| Network Working Group | E. Lear |
| Internet-Draft | Cisco Systems |
| Intended status: Standards Track | R. Droms |
| Expires: December 4, 2018 | |
| D. Romascanu | |
| June 02, 2018 |
Manufacturer Usage Description Specification
draft-ietf-opsawg-mud-23
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.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 4, 2018.
Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
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 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:
MUD consists of three architectural building blocks:
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.
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
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 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) [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:
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 [RFC7230], using the GET method [RFC7231]. They MUST validate the certificate using the rules in [RFC2818], Section 3.1.
Requests for MUD URLs SHOULD include an “Accept” header ([RFC7231], Section 5.3.2) containing “application/mud+json”, an “Accept-Language” header field ([RFC7231], Section 5.3.5), and a “User-Agent” header ([RFC7231], Section 5.5.3).
MUD managers SHOULD automatically process 3xx response status codes.
If a MUD manager is not able to fetch a MUD URL, other means MAY be used to import MUD files and associated signature files. So long as the signature of the file can be validated, the file can be used. In such environments, controllers SHOULD warn administrators when cache-validity expiry is approaching so that they may check for new files.
It may not be possible for a MUD manager to retrieve a MUD file at any given time. Should a MUD manager fail to retrieve a MUD file, it SHOULD consider the existing one safe to use, at least for a time. After some period, it SHOULD log that it has been unable to retrieve the file. There may be very good reasons for such failures, including the possibility that the MUD manager is in an 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:
A printer might have a description that states:
In this way anyone can print to the printer, but local access would be required for the management interface.
The files that are retrieved are intended to be closely aligned to existing network architectures so that they are easy to deploy. We make use of YANG [RFC7950] because it provides accurate and adequate models for use by network devices. JSON[RFC8259] is used as a serialization format for compactness and readability, relative to XML. Other formats may be chosen with later versions of MUD.
While the policy examples given here focus on access control, this is not intended to be the sole focus. By structuring the model described in this document with clear extension points, other descriptions could be included. One that often comes to mind is quality of service.
The YANG modules specified here are extensions of [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 follows:
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.
....................................... . ____________ . _____________ . | | . | | . | MUD |-->get URL-->| MUD | . | Manager | .(https) | File Server | . End system network |____________|<-MUD file<-<|_____________| . . . . . . . _______ _________ . .| | (dhcp et al) | router | . .| Thing |---->MUD URL-->| or | . .|_______| | switch | . . |_________| . .......................................
Figure 1: MUD Architecture
In the above diagram, the switch or router collects MUD URLs and forwards them to the MUD manager (a network management system) for processing. This happens in different ways, depending on how the URL is communicated. For instance, in the case of DHCP, the DHCP server might receive the URL and then process it. In the case of IEEE 802.1X [IEEE8021X], the switch would carry the URL via a certificate to the authentication server via 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 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:
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:
A MUD file consists of a YANG model instance that has been serialized in JSON [RFC7951]. For purposes of MUD, the nodes that can be modified are access lists as augmented by this model. The MUD file is limited to the serialization of only the following YANG schema:
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:
Furthermore, only “accept” or “drop” actions SHOULD be included. A MUD manager MAY choose to interpret “reject” as “drop”. A MUD manager SHOULD ignore all other actions. This is because manufacturers do not have sufficient context within a local deployment to know whether reject is appropriate. That is a decision that should be left to a network administrator.
Given that MUD does not deal with interfaces, the support of the “ietf-interfaces” module [RFC8343] is not required. Specifically, the support of interface-related features and branches (e.g., interface-attachment and interface-stats) of the ACL YANG module is not required.
In fact, MUD managers MAY ignore any particular component of a description or MAY ignore the description in its entirety, and SHOULD carefully inspect all MUD descriptions. Publishers of MUD files MUST NOT include other nodes except as described in Section 3.9. See that section for more information.
This module is structured into three parts:
A valid MUD file will contain two root objects, a “mud” container and an “acls” container. Extensions may add additional root objects as required. As a reminder, when parsing acls, elements within a “match” block are logically ANDed. In general, a single abstraction in a match statement should be used. For instance, it makes little sense to match both “my-controller” and “controller” with an argument, since they are highly unlikely to be the same value.
A simplified graphical representation of the data models is used in this document. The meaning of the symbols in these diagrams is explained in [RFC8340].
module: ietf-mud
+--rw mud!
+--rw mud-version uint8
+--rw mud-url inet:uri
+--rw last-update yang:date-and-time
+--rw mud-signature? inet:uri
+--rw cache-validity? uint8
+--rw is-supported boolean
+--rw systeminfo? string
+--rw mfg-name? string
+--rw model-name? string
+--rw firmware-rev? string
+--rw software-rev? string
+--rw documentation? inet:uri
+--rw extensions* string
+--rw from-device-policy
| +--rw acls
| +--rw access-list* [name]
| +--rw name -> /acl:acls/acl/name
+--rw to-device-policy
+--rw acls
+--rw access-list* [name]
+--rw name -> /acl:acls/acl/name
augment /acl:acls/acl:acl/acl:aces/acl:ace/acl:matches:
+--rw mud
+--rw manufacturer? inet:host
+--rw same-manufacturer? empty
+--rw model? inet:uri
+--rw local-networks? empty
+--rw controller? inet:uri
+--rw my-controller? empty
augment
/acl:acls/acl:acl/acl:aces/acl:ace/acl:matches
/acl:l4/acl:tcp/acl:tcp:
+--rw direction-initiated? direction
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.
[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.
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].
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 Section 16 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 [RFC8348]. Note that firmware-rev and software-rev MUST NOT be populated in a MUD file if the device can be upgraded but the MUD-URL cannot be. This would be the case, for instance, with MUD-URLs that are contained in 802.1AR certificates.
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 Appendix C.
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 Section 17.6.
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. [RFC6092] 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:
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.
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:
https://things.example.org/product_abc123/v5 https://www.example.net/mudfiles/temperature_sensor/ https://example.com/lightbulbs/colour/v1
A manufacturer may construct a MUD URL in any way, so long as it makes use of the “https” schema.
<CODE BEGINS>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.";
}
}
}
<CODE ENDS>
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:acls/acl:acl/acl:aces/acl:ace/
acl:matches/acl:l3/acl:ipv4/acl:ipv4:
+--rw src-dnsname? inet:host
+--rw dst-dnsname? inet:host
augment /acl:acls/acl:acl/acl:aces/acl:ace/
acl:matches/acl:l3/acl:ipv6/acl:ipv6:
+--rw src-dnsname? inet:host
+--rw dst-dnsname? inet:host
The choice of these particular points in the access-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.
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.
<CODE BEGINS>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;
}
}
<CODE ENDS>
This example contains two access lists that are intended to provide outbound access to a cloud service on TCP port 443.
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://lighting.example.com/lightbulb2000",
"last-update": "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:acls": {
"acl": [
{
"name": "mud-76100-v6to",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-todev",
"matches": {
"ipv6": {
"ietf-acldns:src-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"source-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-76100-v6fr",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv6": {
"ietf-acldns:dst-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"destination-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
}
]
}
}
In this example, two policies are declared, one from the Thing and the other to the Thing. Each policy names an access list that applies to the Thing, and one that applies from. 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 | 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*( OCTET ) ; from [RFC5234]
The entire option MUST NOT exceed 255 octets. If a space follows the MUD URL, a reserved string that will be defined in future specifications follows. MUD managers that do not understand this field MUST ignore it.
The IPv6 MUD URL client option has the following format:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_MUD_URL_V6 | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MUDstring | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OPTION_MUD_URL_V6 (112; 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 [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.
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 [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 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 [RFC5280].
Any Internationalized Resource Identifiers (IRIs) MUST be mapped to URIs as specified in Section 3.1 of [RFC3987] before they are placed in the certificate extension.
The semantics of the URL are defined Section 6 of this document.
The choice of id-pe is based on guidance found in Section 4.2.2 of [RFC5280]:
These extensions may be used to direct applications to on-line
information about the issuer or the subject.
The MUD URL is precisely that: online information about the particular subject.
In addition, a separate new extension is defined as id-pe-mudsigner. This contains the subject field of the signing certificate of the MUD file. Processing of this field is specified in Section 13.2.
The purpose of this signature is to make a claim that the MUD file found on the server is valid for a given device, independent of any other factors. There are several security considerations below in Section 16.
A new content-type id-ct-mud is also defined. While signatures are detached today, should a MUD file be transmitted as part of a CMS message, this content-type SHOULD be used.
The new extension is identified as follows:
<CODE BEGINS>
MUDURLExtnModule-2016 { iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-mudURLExtn2016(88) }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
-- EXPORTS ALL --
IMPORTS
-- RFC 5912
EXTENSION
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
-- RFC 5912
id-ct
FROM PKIXCRMF-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-crmf2005-02(55) }
-- RFC 6268
CONTENT-TYPE
FROM CryptographicMessageSyntax-2010
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) }
-- RFC 5912
id-pe, Name
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
--
-- Certificate Extensions
--
MUDCertExtensions EXTENSION ::=
{ ext-MUDURL | ext-MUDsigner, ... }
ext-MUDURL EXTENSION ::=
{ 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
<CODE ENDS>
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 [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 | MUDString | =127 | |= 00 00 5E| = 1 | |(7 bits)|(9 bits)|(3 octets)|(1 octet)|(1-255 octets) +--------+--------+----------+---------+--------------
where:
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) [RFC5652] 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:
% openssl cms -sign -signer mancertfile -inkey mankey \
-in mudfile -binary -outform DER -binary \
-certfile intermediatecert -out mudfile.p7s
Note: A MUD file may need to be re-signed if the signature expires.
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:
% openssl cms -verify -in mudfile.p7s -inform DER -content mudfile
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:
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) [IEEE8021AE] is one means by which this may happen. A similar approach can be used with 802.11i (WPA2) [IEEE80211i]. Other means are available with other lower layer technologies. Implementations using session-oriented access that is not cryptographically bound should take care to remove state when any form of break in the session is detected.
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 Section 10. The meaning of such artifacts is left as future work.
MUD managers SHOULD NOT accept a usage description for a Thing with the same 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[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].
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 [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.
[ 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:
The ietf-acldns module:
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 10.
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 Section 11.
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 MUST be
employed. [RFC3629]
o Security considerations: See Security Considerations
of RFCXXXX and [RFC8259] Section 12.
o Interoperability considerations: n/a
o Published specification: [RFCXXXX]
o Applications that use this media type: MUD managers as
specified by [RFCXXXX].
o Fragment identifier considerations: n/a
o Additional information:
Magic number(s): n/a
File extension(s): n/a
Macintosh file type code(s): n/a
o Person & email address to contact for further information:
Eliot Lear <lear@cisco.com>, Ralph Droms <rdroms@gmail.com>
o Intended usage: COMMON
o Restrictions on usage: none
o Author:
Eliot Lear <lear@cisco.com>
Ralph Droms <rdroms@gmail.com>
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 [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].
The IANA is requested to establish a registry of extensions as follows:
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].
The authors would like to thank Einar Nilsen-Nygaard, who singlehandedly updated the model to match the updated ACL model, Bernie Volz, Tom Gindin, Brian Weis, Sandeep Kumar, Thorsten Dahm, John Bashinski, Steve Rich, Jim Bieda, Dan Wing, Joe Clarke, Henk Birkholz, Adam Montville, Jim Schaad, and Robert Sparks for their valuable advice and reviews. Russ Housley entirely rewrote Section 11 to be a complete module. Adrian Farrel provided the basis for 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.
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:
Draft -16
Draft -13 to -14:
Draft -12 to -13:
Draft -10 to -12:
These are based on WGLC comments:
Draft -10 to -11:
Draft -09 to -10:
Draft -08 to -09:
Draft -07 to -08:
Draft -06 to -07:
Draft -06 to -07:
Draft -05 to -06:
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.
"ietf-access-control-list:acls": {
"acl": [
{
"name": "mud-59776-v4to",
"type": "ipv4-acl-type",
"aces": {
"ace": [
{
"name": "ent0-todev",
"matches": {
"ietf-mud:mud": {
"controller": "urn:ietf:params:mud:dns"
},
"ipv4": {
"protocol": 17
},
"udp": {
"source-port": {
"operator": "eq",
"port": 53
}
}
},
"actions": {
"forwarding": "accept"
}
},
{
"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"
}
}
]
}
}
]
}
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.
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@2018-06-02.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";
}
}
}
<CODE ENDS>
Using the previous example, we now show how the extension would be expressed:
{
"ietf-mud:mud": {
"mud-version": 1,
"mud-url": "https://lighting.example.com/lightbulb2000",
"last-update": "2018-03-02T11:20:51+01:00",
"cache-validity": 48,
"extensions": [
"ietf-mud-detext-example"
],
"ietf-mud-detext-example:is-detnet-required": "false",
"is-supported": true,
"systeminfo": "The BMS Example 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:acls": {
"acl": [
{
"name": "mud-76100-v6to",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-todev",
"matches": {
"ipv6": {
"ietf-acldns:src-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"source-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
},
{
"name": "mud-76100-v6fr",
"type": "ipv6-acl-type",
"aces": {
"ace": [
{
"name": "cl0-frdev",
"matches": {
"ipv6": {
"ietf-acldns:dst-dnsname": "test.example.com",
"protocol": 6
},
"tcp": {
"ietf-mud:direction-initiated": "from-device",
"destination-port": {
"operator": "eq",
"port": 443
}
}
},
"actions": {
"forwarding": "accept"
}
}
]
}
}
]
}
}