Manufacturer Usage Description Specification
draft-ietf-opsawg-mud-00
The information below is for an old version of the document.
| Document | Type | This is an older version of an Internet-Draft that was ultimately published as an RFC. | |
|---|---|---|---|
| Authors | Eliot Lear , Ralph Droms , Dan Romascanu | ||
| Last updated | 2016-08-19 | ||
| Replaces | draft-lear-ietf-netmod-mud | ||
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draft-ietf-opsawg-mud-00
Network Working Group E. Lear
Internet-Draft R. Droms
Intended status: Standards Track Cisco Systems
Expires: February 20, 2017 D. Romascanu
Avaya
August 19, 2016
Manufacturer Usage Description Specification
draft-ietf-opsawg-mud-00
Abstract
This memo specifies the necessary components to implement
manufacturer usage descriptions (MUD). This includes two YANG
modules, IPv4 and IPv6 DHCP options, an LLDP TLV, a URL suffix
specification, an X.509 certificate extension and a means to sign and
verify the descriptions.
Status of This Memo
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 http://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 February 20, 2017.
Copyright Notice
Copyright (c) 2016 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
(http://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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. A Simple Example . . . . . . . . . . . . . . . . . . . . 4
1.2. Determining Intended Use . . . . . . . . . . . . . . . . 4
1.3. Finding A Policy: The MUD URL . . . . . . . . . . . . . . 5
1.4. Types of Policies . . . . . . . . . . . . . . . . . . . . 5
1.5. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.6. The Manufacturer Usage Description Architecture . . . . . 7
2. The MUD Model and Semantic Meaning . . . . . . . . . . . . . 8
3. Element Definitions . . . . . . . . . . . . . . . . . . . . . 8
3.1. last-update . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. previous-mud-file . . . . . . . . . . . . . . . . . . . . 9
3.3. cache-validity . . . . . . . . . . . . . . . . . . . . . 9
3.4. masa-server . . . . . . . . . . . . . . . . . . . . . . . 9
3.5. is-supported . . . . . . . . . . . . . . . . . . . . . . 9
3.6. packet-direction . . . . . . . . . . . . . . . . . . . . 9
3.7. manufacturer . . . . . . . . . . . . . . . . . . . . . . 10
3.8. same-manufacturer . . . . . . . . . . . . . . . . . . . . 10
3.9. model . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.10. local-networks . . . . . . . . . . . . . . . . . . . . . 10
3.11. controller . . . . . . . . . . . . . . . . . . . . . . . 10
3.12. direction-initiated . . . . . . . . . . . . . . . . . . . 10
4. Processing of the MUD file . . . . . . . . . . . . . . . . . 11
5. What does a MUD URL look like? . . . . . . . . . . . . . . . 11
6. The MUD YANG Model . . . . . . . . . . . . . . . . . . . . . 11
7. The Domain Name Extension to the ACL Model . . . . . . . . . 15
7.1. source-dnsname . . . . . . . . . . . . . . . . . . . . . 15
7.2. destination-dnsname . . . . . . . . . . . . . . . . . . . 15
7.3. The ietf-acldns Model . . . . . . . . . . . . . . . . . . 16
8. MUD File Example . . . . . . . . . . . . . . . . . . . . . . 17
9. The MUD URL DHCP Option . . . . . . . . . . . . . . . . . . . 18
9.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 19
9.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 19
9.3. Relay Requirements . . . . . . . . . . . . . . . . . . . 20
10. The Manufacturer Usage Description (MUD) URL X.509 Extension 20
11. The Manufacturer Usage Description LLDP extension . . . . . . 21
12. Creating and Processing of Signed MUD Files . . . . . . . . . 22
12.1. Creating a MUD file signature . . . . . . . . . . . . . 22
12.2. Verifying a MUD file signature . . . . . . . . . . . . . 23
13. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 23
14. Security Considerations . . . . . . . . . . . . . . . . . . . 24
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
15.1. DHCPv4 and DHCPv6 Options . . . . . . . . . . . . . . . 25
15.2. PKIX Extensions . . . . . . . . . . . . . . . . . . . . 25
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15.3. Well Known URI Suffix . . . . . . . . . . . . . . . . . 25
15.4. MIME Media-type Registration for MUD files . . . . . . . 25
15.5. LLDP IANA TLV Subtype Registry . . . . . . . . . . . . . 26
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
17.1. Normative References . . . . . . . . . . . . . . . . . . 27
17.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Changes from Earlier Versions . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
The Internet has largely been constructed on general purpose
computers; those devices that may be used for a purpose that is
specified by those who buy the device. [RFC1984] presumed that an
end device would be most capable of protecting itself. This made
sense when the typical device was a workstation or a mainframe, and
it continues to make sense for general purpose computing devices
today, including laptops, smart phones, and tablets.
[RFC7452] discusses design patterns for, and poses questions about,
smart objects. Let us then posit a group of objects that are
specifically not general purpose computers. These devices therefore
have a purpose to their use. By definition, therefore, all other
purposes are NOT intended. The combination of these two statements
can be restated as a manufacturer usage description (MUD) that can be
applied at various points within a network. Although this memo may
seem to stress access requirements, usage intent also consists of
quality of service needs a device may have.
We use the notion of "manufacturer" loosely in this context, to
simply mean the entity or organization that will state how a device
is intended to be used. 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 integrator of
that device. The key points are that the device itself is expected
to serve a limited purpose, and that there may exist an organization
in the supply chain of that device that will take responsibility for
informing the network about that purpose.
The converse statement holds that general computing systems will
benefit very little from MUD, as their manufacturers cannot envision
a specific communication pattern to describe.
The intent of MUD is to therefore solve for the following problems:
o Substantially reduce the threat surface on a device entering a
network to those communications intended by the manufacturer.
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o Provide for a means to scale network policies to the ever-
increasing number types of devices in the network.
o Provide a means to address at least some vulnerabilities in a way
that is faster than it might take to update systems. This will be
particularly true for systems that are no longer supported by
their manufacturer.
o Keep the cost of implementation of such a system to the bare
minimum.
No matter how good a MUD-enabled network is, it will never replace
the need for manufacturers to patch vulnerabilities. It may,
however, provide network administrators with some additional
protection when those vulnerabilities exist.
1.1. A Simple Example
A light bulb is intended to light a room. It may be remotely
controlled through the network; and it may make use of a rendezvous
service of some form that an app on smart phone accesses. 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 Facebook friends. Therefore, an access list applied to it
that states that it will only connect to the single rendezvous
service will not impede the light bulb in performing its function,
while at the same time allowing the network to provide both it and
other devices an additional layer of protection.
1.2. Determining Intended Use
The notion of intended use is in itself not new. Network
administrators apply access lists every day to allow for only such
use. This notion of white listing was well described by Chapman and
Zwicky in [FW95]. Programmatically profiling systems have existed
for years as well. These systems make use of heuristics that take at
least some time to assert what a system is.
A system could just as easily tell the network what sort of
protection it requires without going into what sort of system it is.
This would, in effect, be the converse of [RFC7488]. In seeking a
general purpose solution, however, we assume that a device has so few
capabilities that it will implement the least necessary capabilities
to function properly. This is a basic economic constraint. Unless
the network would refuse access to such a device, its developers
would have no reason to implement such an approach. To date, such an
assertion has held true.
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1.3. Finding A Policy: The MUD URL
Our work begins, therefore, with the device emitting a Universal
Resource Locator (URL) [RFC3986]. This URL may serves both to
classify the device type and to provide a means to locate a policy
file.
In this memo three means are defined to emit the MUD URL. One is a
DHCP option[RFC2131],[RFC3315] that the DHCP client uses to inform
the DHCP server. The DHCP server may take further actions, such as
retrieve the URL or otherwise pass it along to network management
system or controller. The other method defined is an X.509
constraint. The IEEE has developed [IEEE8021AR] that provides a
certificate-based approach to communicate device characteristics,
which itself relies on [RFC5280]. The MUD URL extension is non-
critical, as required by IEEE 802.1AR. Finally, an LLDP frame is
defined.
1.4. Types of Policies
When the MUD URL is resolved, the MUD controller retrieves a file
that describes what sort of communications a device is designed to
have. The manufacturer may specify either specific hosts for cloud
based services or certain classes for access within an operational
network. An example of a class might be "devices of a specified
manufacturer type", where the manufacturer type itself is indicated
simply by the authority of the MUD URL. Another example might to
allow or disallow local access. Just like other policies, these may
be combined. For example:
Allow access to host controller.example.com with QoS AF11
Allow access to devices of the same manufacturer
Allow access to and from controllers who need to speak COAP
Allow access to local DNS/DHCP
Deny all other access
To add a bit more depth that should not be a stretch of anyone's
imagination, one could also make use of port-based access lists.
Thus 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.
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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 [RFC6020] because of the time and effort spent to
develop accurate and adequate models for use by network devices.
JSON is used as a serialization for compactness and readability,
relative to XML.
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 second 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.
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 therefore, mature. Therefore, only a a
limited subset YANG-based configuration of is permitted in a MUD
file.
1.5. Terminology
MUD: manufacturer usage description.
MUD file: a file containing YANG-based JSON that describes a
recommended behavior.
MUD file server: a web server that hosts a MUD file.
MUD controller: the system that requests and receives the MUD file
from the MUD server. After it has processed a MUD file it may
direct changes to relevant network elements.
MUD URL: a URL that can be used by the MUD controller to receive the
MUD file.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.6. The Manufacturer Usage Description Architecture
With these components laid out we now have the basis for an
archicture. This leads us to ASCII art.
.........................................
. ____________ . _____________
. | | . | |
. | MUD |----->get URL->| MUD |
. | Controller | .(https) | File Server |
. End system network |____________|<--MUD file<--<|_____________|
. . .
. . .
. _______ _________ .
.| | (dhcp et al) | router | .
.| Thing |---->MUD URL-->| or | .
.|_______| | switch | .
. |_________| .
.........................................
Figure 1: MUD Architecture
In the above diagram, the switch or router collects MUD URLs and
forwards them to the network management system for processing. This
happens in different ways, depending on how the URI is communicated.
For instance, in the case of DHCP, the DHCP server might receive the
URI and then process it. In the case of IEEE 802.1X, the switch
would tunnel the URI to the authentication server, who would then
process it.
The information returned by the web site is valid for the duration of
the device's connection, or as specified in the description. Thus if
the device is mobile, when it moves on, any configuration in the
switch is removed. Similarly, from time to time the description may
be refreshed, based on new capabilities or communication patterns or
vulnerabilities.
The web site 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 URI, it may proxy it, the trivial cases
being a map between some registered device or port and a URL.
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2. The MUD Model and Semantic Meaning
A MUD file consists of JSON based on a YANG model. For purposes of
MUD, the elements that can be modified are access lists as augmented
by this model. The MUD file is limited to the serialization of a
small number of YANG schema, including the models specified in the
following documents:
o [I-D.ietf-netmod-acl-model]
o [RFC6991]
Publishers of MUD files MUST NOT include other elements except as
described in Section 13, and MUST only contain information relevant
to the device being described. Devices parsing MUD files MUST cease
processing if they find other elements.
This module is structured into three parts. The first container
holds information that is relevant to retrieval and validity of the
MUD file itself. The second container augments the access list to
indicate direction the ACL is to be applied. The final container
augments the matching container of the ACL model to add several
elements that are relevant to the MUD URL, or other otherwise
abstracted for use within a local environment.
module: ietf-mud
+--rw meta-information
+--rw last-update? yang:date-and-time
+--rw previous-mud-file? yang:uri
+--rw cache-validity? uint32
+--rw masa-server? inet:uri
+--rw is-supported? boolean
augment /acl:access-lists/acl:acl:
+--rw packet-direction? direction
augment /acl:access-lists/acl:acl
/acl:access-list-entries/acl:ace/acl:matches:
+--rw manufacturer? inet:host
+--rw same-manufacturer? empty
+--rw model? string
+--rw local-networks? empty
+--rw controller? inet:uri
+--rw direction-initiated? direction
3. Element Definitions
The following elements are defined.
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3.1. last-update
This is a date-and-time value of the last time the MUD file was
updated. This is akin to a version number. Its form is taken from
[RFC6991] which, for those keeping score, turn was taken from
Section 5.6 of [RFC3339], which was taken from [ISO.8601.1988].
3.2. previous-mud-file
This is a URL that should point to the previous MUD URL for auditing
purposes. Because it should not be necessary to resign a MUD file
when a new one is released, the archival location of a current MUD
file should be identified prior to its release. Note the signature
file MUST also be available. For example, if previous-mud-file is
set to "https://example.com/.mud/v1/xxx", the corresponding signature
would be found at "https://example.com/.mud/v1/xxx.p7s".
3.3. cache-validity
This uint32 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 no
more than 1440 for any device that is supported.
3.4. masa-server
This optional element refers to the URL that should be used to
resolve the location any MASA service, as specified in
[I-D.ietf-anima-bootstrapping-keyinfra].
3.5. is-supported
This boolean is an indication from the manufacturer to the network
administrator as to whether or not the device is supported. In this
context a device is said to be supported if the manufacturer might
issue an update to the device or if the manufacturer might update the
MUD file.
3.6. packet-direction
[I-D.ietf-netmod-acl-model] describes access-lists but does not
attempt to indicate where they are applied as that is handled
elsewhere in a configuration. However, in this case, a MUD file must
be explicit in describing the communcation pattern of a device, and
that includes indicating what is to be permitted or denied in either
direction of communication. This element takes a single value of
either "to-device" or "from-device", based on a typedef "direction".
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3.7. manufacturer
This element consists of a hostname that would be matched against the
authority section of another device's MUD URL.
3.8. same-manufacturer
This is an equivalent for when the manufacturer element is used to
indicate the authority that is found in another device's MUD URL
matches that of the authority found in this device's MUD URL.
3.9. model
This string matches the one and only segment following the authority
section of the MUD URL. It refers to a model that is unique within
the context of the authority. It may also include product version
information. Thus how this field is constructed is entirely a local
matter for the manufacturer.
3.10. local-networks
This null-valued element expands to include local networks. Its
default expansion is that packets must not traverse toward a default
route that is received from the router.
3.11. controller
This URI specifies a value that a controller will register with the
network management station. The element then is expanded to the set
of hosts that are so registered.
In addition, some meta information is defined in order to determine
when a usage description should be refreshed.
3.12. direction-initiated
When applied this matches packets when the flow was initiated in the
corresponding direction. [RFC6092] provides guidance for IPv6
guidance best practices. While that document is scoped specifically
to IPv6, its contents are applicable for IPv4 as well. When this
flag is set, and the system has no reason to believe a flow has been
initiated it MUST drop the packet. This match SHOULD be applied with
specific transport parameters, such as protocol.
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4. Processing of the MUD file
To keep things relatively simple in addition to whatever definitions
exist, we also apply two additional default behaviors:
o Anything not explicitly permitted is denied.
o Local DNS, DHCP, and NTP are, by default, permitted to and from
the device.
5. What does a MUD URL look like?
To begin with, MUD takes full advantage of both the https: scheme and
the use of .well-known. HTTPS is important in this case because a
man in the middle attack could otherwise harm the operation of a
class of devices. .well-known is used because we wish to add
additional structure to the URL. And so the URL appears as follows:
mud-url = "https://" authority "/.well-known/mud/" mud-rev
"/" model ( "?" extras )
; authority is from RFC3986
mud-rev = "v1"
model = segment ; from RFC3986
extras = query ; from RFC3986
mud-rev signifies the version of the manufacturer usage description
file. This memo specifies "v1" of that file. Later versions may
permit additional schemas or modify the format.
"model" represents a device model as the manufacturer wishes to
represent it. It could be a brand name or something more specific.
It also may provide a means to indicate what version the product is.
Specifically if it has been updated in the field, this is the place
where evidence of that update would appear. The field should be
changed when the intended communication patterns of a device change.
While from a controller standpoint, only comparison and matching
operations are safe, it is envisioned that updates will require some
administrative review. Processing of this URL occurs as specified in
[RFC2818] and [RFC3986].
6. The MUD YANG Model
<CODE BEGINS>file "ietf-mud@2016-07-20.yang";
module ietf-mud {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-mud";
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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
WG Chair: Warren Kumari
warren@kumari.net
WG Chair: Zhou Tianran
zhoutianran@huawei.com
Editor: Eliot Lear
lear@cisco.com
Editor: Ralph Droms
rdroms@cisco.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.
Copyright (c) 2016 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 "2016-07-20" {
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description "Base version of MUD extensions to ACL model";
reference "RFC XXXX: Manufacturer Usage Description Specification";
}
typedef direction {
type enumeration {
enum to-device {
description "packets or flows destined to the target device";
}
enum from-device {
description "packets or flows destined from
the target device";
}
}
description "Which way are we talking about?";
}
container meta-information {
description "Information about when support end(ed), and
when to refresh";
leaf last-update {
type yang:date-and-time;
description "This is intended to be the time and date that
the MUD file was generated.";
}
leaf previous-mud-file {
type inet:uri;
description "Use to find the previous MUD file location
for auditing purposes.";
}
leaf cache-validity {
type uint32;
description "The information retrieved from the MUD server is
valid for these many hours, after which it should
be refreshed.";
}
leaf masa-server {
type inet:uri;
description "The URI of the MASA server that network
elements should forward requests to for this device.";
}
leaf is-supported {
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type boolean;
description "The element is currently supported
by the manufacturer.";
}
}
augment "/acl:access-lists/acl:acl" {
description "add inbound or outbound. Normally access lists
are applied in an inbound or outbound direction
separately from their definition. This is not
possible with MUD.";
leaf packet-direction
{
type direction;
description "inbound or outbound ACL.";
}
}
augment "/acl:access-lists/acl:acl/" +
"acl:access-list-entries/acl:ace/" +
"acl:matches" {
description "adding abstractions to avoid need of IP addresses";
leaf manufacturer {
type inet:host;
description "authority component of the manufacturer URI";
}
leaf same-manufacturer {
type empty;
description "expand to ACEs for each device
with the same origin";
}
leaf model {
type string;
description "specific model (including version) for a
given manufacturer";
}
leaf local-networks {
type empty;
description "this string is used to indicate networks
considered local in a given environment.";
}
leaf controller {
type inet:uri;
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description "expands to one or more controllers for a
given service that is codified by inet:uri.";
}
leaf direction-initiated {
type direction;
description "which direction a flow was initiated";
}
}
}
<CODE ENDS>
7. The Domain Name Extension to the ACL Model
This module specifies an extension to IETF-ACL model such that domain
names may be referenced by augmenting the "matches" element.
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:
augment
/acl:access-lists/acl:acl/acl:access-list-entries
/acl:ace/acl:matches/acl:ace-type/acl:ace-ip:
+--rw src-dnsname? inet:host
+--rw dst-dnsname? inet:host
The choice of this particular point 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 following elements are defined.
7.1. source-dnsname
The argument corresponds to a domain name of a source as specified by
inet:host. Depending on how the model is used, it may or may not be
resolved, as required by the implementation and circumstances.
7.2. destination-dnsname
The argument corresponds to a domain name of a destination as
specified by inet:host. Depending on how the model is used, it may
or may not be resolved, as required by the implementation and
circumstances.
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7.3. The ietf-acldns Model
<CODE BEGINS>file "ietf-acldns@2007-07020.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
WG Chair: Warren Kumari
warren@kumari.net
WG Chair: Zhou Tianran
zhoutianran@huawei.com
Editor: Eliot Lear
lear@cisco.com
Editor: Ralph Droms
rdroms@cisco.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 "2016-07-20" {
description "Base version of dnsname extension of ACL model";
reference "RFC XXXX: Manufacturer Usage Description Specification";
}
augment "/acl:access-lists/acl:acl/" +
"acl:access-list-entries/acl:ace/" +
"acl:matches/acl:ace-type/acl:ace-ip" {
description "adding domain names to matching";
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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";
}
}
}
<CODE ENDS>
8. MUD File Example
This example contains two access lists that are intended to provide
outbound access to a cloud service on TCP port 443.
{
"ietf-mud:support-information": {
"last-update": "2016-05-18T20:00:50Z",
"cache-validity": 1440
},
"ietf-access-control-list:access-lists": {
"acl": [ {
"acl-name": "inbound-stuff",
"acl-type" : "ipv4-acl",
"ietf-mud:direction" : "to-device",
"access-list-entries": {
"ace": [
{
"rule-name": "access-cloud",
"matches": {
"ietf-acldns:src-dnsname":
"lighting-system.example.com",
"protocol" : 6,
"source-port-range" : {
"lower-port" : 443,
"upper-port" : 443
}
},
"actions" : {
"permit" : [null]
}
}
]
}
},
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{
"acl-name": "outbound-stuff",
"acl-type" : "ipv4-acl",
"ietf-mud:direction" : "from-device",
"access-list-entries": {
"ace": [
{
"rule-name": "access-cloud",
"matches": {
"ietf-acldns:dst-dnsname":
"lighting-system.example.com",
"protocol" : 6,
"destination-port-range" : {
"lower-port" : 443,
"upper-port" : 443
}
},
"actions" : {
"permit" : [null]
}
}
]
}
}
]
}
}
9. The MUD URL DHCP Option
The IPv4 MUD URL client option has the following format:
+------+-----+------------------------------
| code | len | MUD URL
+------+-----+------------------------------
Code OPTION_MUD_URL_V4 (TBD) is assigned by IANA. len is a single
octet that indicates the length of the URL in octets. MUD URL is a
URL. The length of a MUD URL does not exceed 255 bytes.
The IPv6 MUD URL client option has the following format:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MUD URL |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OPTION_MUD_URL_V6 (TBD; assigned by IANA).
option-length contains the length of the URL in octets. The length
MUST NOT exceed 255 octets.
The intent of this option is to provide both a new device 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 device to the network in a
structured way such that the policy can be easily found with existing
toolsets.
9.1. Client Behavior
A DHCP client MAY emit either a DHCPv4 or DHCPv6 option or both.
These options singletons, as specified in [RFC7227]. Because clients
are intended to have at most one MUD URL associated with them, they
may emit at most one MUD URL option via DHCPv4 and one MUD URL option
via DHCPv6. In the case where both v4 and v6 DHCP options are
emitted, the same URL MUST be used.
Clients SHOULD log or otherwise report improper acknowledgments from
servers, but they MUST NOT modify their MUD URL configuration based
on a server's response. The server's response is only an
acknowledgment that the server has processed the option, and promises
no specific network behavior to the client. In particular, it may
not be possible for the server to retrieve the file associated with
the MUD URL, or the local network administration may not wish to use
the usage description. Neither of these situations should be
considered in any way exceptional.
9.2. Server Behavior
A DHCP server may ignore these options or take action based on
receipt of these options. For purposes of debugging, if a server
successfully parses the option and the URL, it MUST return the option
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with the same URL as an acknowledgment. Even in this circumstance,
no specific network behavior is guaranteed. When a server consumes
this option, it will either forward the URL and relevant client
information to a network management system (such as the giaddr), or
it will retrieve the usage description by resolving the URL.
DHCP servers may implement MUD functionality themselves or they may
pass along appropriate information to a network management system or
controller. A DHCP server that does process the MUD URL MUST adhere
to the process specified in [RFC2818] and [RFC5280] to validate the
TLS certificate of the web server hosting the MUD file. Those
servers will retrieve the file, process it, create and install the
necessary configuration on the relevant network element. Servers
SHOULD monitor the gateway for state changes on a given interface. A
DHCP server that does not provide MUD functionality and has forwarded
a MUD URL to a network management system MUST notify the network
management of any corresponding change to the DHCP state of the
client (such as expiration or explicit release of a network address
lease).
9.3. Relay Requirements
There are no additional requirements for relays.
10. The Manufacturer Usage Description (MUD) URL X.509 Extension
[RFC7299] provides a procedure and means to specify extensions to
X.509 certificates. The MUD URL is a non-critical Certificate
extension that points to an on-line Manufacturer Usage Description
concerning the certificate subject. This extension contains a single
Uniform Resource Identifier (URI). Internationalized Resource
Identifiers must be represented as URI's in the way described in RFC
5280, section 7.4.
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.
The new extension is identified as follows:
- The MUD URL extension id-pe-mud-url OBJECT IDENTIFER ::= { id-pe
TBD }
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The extension returns a single value:
mudURLSyntax ::= IA5String - for use with MUD architecture.
The semantics of the URI are defined Section 5.
11. The Manufacturer Usage Description LLDP extension
The IEEE802.1AB Link Layer Discovery Protocol (LLDP) [IEEE8021AB] is
a one hop vendor-neutral link layer protocols used by end hosts
network devices for advertising their identity, capabilities, and
neighbors on an IEEE 802 local area network. Its Type-Length-Value
(TLV) design allows for 'vendor-specific' extensions to be defined.
IANA has a registered IEEE 802 organizationally unique identifier
(OUI) defined as documented in [RFC7042]. The MUD LLDP extension
uses a subtype defined in this document to carry the MUD URL.
The LLDP vendor specific frame has the following format:
+--------+--------+----------+---------+--------------
|TLV Type| len | OUI |subtype | MUD URL
| =127 | |= 00 00 5E| = 1 |
|(7 bits)|(9 bits)|(3 octets)|(1 octet)|(1-256 octets)
+--------+--------+----------+---------+--------------
where:
o TLV Type = 127 indicates a vendor-specific TLV
o len - indicates the TLV string length
o OUI = 00 00 5E is the organizationally unique identifier of IANA
o subtype = 1 (to be assigned by IANA for the MUD URL)
o MUD URL - the length MUST NOT exceed 256 octets (consistent with
the DHCP option defined in Section 9)
The intent of this extension is to provide both a new device
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 device to the network in
a structured way such that the policy can be easily found with
existing toolsets.
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Hosts, routers, or other network devices 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 devices 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 device and response sent by another
device. The other devices do not acknowledge LLDP information
received from a device. No specific network behavior is guaranteed.
When a device consumes this extension, it may either forward the URL
and relevant remote device information to a network management
system, or it will retrieve the usage description by resolving the
URL.
12. Creating and Processing of Signed MUD Files
Because MUD files contain information that may be used to configure
network access lists, they are sensitive. To insure that they have
not been tampered with, it is important that they be signed. We make
use of DER-encoded Cryptographic Message Syntax (CMS) [RFC5652] for
this purpose.
12.1. Creating a MUD file signature
A MUD file MUST be signed using CMS as an opaque binary object. In
order to make successful verification more likely, intermediate
certificates SHOULD be included. If the device that is being
described supports IEEE 802.1AR, its manufacturer certificate and the
certificate in the MUD file MUST share a common trust anchor in order
to insure that manufacturer of the device is also the provider of the
MUD file. The signature is stored at the same location as the MUD
URL but with the suffix of ".p7s". Signatures are transferred using
content-type "Application/pkcs7-signature".
For example:
% openssl cms -sign -signer mancertfile -inkey mankey \
-in mudfile -binary -outform DER - \
-certfile intermediatecert -out mudfile.p7s
Note: A MUD file may need to be resigned if the signature expires.
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12.2. Verifying a MUD file signature
Prior to retrieving a MUD file the MUD controller SHOULD retrieve the
MUD signature file using the MUD URL with a suffix of ".p7s". For
example, if the MUD URL is "https://example.com/.well-known/v1/
modela", the MUD signature URL will be "https://example.com/.well-
known/v1/modela.p7s".
Upon retrieving a MUD file, a MUD controller MUST validate the
signature of the file before continuing with further processing. A
MUD controller SHOULD produce an error and it MUST cease all
processing of that file if the signature cannot be validated. If the
MUD controller has received the MUD URL via IEEE 802.1AR containing
an IDevID (a manufacturer certificate), it MUST further confirm that
the manufacturer certificate and that of the MUD file share a common
trust anchor.
For Example:
% openssl cms -verify -in mudfile.p7s -inform DER -content mudfile
Note the additional step of verifying the common trust root.
13. Extensibility
One of our design goals is to see that MUD files are able to be
understood by as broad a cross-section of systems as is possible.
Coupled with the fact that we have also chosen to leverage existing
mechanisms, we are left with no ability to negotiate extensions and a
limited desire for those extensions in any event. A such, a two-tier
extensibility framework is employed, as follows:
1. At a coarse grain, a protocol version is included in a MUD URL.
This memo specifies MUD version 1. Any and all changes are
entertained when this version is bumped. Transition approaches
between versions would be a matter for discussion in future
versions.
2. At a finer grain, only extensions that would not incur additional
risk to the device are permitted. Specifically, augmenting of
the meta-information container is permitted with the
understanding that such additions may be ignored. In addition,
augmentation of the ACL model is permitted so long as it remains
safe for a given ACE to be ignored by the MUD Controller or the
network elements it configures. Most specifically, is is not
permitted to include as an augmentation that modifies "deny"
behavior without bumping the version. Furthermore,
implementations that are not able to parse a component of the ACE
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array MUST ignore the entire array entry (e.g., not the entire
array) and MAY ignore the entire MUD file.
14. Security Considerations
Based on the means a URL is procured, a device may be able to lie
about what it is, thus gaining additional network access. There are
several means to limit risk in this case. The most obvious is to
only believe devices that make use of certificate-based
authentication such as IEEE 802.1AR certificates. When those
certificates are not present, devices claiming to be of a certain
manufacturer SHOULD NOT be included in that manufacturer grouping
without additional validation of some form. This will occur when it
makes use of primitives such as "manufacturer" for the purpose of
accessing devices of a particular type.
Network management systems SHOULD NOT deploy a usage description for
a device with the same MAC address that has indicated a change of
authority without some additional validation (such as review of the
class). New devices that present some form of unauthenticated MUD
URL SHOULD be validated by some external means when they would be
otherwise be given increased network access.
It may be possible for a rogue manufacturer to inappropriately
exercise the MUD file parser, in order to exploit a vulnerability.
There are three recommended approaches to address this threat. The
first is to validate the signature of the MUD file. The second is to
have a system do a primary scan of the file to ensure that it is both
parseable and believable at some level. MUD files will likely be
relatively small, to start with. The number of ACEs used by any
given device should be relatively small as well. Second, it may be
useful to limit retrieval of MUD URLs to only those sites that are
known to have decent web reputations.
Use of a URL necessitates the use of domain names. If a domain name
changes ownership, the new owner of that domain may be able to
provide MUD files that MUD controllers would consider valid. There
are a few approaches that can mitigate this attack. First, MUD file
servers SHOULD cache certificates used by the MUD file server. When
a new certificate is retrieved for whatever reason, the MUD
controller should check to see if ownership of the domain has
changed. A fair programmatic approximation of this is when the name
servers for the domain have changed. If the actual MUD file has
changed, the controller MAY check the WHOIS database to see if
registration ownership of a domain has changed. If a change has
occured, or if for some reason it is not possible to determine
whether ownership has changed, further review may be warranted.
Note, this remediation does not take into account the case of a
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device that was produced long ago and only recently fielded, or the
case where a new MUD controller has been installed.
15. IANA Considerations
15.1. DHCPv4 and DHCPv6 Options
IANA is requested to allocated the DHCPv4 and v6 options as specified
in Section 9.
15.2. PKIX Extensions
The IANA is requested to assign a value for id-pe-mud-uri in the "SMI
Security for PKIX Certificate Extension" Registry. Its use is
specified in Section 10.
15.3. Well Known URI Suffix
The IANA is requested to register the URL suffix of "mud" as follows:
o URI Suffix: "mud" o Specification documents: this document o
Related information: n/a
15.4. MIME Media-type Registration for MUD files
The following media-type is defined for transfer of MUD file:
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o Type name: application
o Subtype name: mud+json
o Required parameters: n/a
o Optional parameters: n/a
o Encoding considerations: 8bit; application/mud+json values
are represented as a JSON object; UTF-8 encoding SHOULD be
employed.
o Security considerations: See {{secon}} of this document.
o Interoperability considerations: n/a
o Published specification: this document
o Applications that use this media type: MUD controllers as
specified by this document.
o Fragment identifier considerations: n/a
o Additional information:
Magic number(s): n/a
File extension(s): n/a
Macintosh file type code(s): n/a
o Person & email address to contact for further information:
Eliot Lear <lear@cisco.com>, Ralph Droms <rdroms@cisco.com>
o Intended usage: COMMON
o Restrictions on usage: none
o Author: Eliot Lear <lear@cisco.com>, Ralph Droms <rdroms@cisco.com>
o Change controller: IESG
o Provisional registration? (standards tree only): No.
15.5. LLDP IANA TLV Subtype Registry
IANA is requested to create a new registry for IANA Link Layer
Discovery Protocol (LLDP) TLV subtype values. The recommended policy
for this registry is Expert Review. The maximum number of entries in
the registry is 256.
IANA is required to populate the initial registry with the value:
LLDP subtype value = 1
Description = the Manufacturer Usage Description (MUD) Uniform
Resource Locator (URL)
Reference = < this document >
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16. Acknowledgments
The authors would like to thank Einar Nilsen-Nygaard, Bernie Volz,
Tom Gindin, Brian Weis, Sandeep Kumar, Thorsten Dahm, John Bashinski,
Steve Rich, Jim Bieda, and Dan Wing for their valuable advice and
reviews. The remaining errors in this work are entirely the
responsibility of the author.
17. References
17.1. Normative References
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., and S.
Bjarnason, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-03 (work in progress), June 2016.
[I-D.ietf-netmod-acl-model]
Bogdanovic, D., Koushik, K., Huang, L., and D. Blair,
"Network Access Control List (ACL) YANG Data Model",
draft-ietf-netmod-acl-model-08 (work in progress), July
2016.
[IEEE8021AB]
Institute for Electrical and Electronics Engineers, "IEEE
Standard for Local and Metropolitan Area Networks--
Station and Media Access Control Connectivity Discovery",
n.d..
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
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[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://www.rfc-editor.org/info/rfc5652>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
DOI 10.17487/RFC6092, January 2011,
<http://www.rfc-editor.org/info/rfc6092>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<http://www.rfc-editor.org/info/rfc6991>.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
<http://www.rfc-editor.org/info/rfc7227>.
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<http://www.rfc-editor.org/info/rfc7299>.
17.2. Informative References
[FW95] Chapman, D. and E. Zwicky, "Building Internet Firewalls",
January 1995.
[IEEE8021AR]
Institute for Electrical and Electronics Engineers,
"Secure Device Identity", 1998.
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[ISO.8601.1988]
International Organization for Standardization, "Data
elements and interchange formats - Information interchange
- Representation of dates and times", ISO Standard 8601,
June 1988.
[RFC1984] IAB and IESG, "IAB and IESG Statement on Cryptographic
Technology and the Internet", BCP 200, RFC 1984,
DOI 10.17487/RFC1984, August 1996,
<http://www.rfc-editor.org/info/rfc1984>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<http://www.rfc-editor.org/info/rfc3339>.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <http://www.rfc-editor.org/info/rfc7042>.
[RFC7452] Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson,
"Architectural Considerations in Smart Object Networking",
RFC 7452, DOI 10.17487/RFC7452, March 2015,
<http://www.rfc-editor.org/info/rfc7452>.
[RFC7488] Boucadair, M., Penno, R., Wing, D., Patil, P., and T.
Reddy, "Port Control Protocol (PCP) Server Selection",
RFC 7488, DOI 10.17487/RFC7488, March 2015,
<http://www.rfc-editor.org/info/rfc7488>.
Appendix A. Changes from Earlier Versions
RFC Editor to remove this section prior to publication.
Draft -03 to -04: * add LLDP extension. * add Dan Romascanu as co-
author.
Draft -02 to -03: * incorporate domain name model. * discuss
extensibility. * leave placeholder for LLDP TLV.
Draft -01 to -02:
o XML->JSON
o Remove device versioning information from URL
o Add PKIX and DHCP options
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o Add Content-type information
o Clean up IANA considerations to match registration templates
o Ralph Droms carried over as author from DHCP option.
o Signing information
o Expanded Security Considerations
o Add directionality for both packets and flows.
o add previous-mud-file
Draft -00 to -01:
o Add MASA server element
Authors' Addresses
Eliot Lear
Cisco Systems
Richtistrasse 7
Wallisellen CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
Ralph Droms
Cisco Systems
55 Cambridge Parkway
Cambridge 1057
United States
Phone: +1 617 621 1904
Email: rdroms@cisco.com
Dan Romascanu
Avaya
26, HaRokhmim Str., Bldg. D
Holon 5885849
Israel
Phone: +972-3-645-8414
Email: dromasca@avaya.com
Lear, et al. Expires February 20, 2017 [Page 30]