposedly removed.
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
6.2.2.1.  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
6.2.2.2.  Controller Plane Spoofing
A successful controller plane spoofing-attack will potentionally have
adverse effects.  It can do virtually anything from:
o  modifying existing DetNet flows by changing the available
o  add or remove endpoints from a DetNet flow
o  drop DetNet flows completely
o  falsely create new DetNet flows (exhaust the systems resources, or
to enable DetNet flows that are outside the control of the Network
Engineer)
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 the resource budget of that flow.
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
o  create new DetNet flows (exhausting resources)
o  drop existing DetNet flows (denial of service)
o  add end-stations to a multicast group (loss of privacy)
o  remove end-stations from a multicast group (reduction of service)
o  modify the DetNet flow attributes (affecting available bandwidth)
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
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 Synchronization Mechanisms
Attacks on time synchronization 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.
Some of the technology-specific security considerations and
mitigation approaches are further discussed in the DETNET data plane
solution documents, such as [RFC8939], [RFC8938],
[I-D.ietf-detnet-mpls-over-udp-ip], and
[I-D.ietf-detnet-ip-over-mpls].
7.1.  Path Redundancy
A DetNet flow that can be forwarded simultaneously over multiple
paths.  Path replication and elimination [RFC8655] provides
resiliency to dropped or delayed packets.  This redundancy
improves the robustness to failures and to on-path attacks.  Note:
At the time of this writing, PREOF is not defined for the IP data
plane.
Related attacks
Path redundancy can be used to mitigate various on-path attacks,
including attacks described in Section 5.2.1, Section 5.2.2,
Section 5.2.3, and Section 5.2.7.  However it is also possible
that multiple paths may make it more difficult to locate the
source of an on-path attacker.
A delay modulation attack could result in extensively exercising
parts of the code that wouldn't normally be extensively exercised
and thus might expose flaws in the system that might otherwise not
be exposed.
7.2.  Integrity Protection
Integrity Protection in the scope of DetNet is the ability to
detect if a header has been modified (either maliciously or by
chance) and propagate a warning to a responsible monitoring agent.
An integrity protection mechanism is designed to counteract header
modification attacks where a Message Authentication Code (MAC) is
the most common.  The MAC can be distributed either in-line
(included in the same packet) or via a side channel.  Due to the
nature of DetNet traffic.  Note: a sideband approach may yield too
high overhead and complexity and should only be used as a very
last resort if in-line approaches are not viable.
There are different levels of security available for integrity
protection, ranging from the basic ability to detect if a header
has been corrupted in transit (no malicious attack) to stopping a
skilled and determined attacker capable of both subtly modifying
fields in the headers as well as updating an unsigned MAC.  Common
for all are the 2 steps that need to be performed in both ends.
The first is computing the checksum or MAC.  The corresponding
verification step must perform the same steps before comparing the
provided with the computed value.  Only then can the receiver be
reasonably sure that the header is authentic.
The most basic protection mechanism consists of computing a simple
checksum of the header fields and provide it to the next entity in
the packets path for verification.  Using a MAC combined with a
secret key provides the best protection against modification and
replication attacks (see Section 5.2.2 and Section 5.2.4).  This
MAC usage needs to be part of a security association that is
established and managed by a security association protocol (such
as IKEv2 for IPsec security associations).  Integrity protection
in the controller plane is discussed in Section 7.6.  The secret
key, regardless of MAC used, must be protected from falling into
the hands of unauthorized users.
DetNet system- and/or component- level designers need to be aware
of these distinctions and enforce appropriate integrity protection
mechanisms as needed based on a threat analysis.  Note that adding
integrity protection mechanisms may introduce latency, thus many
of the same considerations in Section 7.5.1 also apply here.
Packet Sequence Number Integrity Considerations
The use of PREOF in a DetNet implementation implies the use of a
sequence number for each packet.  There is a trust relationship
between the component that adds the sequence number and the
component that removes the sequence number.  The sequence number
may be end-to-end source to destination, or may be added/deleted
by network edge components.  The adder and remover(s) have the
trust relationship because they are the ones that ensure that the
sequence numbers are not modifiable.  Thus, sequence numbers can
be protected by using encryption, or by a MAC without using
encryption.  Between the adder and remover there may or may not be
replication and elimination functions.  The elimination functions
must be able to see the sequence numbers.  Therefore, if
encryption is done between adders and removers it must not obscure
the sequence number.  If the sequence removers and the eliminators
are in the same physical component, it may be possible to obscure
the sequence number, however that is a layer violation, and is not
recommended practice.  Note: At the time of this writing, PREOF is
not defined for the IP data plane.
Integrity protection mitigates attacks related to modification and
tampering, including the attacks described in Section 5.2.2 and
Section 5.2.4.
7.3.  DetNet Node Authentication
Authentication verifies the identity of DetNet nodes (including
DetNet Controller Plane nodes), and this enables mitigation of
spoofing attacks.  While integrity protection ( Section 7.2)
prevents intermediate nodes from modifying information,
authentication (such as IPsec [RFC4301] or MACsec
[IEEE802.1AE-2018]) can provide traffic origin verification, i.e.
to verify that each packet in a DetNet flow is from a known
DetNet node authentication is used to mitigate attacks related to
spoofing, including the attacks of Section 5.2.2, and
7.4.  Dummy Traffic Insertion
With some queueing methods such as [IEEE802.1Qch-2017] it is
possible to introduce dummy traffic in order to regularize the
timing of packet transmission.
Removing distinctive temporal properties of individual packets or
flows can be used to mitigate against reconnaissance attacks
Section 5.2.6.  For example, dummy traffic can be used to
synthetically maintain constant traffic rate even when no user
data is transmitted, thus making it difficult to collect
information about the times at which users are active, and the
times at which DETNET flows are added or removed.
7.5.  Encryption
Reconnaissance attacks (Section 5.2.6) can be mitigated by using
encryption.  Specific encryption protocols will depend on the
lower layers that DetNet is forwarded over.  For example, IP flows
may be forwarded over IPsec [RFC4301], and Ethernet flows may be
secured using MACsec [IEEE802.1AE-2018].
DetNet nodes do not have any need to inspect the payload of any
DetNet packets, making them data-agnostic.  This means that end-
to-end encryption at the application layer is an acceptable way to
protect user data.
Note that reconnaissance is a threat that is not specific to
DetNet flows, and therefore reconnaissance mitigation will
typically be analyzed and addressed by a network operator
regardless of whether DetNet flows are deployed.  Thus, encryption
requirements will typically not be defined in DetNet technology-
specific specifications, but considerations of using DetNet in
encrypted environments will be discussed in these specifications.
For example, Section 5.1.2.3. of [RFC8939] discusses flow
identification of DetNet flows running over IPsec.
As noted above, encryption can be used to mitigate reconnaissance
attacks ( Section 5.2.6).  However, for a DetNet to provide
differentiated quality of service on a flow-by-flow basis, the
network must be able to identify the flows individually.  This
implies that in a reconnaissance attack the attacker may also be
able to track individual flows to learn more about the system.
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 (v1.3 [RFC8446], in particular section 4.1 "Key exchange") and
IKEv2 [RFC6071]) are examples of this for endpoint checks.
However, if secret symmetric 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 faulty
then it may inject traffic into the flow.  Group key management
protocols can be used to automate management of such symmetric keys;
for an example in the context of IPsec, see
[I-D.ietf-ipsecme-g-ikev2].
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
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
7.6.  Control and Signaling Message Protection
Control and signaling messages can be protected through the use of
any or all of encryption, authentication, and integrity protection
mechanisms.
These mechanisms can be used to mitigate various attacks on the
controller plane, as described in Section 5.2.5, Section 5.2.7 and
Section 5.2.5.1.
7.7.  Dynamic Performance Analytics
Incorporating Dynamic Performance Analytics ("DPA") implies that
the DetNet design includes a performance monitoring system to
validate that timing guarantees are being met and to detect timing
violations or other anomalies that may be the symptom of a
security attack or system malfunction.  If this monitoring system
detects unexpected behavior, it must then cause action to be
initiated to address the situation in an appropriate and timely
manner, either at the data plane or controller plane, or both in
The overall DPA system can thus be decomposed into the "detection"
and "notification" functions.  Although the time-specific DPA
performance indicators and their implementation will likely be
specific to a given DetNet, and as such are nascent technology at
the time of this writing, DPA is commonly used in existing
networks so we can make some observations on how such a system
might be implemented for a DetNet, given that it would need to be
adapted to address the time-specific performance indicators.
Detection Mechanisms
Measurement of timing performance can be done via "passive" or
"active" monitoring, as discussed below.
Examples of passive monitoring strategies include
*  Monitoring of queue and buffer levels, e.g. via Active Queue
Management (e.g.  [RFC7567]
*  Monitoring of per-flow counters
*  Measurement of link statistics such as traffic volume,
bandwidth, and QoS
*  Detection of dropped packets
*  Use of commercially available Network Monitoring tools
Examples of active monitoring include
*  In-band timing measurements (such as packet arrival times) e.g.
by timestamping and packet inspection
*  Use of OAM.  For DetNet-specific OAM considerations see
[I-D.ietf-detnet-ip-oam], [I-D.ietf-detnet-mpls-oam].  Note: At
the time of this writing, specifics of DPA have not been
developed for the DetNet OAM, but could be a subject for future
*  For OAM for Ethernet specifically, see also Connectivity Fault
Management (CFM, [IEEE802.1Q]) which defines protocols and
practices for OAM for paths through 802.1 bridges and LANs
*  Out-of-band detection. following the data path or parts of a
data path, for example Bidirectional Forwarding Detection (BFD,
e.g.  [RFC5880])
Note that for some measurements (e.g. packet delay) it may be
necessary to make and reconcile measurements from more than one
physical location (e.g. a source and destination), possibly in
both directions, in order to arrive at a given performance
indicator value.
Notification Mechanisms
Making DPA measurement results available at the right place(s) and
time(s) to effect timely response can be challenging.  Two
notification mechanisms that are in general use are Netconf/YANG
Notifications (e.g.  [RFC5880]) and the proprietary local
telemetry interfaces provided with components from some vendors.
At the time of this writing YANG Notifications are not addressed
by the DetNet YANG drafts, however this may be a topic for future
work.  It is possible that some of the passive mechanisms could be
covered by notifications from non-DetNet-specific YANG modules;
for example if there is OAM or other performance monitoring that
can monitor delay bounds then that could have its own associated
YANG model which could be relevant to DetNet, for example some
"threshold" values for timing measurement notifications.
At the time of this writing there is an IETF Working Group for
network/performance monitoring (IP Performance Measurement, ippm).
See also previous work by the completed Remote Network Monitoring
Working Group (rmonmib).  See also [RFC6632], An Overview of the
IETF Network Management Standards.
Vendor-specific local telemetry may be available on some
commercially available systems, whereby the system can be
programmed (via a proprietary dedicated port and API) to monitor
and report on specific conditions, based on both passive and
active measurements.
Performance analytics can be used to mitigate various attacks,
including the ones described in Section 5.2.1 (Delay Attack),
Section 5.2.3 (Resource Segmentation Attack), and Section 5.2.7
(Time Synchronization Attack).
For example, in the case of data plane delay attacks, one possible
mitigation is to timestamp the data at the source, and timestamp
it again at the destination, and if the resulting latency exceeds
the promised bound, take appropriate action.  Note that DetNet
specifies packet sequence numbering, however it does not specify
use of packet timestamps, although they may be used by the
underlying transport (for example TSN, [IEEE802.1BA]) to provide
the service.
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         |
|Replication: Increased|-All impacts of other|-Integrity protection|
|attack surface        | attacks             |-DetNet Node         |
|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     |                     |
|Packet Injection      | consumption         | protection          |
|Attacks on Time       |-Non-deterministic   |-Path redundancy     |
|Synchronization       | delay               |-Control message     |
|Mechanisms            |-Increased resource  | protection          |
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
All attacks named in this document which are relevant to controller
plane packets (and the controller itself) are relevant to this theme,
including Path Manipulation, Path Choice, Control Packet Modification
or Injection, Reconaissance and Attacks on Time Synchronization
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
An attack surface related to Hot Swap is that the DetNet network must
at least consider input at runtime from components that were not part
of the initial configuration of the network.  Even a "perfect" (or
"hitless") replacement of a component 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 component).
This implies that an attack such as Flow Modification, Spoofing or
Inter-segment (which could introduce packets from a "new" component,
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 component).
To mitigate this situation, deployments should provide a method for
dynamic and secure registration of new components, and (possibly
manual) deregistration of retired components.  This would avoid the
situation in which the network must accommodate potentially insecure
packet flows from unknown components.
Similarly if the network was designed to support runtime replacement
of a clock component, then presence (or apparent presence) and thus
consideration of packets from a new such component could affect the
network, or the time synchronization of the network, for example by
initiating a new Best Master Clock selection process.  These types of
attacks should therefore be considered when designing hot swap type
functionality (see [RFC7384]).
8.1.4.  Data Flow Information Models
DetNet specifies new YANG models which may present new attack
surfaces.  Per IETF guidelines, security considerations for any YANG
model are expected to be part of the YANG model specification, as
described in [IETF_YANG_SEC].
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 (e.g.  IP) via the use of well-
known protocols such as IP, MPLS Pseudowire, and Ethernet.  Various
DetNet drafts address many specific aspects of Layer 2 and Layer 3
integration within a DetNet, and these are not individually
referenced here; security considerations for those aspects are
covered within those drafts or within the related subsections of the
present document.
Please note that although there are no entries in the L2 and L3
Integration line of the Mapping Between Themes and Attacks table
Figure 4, this 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 on-path
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 Synchronization 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
There are many proprietary "field buses" used in 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 handling of IT traffic by the DetNet 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.
The network design as a whole also needs to consider possible
application-level dependencies of "OT"-type applications on services
provided by the "IT part" of the network; for example, does the OT
application depend on IT network services such as DNS or OAM?  If
such dependencies exist, how are malicious packet flows handled?
Such considerations are typically outside the scope of DetNet proper,
but nonetheless need to be addressed in the overall DetNet network
design for a given use case.
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 component diversity and potentially higher numbers of each
component manufactured.
The security mechanisms and protocols that are discussed in this
document also require interoperability.  It is expected that DETNET
network specifications that define security measures and protocols
will be defined in a way that allows interoperability.
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
promoting higher numbers of each component 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 Components
component 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 component 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 components, such as implementing a dedicated security
layer around the component.
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 Synchronization 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 reply from the network.
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 Synchronization attacks can corrupt the time reference of the
system, 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.
system, 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.
In practice, network designers can adopt a risk-based approach, in
which only those attacks are mitigated whose potential cost is higher
than the cost of mitigation.
8.1.22.  Redundant Paths
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 sufficiently secure against problematic
component or traffic behavior, whether malicious or incidental, and
whether affecting a single component or multiple components.  If any
of the security mechanisms which protect the DetNet from such
problems are attacked or subverted, this can result in malfunction of
the network.  Thus the design of the security system itself needs to
be robust against attacks.
The general topic of protection of security mechanisms is not unique
to DetNet; it is identical to the case of securing any security
mechanism for any network.  This document addresses these concerns
only to the extent that they are unique to DetNet.
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                                    |
|  1 |Delay Attack                               |
|  2 |DetNet Flow Modification or Spoofing       |
|  3 |Inter-Segment Attack                       |
|  4 |Replication: Increased attack surface      |
|  5 |Replication-related Header Manipulation    |
|  6 |Path Manipulation                          |
|  7 |Path Choice: Increased Attack Surface      |
|  8 |Control or Signaling Packet Modification   |
|  9 |Control or Signaling Packet Injection      |
| 10 |Reconnaissance                             |
| 11 |Attacks on Time Synchronization Mechanisms |
Figure 4: List of Attacks
The Mapping Between Themes and Attacks table Figure 5maps 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 '+'.  The row items which
have no threats associated with them are included in the table for
completeness of the list of Use Case Common Themes, and do not have
DetNet-specific threats associated with them.
+----------------------------+--------------------------------+
| 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       |  |  |  |  |  |  |  |  |  |  |  |
|Components                  |  |  |  |  |  |  |  |  |  |  |  |
|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
o  OAM traffic generated by the network itself.  The additional
bandwidth required for such packets is added by the network
administration, presumably transparent to the customer.  Security
considerations for such traffic are not DetNet-specific (apart
from such traffic being subject to the same DetNet-specific
security considerations as any other DetNet data flow) and are
thus not covered in this document.
o  OAM traffic generated by the customer.  From a DetNet security
point of view, DetNet security considerations for such traffic are
exactly the same as for any other customer data flows.
From the perspective of an attack, OAM traffic is indistinguishable
from DetNet traffic and the network needs to be secure against
injection, removal, or modification of traffic of any kind, including
OAM traffic.  A DetNet is sensitive to any form of packet injection,
removal or manipulation and in this respect DetNet OAM traffic is no
different.  Techniques for securing a DetNet against these threats
have been discussed elsewhere in this document.
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 ( [RFC8939])
and delivers service over sub-layer technologies such as MPLS
([RFC8938]) 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, for example for IP flows, IPSec [RFC4301].  For IP over
Ethernet (Layer 2) flows using an underlying sub-net, MACSec
[IEEE802.1AE-2018] may be appropriate.  For some use cases packet
integrity protection without encryption may be sufficient.
However, if the DetNet nodes cannot decrypt IPsec traffic, then
DetNet flow identification for encrypted IP traffic flows must be
performed in a different way than it would be for unencrypted IP
DetNet flows.  The DetNet IP Data Plane identifies unencrypted 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, leaving only three components of the 6-tuple,
which are the two IP addresses and the DSCP.  Identification of
DetNet flows over IPsec is further discussed in Section 5.1.2.3.  of
Sections below discuss threats specific to IP and MPLS in more
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
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 the data plane of that
network, for example through the use of queueing mechanisms.
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 [RFC8077],
[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.  New work on MPLS security may also be applicable, for
example [I-D.ietf-mpls-opportunistic-encrypt].
10.  IANA Considerations
This document includes no requests from IANA.
11.  Security Considerations
The security considerations of DetNet networks are presented
throughout this document.
12.  Privacy Considerations
Privacy in the context of DetNet is maintained by the base
technologies specific to the DetNet and user traffic.  For example
TSN can use MACsec, IP can use IPsec, applications can use IP
transport protocol-provided methods e.g.  TLS and DTLS.  MPLS
typically uses L2/L3 VPNs combined with the previously mentioned
privacy methods.
13.  Contributors
The Editor would like to recognize the contributions of the following
individuals to this draft.
Subir Das (Applied Communication Sciences)
150 Mount Airy Road, Basking Ridge, New Jersey, 07920, USA
email sdas@appcomsci.com
John Dowdell (Airbus Defence and Space)
Celtic Springs, Newport, NP10 8FZ, United Kingdom
email john.dowdell.ietf@gmail.com
Henrik Austad (SINTEF Digital)
Klaebuveien 153, Trondheim, 7037, Norway
email henrik@austad.us
Norman Finn (Huawei)
3101 Rio Way, Spring Valley, California 91977, USA
email nfinn@nfinnconsulting.com
Stewart Bryant (Futurewei Technologies)
email: stewart.bryant@gmail.com
David Black (Dell EMC)
176 South Street, Hopkinton, MA  01748, USA
email: david.black@dell.com
Carsten Bormann (Universitat Bremen TZI)
Postfach 330440, D-28359 Bremen, Germany
email: cabo@tzi.org
14.  References
14.1.  Normative References
[RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC8938]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
Bryant, "Deterministic Networking (DetNet) Data Plane
Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,
[RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
Bryant, "Deterministic Networking (DetNet) Data Plane:
IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
14.2.  Informative References
[ARINC664P7]
ARINC, "ARINC 664 Aircraft Data Network, Part 7, Avionics
Full-Duplex Switched Ethernet Network", 2009.
[I-D.ietf-detnet-flow-information-model]
Varga, B., Farkas, J., Cummings, R., Jiang, Y., and D.
Fedyk, "DetNet Flow Information Model", draft-ietf-detnet-
flow-information-model-12 (work in progress), December
[I-D.ietf-detnet-ip-oam]
Mirsky, G., Chen, M., and D. Black, "Operations,
Administration and Maintenance (OAM) for Deterministic
Networks (DetNet) with IP Data Plane", draft-ietf-detnet-
ip-oam-00 (work in progress), September 2020.
[I-D.ietf-detnet-ip-over-mpls]
Varga, B., Berger, L., Fedyk, D., Bryant, S., and J.
Korhonen, "DetNet Data Plane: IP over MPLS", draft-ietf-
detnet-ip-over-mpls-09 (work in progress), October 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)", draft-ietf-detnet-ip-over-tsn-04 (work in
progress), November 2020.
[I-D.ietf-detnet-mpls-oam]
Mirsky, G. and M. Chen, "Operations, Administration and
Maintenance (OAM) for Deterministic Networks (DetNet) with
MPLS Data Plane", draft-ietf-detnet-mpls-oam-01 (work in
progress), July 2020.
[I-D.ietf-detnet-mpls-over-udp-ip]
Varga, B., Farkas, J., Berger, L., Malis, A., and S.
Bryant, "DetNet Data Plane: MPLS over UDP/IP", draft-ietf-
detnet-mpls-over-udp-ip-07 (work in progress), October
[I-D.ietf-ipsecme-g-ikev2]
Smyslov, V. and B. Weis, "Group Key Management using
IKEv2", draft-ietf-ipsecme-g-ikev2-01 (work in progress),
[I-D.ietf-mpls-opportunistic-encrypt]
Farrel, A. and S. Farrell, "Opportunistic Security in MPLS
Networks", draft-ietf-mpls-opportunistic-encrypt-03 (work
in progress), March 2017.
[I-D.varga-detnet-service-model]
Varga, B. and J. Farkas, "DetNet Service Model", draft-
varga-detnet-service-model-02 (work in progress), May
[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,
<https://ieeexplore.ieee.org/document/8585421>.
[IEEE802.1BA]
IEEE Standards Association, "IEEE Standard for Local and
Metropolitan Area Networks -- Audio Video Bridging (AVB)
Systems", 2011,
[IEEE802.1Q]
metropolitan area networks--Bridges and Bridged Networks -
Annex J - Connectivity Fault Management", 2014,
[IEEE802.1Qbv-2015]
metropolitan area networks -- Bridges and Bridged Networks
- Amendment 25: Enhancements for Scheduled Traffic", 2015,
[IEEE802.1Qch-2017]
metropolitan area networks--Bridges and Bridged Networks--
Amendment 29: Cyclic Queuing and Forwarding", 2017,
[IETF_YANG_SEC]
IETF, "YANG Module Security Considerations", 2018,
<https://trac.ietf.org/trac/ops/wiki/yang-security-
guidelines>.
[IT_DEF]   Wikipedia, "IT Definition", 2020,
<https://en.wikiquote.org/wiki/Information_technology>.
[OT_DEF]   Wikipedia, "OT Definition", 2020,
<https://en.wikipedia.org/wiki/Operational_technology>.
[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., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
RFC 3931, DOI 10.17487/RFC3931, March 2005,
[RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "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, <https://www.rfc-editor.org/info/rfc4301>.
[RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
[RFC5905]  Mills, D., Martin, J., Ed., 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., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
[RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
L., and L. Berger, "A Framework for MPLS in Transport
[RFC6071]  Frankel, S. and S. Krishnan, "IP Security (IPsec) and
Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
DOI 10.17487/RFC6071, February 2011,
[RFC6073]  Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073,
DOI 10.17487/RFC6073, January 2011,
[RFC6274]  Gont, F., "Security Assessment of the Internet Protocol
Version 4", RFC 6274, DOI 10.17487/RFC6274, July 2011,
[RFC6478]  Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", RFC 6478,
DOI 10.17487/RFC6478, May 2012,
[RFC6632]  Ersue, M., Ed. and B. Claise, "An Overview of the IETF
Network Management Standards", RFC 6632,
DOI 10.17487/RFC6632, June 2012,
[RFC6941]  Fang, L., Ed., Niven-Jenkins, B., Ed., Mansfield, S., Ed.,
and R. Graveman, Ed., "MPLS Transport Profile (MPLS-TP)
Security Framework", RFC 6941, DOI 10.17487/RFC6941, April
2013, <https://www.rfc-editor.org/info/rfc6941>.
[RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
[RFC7567]  Baker, F., Ed. and G. Fairhurst, Ed., "IETF
Recommendations Regarding Active Queue Management",
BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,
[RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Threat Analysis", RFC 7835,
DOI 10.17487/RFC7835, April 2016,
[RFC8077]  Martini, L., Ed. and G. Heron, Ed., "Pseudowire Setup and
Maintenance Using the Label Distribution Protocol (LDP)",
STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017,
[RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
[RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
[RS_DEF]   Wikipedia, "RS Definition", 2020,
<https://en.wikipedia.org/wiki/Network_segmentation>.
Authors' Addresses
Ethan Grossman (editor)
Dolby Laboratories, Inc.
San Francisco, CA  94103
Email: ethan@ieee.org
URI:   http://www.dolby.com
Tal Mizrahi
Huawei Network.IO Innovation Lab
Email: tal.mizrahi.phd@gmail.com
Andrew  J. Hacker
MistIQ Technologies, Inc
Email: ajhacker@mistiqtech.com
URI:   http://www.mistiqtech.com