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Internet-Draft This memo specifies a component-based architecture for manufacturer usage descriptions (MUD). The goal of MUD is to provide a means for end devices to signal to the network what sort of access and network functionality they require to properly function. The initial focus is on access control. Later work can delve into other aspects. This memo specifies two YANG modules, IPv4 and IPv6 DHCP options, an LLDP TLV, a URL, an X.509 certificate extension and a means to sign and verify the descriptions.

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. 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. discusses design patterns for, and poses questions about, smart objects. Let us then posit a group of objects that are specifically not intended to be used for general purpose computing tasks. These devices, which this memo refers to as Things, have a specific purpose. By definition, therefore, all other uses are not intended. If a small number of communication patterns follows from those small number of uses, the combination of these two statements can be restated as a manufacturer usage description (MUD) that can be applied at various points within a network. MUD primarily addresses threats to the device rather than the device as a threat. In some circumstances, however, MUD may offer some protection in the latter case, depending on the MUD-URL is communicated, and how devices and their communications are authenticated. We use the notion of “manufacturer” loosely in this context to refer to the entity or organization that will state how a device is intended to be used. For example, in the context of a 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 exists an organization in the supply chain of that device that will take responsibility for informing the network about that purpose. The intent of MUD is to provide the following: Substantially reduce the threat surface on a device to those communications intended by the manufacturer. Provide a means to scale network policies to the ever-increasing number of types of devices in the network. 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. Keep the cost of implementation of such a system to the bare minimum. Provide a means of extensibility for manufacturers to express other device capabilities or requirements. MUD consists of three architectural building blocks: A URL that can be used to locate a description; The description itself, including how it is interpreted, and; A means for local network management systems to retrieve the description. MUD is most effective when the network is able to identify in some way the remote endpoints that Things will talk to. In this specification we describe each of these building blocks and how they are intended to be used together. However, they may also be used separately, independent of this specification, by local deployments for their own purposes.

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.

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.

manufacturer usage description. a file containing YANG-based JSON that describes a Thing and associated suggested specific network behavior. a web server that hosts a MUD file. 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. a synonym that has been used in the past for MUD manager. a URL that can be used by the MUD manager to receive the MUD file. the device emitting a MUD URL. the entity that configures the Thing to emit the MUD URL and the one who asserts a recommendation in a MUD file. The manufacturer might not always be the entity that constructs a Thing. It could, for instance, be a systems integrator, or even a component provider. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

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 . 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 . In seeking a general solution, however, we assume that a device will implement functionality necessary to fulfill its limited purpose. This is basic economic constraint. Unless the network would refuse access to such a device, its developers would have no reason to provide the network any information. To date, such an assertion has held true.

Our work begins with the device emitting a Universal Resource Locator (URL) . 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 . In this memo three means are defined to emit the MUD URL, as follows: A DHCP option, that the DHCP client uses to inform the DHCP server. The DHCP server may take further actions, such as act as the MUD manager or otherwise pass it along to the MUD manager. An X.509 constraint. The IEEE has developed that provides a certificate-based approach to communicate device characteristics, which itself relies on . 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) . 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 are encouraged to allow for this sort of flexibility of how MUD URLs may be learned.

MUD managers that are able to do so SHOULD retrieve MUD URLs and signature files as per , using the GET method . They MUST validate the certificate using the rules in , Section 3.1. Requests for MUD URLs SHOULD include an “Accept” header (, Section 5.3.2) containing “application/mud+json”, an “Accept-Language” header field (, Section 5.3.5), and a “User-Agent” header (, Section 5.5.3). MUD managers SHOULD automatically process 3xx response status codes. If a MUD manager is not able to fetch a MUD URL, other means MAY be used to import MUD files and associated signature files. So long as the signature of the file can be validated, the file can be used. In such environments, controllers SHOULD warn administrators when cache-validity expiry is approaching so that they may check for new files. It may not be possible for a MUD manager to retrieve a MUD file at any given time. Should a MUD manager fail to retrieve a MUD file, it SHOULD consider the existing one safe to use, at least for a time. After some period, it SHOULD log that it has been unable to retrieve the file. There may be very good reasons for such failures, including the possibility that the MUD manager is in an 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 interfere with the deployment of a device. It is a local decision as to how to handle such circumstances.

When the MUD URL is resolved, the MUD manager retrieves a file that describes what sort of communications a device is designed to have. The manufacturer may specify either specific hosts for cloud based services or certain classes for access within an operational network. An example of a class might be “devices of a specified manufacturer type”, where the manufacturer type itself is indicated simply by the authority component (e.g, the domain name) of the MUD URL. Another example might be to allow or disallow local access. Just like other policies, these may be combined. For example: Allow access to devices of the same manufacturer Allow access to and from controllers via Constrained Application Protocol (COAP) Allow access to local DNS/NTP Deny all other access A printer might have a description that states: Allow access for port IPP or port LPD Allow local access for port HTTP 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 because it provides accurate and adequate models for use by network devices. JSON is used as a serialization format for compactness and readability, relative to XML. Other formats may be chosen with later versions of MUD. While the policy examples given here focus on access control, this is not intended to be the sole focus. By structuring the model described in this document with clear extension points, other descriptions could be included. One that often comes to mind is quality of service. The YANG modules specified here are extensions of . 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 follows: A device made by a particular manufacturer, as identified by the authority component of its MUD URL Devices that have the same authority component of their MUD URL. Devices that the local network administrator admits to the particular class. Devices intended to serve as controllers for the MUD-URL that the Thing emitted. The class of IP addresses that are scoped within some administrative boundary. By default it is suggested that this be the local subnet. The “manufacturer” classes can be easily specified by the manufacturer, whereas controller classes are initially envisioned to be specified by the administrator. Because manufacturers do not know who will be using their devices, it is important for functionality referenced in usage descriptions to be relatively ubiquitous and mature. For these reasons the YANG-based configuration in a MUD file is limited to either the modules specified or referenced in this document, or those specified in documented extensions.

With these components laid out we now have the basis for an architecture. This leads us to ASCII art.

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

In the above diagram, the switch or router collects MUD URLs and forwards them to the MUD manager (a network management system) for processing. This happens in different ways, depending on how the URL is communicated. For instance, in the case of DHCP, the DHCP server might receive the URL and then process it. In the case of IEEE 802.1X , the switch would carry the URL via a certificate to the authentication server via EAP over Radius, which would then process it. One method to do this is TEAP, described in . The certificate extension is described below. The information returned by the MUD file server is valid for as long as the Thing is connected. There is no expiry. However, if the MUD manager has detected that the MUD file for a Thing has changed, it SHOULD update the policy expeditiously, taking into account whatever approval flow is required in a deployment. In this way, new recommendations from the manufacturer can be processed in a timely fashion. The information returned by the MUD file server (a web server) is valid for the duration of the Thing’s connection, or as specified in the description. Thus if the Thing is disconnected, any associated configuration in the switch can be removed. Similarly, from time to time the description may be refreshed, based on new capabilities or communication patterns or vulnerabilities. The web server is typically run by or on behalf of the manufacturer. Its domain name is that of the authority found in the MUD URL. For legacy cases where Things cannot emit a URL, if the switch is able to determine the appropriate URL, it may proxy it. In the trivial case it may hardcode MUD-URL on a switch port or a map from some available identifier such as an L2 address or certificate hash to a MUD-URL. The role of the MUD manager in this environment is to do the following: receive MUD URLs, fetch MUD files, translate abstractions in the MUD files to specific network element configuration, maintain and update any required mappings of the abstractions, and update network elements with appropriate configuration. A MUD manager 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.

As mentioned above, MUD contains architectural building blocks, and so order of operation may vary. However, here is one clear intended example: Thing emits URL. That URL is forwarded to a MUD manager by the nearest switch (how this happens depends on the way in which the MUD URL is emitted). The MUD manager retrieves the MUD file and signature from the MUD file server, assuming it doesn’t already have copies. After validating the signature, it may test the URL against a web or domain reputation service, and it may test any hosts within the file against those reputation services, as it deems fit. The MUD manager may query the administrator for permission to add the Thing and associated policy. If the Thing is known or the Thing type is known, it may skip this step. The MUD manager instantiates local configuration based on the abstractions defined in this document. The MUD manager configures the switch nearest the Thing. Other systems may be configured as well. When the Thing disconnects, policy is removed.

A MUD file consists of a YANG model instance that has been serialized in JSON . 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: ietf-access-control-list ietf-mud (this document) 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 manager SHOULD NOT automatically implement any MUD file that contains IP addresses, especially those that might have local significance. The addressing of one side of an access list is implicit, based on whether it is applied as to-device-policy or from-device-policy. With the exceptions of “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: match-on-ipv4, match-on-ipv6, match-on-tcp, match-on-udp, match-on-icmp Furthermore, only “accept” or “drop” actions SHOULD be included. A MUD manager MAY choose to interpret “reject” as “drop”. A MUD manager SHOULD ignore all other actions. This is because manufacturers do not have sufficient context within a local deployment to know whether reject is appropriate. That is a decision that should be left to a network administrator. Given that MUD does not deal with interfaces, the support of the “ietf-interfaces” module is not required. Specifically, the support of interface-related features and branches (e.g., interface-attachment and interface-stats) of the ACL YANG module is not required. In fact, MUD managers MAY ignore any particular component of a description or MAY ignore the description in its entirety, and SHOULD carefully inspect all MUD descriptions. Publishers of MUD files MUST NOT include other nodes except as described in . See that section for more information.

This module is structured into three parts: The first component, the “mud” container, holds information that is relevant to retrieval and validity of the MUD file itself, as well as policy intended to and from the Thing. 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. The third component augments the tcp-acl container of the ACL model to add the ability to match on the direction of initiation of a TCP connection. A valid MUD file will contain two root objects, a “mud” container and an “acls” container. Extensions may add additional root objects as required. As a reminder, when parsing acls, elements within a “match” block are logically ANDed. In general, a single abstraction in a match statement should be used. For instance, it makes little sense to match both “my-controller” and “controller” with an argument, since they are highly unlikely to be the same value. A simplified graphical representation of the data models is used in this document. The meaning of the symbols in these diagrams is explained in .

/acl:acls/acl/name +--rw to-device-policy +--rw acls +--rw access-list* [name] +--rw name -> /acl:acls/acl/name augment /acl:acls/acl:acl/acl:aces/acl:ace/acl:matches: +--rw mud +--rw manufacturer? inet:host +--rw same-manufacturer? empty +--rw model? inet:uri +--rw local-networks? empty +--rw controller? inet:uri +--rw my-controller? empty augment /acl:acls/acl:acl/acl:aces/acl:ace/acl:matches /acl:l4/acl:tcp/acl:tcp: +--rw direction-initiated? direction ]]>

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

This URL identifies the MUD file. This is useful when the file and associated signature are manually uploaded, say, in an offline mode.

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.

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 which, for those keeping score, in turn was taken from Section 5.6 of , which was taken from .

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 manager to discard the MUD file, nor terminate access to a Thing. See for more information.

This boolean is an indication from the manufacturer to the network administrator as to whether or not the Thing is supported. In this context a Thing is said to not be supported if the manufacturer intends never to issue a firmware or software update to the Thing or never update the MUD file. A MUD manager MAY still periodically check for updates.

This is a textual UTF-8 description of the Thing to be connected. The intent is for administrators to be able to see a brief displayable description of the Thing. It SHOULD NOT exceed 60 characters worth of display space.

These optional fields are filled in as specified by . Note that firmware-rev and software-rev MUST NOT be populated in a MUD file if the device can be upgraded but the MUD-URL cannot be. This would be the case, for instance, with MUD-URLs that are contained in 802.1AR certificates.

This optional leaf-list names MUD extensions that are used in the MUD file. Note that MUD extensions MUST NOT be used in a MUD file without the extensions being declared. Implementations MUST ignore any node in this file that they do not understand. Note that extensions can either extend the MUD file as described in the previous paragraph, or they might reference other work. An extension example can be found in .

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

This node consists of a hostname that would be matched against the authority component of another Thing’s MUD URL. In its simplest form “manufacturer” and “same-manufacturer” may be implemented as access-lists. In more complex forms, additional network capabilities may be used. For example, if one saw the line “manufacturer” : “flobbidy.example.com”, then all Things that registered with a MUD URL that contained flobbity.example.com in its authority section would match.

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 https://b1.example.com/ThingV1, then all devices that had MUD URL with an authority section of b1.example.com would match.

This URI consists of a URL that points to documentation relating to the device and the MUD file. This can prove particularly useful when the “controller” class is used, so that its use can be explained.

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.

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.

This URI specifies a value that a controller will register with the MUD manager. The node then is expanded to the set of hosts that are so registered. This node may also be a URN. In this case, the URN describes a well known service, such as DNS or NTP, that has been standardized. Both of those URNs may be found in . When “my-controller” is used, it is possible that the administrator will be prompted to populate that class for each and every model. Use of “controller” with a named class allows the user to populate that class only once for many different models that a manufacturer may produce. Controller URIs MAY take the form of a URL (e.g. “http[s]://”). However, MUD managers MUST NOT resolve and retrieve such files, and it is RECOMMENDED that there be no such file at this time, as their form and function may be defined at a point in the future. For now, URLs should serve simply as class names and may be populated by the local deployment administrator. Great care should be taken by MUD managers when invoking the controller class in the form of URLs. For one thing, it requires some understanding by the administrator as to when it is appropriate. 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.

This null-valued node signals to the MUD manager to use whatever mapping it has for this MUD URL to a particular group of hosts. This may require prompting the administrator for class members. Future work should seek to automate membership management.

This MUST only be applied to TCP. This matches the direction in which a TCP connection is initiated. When direction initiated is “from-device”, packets that are transmitted in the direction of a thing MUST be dropped unless the thing has first initiated a TCP connection. By way of example, this node may be implemented in its simplest form by looking at naked SYN bits, but may also be implemented through more stateful mechanisms. When applied this matches packets when the flow was initiated in the corresponding direction. specifies IPv6 guidance best practices. While that document is scoped specifically to IPv6, its contents are applicable for IPv4 as well.

To keep things relatively simple in addition to whatever definitions exist, we also apply two additional default behaviors: Anything not explicitly permitted is denied. Local DNS and NTP are, by default, permitted to and from the Thing. An explicit description of the defaults can be found in . These are applied AFTER all other explicit rules. Thus, a default behavior can be changed with a “drop” action.

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:

A manufacturer may construct a MUD URL in any way, so long as it makes use of the “https” schema.

file "ietf-mud@2018-06-02.yang" module ietf-mud { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-mud"; prefix ietf-mud; import ietf-access-control-list { prefix acl; } import ietf-yang-types { prefix yang; } import ietf-inet-types { prefix inet; } organization "IETF OPSAWG (Ops Area) Working Group"; contact "WG Web: http://tools.ietf.org/wg/opsawg/ WG List: opsawg@ietf.org Author: Eliot Lear lear@cisco.com Author: Ralph Droms rdroms@gmail.com Author: Dan Romascanu dromasca@gmail.com "; description "This YANG module defines a component that augments the IETF description of an access list. This specific module focuses on additional filters that include local, model, and same-manufacturer. 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 (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2018-06-02 { description "Initial proposed standard."; reference "RFC XXXX: Manufacturer Usage Description Specification"; } typedef direction { type enumeration { enum to-device { description "packets or flows destined to the target Thing"; } enum from-device { description "packets or flows destined from the target Thing"; } } description "Which way are we talking about?"; } container mud { presence "Enabled for this particular MUD URL"; description "MUD related information, as specified by RFC-XXXX [RFC Editor to fill in]."; uses mud-grouping; } grouping mud-grouping { description "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; description "This is the MUD URL associated with the entry found in a MUD file."; } leaf last-update { type yang:date-and-time; mandatory true; description "This is intended to be when the current MUD file was generated. MUD Managers SHOULD NOT check for updates between this time plus cache validity"; } leaf mud-signature { type inet:uri; description "A URI that resolves to a signature as described in this specification."; } leaf cache-validity { type uint8 { range "1..168"; } units "hours"; default "48"; description "The information retrieved from the MUD server is valid for these many hours, after which it should be refreshed. N.B. MUD manager implementations need not discard MUD files beyond this period."; } leaf is-supported { type boolean; mandatory true; description "This boolean indicates whether or not the Thing is currently supported by the manufacturer."; } leaf systeminfo { type string; description "A UTF-8 description of this Thing. This should be a brief description that may be displayed to the user to determine whether to allow the Thing on the network."; } leaf mfg-name { type string; description "Manufacturer name, as described in the ietf-hardware YANG module."; } leaf model-name { type string; description "Model name, as described in the ietf-hardware YANG module."; } leaf firmware-rev { type string; description "firmware-rev, as described in the ietf-hardware YANG module. Note 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 documentation { type inet:uri; description "This URL points to documentation that relates to this device and any classes that it uses in its MUD file. A caution: MUD managers need not resolve this URL on their own, but rather simply provide it to the administrator. Parsing HTML is not an intended function of a MUD manager."; } leaf-list extensions { type string { length "1..40"; } description "A list of extension names that are used in this MUD file. Each name is registered with the IANA and described in an RFC."; } container from-device-policy { description "The policies that should be enforced on traffic coming from the device. These policies are not necessarily intended to be enforced at a single point, but may be rendered by the controller to any relevant enforcement points in the network or elsewhere."; uses access-lists; } container to-device-policy { description "The policies that should be enforced on traffic going to the device. These policies are not necessarily intended to be enforced at a single point, but may be rendered by the controller to any relevant enforcement points in the network or elsewhere."; uses access-lists; } } grouping access-lists { description "A grouping for access lists in the context of device policy."; container access-lists { description "The access lists that should be applied to traffic to or from the device."; list access-list { key "name"; description "Each entry on this list refers to an ACL that should be present in the overall access list data model. Each ACL is identified by name and type."; leaf name { type leafref { path "/acl:acls/acl:acl/acl:name"; } description "The name of the ACL for this entry."; } } } } augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" { description "adding abstractions to avoid need of IP addresses"; container mud { description "MUD-specific matches."; leaf manufacturer { type inet:host; description "A domain that is intended to match the authority section of the MUD URL. This node is used to specify one or more manufacturers a device should be authorized to access."; } leaf same-manufacturer { type empty; description "This node matches the authority section of the MUD URL of a Thing. It is intended to grant access to all devices with the same authority section."; } leaf model { type inet:uri; description "Devices of the specified model type will match if they have an identical MUD URL."; } leaf local-networks { type empty; description "IP addresses will match this node if they are considered local addresses. A local address may be a list of locally defined prefixes and masks that indicate a particular administrative scope."; } leaf controller { type inet:uri; description "This node names a class that has associated with it zero or more IP addresses to match against. These may be scoped to a manufacturer or via a standard URN."; } leaf my-controller { type empty; description "This node matches one or more network elements that have been configured to be the controller for this Thing, based on its MUD URL."; } } } augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" + "/acl:l4/acl:tcp/acl:tcp" { description "add direction-initiated"; leaf direction-initiated { type direction; description "This node matches based on which direction a connection was initiated. The means by which that is determined is discussed in this document."; } } } ]]>

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:

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 . 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.

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.

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

file "ietf-acldns@2018-06-02.yang" module ietf-acldns { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-acldns"; prefix ietf-acldns; import ietf-access-control-list { prefix acl; } import ietf-inet-types { prefix inet; } organization "IETF OPSAWG (Ops Area) Working Group"; contact "WG Web: http://tools.ietf.org/wg/opsawg/ WG List: opsawg@ietf.org Author: Eliot Lear lear@cisco.com Author: Ralph Droms rdroms@gmail.com Author: Dan Romascanu dromasca@gmail.com "; description "This YANG module defines a component that augments the IETF description of an access list to allow DNS names as matching criteria."; revision 2018-06-02 { description "Base version of dnsname extension of ACL model"; reference "RFC XXXX: Manufacturer Usage Description Specification"; } grouping dns-matches { description "Domain names for matching."; leaf src-dnsname { type inet:host; description "domain name to be matched against"; } leaf dst-dnsname { type inet:host; description "domain name to be matched against"; } } augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" + "/acl:l3/acl:ipv4/acl:ipv4" { description "Adding domain names to matching"; uses dns-matches; } augment "/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches" + "/acl:l3/acl:ipv6/acl:ipv6" { description "Adding domain names to matching"; uses dns-matches; } } ]]>

This example contains two access lists that are intended to provide outbound access to a cloud service on TCP port 443.

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 “service.bms.example.com”. For each access list, the enforcement point should expect that the Thing initiated the connection.

The IPv4 MUD URL client option has the following format:

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:

The entire option MUST NOT exceed 255 octets. If a space follows the MUD URL, a reserved string that will be defined in future specifications follows. MUD managers that do not understand this field MUST ignore it. The IPv6 MUD URL client option has the following format:

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 toolsets.

A DHCPv4 client MAY emit a DHCPv4 option and a DHCPv6 client MAY emit DHCPv6 option. These options are singletons, as specified in . 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.

A DHCP server may ignore these options or take action based on receipt of these options. When a server consumes this option, it will either forward the URL and relevant client information (such as the gateway address or giaddr and requested IP address, and lease length) to a network management system, or 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 manager. A DHCP server that does process the MUD URL MUST adhere to the process specified in and 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 manager MUST notify the MUD manager of any corresponding change to the DHCP state of the client (such as expiration or explicit release of a network address lease). Should the DHCP server fail, in the case when it implements the MUD manager functionality, any backup mechanisms SHOULD include the MUD state, and the server SHOULD resolve the status of clients upon its restart, similar to what it would do, absent MUD manager functionality. In the case where the DHCP server forwards information to the MUD manager, the MUD manager will either make use of redundant DHCP servers for information, or otherwise clear state based on other network information, such as monitoring port status on a switch via SNMP, Radius accounting, or similar mechanisms.

There are no additional requirements for relays.

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 before they are placed in the certificate extension. The semantics of the URL are defined of this document. The choice of id-pe is based on guidance found in Section 4.2.2 of :

The MUD URL is precisely that: online information about the particular subject. In addition, a separate new extension is defined as id-pe-mudsigner. This contains the subject field of the signing certificate of the MUD file. Processing of this field is specified in . The purpose of this signature is to make a claim that the MUD file found on the server is valid for a given device, independent of any other factors. There are several security considerations below in . A new content-type id-ct-mud is also defined. While signatures are detached today, should a MUD file be transmitted as part of a CMS message, this content-type SHOULD be used. 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) } DEFINITIONS IMPLICIT TAGS ::= BEGIN -- EXPORTS ALL -- IMPORTS -- RFC 5912 EXTENSION FROM PKIX-CommonTypes-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) } -- RFC 5912 id-ct FROM PKIXCRMF-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-crmf2005-02(55) } -- RFC 6268 CONTENT-TYPE FROM CryptographicMessageSyntax-2010 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) } -- RFC 5912 id-pe, Name FROM PKIX1Explicit-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ; -- -- Certificate Extensions -- MUDCertExtensions EXTENSION ::= { ext-MUDURL | ext-MUDsigner, ... } ext-MUDURL EXTENSION ::= { SYNTAX MUDURLSyntax IDENTIFIED BY id-pe-mud-url } id-pe-mud-url OBJECT IDENTIFIER ::= { id-pe 25 } MUDURLSyntax ::= IA5String ext-MUDsigner EXTENSION ::= { SYNTAX MUDsignerSyntax IDENTIFIED BY id-pe-mudsigner } id-pe-mudsigner OBJECT IDENTIFIER ::= { id-pe TBD } MUDsignerSyntax ::= Name -- -- CMS Content Types -- MUDContentTypes CONTENT-TYPE ::= { ct-mud, ... } ct-mud CONTENT-TYPE ::= { -- directly include the content IDENTIFIED BY id-ct-mudtype } -- The binary data that is in the form -- 'application/mud+json" is directly encoded as the -- signed data. No additional ASN.1 encoding is added. id-ct-mudtype OBJECT IDENTIFIER ::= { id-ct TBD } END ]]>

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 manager implementations maintain a table that maps a Thing to its MUD URL based on IDevIDs.

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 . 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:

where: TLV Type = 127 indicates a vendor-specific TLV len – indicates the TLV string length OUI = 00 00 5E is the organizationally unique identifier of IANA subtype = 1 (to be assigned by IANA for the MUD URL) 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 toolsets. Hosts, routers, or other network elements that implement this option are intended to have at most one MUD URL associated with them, so they may transmit at most one MUD URL value. Hosts, routers, or other network elements that implement this option may ignore these options or take action based on receipt of these options. For example they may fill in information in the respective extensions of the LLDP Management Information Base (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 manager, or it will retrieve the usage description by resolving the URL in accordance with normal HTTP semantics.

Because MUD files contain information that may be used to configure network access lists, they are sensitive. To ensure that they have not been tampered with, it is important that they be signed. We make use of DER-encoded Cryptographic Message Syntax (CMS) for this purpose.

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:

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

Prior to processing the rest of a MUD file, the MUD manager MUST retrieve the MUD signature file by retrieving the value of “mud-signature” and validating the signature across the MUD file. The Key Usage Extension in the signing certificate MUST have the bit digitalSignature(0) set. The subject of this certificate MUST be equal to that of the value of id-pe-mudsigner when that extension is present in the device certificate. If these conditions are not met, or if it cannot validate the chain of trust to a known trust anchor, the MUD manager MUST cease processing the MUD file until an administrator has given approval. The purpose of the signature on the file is to assign accountability to an entity, whose reputation can be used to guide administrators on whether or not to accept a given MUD file. It is already common place to check web reputation on the location of a server on which a file resides. While it is likely that the manufacturer will be the signer of the file, this is not strictly necessary, and may not be desirable. For one thing, in some environments, integrators may install their own certificates. For another, what is more important is the accountability of the recommendation, and not just the relationship between the Thing and the file. An example:

Note the additional step of verifying the common trust root.

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: At a coarse grain, a protocol version is included in a MUD URL. This memo specifies MUD version 1. Any and all changes are entertained when this version is bumped. Transition approaches between versions would be a matter for discussion in future versions. At a finer grain, only extensions that would not incur additional risk to the Thing are permitted. Specifically, adding nodes to the mud container is permitted with the understanding that such additions will be ignored by unaware implementations. Any such extensions SHALL be standardized through the IETF process, and MUST be named in the “extensions” list. MUD managers MUST ignore YANG nodes they do not understand and SHOULD create an exception to be resolved by an administrator, so as to avoid any policy inconsistencies.

Because MUD consists of a number of architectural building blocks, it is possible to assemble different deployment scenarios. One key aspect is where to place policy enforcement. In order to protect the Thing from other Things within a local deployment, policy can be enforced on the nearest switch or access point. In order to limit unwanted traffic within a network, it may also be advisable to enforce policy as close to the Internet as possible. In some circumstances, policy enforcement may not be available at the closest hop. At that point, the risk of lateral infection (infection of devices that reside near one another) is increased to the number of Things that are able to communicate without protection. A caution about some of the classes: admission of a Thing into the “manufacturer” and “same-manufacturer” class may have impact on 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 allowed 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. Finally, please see directly below regarding device lifetimes and use of domain names.

Based on how a MUD URL is emitted, a Thing may be able to lie about what it is, thus gaining additional network access. This happens when a device emits a MUD URL using DHCP or LLDP, and is either inappropriately admitted to a class such as “same-manufacturer” or given access to a device such as “my-controller”, where such access would otherwise be disallowed. Whether that is the case will depend on the deployment. Implementations SHOULD be configurable to disallow additive access for devices using MUD-URLs that not emitted in a secure fashion such as in a certificate. Similarly, implementations SHOULD NOT grant elevated permissions (beyond those of devices presenting no MUD policy) to devices which do not strongly bind their identity to their L2/L3 transmissions. When insecure methods are used by the MUD Manager, the classes SHOULD NOT contain devices that use both insecure and secure methods, in order to prevent privilege escalation attacks, and MUST NOT contain devices with the same MUD-URL that are derived from both strong and weak authentication methods. Devices may forge source (L2/L3) information. Deployments should apply appropriate protections to bind communications to the authentication that has taken place. For 802.1X authentication, IEEE 802.1AE (MACsec) is one means by which this may happen. A similar approach can be used with 802.11i (WPA2) . Other means are available with other lower layer technologies. Implementations using session-oriented access that is not cryptographically bound should take care to remove state when any form of break in the session is detected. A rogue CA may sign a certificate that contains the same subject name as is listed in the MUDsigner field in the manufacturer certificate, thus seemingly permitting a substitute MUD file for a device. There are two mitigations available: first, if the signer changes, this may be flagged as an exception by the MUD manager. If the MUD file also changes, the MUD manager SHOULD seek administrator approval (it should do this in any case). In all circumstances, the MUD manager MUST maintain a cache of trusted CAs for this purpose. When such a rogue is discovered, it SHOULD be removed. Additional mitigations are described below. When certificates are not present, Things claiming to be of a certain manufacturer SHOULD NOT be included in that manufacturer grouping without additional validation of some form. This will be relevant when 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 artifacts to the MUD string in the form of the reserved field discussed in . The meaning of such artifacts is left as future work. MUD managers SHOULD NOT accept a usage description for a Thing with the same MAC address that has indicated a change of the URL authority without some additional validation (such as review by a network administrator). New Things that present some form of unauthenticated MUD URL SHOULD be validated by some external means when they would be 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 that the signer of the MUD file is known to and trusted by the MUD manager. The second is to have a system do a primary scan of the file to ensure that it is both parseable and believable at some level. MUD files will likely be relatively small, to start with. The number of ACEs used by any given Thing should be relatively small as well. It may also be useful to limit retrieval of MUD URLs to only those sites that are known to have decent web or domain reputations. Use of a URL necessitates the use of domain names. If a domain name changes ownership, the new owner of that domain may be able to provide MUD files that MUD managers would consider valid. There are a few approaches that can mitigate this attack. First, MUD managers SHOULD cache certificates used by the MUD file server. When a new certificate is retrieved for whatever reason, the MUD manager should check to see if ownership of the domain has changed. A fair programmatic approximation of this is when the name servers for the domain have changed. If the actual MUD file has changed, the MUD manager MAY check the WHOIS database to see if registration ownership of a domain has changed. If a change has occurred, or if for some reason it is not possible to determine whether ownership has changed, further review may be warranted. Note, this remediation does not take into account the case of a Thing that was produced long ago and only recently fielded, or the case where a new MUD manager has been installed. The release of a MUD URL by a Thing reveals what the Thing is, and provides an attacker with guidance on what vulnerabilities may be present. While the MUD URL itself is not intended to be unique to a specific Thing, the release of the URL may aid an observer in identifying individuals when combined with other information. This is a privacy consideration. In addressing both of these concerns, implementors should take into account what other information they are advertising through mechanisms such as mDNS, 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 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 . There is the risk of the MUD manager itself being spied on to determine what things are connected to the network. To address this risk, MUD managers may choose to make use of TLS proxies that they trust that would aggregate other information. Please note that the security considerations mentioned in Section 4.7 of 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 . The basic purpose of MUD is to configure access, and so by its very nature can be disruptive if used by unauthorized parties.

[ There was originally a registry entry for .well-known suffixes. This has been removed from the draft and may be marked as deprecated in the registry. RFC Editor: please remove this comment. ]

The following YANG modules are requested to be registered in the “IANA Module Names” registry: The ietf-mud module: Name: ietf-mud URN: urn:ietf:params:xml:ns:yang:ietf-mud Prefix: ietf-mud Registrant conact: The IESG Reference: [RFCXXXX] The ietf-acldns module: Name: ietf-acldns URI: urn:ietf:params:xml:ns:yang:ietf-acldns Prefix: ietf-acldns Registrant: the IESG Reference: [RFCXXXX]

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 .

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 (1.3.6.1.5.5.7.0). o id-pe-mud-url object identifier from the “SMI Security for PKIX Certificate Extension” registry (1.3.6.1.5.5.7.1). o id-pe-mudsigner object identifier from the “SMI Security for PKIX Certificate Extension” registry (TBD). o id-ct-mud object identifier from the “SMI Security for S/MIME CMS Content Type” registry. The use of these values is specified in .

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

, 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. ]]>

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 >

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

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 . “urn:ietf:params:mud:ntp” refers to the service specified by .

The IANA is requested to establish a registry of extensions as follows:

Each extension MUST follow the rules specified in this specification. As is usual, the IANA issues early allocations based in accordance with .

The authors would like to thank Einar Nilsen-Nygaard, who singlehandedly updated the model to match the updated ACL model, Bernie Volz, Tom Gindin, Brian Weis, Sandeep Kumar, Thorsten Dahm, John Bashinski, Steve Rich, Jim Bieda, Dan Wing, Joe Clarke, Henk Birkholz, Adam Montville, Jim Schaad, and Robert Sparks for their valuable advice and reviews. Russ Housley entirely rewrote 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.

This RFC is an official specification for the Internet community. It incorporates by reference, amends, corrects, and supplements the primary protocol standards documents relating to hosts. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo describes how to use Transport Layer Security (TLS) to secure Hypertext Transfer Protocol (HTTP) connections over the Internet. This memo provides information for the Internet community. ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279. This document defines the Extensible Authentication Protocol (EAP), an authentication framework which supports multiple authentication methods. EAP typically runs directly over data link layers such as Point-to-Point Protocol (PPP) or IEEE 802, without requiring IP. EAP provides its own support for duplicate elimination and retransmission, but is reliant on lower layer ordering guarantees. Fragmentation is not supported within EAP itself; however, individual EAP methods may support this. This document obsoletes RFC 2284. A summary of the changes between this document and RFC 2284 is available in Appendix A. [STANDARDS-TRACK] A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] This document defines a new protocol element, the Internationalized Resource Identifier (IRI), as a complement of the Uniform Resource Identifier (URI). An IRI is a sequence of characters from the Universal Character Set (Unicode/ISO 10646). A mapping from IRIs to URIs is defined, which means that IRIs can be used instead of URIs, where appropriate, to identify resources. The approach of defining a new protocol element was chosen instead of extending or changing the definition of URIs. This was done in order to allow a clear distinction and to avoid incompatibilities with existing software. Guidelines are provided for the use and deployment of IRIs in various protocols, formats, and software components that currently deal with URIs. This document defines a data model for Access Control List (ACL). An ACL is a user-ordered set of rules, used to configure the forwarding behavior in device. Each rule is used to find a match on a packet, and define actions that will be performed on the packet. The Network Time Protocol (NTP) is widely used to synchronize computer clocks in the Internet. This document describes NTP version 4 (NTPv4), which is backwards compatible with NTP version 3 (NTPv3), described in RFC 1305, as well as previous versions of the protocol. NTPv4 includes a modified protocol header to accommodate the Internet Protocol version 6 address family. NTPv4 includes fundamental improvements in the mitigation and discipline algorithms that extend the potential accuracy to the tens of microseconds with modern workstations and fast LANs. It includes a dynamic server discovery scheme, so that in many cases, specific server configuration is not required. It corrects certain errors in the NTPv3 design and implementation and includes an optional extension mechanism. [STANDARDS-TRACK] This document introduces a collection of common data types to be used with the YANG data modeling language. This document obsoletes RFC 6021. The Dynamic Host Configuration Protocol (DHCP) provides a framework for passing configuration information to hosts on a TCPIP network. DHCP is based on the Bootstrap Protocol (BOOTP), adding the capability of automatic allocation of reusable network addresses and additional configuration options. [STANDARDS-TRACK] This document provides guidance to prospective DHCPv6 option developers to help them create option formats that are easily adoptable by existing DHCPv6 software. It also provides guidelines for expert reviewers to evaluate new registrations. This document updates RFC 3315. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations. This document specifies a mechanism for protecting hosts connected to a switched network against rogue DHCPv6 servers. It is based on DHCPv6 packet filtering at the layer 2 device at which the packets are received. A similar mechanism has been widely deployed in IPv4 networks ('DHCP snooping'); hence, it is desirable that similar functionality be provided for IPv6 networks. This document specifies a Best Current Practice for the implementation of DHCPv6-Shield. YANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols. This document describes the syntax and semantics of version 1.1 of the YANG language. YANG version 1.1 is a maintenance release of the YANG language, addressing ambiguities and defects in the original specification. There are a small number of backward incompatibilities from YANG version 1. This document also specifies the YANG mappings to the Network Configuration Protocol (NETCONF). This document defines encoding rules for representing configuration data, state data, parameters of Remote Procedure Call (RPC) operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text. This memo describes the process for early allocation of code points by IANA from registries for which "Specification Required", "RFC Required", "IETF Review", or "Standards Action" policies apply. This process can be used to alleviate the problem where code point allocation is needed to facilitate desired or required implementation and deployment experience prior to publication of an RFC, which would normally trigger code point allocation. The procedures in this document are intended to apply only to IETF Stream documents. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK] The Cryptographic Message Syntax (CMS) format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. The Public Key Infrastructure using X.509 (PKIX) certificate format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. This document defines the procedures that the Internet Assigned Numbers Authority (IANA) uses when handling assignment and other requests related to the Service Name and Transport Protocol Port Number registry. It also discusses the rationale and principles behind these procedures and how they facilitate the long-term sustainability of the registry.This document updates IANA's procedures by obsoleting the previous UDP and TCP port assignment procedures defined in Sections 8 and 9.1 of the IANA Allocation Guidelines, and it updates the IANA service name and port assignment procedures for UDP-Lite, the Datagram Congestion Control Protocol (DCCP), and the Stream Control Transmission Protocol (SCTP). It also updates the DNS SRV specification to clarify what a service name is and how it is registered. This memo documents an Internet Best Current Practice. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. This document captures the current syntax used in YANG module tree diagrams. The purpose of this document is to provide a single location for this definition. This syntax may be updated from time to time based on the evolution of the YANG language. This document defines a YANG data model for the management of hardware on a single server. Institute for Electrical and Electronics Engineers The Hypertext Transfer Protocol (HTTP) is a stateless \%application- level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation. IAB IESG The Internet Architecture Board (IAB) and the Internet Engineering Steering Group (IESG), the bodies which oversee architecture and standards for the Internet, are concerned by the need for increased protection of international commercial transactions on the Internet, and by the need to offer all Internet users an adequate degree of privacy. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. This document describes a new sub-delegation for the 'ietf' URN namespace for registered protocol items. The 'ietf' URN namespace is defined in RFC 2648 as a root for persistent URIs that refer to IETF- defined resources. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document identifies a set of recommendations for the makers of devices and describes how to provide for "simple security" capabilities at the perimeter of local-area IPv6 networks in Internet-enabled homes and small offices. This document is not an Internet Standards Track specification; it is published for informational purposes. Well-known web servers such as Apache and web proxies like Squid support event logging using a common log format. The logs produced using these de facto standard formats are invaluable to system administrators for troubleshooting a server and tool writers to craft tools that mine the log files and produce reports and trends. Furthermore, these log files can also be used to train anomaly detection systems and feed events into a security event management system. The Session Initiation Protocol (SIP) does not have a common log format, and, as a result, each server supports a distinct log format that makes it unnecessarily complex to produce tools to do trend analysis and security detection. This document describes a framework, including requirements and analysis of existing approaches, and specifies an information model for development of a SIP common log file format that can be used uniformly by user agents, proxies, registrars, and redirect servers as well as back-to-back user agents. Some IETF protocols make use of Ethernet frame formats and IEEE 802 parameters. This document discusses several uses of such parameters in IETF protocols, specifies IANA considerations for assignment of points under the IANA OUI (Organizationally Unique Identifier), and provides some values for use in documentation. This document obsoletes RFC 5342. This document defines the Tunnel Extensible Authentication Protocol (TEAP) version 1. TEAP is a tunnel-based EAP method that enables secure communication between a peer and a server by using the Transport Layer Security (TLS) protocol to establish a mutually authenticated tunnel. Within the tunnel, TLV objects are used to convey authentication-related data between the EAP peer and the EAP server. The term "Internet of Things" (IoT) denotes a trend where a large number of embedded devices employ communication services offered by Internet protocols. Many of these devices, often called "smart objects", are not directly operated by humans but exist as components in buildings or vehicles, or are spread out in the environment. Following the theme "Everything that can be connected will be connected", engineers and researchers designing smart object networks need to decide how to achieve this in practice.This document offers guidance to engineers designing Internet- connected smart objects. 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The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation.CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. International Organization for Standardization This memo provides guidelines for authors and reviewers of specifications containing YANG data model modules. Recommendations and procedures are defined, which are intended to increase interoperability and usability of Network Configuration Protocol (NETCONF) and RESTCONF protocol implementations that utilize YANG data model modules. This document obsoletes RFC 6087. Institute for Electrical and Electronics Engineers Institute for Electrical and Electronics Engineers Institute for Electrical and Electronics Engineers Institute for Electrical and Electronics Engineers

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: One editorial. Draft -16 add mud-signature element based on review comments redo mud-url make clear that systeminfo uses UTF8 Draft -13 to -14: Final WGLC comments and review comments Move version from MUD-URL to Model Have MUD-URL in model Update based on update to draft-ietf-netmod-acl-model Point to tree diagram draft instead of 6087bis. Draft -12 to -13: Additional WGLC comments Draft -10 to -12: These are based on WGLC comments: Correct examples based on ACL model changes. Change ordering nodes. Additional explanatory text around systeminfo. Change ordering in examples. Make it VERY VERY VERY VERY clear that these are recommendations, not mandates. DHCP -> NTP in some of the intro text. Remove masa-server “Things” to “network elements” in a few key places. Reference to JSON YANG RFC added. Draft -10 to -11: Example corrections Typo Fix two lists. Addition of ‘any-acl’ and ‘mud-acl’ in the list of allowed features. Clarification of what should be in a MUD file. Draft -09 to -10: AD input. Correct dates. Add compliance sentence as to which ACL module features are implemented. Draft -08 to -09: Resolution of Security Area review, IoT directorate review, GenART review, YANG doctors review. change of YANG structure to address mandatory nodes. Terminology cleanup. specify out extra portion of MUD-URL. consistency changes. improved YANG descriptions. Remove extra revisions. Track ACL model changes. Additional cautions on use of ACL model; further clarifications on extensions. Draft -07 to -08: a number of editorials corrected. definition of MUD file tweaked. Draft -06 to -07: Examples updated. Additional clarification for direction-initiated. Additional implementation guidance given. Draft -06 to -07: Update models to match new ACL model extract directionality from the ACL, introducing a new device container. Draft -05 to -06: Make clear that this is a component architecture (Polk and Watson) Add order of operations (Watson) Add extensions leaf-list (Pritikin) Remove previous-mud-file (Watson) Modify text in last-update (Watson) Clarify local networks (Weis, Watson) Fix contact info (Watson) Terminology clarification (Weis) Advice on how to handle LDevIDs (Watson) Add deployment considerations (Watson) Add some additional text about fingerprinting (Watson) Appropriate references to 6087bis (Watson) 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

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 manager might further decide to optimize to simply not include the defaults when they are overridden. Four “acl” list entries that implement default MUD nodes are listed below. Two are for IPv4 and two are for IPv6 (one in each direction for both versions of IP). Note that neither access-list name nor ace name need be retained or used in any way by local implementations, but are simply there for completeness’ sake.

In this sample extension we augment the core MUD model to indicate whether the device implements DETNET. If a device claims not to use NETNET, but then later attempts to do so, a notification or exception might be generated. Note that this example is intended only for illustrative purposes.

This extension augments the MUD model to include a single node, using the following sample module that has the following tree structure:

The model is defined as follows:

file "ietf-mud-detext-example@2018-06-02.yang" module ietf-mud-detext-example { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-mud-detext-example"; prefix ietf-mud-detext-example; import ietf-mud { prefix ietf-mud; } organization "IETF OPSAWG (Ops Area) Working Group"; contact "WG Web: http://tools.ietf.org/wg/opsawg/ WG List: opsawg@ietf.org Author: Eliot Lear lear@cisco.com Author: Ralph Droms rdroms@gmail.com Author: Dan Romascanu dromasca@gmail.com "; description "Sample extension to a MUD module to indicate a need for DETNET support."; revision 2018-06-02 { description "Initial revision."; reference "RFC XXXX: Manufacturer Usage Description Specification"; } augment "/ietf-mud:mud" { description "This adds a simple extension for a manufacturer to indicate whether DETNET is required by a device."; leaf is-detnet-required { type boolean; description "This value will equal true if a device requires detnet to properly function"; } } } ]]>

Using the previous example, we now show how the extension would be expressed: