Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                R. Droms
Expires: October 5, 11, 2018                                         Google
                                                            D. Romascanu
                                                          April 03, 09, 2018

              Manufacturer Usage Description Specification


   This memo specifies a component-based architecture for manufacturer
   usage descriptions (MUD).  The goal of MUD is to provide a means for
   Things 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, an
   LLDP TLV, a URL, an X.509 certificate extension and a means to sign
   and verify the descriptions.

Status of This Memo

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   This Internet-Draft will expire on October 5, 11, 2018.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  What MUD Doesn't Do . . . . . . . . . . . . . . . . . . .   4
     1.2.  A Simple Example  . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
     1.4.  Determining Intended Use  . . . . . . . . . . . . . . . .   6
     1.5.  Finding A Policy: The MUD URL . . . . . . . . . . . . . .   6
     1.6.  Processing of the MUD URL . . . . . . . . . . . . . . . .   7
     1.7.  Types of Policies . . . . . . . . . . . . . . . . . . . .   7
     1.8.  The Manufacturer Usage Description Architecture . . . . .   9
     1.9.  Order of operations . . . . . . . . . . . . . . . . . . .  11
   2.  The MUD Model and Semantic Meaning  . . . . . . . . . . . . .  11
     2.1.  The IETF-MUD YANG Module  . . . . . . . . . . . . . . . .  13
   3.  Data Node Definitions . . . . . . . . . . . . . . . . . . . .  14
     3.1.  mud-version . . . . . . . . . . . . . . . . . . . . . . .  14
     3.2.  to-device-policy and from-device-policy containers  . . .  15
     3.3.  last-update . . . . . . . . . . . . . . . . . . . . . . .  15
     3.4.  cache-validity  . . . . . . . . . . . . . . . . . . . . .  15
     3.5.  is-supported  . . . . . . . . . . . . . . . . . . . . . .  15
     3.6.  systeminfo  . . . . . . . . . . . . . . . . . . . . . . .  15
     3.7.  mfg-name, software-rev, model-name firmware-rev . . . . .  16
     3.8.  extensions  . . . . . . . . . . . . . . . . . . . . . . .  16
     3.9.  manufacturer  . . . . . . . . . . . . . . . . . . . . . .  16
     3.10. same-manufacturer . . . . . . . . . . . . . . . . . . . .  16
     3.11. model . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     3.12. local-networks  . . . . . . . . . . . . . . . . . . . . .  17
     3.13. controller  . . . . . . . . . . . . . . . . . . . . . . .  17
     3.14. my-controller . . . . . . . . . . . . . . . . . . . . . .  17
     3.15. direction-initiated . . . . . . . . . . . . . . . . . . .  17
   4.  Processing of the MUD file  . . . . . . . . . . . . . . . . .  18
   5.  What does a MUD URL look like?  . . . . . . . . . . . . . . .  18
   6.  The MUD YANG Model  . . . . . . . . . . . . . . . . . . . . .  18
   7.  The Domain Name Extension to the ACL Model  . . . . . . . . .  25
     7.1.  src-dnsname . . . . . . . . . . . . . . . . . . . . . . .  25
     7.2.  dst-dnsname . . . . . . . . . . . . . . . . . . . . . . .  25
     7.3.  The ietf-acldns Model . . . . . . . . . . . . . . . . . .  26
   8.  MUD File Example  . . . . . . . . . . . . . . . . . . . . . .  27
   9.  The MUD URL DHCP Option . . . . . . . . . . . . . . . . . . .  29
     9.1.  Client Behavior . . . . . . . . . . . . . . . . . . . . .  30
     9.2.  Server Behavior . . . . . . . . . . . . . . . . . . . . .  31
     9.3.  Relay Requirements  . . . . . . . . . . . . . . . . . . .  31
   10. The Manufacturer Usage Description (MUD) URL X.509 Extension   31
   11. The Manufacturer Usage Description LLDP extension . . . . . .  33
   12. Creating and Processing of Signed MUD Files . . . . . . . . .  34
     12.1.  Creating a MUD file signature  . . . . . . . . . . . . .  34
     12.2.  Verifying a MUD file signature . . . . . . . . . . . . .  34
   13. Extensibility . . . . . . . . . . . . . . . . . . . . . . . .  35
   14. Deployment Considerations . . . . . . . . . . . . . . . . . .  35
   15. Security Considerations . . . . . . . . . . . . . . . . . . .  36
   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38
     16.1.  YANG Module Registrations  . . . . . . . . . . . . . . .  38
     16.2.  DHCPv4 and DHCPv6 Options  . . . . . . . . . . . . . . .  39
     16.3.  PKIX Extensions  . . . . . . . . . . . . . . . . . . . .  39
     16.4.  MIME Media-type Registration for MUD files . . . . . . .  39
     16.5.  LLDP IANA TLV Subtype Registry . . . . . . . . . . . . .  40
     16.6.  The MUD Well Known Universal Resource Name (URNs)  . . .  41
     16.7.  Extensions Registry  . . . . . . . . . . . . . . . . . .  41
   17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  41
   18. References  . . . . . . . . . . . . . . . . . . . . . . . . .  42
     18.1.  Normative References . . . . . . . . . . . . . . . . . .  42
     18.2.  Informative References . . . . . . . . . . . . . . . . .  44
   Appendix A.  Changes from Earlier Versions  . . . . . . . . . . .  46
   Appendix B.  Default MUD nodes  . . . . . . . . . . . . . . . . .  50
   Appendix C.  A Sample Extension: DETNET-indicator . . . . . . . .  54
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  58

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.  [RFC1984] 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 general purpose computers.  These devices, which
   this memo refers to as Things, have a specific purpose.  By
   definition, therefore, all other uses are not intended.  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.

   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 lightbulb,
   this might indeed be the lightbulb 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 may exist 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 entering a
      network 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 by their manufacturer.

   o  Keep the cost of implementation of such a system to the bare

   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 is 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

   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 of some form that 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 speak to the
   refrigerator, and it has no need of a printer or other devices.  It
   has no social networking friends.  Therefore, an access list applied
   to it that states that it will only connect to the single rendezvous
   service will not impede the light bulb in performing its function,
   while at the same time allowing the network to provide both it 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 controller:  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 URL:  a URL that can be used by the MUD controller 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",
   document are to be interpreted as described in [RFC2119].

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.

   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
   purpose solution, however, we assume that a device has so few
   capabilities that it will implement the least necessary capabilities
   to function properly.  This is a 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],[RFC3315] that the DHCP client uses to
      inform the DHCP server.  The DHCP server may take further actions,
      such as retrieve the URL or otherwise pass it along to network
      management system or controller.

   o  An X.509 constraint.  The IEEE has developed [IEEE8021AR] that
      provides 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
      Tunnel Extensible Authentication Protocol (TEAP) [RFC7170].

   o  Finally, a Link Layer Discovery Protocol (LLDP) frame is defined

   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 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 are
   possible.  Implementors should allow for this sort of flexibility of
   how MUD URLs may be learned.

1.6.  Processing of the MUD URL

   MUD controllers 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 [RFC2618],
   Section 3.1.

   Requests for MUD URLs SHOULD include an "Accept" header ([RFC7231],
   Section 5.3.2) containing "application/mud+json", an "Accept-
   Language" header ([RFC7231], Section 5.3.5), and a "User-Agent"
   header ([RFC7231], Section 5.5.3).

   MUD controllers SHOULD automatically process 3xx response status

   If a MUD controller 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

1.7.  Types of Policies

   When the MUD URL is resolved, the MUD controller 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 Constrained Application
      Protocol (COAP)[RFC7252]

   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 of the time and effort spent to
   develop accurate and adequate models for use by network devices.
   JSON is used as a serialization for compactness and readability,
   relative to XML.  Other formats may be chosen with later versions of

   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
   [I-D.ietf-netmod-acl-model].  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 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

   Manufacturer:  A device made by a particular manufacturer, as
      identified by the authority component of its MUD URL

   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 associated with the MUD URL of a device that
      the administrator admits.

   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 only a limited
   subset YANG-based configuration is permitted in a MUD file.

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       |
    .                     | Controller |  .(https)   | File Server |
    .  End system network |____________|<-MUD file<-<|_____________|
    .                             .       .
    .                             .       .
    . _______                 _________   .
    .|       |  (dhcp et al) | router  |  .
    .| Thing |---->MUD URL-->|   or    |  .
    .|_______|               | switch  |  .
    .                        |_________|  .

                        Figure 1: MUD Architecture

   In the above diagram, the switch or router collects MUD URLs and
   forwards them to the MUD controller (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, the switch would carry the URL via a certificate to the
   authentication server via EAP over Radius[RFC3748], which would then
   process it.  One method to do this is TEAP, described in [RFC7170].
   The certificate extension is described below.

   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, the trivial cases
   being a hardcoded MUD-URL on a switch port, or a mapping from some
   available identifier such as an L2 address or certificate hash to a

   The role of the MUD controller in this environment is to do the

   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.

   A MUD controller may be a component of a AAA or 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, and
   so order of operation may vary.  However, here is one clear intended

   1.  Thing emits URL.

   2.  That URL is forwarded to a MUD controller by the nearest switch
       (how this happens depends on the way in which the MUD URL is

   3.  The MUD controller 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 controller 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 controller instantiates local configuration based on the
       abstractions defined in this document.

   6.  The MUD controller 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 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 [I-D.ietf-netmod-acl-model]

   o  ietf-mud (this document)

   o  ietf-acldns (this document)

   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 controller 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 "name" of the ACL, "type", "name" of the 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-

   Furthermore, only "accept" or "drop" actions SHOULD be included.  A
   MUD controller MAY choose to interpret "reject" as "drop".  A MUD
   controller 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 [RFC7223] 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 controllers MAY ignore any particular component of a
   description or MAY ignore the description in its entirety, and SHOULD
   carefully inspect all MUD descriptions.  Publishers of MUD files MUST
   NOT include other nodes except as described in Section 3.8.  See that
   section for more information.

2.1.  The IETF-MUD YANG Module

   This module is structured into three parts:

   o  The first container "mud" 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
      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 access-lists, 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

   A simplified graphical representation of the data models is used in
   this document.  The meaning of the symbols in these diagrams is
   explained in [I-D.ietf-netmod-yang-tree-diagrams].

   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 extensions*           string
          +--rw from-device-policy
          |  +--rw access-lists
          |     +--rw access-list* [name]
          |        +--rw name    -> /acl:access-lists/acl/name
          +--rw to-device-policy
             +--rw access-lists
                +--rw access-list* [name]
                   +--rw name    -> /acl:access-lists/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:access-lists/acl:acl/acl:aces/acl:ace
       +--rw direction-initiated?   direction

3.  Data Node Definitions

   Note that in this section, when we use the term "match" we are
   referring to the ACL model "matches" node.

   The following nodes are defined.

3.1.  mud-version

   This node specifies the integer version of the MUD specification.
   This memo specifies version 1.

3.2.  to-device-policy and from-device-policy containers

   [I-D.ietf-netmod-acl-model] 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.

3.3.  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]
   which, for those keeping score, in turn was taken from Section 5.6 of
   [RFC3339], which was taken from [ISO.8601.1988].

3.4.  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
   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.,
   expiring of this timer does not require the MUD controller to discard
   the MUD file, nor terminate access to a Thing.  See Section 15 for
   more information.

3.5.  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 an update to the Thing or never update the MUD
   file.  A MUD controller MAY still periodically check for updates.

3.6.  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 localized name
   associated with the Thing.  It SHOULD NOT exceed 60 characters worth
   of display space (that is- what the administrator actually sees).

3.7.  mfg-name, software-rev, model-name firmware-rev

   These optional fields are filled in as specified by
   [I-D.ietf-netmod-entity].  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
   MUR-URLs that are contained in 802.1AR certificates.

3.8.  extensions

   This optional leaf-list names MUD extensions that are used in the MUD
   file.  Note that NO MUD extensions may 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 they might reference other work.  An
   extension example can be found in Appendix C.

3.9.  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" :
   "", then all Things that registered with a MUD
   URL that contained in its authority section
   would match.

3.10.  same-manufacturer

   This null-valued node is an equivalent for when the manufacturer
   element is used to indicate the authority that is 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, then all devices that had MUD URL
   with an authority section of would match.

3.11.  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.

3.12.  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.

3.13.  controller

   This URI specifies a value that a controller will register with the
   MUD controller.  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.

   Great care should be used when invoking the controller class.  For
   one thing, it requires some understanding by the administrator as to
   when it is appropriate.  Classes that are standardized may make it
   possible to easily name devices that support standard functions.  For
   instance, the MUD controller could have some knowledge of which DNS
   servers should be used for any particular group of Things.  Non-
   standard classes will likely require some sort of administrator
   interaction.  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.

   Controller URIs MAY take the form of a URL (e.g. "http[s]://").
   However, MUD controllers 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.

3.14.  my-controller

   This null-valued node signals to the MUD controller 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.

3.15.  direction-initiated

   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.  When this flag is set, and
   the system has no reason to believe a flow has been initiated it MUST
   drop the packet.  This node may be implemented in its simplest form
   by looking at naked SYN bits, but may also be implemented through
   more stateful mechanisms.

4.  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

   An explicit description of the defaults can be found in Appendix B.
   These are applied AFTER all other explicit rules.  Thus, a default
   behavior can be changed with a "drop" action.

5.  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.

   Any "https://" URL can be a MUD URL.  For example:

   The MUD URL identifies a Thing with a specificity according to the
   manufacturer's wishes.  It could include a brand name, model number,
   or something more specific.  It also could provide a means to
   indicate what version the product is.

   Specifically, if the intended communication patterns of a Thing
   change, as compared to other things, the MUD URL should change.  For
   example, if a new model of light bulb is released that requires
   access to different network services, it would have a separate MUD
   URL from those that do not.

6.  The MUD YANG Model

   <CODE BEGINS>file "ietf-mud@2018-03-01.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;

       "IETF OPSAWG (Ops Area) Working Group";
       "WG Web:
        WG List:
        Author: Eliot Lear
        Author: Ralph Droms
        Author: Dan Romascanu

       "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.

        This module is intended to be serialized via JSON and stored
        as a file, as described in RFC XXXX [RFC Editor to fill in with
        this document #].

        Copyright (c) 2016,2017 IETF Trust and the persons
        identified as the document authors.  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
        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     revision 2018-03-01 {
         "Initial proposed standard.";
         "RFC XXXX: Manufacturer Usage Description

     typedef direction {
       type enumeration {
         enum "to-device" {
             "packets or flows destined to the target
         enum "from-device" {
             "packets or flows destined from
              the target Thing";
         "Which way are we talking about?";

     container mud {
       presence "Enabled for this particular MUD URL";
         "MUD related information, as specified
          by RFC-XXXX [RFC Editor to fill in].";
       uses mud-grouping;

     grouping mud-grouping {
         "Information about when support end(ed), 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;
           "This is the MUD URL associated with the entry found
            in a MUD file.";
       leaf last-update {
         type yang:date-and-time;
         mandatory true;
           "This is intended to be when the current MUD file
            was generated.  MUD Controllers 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";
           "The information retrieved from the MUD server is
            valid for these many hours, after which it should
            be refreshed.  N.B. MUD controller implementations
            need not discard MUD files beyond this period.";
       leaf is-supported {
         type boolean;
         mandatory true;
           "This boolean indicates whether or not the Thing is
            currently supported by the manufacturer.";
       leaf systeminfo {
         type string;
           "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

       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 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 this field MUST
            NOT be included when the device can be updated
            but the MUD-URL cannot.";

       leaf-list extensions {
         type string {
            length "1..40";
           "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 {
           "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 enorcement points in the network or
         uses access-lists;
       container to-device-policy {
           "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 enorcement points in the network or
         uses access-lists;

     grouping access-lists {
         "A grouping for access lists in the context of device
       container access-lists {
           "The access lists that should be applied to traffic
              to or from the device.";
         list access-list {
           key "name";
             "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
           leaf name {
             type leafref {
               path "/acl:acls/acl:acl/acl:name";
               "The name of the ACL for this entry.";
     augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" {
         "adding abstractions to avoid need of IP addresses";
       container mud {
           "MUD-specific matches.";
         leaf manufacturer {
           type inet:host;
             "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;
             "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;
             "Devices of the specified  model type will match if
              they have an identical MUD URL.";
         leaf local-networks {
           type empty;
             "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;
             "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
         leaf my-controller {
           type empty;
             "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" {
         "add direction-initiated";
       leaf direction-initiated {
         type direction;
           "This node matches based on which direction a
            connection was initiated. The means by which that
            is determined is discussed in this document.";



7.  The Domain Name Extension to the ACL Model

   This module specifies an extension to 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 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.

   The structure of the change is as follows:

   module: ietf-acldns
     augment /acl:access-lists/acl:acl/acl:aces/acl:ace/
       +--rw src-dnsname?   inet:host
       +--rw dst-dnsname?   inet:host
     augment /acl:access-lists/acl:acl/acl:aces/acl:ace/
       +--rw src-dnsname?   inet:host
       +--rw dst-dnsname?   inet:host

   The choice of these particular points in the access-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 node are defined.

7.1.  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 required
   by Things to properly operate.

7.2.  dst-dnsname

   The argument corresponds to a domain name of a destination as
   specified by inet:host See the previous section relating to

   Note 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.

7.3.  The ietf-acldns Model

   <CODE BEGINS>file "ietf-acldns@2018-03-01.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";

       "IETF OPSAWG (Ops Area) Working Group";

          "WG Web:
          WG List:
          Author: Eliot Lear

          Author: Ralph Droms

          Author: Dan Romascanu


       "This YANG module defines a component that augments the
        IETF description of an access list to allow dns names
        as matching criteria.";

     revision 2018-03-01 {
       description "Base version of dnsname extension of ACL model";
       reference "RFC XXXX: Manufacturer Usage Description

     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;

8.  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": "",
       "last-update": "2018-03-02T11:20:51+01:00",
       "cache-validity": 48,
       "is-supported": true,
       "systeminfo": "The BMS Example Lightbulb",
       "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:access-lists": {
       "acl": [
           "name": "mud-76100-v6to",
           "type": "ipv6-acl-type",
           "aces": {
             "ace": [
                 "name": "cl0-todev",
                 "matches": {
                   "ipv6": {
                     "ietf-acldns:src-dnsname": "",
                     "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": "",
                     "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.  Within each access
   list, access is permitted to packets flowing to or from the Thing
   that can be mapped to the domain name of "".
   For each access list, the enforcement point should expect that the
   Thing initiated the connection.

9.  The MUD URL DHCP Option

   The IPv4 MUD URL client option has the following format:

     | code | len |  MUDstring

   Code OPTION_MUD_URL_V4 (161) is assigned by IANA.  len is a single
   octet that indicates the length of MUD string in octets.  The MUD
   string is defined as follows:

    MUDstring = mudurl [ " " reserved ]
    mudurl = URI; a URL [RFC3986] that uses the "https" schema [RFC7230]
    reserved = 1*( CHAR ) ; 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 controllers 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; assigned by IANA).

   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 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
   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

9.1.  Client Behavior

   A DHCPv4 client MAY emit a DHCPv4 option and a DHCPv6 client MAY emit
   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.

   Clients SHOULD log or otherwise report improper acknowledgments from
   servers, but they MUST NOT modify their MUD URL configuration based
   on a server's response.  The server's response is only an
   acknowledgment that the server has processed the option, and promises
   no specific network behavior to the client.  In particular, it may
   not be possible for the server to retrieve the file associated with
   the MUD URL, or the local network administration may not wish to use
   the usage description.  Neither of these situations should be
   considered in any way exceptional.

9.2.  Server Behavior

   A DHCP server may ignore these options or take action based on
   receipt of these options.  If a server successfully parses the option
   and the URL, it MUST return the option with length field set to zero
   and a corresponding null URL field as an acknowledgment.  Even in
   this circumstance, no specific network behavior is guaranteed.  When
   a server consumes this option, it will either forward the URL and
   relevant client information (such as the gateway address or giaddr)
   to a network management system, or it will 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 controller.  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, 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 controller MUST notify the MUD controller of any
   corresponding change to the DHCP state of the client (such as
   expiration or explicit release of a network address lease).

9.3.  Relay Requirements

   There are no additional requirements for relays.

10.  The Manufacturer Usage Description (MUD) URL X.509 Extension

   This section defines an X.509 non-critical certificate extension that
   contains a single Uniform Resource Locator (URL) that points to an
   on-line Manufacturer Usage Description concerning the certificate
   subject.  URI must be represented as described in Section 7.4 of

   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 5 of this document.

   The choice of id-pe is based on guidance found in Section 4.2.2 of

         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.

   The new extension is identified as follows:


     MUDURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
                  internet(1) security(5) mechanisms(5) pkix(7)
                  id-mod(0) id-mod-mudURLExtn2016(88) }


     -- EXPORTS ALL --

       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) }

       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) } ;
       MUDCertExtensions EXTENSION ::= { ext-MUDURL, ... }
       IDENTIFIED BY id-pe-mud-url }

       id-pe-mud-url OBJECT IDENTIFIER ::= { id-pe 25 }

       MUDURLSyntax ::= IA5String



   While this extension can appear in either an 802.AR manufacturer
   certificate (IDevID) or deployment certificate (LDevID), of course it
   is not guaranteed in either, nor is it guaranteed to be carried over.
   It is RECOMMENDED that MUD controller implementations maintain a
   table that maps a Thing to its MUD URL based on IDevIDs.

11.  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 hosts 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.

   The LLDP vendor specific frame has the following format:

   |TLV Type|  len   |   OUI    |subtype  | MUD URL
   |  =127  |        |= 00 00 5E|  = 1    |
   |(7 bits)|(9 bits)|(3 octets)|(1 octet)|(1-255 octets)


   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 (to be assigned by IANA for the MUD URL)

   o  MUD URL - 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 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

   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 (LLDP MIB).  LLDP
   operates in a one-way direction.  LLDPDUs are not exchanged as
   information requests by one Thing and response 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 controller, or it will retrieve the
   usage description by resolving the URL in accordance with normal HTTP

12.  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 insure 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.

12.1.  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 - \
                 -certfile intermediatecert -out mudfile.p7s

   Note: A MUD file may need to be re-signed if the signature expires.

12.2.  Verifying a MUD file signature

   Prior to retrieving a MUD file the MUD controller SHOULD retrieve the
   MUD signature file by retrieving the value of "mud-signature" and
   validating the signature across the MUD file.

   Upon retrieving a MUD file, a MUD controller MUST validate the
   signature of the file before continuing with further processing.  A
   MUD controller MUST cease processing of that file it cannot validate
   the chain of trust to a known trust anchor 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 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 the
   cryptographic relationship between the device and the file.

   An example:

   % openssl cms -verify -in mudfile.p7s -inform DER -content mudfile

   Note the additional step of verifying the common trust root.

13.  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.  A 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

   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 controllers 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.

14.  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 so-called east-west infection 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
   access of other Things.  Put another way, the admission may grow the
   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 alloewed broad or limited access.  Furthermore, as
   mentioned in the introduction, a deployment may choose to ignore a
   MUD policy in its entirety, but simply taken into account the MUD URL
   as a classifier to be used as part of a local policy decision.

15.  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.  There are
   several means to limit risk in this case.  The most obvious is to
   only believe Things that make use of certificate-based authentication
   such as IEEE 802.1AR certificates.  When those 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 occur when it 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 artificats to the MUD URL.  The meaning of such
   artifacts is left as future work.

   Network management systems SHOULD NOT accept a usage description for
   a Thing with the same MAC address that has indicated a change of
   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 otherwise 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 three recommended approaches to address this threat.  The
   first is to validate the signature of the MUD file.  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 controllers would consider valid.  There
   are a few approaches that can mitigate this attack.  First, MUD
   controllers SHOULD cache certificates used by the MUD file server.
   When a new certificate is retrieved for whatever reason, the MUD
   controller 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 controller MAY check the WHOIS database to see if
   registration ownership of a domain has changed.  If a change has
   occured, 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 controller has been installed.

   It may not be possible for a MUD controller to retrieve a MUD file at
   any given time.  Should a MUD controller 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 controller is in an off-line
   environment, the local Internet connection has failed, or the remote
   Internet connection has failed.  It is also possible that an attacker
   is attempting to prevent onboarding of a device.  It is a local
   deployment decision as to whether or not devices may be onboarded in
   the face of such failures.

   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

   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

   In addressing both of these concerns, implementors should take into
   account what other information they are advertising through
   mechanisms such as mDNS[RFC6872], how a Thing might otherwise be
   identified, perhaps through how it behaves when it is connected to
   the network, 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].

   Please note that the security considerations mentioned in Section 4.7
   of [I-D.ietf-netmod-rfc6087bis] 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 NETCONF, all objects in each model in this draft
   exhibit similar security characteristics as
   [I-D.ietf-netmod-acl-model].  The basic purpose of MUD is to
   configure access, and so by its very nature can be disruptive if used
   by unauthorized parties.

16.  IANA Considerations

16.1.  YANG Module Registrations

   The following YANG modules are requested to be registred in the "IANA
   Module Names" registry:

   The ietf-mud module:

   o  Name: ietf-mud

   o  XML Namespace: urn:ietf:params:xml:ns:yang:ietf-mud

   o  Prefix: ief-mud

   o  Reference: This memo

   The ietf-acldns module:

   o  Name: ietf-acldns

   o  XML Namespace: urn:ietf:params:xml:ns:yang:ietf-acldns

   o  Prefix: ietf-acldns

   o  Reference: This memo

16.2.  DHCPv4 and DHCPv6 Options

   The IANA has allocated option 161 in the Dynamic Host Configuration
   Protocol (DHCP) and Bootstrap Protocol (BOOTP) Parameters registry
   for the MUD DHCPv4 option, and option 112 for DHCPv6, as described in
   Section 9.

16.3.  PKIX Extensions

   IANA is kindly requested to make the following assignments for:

   o The MUDURLExtnModule-2016 ASN.1 module in the "SMI Security for
   PKIX Module Identifier" registry (

   o id-pe-mud-url object identifier from the "SMI Security for PKIX
   Certificate Extension" registry (

   The use of these values is specified in Section 10.

16.4.  MIME Media-type Registration for MUD files

   The following media-type is defined for transfer of MUD file:

    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 a JSON object; UTF-8 encoding SHOULD be
    o Security considerations: See Security Considerations
      of this document.
    o Interoperability considerations: n/a
    o Published specification: this document
    o Applications that use this media type: MUD controllers as
      specified by this document.
    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 <>, Ralph Droms <>
    o Intended usage: COMMON
    o Restrictions on usage: none
    o Author:
         Eliot Lear <>
         Ralph Droms <>
    o Change controller: IESG
    o Provisional registration? (standards tree only): No.

16.5.  LLDP IANA TLV Subtype Registry

   IANA is requested to create a new registry for IANA Link Layer
   Discovery Protocol (LLDP) TLV subtype values.  The recommended policy
   for this registry is Expert Review.  The maximum number of entries in
   the registry is 256.

   IANA is required to populate the initial registry with the value:

   LLDP subtype value = 1 (All the other 255 values should be initially
   marked as 'Unassigned'.)

   Description = the Manufacturer Usage Description (MUD) Uniform
   Resource Locator (URL)

   Reference = < this document >

16.6.  The MUD Well Known Universal Resource Name (URNs)

   The following parameter registry is requested to be added in
   accordance with [RFC3553]

      Registry name: "urn:ietf:params:mud" is requested.
      Specification: this document
      Repository: this document
      Index value:  Encoded identically to a TCP/UDP port service
                    name, as specified in Section 5.1 of [RFC6335]

   The following entries should be added to the "urn:ietf:params:mud"
   name space:

   "urn:ietf:params:mud:dns" refers to the service specified by
   [RFC1123].  "urn:ietf:params:mud:ntp" refers to the service specified
   by [RFC5905].

16.7.  Extensions Registry

   The IANA is requested to establish a registry of extensions as

      Registry name: MUD extensions registry
      Registry policy: Standards action
      Standard reference: document
      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 based in accordance
   with [RFC7120].

17.  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, and Robert Sparks for their valuable advice
   and reviews.  Russ Housley entirely rewrote Section 10 to be a
   complete module.  Adrian Farrel provided the basis for 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.

18.  References

18.1.  Normative References

              Jethanandani, M., Huang, L., Agarwal, S., and D. Blair,
              "Network Access Control List (ACL) YANG Data Model",
              draft-ietf-netmod-acl-model-18 (work in progress), March

              Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A
              YANG Data Model for Hardware Management", draft-ietf-
              netmod-entity-08 (work in progress), January 2018.

              Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
              ietf-netmod-yang-tree-diagrams-06 (work in progress),
              February 2018.

              Institute for Electrical and Electronics Engineers, "IEEE
              Standard for Local and Metropolitan Area Networks--
              Station and Media Access Control Connectivity Discovery",

   [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts -
              Application and Support", STD 3, RFC 1123,
              DOI 10.17487/RFC1123, October 1989,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,

   [RFC2618]  Aboba, B. and G. Zorn, "RADIUS Authentication Client MIB",
              RFC 2618, DOI 10.17487/RFC2618, June 1999,

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <>.

   [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,

   [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,

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
              January 2005, <>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,

   [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,

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,

   [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,

   [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,

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <>.

   [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,

   [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,

   [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,

   [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,

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,

18.2.  Informative References

   [FW95]     Chapman, D. and E. Zwicky, "Building Internet Firewalls",
              January 1995.

              Bierman, A., "Guidelines for Authors and Reviewers of YANG
              Data Model Documents", draft-ietf-netmod-rfc6087bis-20
              (work in progress), March 2018.

              Institute for Electrical and Electronics Engineers,
              "Secure Device Identity", 1998.

              International Organization for Standardization, "Data
              elements and interchange formats - Information interchange
              - Representation of dates and times", ISO Standard 8601,
              June 1988.

   [RFC1984]  IAB and IESG, "IAB and IESG Statement on Cryptographic
              Technology and the Internet", BCP 200, RFC 1984,
              DOI 10.17487/RFC1984, August 1996,

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,

   [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, <>.

   [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,

   [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, <>.

   [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, <>.

   [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,

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,

   [RFC7452]  Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson,
              "Architectural Considerations in Smart Object Networking",
              RFC 7452, DOI 10.17487/RFC7452, March 2015,

   [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,

Appendix A.  Changes from Earlier Versions

   RFC Editor to remove this section prior to publication.

   Draft -19: * Edits after discussion with apps area to address
   reserved field for the future.  * Correct systeminfo to be utf8.  *
   Remove "hardware-rev" from list.

   Draft -18: * Correct an error in the augment statement * Changes to
   the ACL model re ports.

   Draft -17:

   o  One editorial.

   Draft -16

   o  add mud-signature element based on review comments

   o  redo mud-url

   o  make clear that systeminfo uses UTF8

   Draft -13 to -14:

   o  Final WGLC comments and review comments

   o  Move version from MUD-URL to Model
   o  Have MUD-URL in model

   o  Update based on update to draft-ietf-netmod-acl-model

   o  Point to tree diagram draft instead of 6087bis.

   Draft -12 to -13:

   o  Additional WGLC comments

   Draft -10 to -12:

   These are based on WGLC comments:

   o  Correct examples based on ACL model changes.

   o  Change ordering nodes.

   o  Additional explanatory text around systeminfo.

   o  Change ordering in examples.

   o  Make it VERY VERY VERY VERY clear that these are recommendations,
      not mandates.

   o  DHCP -> NTP in some of the intro text.

   o  Remove masa-server

   o  "Things" to "network elements" in a few key places.

   o  Reference to JSON YANG RFC added.

   Draft -10 to -11:

   o  Example corrections

   o  Typo

   o  Fix two lists.

   o  Addition of 'any-acl' and 'mud-acl' in the list of allowed

   o  Clarification of what should be in a MUD file.

   Draft -09 to -10:

   o  AD input.

   o  Correct dates.

   o  Add compliance sentence as to which ACL module features are

   Draft -08 to -09:

   o  Resolution of Security Area review, IoT directorate review, GenART
      review, YANG doctors review.

   o  change of YANG structure to address mandatory nodes.

   o  Terminology cleanup.

   o  specify out extra portion of MUD-URL.

   o  consistency changes.

   o  improved YANG descriptions.

   o  Remove extra revisions.

   o  Track ACL model changes.

   o  Additional cautions on use of ACL model; further clarifications on

   Draft -07 to -08:

   o  a number of editorials corrected.

   o  definition of MUD file tweaked.

   Draft -06 to -07:

   o  Examples updated.

   o  Additional clarification for direction-initiated.

   o  Additional implementation guidance given.

   Draft -06 to -07:

   o  Update models to match new ACL model
   o  extract directionality from the ACL, introducing a new device

   Draft -05 to -06:

   o  Make clear that this is a component architecture (Polk and Watson)

   o  Add order of operations (Watson)

   o  Add extensions leaf-list (Pritikin)

   o  Remove previous-mud-file (Watson)

   o  Modify text in last-update (Watson)

   o  Clarify local networks (Weis, Watson)

   o  Fix contact info (Watson)

   o  Terminology clarification (Weis)

   o  Advice on how to handle LDevIDs (Watson)

   o  Add deployment considerations (Watson)

   o  Add some additional text about fingerprinting (Watson)

   o  Appropriate references to 6087bis (Watson)

   o  Change systeminfo to a URL to be referenced (Lear)

   Draft -04 to -05: * syntax error correction

   Draft -03 to -04: * Re-add my-controller

   Draft -02 to -03: * Additional IANA updates * Format correction in
   YANG.  * Add reference to TEAP.

   Draft -01 to -02: * Update IANA considerations * Accept Russ Housley
   rewrite of X.509 text * Include privacy considerations text * Redo
   the URL limit.  Still 255 bytes, but now stated in the URL
   definition.  * Change URI registration to be under urn:ietf:params

   Draft -00 to -01: * Fix cert trust text.  * change supportInformation
   to meta-info * Add an informational element in.  * add urn registry
   and create first entry * add default elements

Appendix B.  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 "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 controller might
   further decide to optimize to simply not include the defaults when
   they are overriden.

   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 access-list name nor ace
   name need be retained or used in any way by local implementations,
   but are simply there for completeness' sake.

    "ietf-access-control-list:access-lists": {
       "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"
                 "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"
                 "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"
                 "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"
                 "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 C.  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 later attempts to
   make use of DETNET, an 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: this document (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

   The model is defined as follows:

   <CODE BEGINS>file "ietf-mud-detext-example@2018-03-01.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;

       "IETF OPSAWG (Ops Area) Working Group";
       "WG Web:
        WG List:
        Author: Eliot Lear
        Author: Ralph Droms
        Author: Dan Romascanu

       "Sample extension to a MUD module to indicate a need
        for DETNET support.";

     revision 2018-03-01 {
         "Initial revision.";
         "RFC XXXX: Manufacturer Usage Description

     augment "/ietf-mud:mud" {
         "This adds a simple extension for a manufacturer
           to indicate whether DETNET is required by a
       leaf is-detnet-required {
         type boolean;
           "This value will equal true if a device requires
            detnet to properly function";
   Using the previous example, we now show how the extension would be

     "ietf-mud:mud": {
       "mud-version": 1,
       "mud-url": "",
       "last-update": "2018-03-02T11:20:51+01:00",
       "cache-validity": 48,
       "extensions": [
       "ietf-mud-detext-example:is-detnet-required": "false",
       "is-supported": true,
       "systeminfo": "The BMS Example Lightbulb",
       "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:access-lists": {
       "acl": [
           "name": "mud-76100-v6to",
           "type": "ipv6-acl-type",
           "aces": {
             "ace": [
                 "name": "cl0-todev",
                 "matches": {
                   "ipv6": {
                     "ietf-acldns:src-dnsname": "",
                     "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": "",
                     "protocol": 6
                   "tcp": {
                     "ietf-mud:direction-initiated": "from-device",
                     "destination-port": {
                       "operator": "eq",
                       "port": 443
                 "actions": {
                   "forwarding": "accept"

Authors' Addresses

   Eliot Lear
   Cisco Systems
   Richtistrasse 7
   Wallisellen  CH-8304

   Phone: +41 44 878 9200

   Ralph Droms
   355 Main St., 5th Floor

   Phone: +1 978 376 3731

   Dan Romascanu

   Phone: +972 54 5555347