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Internet Engineering Task Force (IETF) E. Lear
Request for Comments: 8520 Cisco Systems
Category: Standards Track R. Droms
ISSN: 2070-1721 Google
D. Romascanu
March 2019
Manufacturer Usage Description Specification
Abstract
This memo specifies a component-based architecture for Manufacturer
Usage Descriptions (MUDs). The goal of MUD is to provide a means for
end devices to signal to the network what sort of access and network
functionality they require to properly function. The initial focus
is on access control. Later work can delve into other aspects.
This memo specifies two YANG modules, IPv4 and IPv6 DHCP options, a
Link Layer Discovery Protocol (LLDP) TLV, a URL, an X.509 certificate
extension, and a means to sign and verify the descriptions.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8520.
Lear, et al. Standards Track [Page 1]
RFC 8520 Manufacturer Usage Descriptions March 2019
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. What MUD Doesn't Do . . . . . . . . . . . . . . . . . . . 5
1.2. A Simple Example . . . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Determining Intended Use . . . . . . . . . . . . . . . . 6
1.5. Finding a Policy: The MUD URL . . . . . . . . . . . . . . 7
1.6. Processing of the MUD URL . . . . . . . . . . . . . . . . 8
1.7. Types of Policies . . . . . . . . . . . . . . . . . . . . 8
1.8. The Manufacturer Usage Description Architecture . . . . . 10
1.9. Order of Operations . . . . . . . . . . . . . . . . . . . 12
2. The MUD Model and Semantic Meaning . . . . . . . . . . . . . 12
2.1. The IETF-MUD YANG Module . . . . . . . . . . . . . . . . 14
3. MUD Model Definitions for the Root "mud" Container . . . . . 15
3.1. mud-version . . . . . . . . . . . . . . . . . . . . . . . 15
3.2. MUD URL . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3. to-device-policy and from-device-policy Containers . . . 16
3.4. last-update . . . . . . . . . . . . . . . . . . . . . . . 16
3.5. cache-validity . . . . . . . . . . . . . . . . . . . . . 16
3.6. is-supported . . . . . . . . . . . . . . . . . . . . . . 16
3.7. systeminfo . . . . . . . . . . . . . . . . . . . . . . . 16
3.8. mfg-name, software-rev, model-name, and firmware-rev . . 17
3.9. extensions . . . . . . . . . . . . . . . . . . . . . . . 17
4. Augmentation to the ACL Model . . . . . . . . . . . . . . . . 17
4.1. manufacturer . . . . . . . . . . . . . . . . . . . . . . 17
4.2. same-manufacturer . . . . . . . . . . . . . . . . . . . . 17
4.3. documentation . . . . . . . . . . . . . . . . . . . . . . 18
4.4. model . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5. local-networks . . . . . . . . . . . . . . . . . . . . . 18
4.6. controller . . . . . . . . . . . . . . . . . . . . . . . 18
4.7. my-controller . . . . . . . . . . . . . . . . . . . . . . 19
4.8. direction-initiated . . . . . . . . . . . . . . . . . . . 19
Lear, et al. Standards Track [Page 2]
RFC 8520 Manufacturer Usage Descriptions March 2019
5. Processing of the MUD File . . . . . . . . . . . . . . . . . 19
6. What Does a MUD URL Look Like? . . . . . . . . . . . . . . . 19
7. The MUD YANG Model . . . . . . . . . . . . . . . . . . . . . 20
8. The Domain Name Extension to the ACL Model . . . . . . . . . 26
8.1. src-dnsname . . . . . . . . . . . . . . . . . . . . . . . 27
8.2. dst-dnsname . . . . . . . . . . . . . . . . . . . . . . . 27
8.3. The ietf-acldns Model . . . . . . . . . . . . . . . . . . 28
9. MUD File Example . . . . . . . . . . . . . . . . . . . . . . 30
10. The MUD URL DHCP Option . . . . . . . . . . . . . . . . . . . 32
10.1. Client Behavior . . . . . . . . . . . . . . . . . . . . 33
10.2. Server Behavior . . . . . . . . . . . . . . . . . . . . 33
10.3. Relay Requirements . . . . . . . . . . . . . . . . . . . 33
11. The Manufacturer Usage Description (MUD) URL X.509 Extension 34
12. The Manufacturer Usage Description LLDP Extension . . . . . . 36
13. The Creating and Processing of Signed MUD Files . . . . . . . 38
13.1. Creating a MUD File Signature . . . . . . . . . . . . . 38
13.2. Verifying a MUD File Signature . . . . . . . . . . . . . 38
14. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 39
15. Deployment Considerations . . . . . . . . . . . . . . . . . . 39
16. Security Considerations . . . . . . . . . . . . . . . . . . . 40
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
17.1. YANG Module Registrations . . . . . . . . . . . . . . . 43
17.2. URI Registrations . . . . . . . . . . . . . . . . . . . 43
17.3. DHCPv4 and DHCPv6 Options . . . . . . . . . . . . . . . 43
17.4. PKIX Extensions . . . . . . . . . . . . . . . . . . . . 43
17.5. Media Type Registration for MUD Files . . . . . . . . . 44
17.6. IANA LLDP TLV Subtype Registry . . . . . . . . . . . . . 45
17.7. The MUD Well-Known Universal Resource Name (URNs) . . . 45
17.8. Extensions Registry . . . . . . . . . . . . . . . . . . 46
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 46
18.1. Normative References . . . . . . . . . . . . . . . . . . 46
18.2. Informative References . . . . . . . . . . . . . . . . . 49
Appendix A. Default MUD Nodes . . . . . . . . . . . . . . . . . 52
Appendix B. A Sample Extension: DETNET-indicator . . . . . . . . 56
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 60
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60
Lear, et al. Standards Track [Page 3]
RFC 8520 Manufacturer Usage Descriptions March 2019
1. Introduction
The Internet has largely been constructed for general purpose
computers, those devices that may be used for a purpose that is
specified by those who own the device. In [RFC1984], it was presumed
that an end device would be most capable of protecting itself. This
made sense when the typical device was a workstation or a mainframe,
and it continues to make sense for general purpose computing devices
today, including laptops, smart phones, and tablets.
[RFC7452] discusses design patterns for, and poses questions about,
smart objects. Let us then posit a group of objects that are
specifically not intended to be used for general purpose computing
tasks. These devices, which this memo refers to as Things, have a
specific purpose. By definition, therefore, all other uses are not
intended. If a small number of communication patterns follows from
those small number of uses, the combination of these two statements
can be restated as a Manufacturer Usage Description (MUD) that can be
applied at various points within a network. MUD primarily addresses
threats to the device rather than the device as a threat. In some
circumstances, however, MUD may offer some protection in the latter
case, depending on how the MUD URL is communicated and how devices
and their communications are authenticated.
We use the notion of "manufacturer" loosely in this context to refer
to the entity or organization that will state how a device is
intended to be used. For example, in the context of a light bulb,
this might indeed be the light bulb manufacturer. In the context of
a smarter device that has a built in Linux stack, it might be an
integrator of that device. The key points are that the device itself
is assumed to serve a limited purpose, and that there exists an
organization in the supply chain of that device that will take
responsibility for informing the network about that purpose.
The intent of MUD is to provide the following:
o Substantially reduce the threat surface on a device to those
communications intended by the manufacturer.
o Provide a means to scale network policies to the ever-increasing
number of types of devices in the network.
o Provide a means to address at least some vulnerabilities in a way
that is faster than the time it might take to update systems.
This will be particularly true for systems that are no longer
supported.
Lear, et al. Standards Track [Page 4]
RFC 8520 Manufacturer Usage Descriptions March 2019
o Keep the cost of implementation of such a system to the bare
minimum.
o Provide a means of extensibility for manufacturers to express
other device capabilities or requirements.
MUD consists of three architectural building blocks:
o A URL that can be used to locate a description;
o The description itself, including how it is interpreted; and
o A means for local network management systems to retrieve the
description.
MUD is most effective when the network is able to identify in some
way the remote endpoints that Things will talk to.
In this specification, we describe each of these building blocks and
how they are intended to be used together. However, they may also be
used separately, independent of this specification, by local
deployments for their own purposes.
1.1. What MUD Doesn't Do
MUD is not intended to address network authorization of general
purpose computers, as their manufacturers cannot envision a specific
communication pattern to describe. In addition, even those devices
that have a single or small number of uses might have very broad
communication patterns. MUD on its own is not for them either.
Although MUD can provide network administrators with some additional
protection when device vulnerabilities exist, it will never replace
the need for manufacturers to patch vulnerabilities.
Finally, no matter what the manufacturer specifies in a MUD file,
these are not directives, but suggestions. How they are instantiated
locally will depend on many factors and will be ultimately up to the
local network administrator, who must decide what is appropriate in a
given circumstances.
1.2. A Simple Example
A light bulb is intended to light a room. It may be remotely
controlled through the network, and it may make use of a rendezvous
service (which could be accessed by an application on a smart phone).
What we can say about that light bulb, then, is that all other
network access is unwanted. It will not contact a news service, nor
Lear, et al. Standards Track [Page 5]
RFC 8520 Manufacturer Usage Descriptions March 2019
speak to the refrigerator, and it has no need of a printer or other
devices. It has no social networking friends. Therefore, applying
an access list to it that states it will only connect to the single
rendezvous service will not impede performing its function; at the
same time, this will allow the network to provide the light bulb and
other devices an additional layer of protection.
1.3. Terminology
MUD: Manufacturer Usage Description.
MUD file: a file containing YANG-based JSON that describes a Thing
and associated suggested specific network behavior.
MUD file server: a web server that hosts a MUD file.
MUD manager: the system that requests and receives the MUD file from
the MUD server. After it has processed a MUD file, it may direct
changes to relevant network elements.
MUD controller: a synonym that has been used in the past for MUD
manager.
MUD URL: a URL that can be used by the MUD manager to receive the
MUD file.
Thing: the device emitting a MUD URL.
Manufacturer: the entity that configures the Thing to emit the MUD
URL and the one who asserts a recommendation in a MUD file. The
manufacturer might not always be the entity that constructs a
Thing. It could, for instance, be a systems integrator, or even a
component provider.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.4. Determining Intended Use
The notion of intended use is in itself not new. Network
administrators apply access lists every day to allow for only such
use. This notion of white listing was well described by Chapman and
Zwicky in [FW95]. Profiling systems that make use of heuristics to
identify types of systems have existed for years as well.
Lear, et al. Standards Track [Page 6]
RFC 8520 Manufacturer Usage Descriptions March 2019
A Thing could just as easily tell the network what sort of access it
requires without going into what sort of system it is. This would,
in effect, be the converse of [RFC7488]. In seeking a general
solution, however, we assume that a device will implement
functionality necessary to fulfill its limited purpose. This is
basic economic constraint. Unless the network would refuse access to
such a device, its developers would have no reason to provide the
network any information. To date, such an assertion has held true.
1.5. Finding a Policy: The MUD URL
Our work begins with the device emitting a Universal Resource Locator
(URL) [RFC3986]. This URL serves both to classify the device type
and to provide a means to locate a policy file.
MUD URLs MUST use the "https" scheme [RFC7230].
In this memo, three means are defined to emit the MUD URL, as
follows:
o A DHCP option [RFC2131] [RFC8415] that the DHCP client uses to
inform the DHCP server. The DHCP server may take further actions,
such as acting as the MUD manager or passing the MUD URL along to
the MUD manager.
o An X.509 constraint. The IEEE has developed IEEE 802.1AR
[IEEE8021AR] to provide a certificate-based approach to
communicate device characteristics, which itself relies on
[RFC5280]. The MUD URL extension is non-critical, as required by
IEEE 802.1AR. Various means may be used to communicate that
certificate, including the Tunnel Extensible Authentication
Protocol (TEAP) [RFC7170].
o Finally, a Link Layer Discovery Protocol (LLDP) frame is defined
[IEEE8021AB].
It is possible that there may be other means for a MUD URL to be
learned by a network. For instance, some devices may already be
fielded or have very limited ability to communicate a MUD URL, and
yet they can be identified through some means, such as a serial
number or a public key. In these cases, manufacturers may be able to
map those identifiers to particular MUD URLs (or even the files
themselves). Similarly, there may be alternative resolution
mechanisms available for situations where Internet connectivity is
limited or does not exist. Such mechanisms are not described in this
memo, but they are possible. Implementors are encouraged to allow
for the flexibility of how MUD URLs may be learned.
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RFC 8520 Manufacturer Usage Descriptions March 2019
1.6. Processing of the MUD URL
MUD managers that are able to do so SHOULD retrieve MUD URLs and
signature files as per [RFC7230], using the GET method [RFC7231].
They MUST validate the certificate using the rules in [RFC2818],
Section 3.1.
Requests for MUD URLs SHOULD include an "Accept" header field
([RFC7231], Section 5.3.2) containing "application/mud+json", an
"Accept-Language" header field ([RFC7231], Section 5.3.5), and a
"User-Agent" header field ([RFC7231], Section 5.5.3).
MUD managers SHOULD automatically process 3xx response status codes.
If a MUD manager is not able to fetch a MUD URL, other means MAY be
used to import MUD files and associated signature files. So long as
the signature of the file can be validated, the file can be used. In
such environments, controllers SHOULD warn administrators when cache-
validity expiry is approaching so that they may check for new files.
It may not be possible for a MUD manager to retrieve a MUD file at
any given time. Should a MUD manager fail to retrieve a MUD file, it
SHOULD consider the existing one safe to use, at least for a time.
After some period, it SHOULD log that it has been unable to retrieve
the file. There may be very good reasons for such failures,
including the possibility that the MUD manager is in an offline
environment, the local Internet connection has failed, or the remote
Internet connection has failed. It is also possible that an attacker
is attempting to interfere with the deployment of a device. How to
handle such circumstances is a local decision.
1.7. Types of Policies
When the MUD URL is resolved, the MUD manager retrieves a file that
describes what sort of communications a device is designed to have.
The manufacturer may specify either specific hosts for cloud-based
services or certain classes for access within an operational network.
An example of a class might be "devices of a specified manufacturer
type", where the manufacturer type itself is indicated simply by the
authority component (e.g., the domain name) of the MUD URL. Another
example might be to allow or disallow local access. Just like other
policies, these may be combined. For example:
o Allow access to devices of the same manufacturer
o Allow access to and from controllers via the Constrained
Application Protocol (COAP) [RFC7252]
Lear, et al. Standards Track [Page 8]
RFC 8520 Manufacturer Usage Descriptions March 2019
o Allow access to local DNS/NTP
o Deny all other access
A printer might have a description that states:
o Allow access for port IPP or port LPD
o Allow local access for port HTTP
o Deny all other access
In this way, anyone can print to the printer, but local access would
be required for the management interface.
The files that are retrieved are intended to be closely aligned to
existing network architectures so that they are easy to deploy. We
make use of YANG [RFC7950] because it provides accurate and adequate
models for use by network devices. JSON [RFC8259] is used as a
serialization format for compactness and readability, relative to
XML. Other formats may be chosen with later versions of MUD.
While the policy examples given here focus on access control, this is
not intended to be the sole focus. By structuring the model
described in this document with clear extension points, other
descriptions could be included. One that often comes to mind is
quality of service.
The YANG modules specified here are extensions of [RFC8519]. The
extensions to this model allow for a manufacturer to express classes
of systems that a manufacturer would find necessary for the proper
function of the device. Two modules are specified. The first module
specifies a means for domain names to be used in Access Control Lists
(ACLs) so that devices that have their controllers in the cloud may
be appropriately authorized with domain names, where the mapping of
those names to addresses may rapidly change.
The other module abstracts away IP addresses into certain classes
that are instantiated into actual IP addresses through local
processing. Through these classes, manufacturers can specify how the
device is designed to communicate, so that network elements can be
configured by local systems that have local topological knowledge.
That is, the deployment populates the classes that the manufacturer
specifies. The abstractions below map to zero or more hosts, as
follows:
Manufacturer: A device made by a particular manufacturer, as
identified by the authority component of its MUD URL.
Lear, et al. Standards Track [Page 9]
RFC 8520 Manufacturer Usage Descriptions March 2019
same-manufacturer: Devices that have the same authority component of
their MUD URL.
controller: Devices that the local network administrator admits to
the particular class.
my-controller: Devices intended to serve as controllers for the MUD
URL that the Thing emitted.
local: The class of IP addresses that are scoped within some
administrative boundary. By default, it is suggested that this be
the local subnet.
The "manufacturer" classes can be easily specified by the
manufacturer, whereas controller classes are initially envisioned to
be specified by the administrator.
Because manufacturers do not know who will be using their devices, it
is important for functionality referenced in usage descriptions to be
relatively ubiquitous and mature. For these reasons, the YANG-based
configuration in a MUD file is limited to the modules either
specified or referenced in this document, or specified in documented
extensions.
1.8. The Manufacturer Usage Description Architecture
With these components laid out, we now have the basis for an
architecture. This leads us to ASCII art.
.......................................
. ____________ . _____________
. | | . | |
. | MUD |-->get URL-->| MUD |
. | Manager | .(https) | File Server |
. End system network |____________|<-MUD file<-<|_____________|
. . .
. . .
. _______ _________ .
.| | (DHCP et al.) | router | .
.| Thing |---->MUD URL-->| or | .
.|_______| | switch | .
. |_________| .
.......................................
Figure 1: MUD Architecture
Lear, et al. Standards Track [Page 10]
RFC 8520 Manufacturer Usage Descriptions March 2019
In the above diagram, the switch or router collects MUD URLs and
forwards them to the MUD manager (a network management system) for
processing. This happens in different ways, depending on how the URL
is communicated. For instance, in the case of DHCP, the DHCP server
might receive the URL and then process it. In the case of IEEE
802.1X [IEEE8021X], the switch would carry the URL via a certificate
to the authentication server via the Extensible Authentication
Protocol (EAP) over Radius [RFC3748], which would then process it.
One method to do this is TEAP, as described in [RFC7170]. The
certificate extension is described below.
The information returned by the MUD file server is valid for as long
as the Thing is connected. There is no expiry. However, if the MUD
manager has detected that the MUD file for a Thing has changed, it
SHOULD update the policy expeditiously, taking into account whatever
approval flow is required in a deployment. In this way, new
recommendations from the manufacturer can be processed in a timely
fashion.
The information returned by the MUD file server (a web server) is
valid for the duration of the Thing's connection, or as specified in
the description. Thus, if the Thing is disconnected, any associated
configuration in the switch can be removed. Similarly, from time to
time the description may be refreshed, based on new capabilities or
communication patterns or vulnerabilities.
The web server is typically run by or on behalf of the manufacturer.
Its domain name is that of the authority found in the MUD URL. For
legacy cases where Things cannot emit a URL, if the switch is able to
determine the appropriate URL, it may proxy it. In a trivial case,
it may hardcode a MUD URL on a switch port or a map from some
available identifier such as an L2 address or certificate hash to a
MUD URL.
The role of the MUD manager in this environment is to do the
following:
o receive MUD URLs,
o fetch MUD files,
o translate abstractions in the MUD files to specific network
element configuration,
o maintain and update any required mappings of the abstractions, and
o update network elements with appropriate configuration.
Lear, et al. Standards Track [Page 11]
RFC 8520 Manufacturer Usage Descriptions March 2019
A MUD manager may be a component of an Authentication, Authorization,
and Accounting (AAA) system or a network management system.
Communication within those systems and from those systems to network
elements is beyond the scope of this memo.
1.9. Order of Operations
As mentioned above, MUD contains architectural building blocks, so
the order of operation may vary. However, here is one clear intended
example:
1. Thing emits a URL.
2. That URL is forwarded to a MUD manager by the nearest switch (how
this happens depends on the way in which the MUD URL is emitted).
3. The MUD manager retrieves the MUD file and signature from the MUD
file server, assuming it doesn't already have copies. After
validating the signature, it may test the URL against a web or
domain reputation service, and it may test any hosts within the
file against those reputation services, as it deems fit.
4. The MUD manager may query the administrator for permission to add
the Thing and associated policy. If the Thing is known or the
Thing type is known, it may skip this step.
5. The MUD manager instantiates local configuration based on the
abstractions defined in this document.
6. The MUD manager configures the switch nearest the Thing. Other
systems may be configured as well.
7. When the Thing disconnects, policy is removed.
2. The MUD Model and Semantic Meaning
A MUD file consists of a YANG model instance that has been serialized
in JSON [RFC7951]. For purposes of MUD, the nodes that can be
modified are access lists as augmented by this model. The MUD file
is limited to the serialization of only the following YANG schema:
o ietf-access-control-list [RFC8519]
o ietf-mud (RFC 8520)
o ietf-acldns (RFC 8520)
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RFC 8520 Manufacturer Usage Descriptions March 2019
Extensions may be used to add additional schema. This is described
further on.
To provide the widest possible deployment, publishers of MUD files
SHOULD make use of the abstractions in this memo and avoid the use of
IP addresses. A MUD manager SHOULD NOT automatically implement any
MUD file that contains IP addresses, especially those that might have
local significance. The addressing of one side of an access list is
implicit, based on whether it is applied as to-device-policy or
from-device-policy.
With the exceptions of the "name" of the ACL, "type", "name" of the
Access Control Entry (ACE), and TCP and UDP source and destination
port information, publishers of MUD files SHOULD limit the use of ACL
model leaf nodes expressed to those found in this specification.
Absent any extensions, MUD files are assumed to implement only the
following ACL model features:
o match-on-ipv4, match-on-ipv6, match-on-tcp, match-on-udp,
match-on-icmp
Furthermore, only "accept" or "drop" actions SHOULD be included. A
MUD manager MAY choose to interpret "reject" as "drop". A MUD
manager SHOULD ignore all other actions. This is because
manufacturers do not have sufficient context within a local
deployment to know whether reject is appropriate. That is a decision
that should be left to a network administrator.
Given that MUD does not deal with interfaces, the support of the
"ietf-interfaces" module [RFC8343] is not required. Specifically,
the support of interface-related features and branches (e.g.,
interface-attachment and interface-stats) of the ACL YANG module is
not required.
In fact, MUD managers MAY ignore any particular component of a
description or MAY ignore the description in its entirety, and they
SHOULD carefully inspect all MUD descriptions. Publishers of MUD
files MUST NOT include other nodes except as described in
Section 3.9. See that section for more information.
Lear, et al. Standards Track [Page 13]
RFC 8520 Manufacturer Usage Descriptions March 2019
2.1. The IETF-MUD YANG Module
This module is structured into three parts:
o The first component, the "mud" container, holds information that
is relevant to retrieval and validity of the MUD file itself, as
well as policy intended to and from the Thing.
o The second component augments the matching container of the ACL
model to add several nodes that are relevant to the MUD URL, or
they are otherwise abstracted for use within a local environment.
o The third component augments the tcp-acl container of the ACL
model to add the ability to match on the direction of initiation
of a TCP connection.
A valid MUD file will contain two root objects: a "mud" container and
an "acls" container. Extensions may add additional root objects as
required. As a reminder, when parsing acls, elements within a
"match" block are logically ANDed. In general, a single abstraction
in a match statement should be used. For instance, it makes little
sense to match both "my-controller" and "controller" with an
argument, since they are highly unlikely to be the same value.
A simplified graphical representation of the data models is used in
this document. The meaning of the symbols in these diagrams is
explained in [RFC8340].
Lear, et al. Standards Track [Page 14]
RFC 8520 Manufacturer Usage Descriptions March 2019
module: ietf-mud
+--rw mud!
+--rw mud-version uint8
+--rw mud-url inet:uri
+--rw last-update yang:date-and-time
+--rw mud-signature? inet:uri
+--rw cache-validity? uint8
+--rw is-supported boolean
+--rw systeminfo? string
+--rw mfg-name? string
+--rw model-name? string
+--rw firmware-rev? string
+--rw software-rev? string
+--rw documentation? inet:uri
+--rw extensions* string
+--rw from-device-policy
| +--rw acls
| +--rw access-list* [name]
| +--rw name -> /acl:acls/acl/name
+--rw to-device-policy
+--rw acls
+--rw access-list* [name]
+--rw name -> /acl:acls/acl/name
augment /acl:acls/acl:acl/acl:aces/acl:ace/acl:matches:
+--rw mud
+--rw manufacturer? inet:host
+--rw same-manufacturer? empty
+--rw model? inet:uri
+--rw local-networks? empty
+--rw controller? inet:uri
+--rw my-controller? empty
augment
/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches
/acl:l4/acl:tcp/acl:tcp:
+--rw direction-initiated? direction
3. MUD Model Definitions for the Root "mud" Container
3.1. mud-version
This node specifies the integer version of the MUD specification.
This memo specifies version 1.
3.2. MUD URL
This URL identifies the MUD file. This is useful when the file and
associated signature are manually uploaded, say, in an offline mode.
Lear, et al. Standards Track [Page 15]
RFC 8520 Manufacturer Usage Descriptions March 2019
3.3. to-device-policy and from-device-policy Containers
[RFC8519] describes access lists. In the case of MUD, a MUD file
must be explicit in describing the communication pattern of a Thing,
and that includes indicating what is to be permitted or denied in
either direction of communication. Hence, each of these containers
indicates the appropriate direction of a flow in association with a
particular Thing. They contain references to specific access lists.
3.4. last-update
This is a date-and-time value of when the MUD file was generated.
This is akin to a version number. Its form is taken from [RFC6991].
3.5. cache-validity
This uint8 is the period of time in hours that a network management
station MUST wait since its last retrieval before checking for an
update. It is RECOMMENDED that this value be no less than 24, and it
MUST NOT be more than 168 for any Thing that is supported. This
period SHOULD be no shorter than any period determined through HTTP
caching directives (e.g., "cache-control" or "Expires"). N.B., the
expiring of this timer does not require the MUD manager to discard
the MUD file, nor terminate access to a Thing. See Section 16 for
more information.
3.6. is-supported
This boolean is an indication from the manufacturer to the network
administrator as to whether or not the Thing is supported. In this
context, a Thing is said to not be supported if the manufacturer
intends never to issue a firmware or software update to the Thing or
never to update the MUD file. A MUD manager MAY still periodically
check for updates.
3.7. systeminfo
This is a textual UTF-8 description of the Thing to be connected.
The intent is for administrators to be able to see a brief
displayable description of the Thing. It SHOULD NOT exceed 60
characters worth of display space.
Lear, et al. Standards Track [Page 16]
RFC 8520 Manufacturer Usage Descriptions March 2019
3.8. mfg-name, software-rev, model-name, and firmware-rev
These optional fields are filled in as specified by [RFC8348]. Note
that firmware-rev and software-rev MUST NOT be populated in a MUD
file if the device can be upgraded but the MUD URL cannot be. This
would be the case, for instance, with MUD URLs that are contained in
802.1AR certificates.
3.9. extensions
This optional leaf-list names MUD extensions that are used in the MUD
file. Note that MUD extensions MUST NOT be used in a MUD file
without the extensions being declared. Implementations MUST ignore
any node in this file that they do not understand.
Note that extensions can either extend the MUD file as described in
the previous paragraph or reference other work. An extension example
can be found in Appendix B.
4. Augmentation to the ACL Model
Note that in this section, when we use the term "match", we are
referring to the ACL model "matches" node.
4.1. manufacturer
This node consists of a hostname that would be matched against the
authority component of another Thing's MUD URL. In its simplest
form, "manufacturer" and "same-manufacturer" may be implemented as
access lists. In more complex forms, additional network capabilities
may be used. For example, if one saw the line "manufacturer" :
"flobbidy.example.com", then all Things that registered with a MUD
URL that contained flobbity.example.com in its authority section
would match.
4.2. same-manufacturer
This null-valued node is an equivalent for when the manufacturer
element is used to indicate that the authority found in another
Thing's MUD URL matches that of the authority found in this Thing's
MUD URL. For example, if the Thing's MUD URL were
"https://b1.example.com/ThingV1", then all devices that had a MUD URL
with an authority section of b1.example.com would match.
Lear, et al. Standards Track [Page 17]
RFC 8520 Manufacturer Usage Descriptions March 2019
4.3. documentation
This URI consists of a URL that points to documentation relating to
the device and the MUD file. This can prove particularly useful when
the "controller" class is used, so that its use can be explained.
4.4. model
This string matches the entire MUD URL, thus covering the model that
is unique within the context of the authority. It may contain not
only model information, but versioning information as well, and any
other information that the manufacturer wishes to add. The intended
use is for devices of this precise class to match, to permit or deny
communication between one another.
4.5. local-networks
This null-valued node expands to include local networks. Its default
expansion is that packets must not traverse toward a default route
that is received from the router. However, administrators may expand
the expression as is appropriate in their deployments.
4.6. controller
This URI specifies a value that a controller will register with the
MUD manager. The node then is expanded to the set of hosts that are
so registered. This node may also be a URN. In this case, the URN
describes a well-known service, such as DNS or NTP, that has been
standardized. Both of those URNs may be found in Section 17.7.
When "my-controller" is used, it is possible that the administrator
will be prompted to populate that class for each and every model.
Use of "controller" with a named class allows the user to populate
that class only once for many different models that a manufacturer
may produce.
Controller URIs MAY take the form of a URL (e.g., "http[s]://").
However, MUD managers MUST NOT resolve and retrieve such files, and
it is RECOMMENDED that there be no such file at this time, as their
form and function may be defined at a point in the future. For now,
URLs should serve simply as class names and may be populated by the
local deployment administrator.
Great care should be taken by MUD managers when invoking the
controller class in the form of URLs. For one thing, it requires
some understanding by the administrator as to when it is appropriate.
Lear, et al. Standards Track [Page 18]
RFC 8520 Manufacturer Usage Descriptions March 2019
Pre-registration in such classes by controllers with the MUD server
is encouraged. The mechanism to do that is beyond the scope of this
work.
4.7. my-controller
This null-valued node signals to the MUD manager to use whatever
mapping it has for this MUD URL to a particular group of hosts. This
may require prompting the administrator for class members. Future
work should seek to automate membership management.
4.8. direction-initiated
This MUST only be applied to TCP. This matches the direction in
which a TCP connection is initiated. When the direction initiated is
"from-device", packets that are transmitted in the direction of a
Thing MUST be dropped unless the Thing has first initiated a TCP
connection. By way of example, this node may be implemented in its
simplest form by looking at naked SYN bits, but it may also be
implemented through more stateful mechanisms.
When applied, this matches packets when the flow was initiated in the
corresponding direction. [RFC6092] specifies IPv6 guidance best
practices. While that document is scoped specifically to IPv6, its
contents are applicable for IPv4 as well.
5. Processing of the MUD File
To keep things relatively simple in addition to whatever definitions
exist, we also apply two additional default behaviors:
o Anything not explicitly permitted is denied.
o Local DNS and NTP are, by default, permitted to and from the
Thing.
An explicit description of the defaults can be found in Appendix A.
These are applied AFTER all other explicit rules. Thus, a default
behavior can be changed with a "drop" action.
6. What Does a MUD URL Look Like?
MUD URLs are required to use the "https" scheme, in order to
establish the MUD file server's identity and assure integrity of the
MUD file.
Lear, et al. Standards Track [Page 19]
RFC 8520 Manufacturer Usage Descriptions March 2019
Any "https://" URL can be a MUD URL. For example:
https://things.example.org/product_abc123/v5
https://www.example.net/mudfiles/temperature_sensor/
https://example.com/lightbulbs/colour/v1
A manufacturer may construct a MUD URL in any way, so long as it
makes use of the "https" scheme.
7. The MUD YANG Model
<CODE BEGINS>file "ietf-mud@2019-01-28.yang"
module ietf-mud {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-mud";
prefix ietf-mud;
import ietf-access-control-list {
prefix acl;
}
import ietf-yang-types {
prefix yang;
}
import ietf-inet-types {
prefix inet;
}
organization
"IETF OPSAWG (Operations and Management Area Working Group)";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: opsawg@ietf.org
Author: Eliot Lear
lear@cisco.com
Author: Ralph Droms
rdroms@gmail.com
Author: Dan Romascanu
dromasca@gmail.com
";
description
"This YANG module defines a component that augments the
IETF description of an access list. This specific module
focuses on additional filters that include local, model,
and same-manufacturer.
Lear, et al. Standards Track [Page 20]
RFC 8520 Manufacturer Usage Descriptions March 2019
This module is intended to be serialized via JSON and stored
as a file, as described in RFC 8520.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
'MAY', and 'OPTIONAL' in this document are to be interpreted as
described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8520; see
the RFC itself for full legal notices.";
revision 2019-01-28 {
description
"Initial proposed standard.";
reference
"RFC 8520: Manufacturer Usage Description
Specification";
}
typedef direction {
type enumeration {
enum to-device {
description
"packets or flows destined to the target
Thing.";
}
enum from-device {
description
"packets or flows destined from
the target Thing.";
}
}
description
"Which way are we talking about?";
}
container mud {
Lear, et al. Standards Track [Page 21]
RFC 8520 Manufacturer Usage Descriptions March 2019
presence "Enabled for this particular MUD URL";
description
"MUD-related information, as specified
by RFC 8520.";
uses mud-grouping;
}
grouping mud-grouping {
description
"Information about when support ends (or ended)
and when to refresh.";
leaf mud-version {
type uint8;
mandatory true;
description
"This is the version of the MUD
specification. This memo specifies version 1.";
}
leaf mud-url {
type inet:uri;
mandatory true;
description
"This is the MUD URL associated with the entry found
in a MUD file.";
}
leaf last-update {
type yang:date-and-time;
mandatory true;
description
"This is intended to be when the current MUD file
was generated. MUD managers SHOULD NOT check
for updates between this time plus cache validity.";
}
leaf mud-signature {
type inet:uri;
description
"A URI that resolves to a signature as
described in this specification.";
}
leaf cache-validity {
type uint8 {
range "1..168";
}
units "hours";
default "48";
description
"The information retrieved from the MUD server is
valid for these many hours, after which it should
Lear, et al. Standards Track [Page 22]
RFC 8520 Manufacturer Usage Descriptions March 2019
be refreshed. N.B., MUD manager implementations
need not discard MUD files beyond this period.";
}
leaf is-supported {
type boolean;
mandatory true;
description
"This boolean indicates whether or not the Thing is
currently supported by the manufacturer.";
}
leaf systeminfo {
type string;
description
"A UTF-8 description of this Thing. This
should be a brief description that may be
displayed to the user to determine whether
to allow the Thing on the
network.";
}
leaf mfg-name {
type string;
description
"Manufacturer name, as described in
the ietf-hardware YANG module.";
}
leaf model-name {
type string;
description
"Model name, as described in the
ietf-hardware YANG module.";
}
leaf firmware-rev {
type string;
description
"firmware-rev, as described in the
ietf-hardware YANG module. Note that this field
MUST NOT be included when the device can be
updated but the MUD URL cannot.";
}
leaf software-rev {
type string;
description
"software-rev, as described in the
ietf-hardware YANG module. Note that this field
MUST NOT be included when the device can be
updated but the MUD URL cannot.";
}
leaf documentation {
Lear, et al. Standards Track [Page 23]
RFC 8520 Manufacturer Usage Descriptions March 2019
type inet:uri;
description
"This URL points to documentation that
relates to this device and any classes that it uses
in its MUD file. A caution: MUD managers need
not resolve this URL on their own but rather simply
provide it to the administrator. Parsing HTML is
not an intended function of a MUD manager.";
}
leaf-list extensions {
type string {
length "1..40";
}
description
"A list of extension names that are used in this MUD
file. Each name is registered with the IANA and
described in an RFC.";
}
container from-device-policy {
description
"The policies that should be enforced on traffic
coming from the device. These policies are not
necessarily intended to be enforced at a single
point but may be rendered by the controller to any
relevant enforcement points in the network or
elsewhere.";
uses access-lists;
}
container to-device-policy {
description
"The policies that should be enforced on traffic
going to the device. These policies are not
necessarily intended to be enforced at a single
point but may be rendered by the controller to any
relevant enforcement points in the network or
elsewhere.";
uses access-lists;
}
}
grouping access-lists {
description
"A grouping for access lists in the context of device
policy.";
container access-lists {
description
"The access lists that should be applied to traffic
to or from the device.";
Lear, et al. Standards Track [Page 24]
RFC 8520 Manufacturer Usage Descriptions March 2019
list access-list {
key "name";
description
"Each entry on this list refers to an ACL that
should be present in the overall access list
data model. Each ACL is identified by name and
type.";
leaf name {
type leafref {
path "/acl:acls/acl:acl/acl:name";
}
description
"The name of the ACL for this entry.";
}
}
}
}
augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" {
description
"adding abstractions to avoid the need of IP addresses.";
container mud {
description
"MUD-specific matches.";
leaf manufacturer {
type inet:host;
description
"A domain that is intended to match the authority
section of the MUD URL. This node is used to specify
one or more manufacturers a device should
be authorized to access.";
}
leaf same-manufacturer {
type empty;
description
"This node matches the authority section of the MUD URL
of a Thing. It is intended to grant access to all
devices with the same authority section.";
}
leaf model {
type inet:uri;
description
"Devices of the specified model type will match if
they have an identical MUD URL.";
}
leaf local-networks {
type empty;
description
Lear, et al. Standards Track [Page 25]
RFC 8520 Manufacturer Usage Descriptions March 2019
"IP addresses will match this node if they are
considered local addresses. A local address may be
a list of locally defined prefixes and masks
that indicate a particular administrative scope.";
}
leaf controller {
type inet:uri;
description
"This node names a class that has associated with it
zero or more IP addresses to match against. These
may be scoped to a manufacturer or via a standard
URN.";
}
leaf my-controller {
type empty;
description
"This node matches one or more network elements that
have been configured to be the controller for this
Thing, based on its MUD URL.";
}
}
}
augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches"
+ "/acl:l4/acl:tcp/acl:tcp" {
description
"add direction-initiated";
leaf direction-initiated {
type direction;
description
"This node matches based on which direction a
connection was initiated. The means by which that
is determined is discussed in this document.";
}
}
}
<CODE ENDS>
8. The Domain Name Extension to the ACL Model
This module specifies an extension to the IETF-ACL model such that
domain names may be referenced by augmenting the "matches" node.
Different implementations may deploy differing methods to maintain
the mapping between the IP address and domain name, if indeed any are
needed. However, the intent is that resources that are referred to
using a name should be authorized (or not) within an access list.
Lear, et al. Standards Track [Page 26]
RFC 8520 Manufacturer Usage Descriptions March 2019
The structure of the change is as follows:
module: ietf-acldns
augment /acl:acls/acl:acl/acl:aces/acl:ace/
acl:matches/acl:l3/acl:ipv4/acl:ipv4:
+--rw src-dnsname? inet:host
+--rw dst-dnsname? inet:host
augment /acl:acls/acl:acl/acl:aces/acl:ace/
acl:matches/acl:l3/acl:ipv6/acl:ipv6:
+--rw src-dnsname? inet:host
+--rw dst-dnsname? inet:host
The choice of these particular points in the access control list
model is based on the assumption that we are in some way referring to
IP-related resources, as that is what the DNS returns. A domain name
in our context is defined in [RFC6991]. The augmentations are
replicated across IPv4 and IPv6 to allow MUD file authors the ability
to control the IP version that the Thing may utilize.
The following nodes are defined.
8.1. src-dnsname
The argument corresponds to a domain name of a source as specified by
inet:host. A number of means may be used to resolve hosts. What is
important is that such resolutions be consistent with ACLs that are
required by Things to properly operate.
8.2. dst-dnsname
The argument corresponds to a domain name of a destination as
specified by inet:host. See the previous section (Section 8.1)
relating to resolution.
Note that when using either of these with a MUD file, because access
is associated with a particular Thing, MUD files MUST NOT contain
either a src-dnsname in an ACL associated with from-device-policy or
a dst-dnsname associated with to-device-policy.
Lear, et al. Standards Track [Page 27]
RFC 8520 Manufacturer Usage Descriptions March 2019
8.3. The ietf-acldns Model
<CODE BEGINS>file "ietf-acldns@2019-01-28.yang"
module ietf-acldns {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-acldns";
prefix ietf-acldns;
import ietf-access-control-list {
prefix acl;
}
import ietf-inet-types {
prefix inet;
}
organization
"IETF OPSAWG (Operations and Management Area Working Group)";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: opsawg@ietf.org
Author: Eliot Lear
lear@cisco.com
Author: Ralph Droms
rdroms@gmail.com
Author: Dan Romascanu
dromasca@gmail.com
";
description
"This YANG module defines a component that augments the
IETF description of an access list to allow DNS names
as matching criteria.
Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).";
revision 2019-01-28 {
description
"Base version of dnsname extension of the ACL model.";
Lear, et al. Standards Track [Page 28]
RFC 8520 Manufacturer Usage Descriptions March 2019
reference
"RFC 8520: Manufacturer Usage Description
Specification";
}
grouping dns-matches {
description
"Domain names for matching.";
leaf src-dnsname {
type inet:host;
description
"domain name to be matched against.";
}
leaf dst-dnsname {
type inet:host;
description
"domain name to be matched against.";
}
}
augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches"
+ "/acl:l3/acl:ipv4/acl:ipv4" {
description
"Adding domain names to matching.";
uses dns-matches;
}
augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches"
+ "/acl:l3/acl:ipv6/acl:ipv6" {
description
"Adding domain names to matching.";
uses dns-matches;
}
}
<CODE ENDS>
Lear, et al. Standards Track [Page 29]
RFC 8520 Manufacturer Usage Descriptions March 2019
9. MUD File Example
This example contains two access lists that are intended to provide
outbound access to a cloud service on TCP port 443.
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://lighting.example.com/lightbulb2000",
"last-update": "2019-01-28T11:20:51+01:00",
"cache-validity": 48,
"is-supported": true,
"systeminfo": "The BMS Example Light Bulb",
"from-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-76100-v6fr"
}
]
}
},
"to-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-76100-v6to"
}
]
}
}
},
"ietf-access-control-list:acls": {
"acl": [
{
"name": "mud-76100-v6to",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-todev",
"matches": {
"ipv6": {
"ietf-acldns:src-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
Lear, et al. Standards Track [Page 30]
RFC 8520 Manufacturer Usage Descriptions March 2019
"source-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-76100-v6fr",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv6": {
"ietf-acldns:dst-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"destination-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
}
]
}
}
In this example, two policies are declared: one from the Thing and
the other to the Thing. Each policy names an access list that
applies to the Thing and one that applies from the Thing. Within
each access list, access is permitted to packets flowing to or from
Lear, et al. Standards Track [Page 31]
RFC 8520 Manufacturer Usage Descriptions March 2019
the Thing that can be mapped to the domain name of
"service.bms.example.com". For each access list, the enforcement
point should expect that the Thing initiated the connection.
10. The MUD URL DHCP Option
The IPv4 MUD URL client option has the following format:
+------+-----+------------------------------
| code | len | MUDstring
+------+-----+------------------------------
Code OPTION_MUD_URL_V4 (161) has been assigned by IANA. len is a
single octet that indicates the length of the MUD string in octets.
The MUDstring is defined as follows:
MUDstring = mudurl [ " " reserved ]
mudurl = URI; a URL [RFC3986] that uses the "https" scheme [RFC7230]
reserved = 1*( OCTET ) ; from [RFC5234]
The entire option MUST NOT exceed 255 octets. If a space follows the
MUD URL, a reserved string that will be defined in future
specifications follows. MUD managers that do not understand this
field MUST ignore it.
The IPv6 MUD URL client option has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_MUD_URL_V6 | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MUDstring |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OPTION_MUD_URL_V6 (112).
option-length contains the length of the MUDstring, as defined above,
in octets.
The intent of this option is to provide both a new Thing classifier
to the network as well as some recommended configuration to the
routers that implement the policy. However, it is entirely the
purview of the network system as managed by the network administrator
to decide what to do with this information. The key function of this
Lear, et al. Standards Track [Page 32]
RFC 8520 Manufacturer Usage Descriptions March 2019
option is simply to identify the type of Thing to the network in a
structured way such that the policy can be easily found with existing
toolsets.
10.1. Client Behavior
A DHCPv4 client MAY emit a DHCPv4 option, and a DHCPv6 client MAY
emit a DHCPv6 option. These options are singletons, as specified in
[RFC7227]. Because clients are intended to have at most one MUD URL
associated with them, they may emit at most one MUD URL option via
DHCPv4 and one MUD URL option via DHCPv6. In the case where both v4
and v6 DHCP options are emitted, the same URL MUST be used.
10.2. Server Behavior
A DHCP server may ignore these options or take action based on
receipt of these options. When a server consumes this option, it
will either forward the URL and relevant client information (such as
the gateway address or giaddr and requested IP address, and lease
length) to a network management system or retrieve the usage
description itself by resolving the URL.
DHCP servers may implement MUD functionality themselves or they may
pass along appropriate information to a network management system or
MUD manager. A DHCP server that does process the MUD URL MUST adhere
to the process specified in [RFC2818] and [RFC5280] to validate the
TLS certificate of the web server hosting the MUD file. Those
servers will retrieve the file, process it, and create and install
the necessary configuration on the relevant network element. Servers
SHOULD monitor the gateway for state changes on a given interface. A
DHCP server that does not provide MUD functionality and has forwarded
a MUD URL to a MUD manager MUST notify the MUD manager of any
corresponding change to the DHCP state of the client (such as
expiration or explicit release of a network address lease).
Should the DHCP server fail, in the case when it implements the MUD
manager functionality, any backup mechanisms SHOULD include the MUD
state, and the server SHOULD resolve the status of clients upon its
restart, similar to what it would do absent MUD manager
functionality. In the case where the DHCP server forwards
information to the MUD manager, the MUD manager will either make use
of redundant DHCP servers for information or clear state based on
other network information, such as monitoring port status on a switch
via SNMP, Radius accounting, or similar mechanisms.
10.3. Relay Requirements
There are no additional requirements for relays.
Lear, et al. Standards Track [Page 33]
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11. The Manufacturer Usage Description (MUD) URL X.509 Extension
This section defines an X.509 non-critical certificate extension that
contains a single URL that points to an online Manufacturer Usage
Description concerning the certificate subject. The URI must be
represented as described in Section 7.4 of [RFC5280].
Any Internationalized Resource Identifiers (IRIs) MUST be mapped to
URIs as specified in Section 3.1 of [RFC3987] before they are placed
in the certificate extension.
The semantics of the URL are defined Section 6 of this document.
The choice of id-pe is based on guidance found in Section 4.2.2 of
[RFC5280]:
These extensions may be used to direct applications to on-line
information about the issuer or the subject.
The MUD URL is precisely that: online information about the
particular subject.
In addition, a separate new extension is defined as id-pe-mudsigner.
This contains the subject field of the signing certificate of the MUD
file. Processing of this field is specified in Section 13.2.
The purpose of this signature is to make a claim that the MUD file
found on the server is valid for a given device, independent of any
other factors. There are several security considerations below in
Section 16.
A new content-type id-ct-mud is also defined. While signatures are
detached today, should a MUD file be transmitted as part of a
Cryptographic Message Syntax (CMS) message, this content-type SHOULD
be used.
Lear, et al. Standards Track [Page 34]
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This module imports from [RFC5912] and [RFC6268]. The new extension
is identified as follows:
<CODE BEGINS>
MUDURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-mudURLExtn2016(88) }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
-- EXPORTS ALL --
IMPORTS
-- RFC 5912
EXTENSION
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
-- RFC 5912
id-ct
FROM PKIXCRMF-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-crmf2005-02(55) }
-- RFC 6268
CONTENT-TYPE
FROM CryptographicMessageSyntax-2010
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) }
-- RFC 5912
id-pe, Name
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
--
-- Certificate Extensions
--
MUDCertExtensions EXTENSION ::=
{ ext-MUDURL | ext-MUDsigner, ... }
ext-MUDURL EXTENSION ::=
Lear, et al. Standards Track [Page 35]
RFC 8520 Manufacturer Usage Descriptions March 2019
{ SYNTAX MUDURLSyntax IDENTIFIED BY id-pe-mud-url }
id-pe-mud-url OBJECT IDENTIFIER ::= { id-pe 25 }
MUDURLSyntax ::= IA5String
ext-MUDsigner EXTENSION ::=
{ SYNTAX MUDsignerSyntax IDENTIFIED BY id-pe-mudsigner }
id-pe-mudsigner OBJECT IDENTIFIER ::= { id-pe 30 }
MUDsignerSyntax ::= Name
--
-- CMS Content Types
--
MUDContentTypes CONTENT-TYPE ::=
{ ct-mud, ... }
ct-mud CONTENT-TYPE ::=
{ -- directly include the content
IDENTIFIED BY id-ct-mudtype }
-- The binary data that is in the form
-- "application/mud+json" is directly encoded as the
-- signed data. No additional ASN.1 encoding is added.
id-ct-mudtype OBJECT IDENTIFIER ::= { id-ct 41 }
END
<CODE ENDS>
While this extension can appear in either an 802.AR manufacturer
certificate (IDevID) or a deployment certificate (LDevID), of course
it is not guaranteed in either, nor is it guaranteed to be carried
over. It is RECOMMENDED that MUD manager implementations maintain a
table that maps a Thing to its MUD URL based on IDevIDs.
12. The Manufacturer Usage Description LLDP Extension
The IEEE802.1AB Link Layer Discovery Protocol (LLDP) is a one-hop,
vendor-neutral link-layer protocol used by end host network Things
for advertising their identity, capabilities, and neighbors on an
IEEE 802 local area network. Its Type-Length-Value (TLV) design
allows for "vendor-specific" extensions to be defined. IANA has a
registered IEEE 802 organizationally unique identifier (OUI) defined
as documented in [RFC7042]. The MUD LLDP extension uses a subtype
defined in this document to carry the MUD URL.
Lear, et al. Standards Track [Page 36]
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The LLDP vendor-specific frame has the following format:
+--------+--------+----------+---------+--------------
|TLV Type| len | OUI |subtype | MUDString
| =127 | |= 00 00 5E| = 1 |
|(7 bits)|(9 bits)|(3 octets)|(1 octet)|(1-255 octets)
+--------+--------+----------+---------+--------------
where:
o TLV Type = 127 indicates a vendor-specific TLV
o len = indicates the TLV string length
o OUI = 00 00 5E is the organizationally unique identifier of IANA
o subtype = 1 (as assigned by IANA for the MUDstring)
o MUDstring = the length MUST NOT exceed 255 octets
The intent of this extension is to provide both a new Thing
classifier to the network as well as some recommended configuration
to the routers that implement the policy. However, it is entirely
the purview of the network system as managed by the network
administrator to decide what to do with this information. The key
function of this extension is simply to identify the type of Thing to
the network in a structured way such that the policy can be easily
found with existing toolsets.
Hosts, routers, or other network elements that implement this option
are intended to have at most one MUD URL associated with them, so
they may transmit at most one MUD URL value.
Hosts, routers, or other network elements that implement this option
may ignore these options or take action based on receipt of these
options. For example, they may fill in information in the respective
extensions of the LLDP Management Information Base (MIB). LLDP
operates in a one-way direction. Link Layer Discovery Protocol Data
Units (LLDPDUs) are not exchanged as information requests by one
Thing and responses sent by another Thing. The other Things do not
acknowledge LLDP information received from a Thing. No specific
network behavior is guaranteed. When a Thing consumes this
extension, it may either forward the URL and relevant remote Thing
information to a MUD manager or retrieve the usage description by
resolving the URL in accordance with normal HTTP semantics.
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13. The Creating and Processing of Signed MUD Files
Because MUD files contain information that may be used to configure
network access lists, they are sensitive. To ensure that they have
not been tampered with, it is important that they be signed. We make
use of DER-encoded Cryptographic Message Syntax (CMS) [RFC5652] for
this purpose.
13.1. Creating a MUD File Signature
A MUD file MUST be signed using CMS as an opaque binary object. In
order to make successful verification more likely, intermediate
certificates SHOULD be included. The signature is stored at the
location specified in the MUD file. Signatures are transferred using
content-type "application/pkcs7-signature".
For example:
% openssl cms -sign -signer mancertfile -inkey mankey \
-in mudfile -binary -outform DER -binary \
-certfile intermediatecert -out mudfile.p7s
Note: A MUD file may need to be re-signed if the signature expires.
13.2. Verifying a MUD File Signature
Prior to processing the rest of a MUD file, the MUD manager MUST
retrieve the MUD signature file by retrieving the value of "mud-
signature" and validating the signature across the MUD file. The Key
Usage Extension in the signing certificate MUST be present and have
the bit digitalSignature(0) set. When the id-pe-mudsigner extension
is present in a device's X.509 certificate, the MUD signature file
MUST have been generated by a certificate whose subject matches the
contents of that id-pe-mudsigner extension. If these conditions are
not met, or if it cannot validate the chain of trust to a known trust
anchor, the MUD manager MUST cease processing the MUD file until an
administrator has given approval.
The purpose of the signature on the file is to assign accountability
to an entity, whose reputation can be used to guide administrators on
whether or not to accept a given MUD file. It is already common
place to check web reputation on the location of a server on which a
file resides. While it is likely that the manufacturer will be the
signer of the file, this is not strictly necessary, and it may not be
desirable. For one thing, in some environments, integrators may
install their own certificates. For another, what is more important
is the accountability of the recommendation, and not just the
relationship between the Thing and the file.
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An example:
% openssl cms -verify -in mudfile.p7s -inform DER -content mudfile
Note the additional step of verifying the common trust root.
14. Extensibility
One of our design goals is to see that MUD files are able to be
understood by as broad a cross-section of systems as is possible.
Coupled with the fact that we have also chosen to leverage existing
mechanisms, we are left with no ability to negotiate extensions and a
limited desire for those extensions in any event. As such, a two-
tier extensibility framework is employed, as follows:
1. At a coarse grain, a protocol version is included in a MUD URL.
This memo specifies MUD version 1. Any and all changes are
entertained when this version is bumped. Transition approaches
between versions would be a matter for discussion in future
versions.
2. At a finer grain, only extensions that would not incur additional
risk to the Thing are permitted. Specifically, adding nodes to
the mud container is permitted with the understanding that such
additions will be ignored by unaware implementations. Any such
extensions SHALL be standardized through the IETF process and
MUST be named in the "extensions" list. MUD managers MUST ignore
YANG nodes they do not understand and SHOULD create an exception
to be resolved by an administrator, so as to avoid any policy
inconsistencies.
15. Deployment Considerations
Because MUD consists of a number of architectural building blocks, it
is possible to assemble different deployment scenarios. One key
aspect is where to place policy enforcement. In order to protect the
Thing from other Things within a local deployment, policy can be
enforced on the nearest switch or access point. In order to limit
unwanted traffic within a network, it may also be advisable to
enforce policy as close to the Internet as possible. In some
circumstances, policy enforcement may not be available at the closest
hop. At that point, the risk of lateral infection (infection of
devices that reside near one another) is increased to the number of
Things that are able to communicate without protection.
A caution about some of the classes: admission of a Thing into the
"manufacturer" and "same-manufacturer" class may have impact on the
access of other Things. Put another way, the admission may grow the
Lear, et al. Standards Track [Page 39]
RFC 8520 Manufacturer Usage Descriptions March 2019
access list on switches connected to other Things, depending on how
access is managed. Some care should be given on managing that access
list growth. Alternative methods such as additional network
segmentation can be used to keep that growth within reason.
Because as of this writing MUD is a new concept, one can expect a
great many devices to not have implemented it. It remains a local
deployment decision as to whether a device that is first connected
should be allowed broad or limited access. Furthermore, as mentioned
in the introduction, a deployment may choose to ignore a MUD policy
in its entirety and simply take into account the MUD URL as a
classifier to be used as part of a local policy decision.
Finally, please see directly below information regarding device
lifetimes and use of domain names.
16. Security Considerations
Based on how a MUD URL is emitted, a Thing may be able to lie about
what it is, thus gaining additional network access. This can happen
in a number of ways when a device emits a MUD URL using DHCP or LLDP,
such as being inappropriately admitted to a class such as
"same-manufacturer", being given access to a device such as
"my-controller", or being permitted access to an Internet resource,
where such access would otherwise be disallowed. Whether that is the
case will depend on the deployment. Implementations SHOULD be
configurable to disallow additive access for devices using MUD URLs
that are not emitted in a secure fashion such as in a certificate.
Similarly, implementations SHOULD NOT grant elevated permissions
(beyond those of devices presenting no MUD policy) to devices that do
not strongly bind their identity to their L2/L3 transmissions. When
insecure methods are used by the MUD manager, the classes SHOULD NOT
contain devices that use both insecure and secure methods, in order
to prevent privilege escalation attacks, and MUST NOT contain devices
with the same MUD URL that are derived from both strong and weak
authentication methods.
Devices may forge source (L2/L3) information. Deployments should
apply appropriate protections to bind communications to the
authentication that has taken place. For 802.1X authentication, IEEE
802.1AE (MACsec) [IEEE8021AE] is one means by which this may happen.
A similar approach can be used with 802.11i (Wi-Fi Protected Access 2
(WPA2)) [IEEE80211i]. Other means are available with other lower-
layer technologies. Implementations using session-oriented access
that is not cryptographically bound should take care to remove state
when any form of break in the session is detected.
Lear, et al. Standards Track [Page 40]
RFC 8520 Manufacturer Usage Descriptions March 2019
A rogue certification authority (CA) may sign a certificate that
contains the same subject name as is listed in the MUDsigner field in
the manufacturer certificate, thus seemingly permitting a substitute
MUD file for a device. There are two mitigations available: First,
if the signer changes, this may be flagged as an exception by the MUD
manager. Second, if the MUD file also changes, the MUD manager
SHOULD seek administrator approval (it should do this in any case).
In all circumstances, the MUD manager MUST maintain a cache of
trusted CAs for this purpose. When such a rogue is discovered, it
SHOULD be removed.
Additional mitigations are described below.
When certificates are not present, Things claiming to be of a certain
manufacturer SHOULD NOT be included in that manufacturer grouping
without additional validation of some form. This will be relevant
when the MUD manager makes use of primitives such as "manufacturer"
for the purpose of accessing Things of a particular type. Similarly,
network management systems may be able to fingerprint the Thing. In
such cases, the MUD URL can act as a classifier that can be proven or
disproven. Fingerprinting may have other advantages as well: when
802.1AR certificates are used, because they themselves cannot change,
fingerprinting offers the opportunity to add artifacts to the MUD
string in the form of the reserved field discussed in Section 10.
The meaning of such artifacts is left as future work.
MUD managers SHOULD NOT accept a usage description for a Thing with
the same Media Access Control (MAC) address that has indicated a
change of the URL authority without some additional validation (such
as review by a network administrator). New Things that present some
form of unauthenticated MUD URL SHOULD be validated by some external
means when they would be given increased network access.
It may be possible for a rogue manufacturer to inappropriately
exercise the MUD file parser, in order to exploit a vulnerability.
There are two recommended approaches to address this threat. The
first is to validate that the signer of the MUD file is known to and
trusted by the MUD manager. The second is to have a system do a
primary scan of the file to ensure that it is both parseable and
believable at some level. MUD files will likely be relatively small,
to start with. The number of ACEs used by any given Thing should be
relatively small as well. It may also be useful to limit retrieval
of MUD URLs to only those sites that are known to have decent web or
domain reputations.
Use of a URL necessitates the use of domain names. If a domain name
changes ownership, the new owner of that domain may be able to
provide MUD files that MUD managers would consider valid. MUD
Lear, et al. Standards Track [Page 41]
RFC 8520 Manufacturer Usage Descriptions March 2019
managers SHOULD cache certificates used by the MUD file server. When
a new certificate is retrieved for whatever reason, the MUD manager
should check to see if ownership of the domain has changed. A fair
programmatic approximation of this is when the name servers for the
domain have changed. If the actual MUD file has changed, the MUD
manager MAY check the WHOIS database to see if registration ownership
of a domain has changed. If a change has occurred, or if for some
reason it is not possible to determine whether ownership has changed,
further review may be warranted. Note, this remediation does not
take into account the case of a Thing that was produced long ago and
only recently fielded, or the case where a new MUD manager has been
installed.
The release of a MUD URL by a Thing reveals what the Thing is and
provides an attacker with guidance on what vulnerabilities may be
present.
While the MUD URL itself is not intended to be unique to a specific
Thing, the release of the URL may aid an observer in identifying
individuals when combined with other information. This is a privacy
consideration.
In addressing both of these concerns, implementors should take into
account what other information they are advertising through
mechanisms such as Multicast DNS (mDNS) [RFC6872]; how a Thing might
otherwise be identified, perhaps through how it behaves when it is
connected to the network; and whether a Thing is intended to be used
by individuals or carry personal identifying information, and then
apply appropriate data minimization techniques. One approach is to
make use of TEAP [RFC7170] as the means to share information with
authorized components in the network. Network elements may also
assist in limiting access to the MUD URL through the use of
mechanisms such as DHCPv6-Shield [RFC7610].
There is the risk of the MUD manager itself being spied on to
determine what things are connected to the network. To address this
risk, MUD managers may choose to make use of TLS proxies that they
trust that would aggregate other information.
Please note that the security considerations mentioned in Section 3.7
of [RFC8407] are not applicable in this case because the YANG
serialization is not intended to be accessed via NETCONF. However,
for those who try to instantiate this model in a network element via
the Network Configuration Protocol (NETCONF), all objects in each
model in this document exhibit similar security characteristics as
[RFC8519]. The basic purpose of MUD is to configure access, so by
its very nature, it can be disruptive if used by unauthorized
parties.
Lear, et al. Standards Track [Page 42]
RFC 8520 Manufacturer Usage Descriptions March 2019
17. IANA Considerations
17.1. YANG Module Registrations
The following YANG modules have been registered in the "YANG Module
Names" registry:
Name: ietf-mud
URN: urn:ietf:params:xml:ns:yang:ietf-mud
Prefix: ietf-mud
Registrant contact: The IESG
Reference: RFC 8520
Name: ietf-acldns
URI: urn:ietf:params:xml:ns:yang:ietf-acldns
Prefix: ietf-acldns
Registrant contact: The IESG
Reference: RFC 8520
17.2. URI Registrations
IANA has added the following entries to the "IETF XML registry":
URI: urn:ietf:params:xml:ns:yang:ietf-acldns
Registrant Contact: The IESG.
XML: N/A. The requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:ietf-mud
Registrant Contact: The IESG.
XML: N/A. The requested URI is an XML namespace.
17.3. DHCPv4 and DHCPv6 Options
The IANA has allocated OPTION_MUD_URL_V4 (161) in the "Dynamic Host
Configuration Protocol (DHCP) and Bootstrap Protocol (BOOTP)
Parameters" registry, and OPTION_MUD_URL_V6 (112) in the "Dynamic
Host Configuration Protocol for IPv6 (DHCPv6)" registry, as described
in Section 10.
17.4. PKIX Extensions
IANA has made the following assignments for:
o The MUDURLExtnModule-2016 ASN.1 module (88) in the "SMI Security
for PKIX Module Identifier" registry (1.3.6.1.5.5.7.0).
o id-pe-mud-url object identifier (25) from the "SMI Security for
PKIX Certificate Extension" registry (1.3.6.1.5.5.7.1).
Lear, et al. Standards Track [Page 43]
RFC 8520 Manufacturer Usage Descriptions March 2019
o id-pe-mudsigner object identifier (30) from the "SMI Security for
PKIX Certificate Extension" registry.
o id-ct-mudtype object identifier (41) from the "SMI Security for
S/MIME CMS Content Type" registry.
o The use of these values is specified in Section 11.
17.5. Media Type Registration for MUD Files
The following media type is defined for the transfer of MUD files:
o Type name: application
o Subtype name: mud+json
o Required parameters: N/A
o Optional parameters: N/A
o Encoding considerations: 8bit; "application/mud+json" values are
represented as JSON objects; UTF-8 encoding MUST be employed
[RFC3629].
o Security considerations: See Security Considerations of RFC 8520
and Section 12 of [RFC8259].
o Interoperability considerations: N/A
o Published specification: RFC 8520
o Applications that use this media type: MUD managers as specified
by RFC 8520.
o Fragment identifier considerations: N/A
o Additional information:
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
o Person & email address to contact for further information:
Eliot Lear <lear@cisco.com>, Ralph Droms <rdroms@gmail.com>,
Dan Romascanu <dromasca@gmail.com>
o Intended usage: COMMON
o Restrictions on usage: none
Lear, et al. Standards Track [Page 44]
RFC 8520 Manufacturer Usage Descriptions March 2019
o Author:
Eliot Lear <lear@cisco.com>
Ralph Droms <rdroms@gmail.com>
Dan Romascanu <dromasca@gmail.com>
o Change controller: IESG
o Provisional registration? (standards tree only): No.
17.6. IANA LLDP TLV Subtype Registry
IANA has created a new registry titled "IANA Link Layer Discovery
Protocol (LLDP) TLV Subtypes" under "IEEE 802 Numbers". The policy
for this registry is Expert Review [RFC8126]. The maximum number of
entries in the registry is 256.
IANA has populated the initial registry as follows:
LLDP subtype value: 1 (All the other 255 values are initially marked
as "Unassigned".)
Description: the Manufacturer Usage Description (MUD) Uniform
Resource Locator (URL)
Reference: RFC 8520
17.7. The MUD Well-Known Universal Resource Name (URNs)
The following parameter registry has been added in accordance with
[RFC3553].
Registry name: MUD Well-Known Universal Resource Name (URN)
Specification: RFC 8520
Repository: https://www.iana.org/assignments/mud
Index value: Encoded identically to a TCP/UDP port service
name, as specified in Section 5.1 of [RFC6335]
The following entries have been added to the "MUD Well-Known
Universal Resource Name (URN)" registry:
"urn:ietf:params:mud:dns" refers to the service specified by
[RFC1123]. "urn:ietf:params:mud:ntp" refers to the service specified
by [RFC5905].
Lear, et al. Standards Track [Page 45]
RFC 8520 Manufacturer Usage Descriptions March 2019
17.8. Extensions Registry
The IANA has established a registry of extensions as follows:
Registry name: MUD Extensions
Registry policy: Standards Action
Reference: RFC 8520
Extension name: UTF-8-encoded string, not to exceed 40 characters.
Each extension MUST follow the rules specified in this specification.
As is usual, the IANA issues early allocations in accordance with
[RFC7120].
18. References
18.1. Normative References
[IEEE8021AB]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks-- Station and Media Access Control Connectivity
Discovery", IEEE 802.1AB.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<https://www.rfc-editor.org/info/rfc3748>.
Lear, et al. Standards Track [Page 46]
RFC 8520 Manufacturer Usage Descriptions March 2019
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
January 2005, <https://www.rfc-editor.org/info/rfc3987>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[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,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/info/rfc5912>.
[RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules
for the Cryptographic Message Syntax (CMS) and the Public
Key Infrastructure Using X.509 (PKIX)", RFC 6268,
DOI 10.17487/RFC6268, July 2011,
<https://www.rfc-editor.org/info/rfc6268>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
Lear, et al. Standards Track [Page 47]
RFC 8520 Manufacturer Usage Descriptions March 2019
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <https://www.rfc-editor.org/info/rfc7120>.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
<https://www.rfc-editor.org/info/rfc7227>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7610] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
Protecting against Rogue DHCPv6 Servers", BCP 199,
RFC 7610, DOI 10.17487/RFC7610, August 2015,
<https://www.rfc-editor.org/info/rfc7610>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
Lear, et al. Standards Track [Page 48]
RFC 8520 Manufacturer Usage Descriptions March 2019
[RFC8348] Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A
YANG Data Model for Hardware Management", RFC 8348,
DOI 10.17487/RFC8348, March 2018,
<https://www.rfc-editor.org/info/rfc8348>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC8519] Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
"YANG Data Model for Network Access Control Lists (ACLs)",
RFC 8519, DOI 10.17487/RFC8519, March 2019,
<https://www.rfc-editor.org/info/rfc8519>.
18.2. Informative References
[FW95] Chapman, D. and E. Zwicky, "Building Internet Firewalls",
First Edition, November 1995.
[IEEE80211i]
IEEE, "IEEE Standard for information technology-
Telecommunications and information exchange between
systems-Local and metropolitan area networks-Specific
requirements-Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) specifications: Amendment
6: Medium Access Control (MAC) Security Enhancements",
IEEE 802.11i.
[IEEE8021AE]
IEEE, "IEEE Standard for Local and metropolitan area
networks-Media Access Control (MAC) Security",
IEEE 802.1AE.
[IEEE8021AR]
IEEE, "IEEE Standard for Local and metropolitan area
networks - Secure Device Identity", IEEE 802.1AR.
[IEEE8021X]
IEEE, "IEEE Standard for Local and metropolitan area
networks--Port-Based Network Access Control", IEEE 802.1X.
[RFC1984] IAB and IESG, "IAB and IESG Statement on Cryptographic
Technology and the Internet", BCP 200, RFC 1984,
DOI 10.17487/RFC1984, August 1996,
<https://www.rfc-editor.org/info/rfc1984>.
Lear, et al. Standards Track [Page 49]
RFC 8520 Manufacturer Usage Descriptions March 2019
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
2003, <https://www.rfc-editor.org/info/rfc3553>.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
DOI 10.17487/RFC6092, January 2011,
<https://www.rfc-editor.org/info/rfc6092>.
[RFC6872] Gurbani, V., Ed., Burger, E., Ed., Anjali, T., Abdelnur,
H., and O. Festor, "The Common Log Format (CLF) for the
Session Initiation Protocol (SIP): Framework and
Information Model", RFC 6872, DOI 10.17487/RFC6872,
February 2013, <https://www.rfc-editor.org/info/rfc6872>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <https://www.rfc-editor.org/info/rfc7042>.
[RFC7170] Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
"Tunnel Extensible Authentication Protocol (TEAP) Version
1", RFC 7170, DOI 10.17487/RFC7170, May 2014,
<https://www.rfc-editor.org/info/rfc7170>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7452] Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson,
"Architectural Considerations in Smart Object Networking",
RFC 7452, DOI 10.17487/RFC7452, March 2015,
<https://www.rfc-editor.org/info/rfc7452>.
[RFC7488] Boucadair, M., Penno, R., Wing, D., Patil, P., and T.
Reddy, "Port Control Protocol (PCP) Server Selection",
RFC 7488, DOI 10.17487/RFC7488, March 2015,
<https://www.rfc-editor.org/info/rfc7488>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Lear, et al. Standards Track [Page 50]
RFC 8520 Manufacturer Usage Descriptions March 2019
[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
Lear, et al. Standards Track [Page 51]
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Appendix A. Default MUD Nodes
What follows is the portion of a MUD file that permits DNS traffic to
a controller that is registered with the URN
"urn:ietf:params:mud:dns" and traffic NTP to a controller that is
registered with "urn:ietf:params:mud:ntp". This is considered the
default behavior, and the ACEs are in effect appended to whatever
other "ace" entries that a MUD file contains. To block DNS or NTP,
one repeats the matching statement but replaces the "forwarding"
action "accept" with "drop". Because ACEs are processed in the order
they are received, the defaults would not be reached. A MUD manager
might further decide to optimize to simply not include the defaults
when they are overridden.
Four "acl" list entries that implement default MUD nodes are listed
below. Two are for IPv4 and two are for IPv6 (one in each direction
for both versions of IP). Note that neither the access list name nor
the ace name need be retained or used in any way by local
implementations; they are simply there for the sake of completeness.
"ietf-access-control-list:acls": {
"acl": [
{
"name": "mud-59776-v4to",
"type": "ipv4-acl-type",
"aces": {
"ace": [
{
"name": "ent0-todev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:dns"
},
"ipv4": {
"protocol": 17
},
"udp": {
"source-port": {
"operator": "eq",
"port": 53
}
}
},
"actions": {
"forwarding": "accept"
}
},
{
Lear, et al. Standards Track [Page 52]
RFC 8520 Manufacturer Usage Descriptions March 2019
"name": "ent1-todev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:ntp"
},
"ipv4": {
"protocol": 17
},
"udp": {
"source-port": {
"operator": "eq",
"port": 123
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-59776-v4fr",
"type": "ipv4-acl-type",
"aces": {
"ace": [
{
"name": "ent0-frdev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:dns"
},
"ipv4": {
"protocol": 17
},
"udp": {
"destination-port": {
"operator": "eq",
"port": 53
}
}
},
"actions": {
"forwarding": "accept"
}
},
{
Lear, et al. Standards Track [Page 53]
RFC 8520 Manufacturer Usage Descriptions March 2019
"name": "ent1-frdev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:ntp"
},
"ipv4": {
"protocol": 17
},
"udp": {
"destination-port": {
"operator": "eq",
"port": 123
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-59776-v6to",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "ent0-todev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:dns"
},
"ipv6": {
"protocol": 17
},
"udp": {
"source-port": {
"operator": "eq",
"port": 53
}
}
},
"actions": {
"forwarding": "accept"
}
},
{
Lear, et al. Standards Track [Page 54]
RFC 8520 Manufacturer Usage Descriptions March 2019
"name": "ent1-todev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:ntp"
},
"ipv6": {
"protocol": 17
},
"udp": {
"source-port": {
"operator": "eq",
"port": 123
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-59776-v6fr",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "ent0-frdev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:dns"
},
"ipv6": {
"protocol": 17
},
"udp": {
"destination-port": {
"operator": "eq",
"port": 53
}
}
},
"actions": {
"forwarding": "accept"
}
},
{
Lear, et al. Standards Track [Page 55]
RFC 8520 Manufacturer Usage Descriptions March 2019
"name": "ent1-frdev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:ntp"
},
"ipv6": {
"protocol": 17
},
"udp": {
"destination-port": {
"operator": "eq",
"port": 123
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
}
]
}
Appendix B. A Sample Extension: DETNET-indicator
In this sample extension, we augment the core MUD model to indicate
whether the device implements DETNET. If a device claims not to use
DETNET, but then later attempts to do so, a notification or exception
might be generated. Note that this example is intended only for
illustrative purposes.
Extension Name: "Example-Extension" (to be used in the extensions list)
Standard: RFC 8520 (but do not register the example)
This extension augments the MUD model to include a single node, using
the following sample module that has the following tree structure:
module: ietf-mud-detext-example
augment /ietf-mud:mud:
+--rw is-detnet-required? boolean
Lear, et al. Standards Track [Page 56]
RFC 8520 Manufacturer Usage Descriptions March 2019
The model is defined as follows:
<CODE BEGINS>file "ietf-mud-detext-example@2019-01-28.yang"
module ietf-mud-detext-example {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-mud-detext-example";
prefix ietf-mud-detext-example;
import ietf-mud {
prefix ietf-mud;
}
organization
"IETF OPSAWG (Operations and Management Area Working Group)";
contact
"WG Web: <https://datatracker.ietf.org/wg/opsawg/>
WG List: opsawg@ietf.org
Author: Eliot Lear
lear@cisco.com
Author: Ralph Droms
rdroms@gmail.com
Author: Dan Romascanu
dromasca@gmail.com
";
description
"Sample extension to a MUD module to indicate a need
for DETNET support.";
revision 2019-01-28 {
description
"Initial revision.";
reference
"RFC 8520: Manufacturer Usage Description
Specification";
}
augment "/ietf-mud:mud" {
description
"This adds a simple extension for a manufacturer
to indicate whether DETNET is required by a
device.";
leaf is-detnet-required {
type boolean;
description
"This value will equal 'true' if a device requires
Lear, et al. Standards Track [Page 57]
RFC 8520 Manufacturer Usage Descriptions March 2019
DETNET to properly function.";
}
}
}
<CODE ENDS>
Using the previous example, we now show how the extension would be
expressed:
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://lighting.example.com/lightbulb2000",
"last-update": "2019-01-28T11:20:51+01:00",
"cache-validity": 48,
"extensions": [
"ietf-mud-detext-example"
],
"ietf-mud-detext-example:is-detnet-required": "false",
"is-supported": true,
"systeminfo": "The BMS Example Light Bulb",
"from-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-76100-v6fr"
}
]
}
},
"to-device-policy": {
"access-lists": {
"access-list": [
{
"name": "mud-76100-v6to"
}
]
}
}
},
"ietf-access-control-list:acls": {
"acl": [
{
"name": "mud-76100-v6to",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
Lear, et al. Standards Track [Page 58]
RFC 8520 Manufacturer Usage Descriptions March 2019
"name": "cl0-todev",
"matches": {
"ipv6": {
"ietf-acldns:src-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"source-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-76100-v6fr",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv6": {
"ietf-acldns:dst-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"destination-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
}
Lear, et al. Standards Track [Page 59]
RFC 8520 Manufacturer Usage Descriptions March 2019
]
}
}
Acknowledgments
The authors would like to thank Einar Nilsen-Nygaard, who
singlehandedly updated the model to match the updated ACL model,
Bernie Volz, Tom Gindin, Brian Weis, Sandeep Kumar, Thorsten Dahm,
John Bashinski, Steve Rich, Jim Bieda, Dan Wing, Joe Clarke, Henk
Birkholz, Adam Montville, Jim Schaad, and Robert Sparks for their
valuable advice and reviews. Russ Housley entirely rewrote
Section 11 to be a complete module. Adrian Farrel provided the basis
for the privacy considerations text. Kent Watsen provided a thorough
review of the architecture and the YANG model. The remaining errors
in this work are entirely the responsibility of the authors.
Authors' Addresses
Eliot Lear
Cisco Systems
Richtistrasse 7
Wallisellen CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
Ralph Droms
Google
355 Main St., 5th Floor
Cambridge, MA 02142
United States of America
Phone: +1 978 376 3731
Email: rdroms@gmail.com
Dan Romascanu
Phone: +972 54 5555347
Email: dromasca@gmail.com
Lear, et al. Standards Track [Page 60]