Interconnecting Limited Domains Based on Declared Communication Requirements
draft-bormann-t2trg-interconnect-declared-01
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| Author | Carsten Bormann | ||
| Last updated | 2022-01-11 | ||
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draft-bormann-t2trg-interconnect-declared-01
Network Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Informational 11 January 2022
Expires: 15 July 2022
Interconnecting Limited Domains Based on Declared Communication
Requirements
draft-bormann-t2trg-interconnect-declared-01
Abstract
"Limited Domains" are parts of an internet that may have notable
differences or are just convenient to separate from the general
Internet and can be delimited from that and from other Limited
Domains by a defined boundary (the "border").
This memo focuses on the case where the nodes inside the Limited
Domain want to interact with nodes on (or reachable via) the general
Internet, but need some assistance at the border that is cognizant
about the specific properties of the nodes in the Limited Domain.
Self-Descriptions can provide the information needed for this
assistance.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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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 15 July 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Desirable Communication . . . . . . . . . . . . . . . . . . . 5
2.1. Example: Addressing Desirable Peers Only . . . . . . . . 5
3. Self-Descriptions . . . . . . . . . . . . . . . . . . . . . . 6
4. Directions of Work . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Informative References . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[RFC8799] introduces the concept of "Limited Domains", i.e., parts of
an internet that may have notable differences or are just convenient
to separate from the general Internet and can be delimited from that
and from other Limited Domains by a defined boundary (the "border").
Limited Domains are not a new concept, but they recently have gained
significant attention as a way to accelerate innovation without
always having to wait for the whole Internet to accept a new feature
[USEFUL].
Some Limited Domains can be directly connected to or interconnected
via the Internet -- rules they use internally simply lose their force
outside the Limited Domain. Some require stripping off some
structures or translating some fields on the border to the Internet.
Some can only be interconnected by running tunnels on top of the
Internet.
This memo focuses on the case where the nodes inside the Limited
Domain want to interact with nodes on (or reachable via) the general
Internet, but need some assistance at the border that is cognizant
about the specific properties of the nodes in the Limited Domain.
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6LoWPAN header compression [RFC6282] actually is such an example,
which can be considered a very small Limited Domain -- initially just
the link and adaptation layer between two LoWPAN nodes, which
themselves otherwise feel like standard Internet nodes. (6LoWPAN
neighbor discovery [RFC6775] already extends the Limited Domain out
to the border router (6LBR), but let's focus on header compression
itself for now.) Extending the Limited Domain to more than two nodes
may allow the nodes inside the Limited Domain to make use of the
knowledge that all of them share some common procedures, such as
using the [RFC8138] routing header (6LoRH); it is then the job of the
border router (6LBR) to decapsulate this form into packets that can
be used in the global Internet and to appropriately encapsulate
global Internet packets on the way in. (Virtual Reassembly Buffers
(VRBs, [RFC8930]) simulate a subnet-size Limited Domain based on
[RFC6282]'s hop-by-hop ones.)
This memo uses examples from the area of the Internet of Things
(IoT), both because the author is most familiar with it and because a
concept of self-descriptions has already been developed for this
area, which provide new opportunities for organizing Limited Domains
(Section 3). (To do: add more examples from outside the IoT core.)
1.1. Terminology
Limited Domain: An area in a network that is separate from others by
notable internal differences and/or by a strong administrative
demarcation. Examples are found in Section 4 of [RFC8799],
however this document is not limiting itself to those or to the
definition in [RFC8799]. In contrast to some other usage, the
nodes in a Limited Domain are expected to normally form a
connected graph, possibly by employing tunnels between them.
However, not all nodes in a Limited Domain always need to be aware
of their situation or implement all the internal differences.
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.---------------------. .------------.
| | | |
| .-+-+-. Limited |
| | B | Domain |
| '-+-+-' LD2 |
| | | |
| | '------------'
| Limited Domain |
| LD1 | .---------. .------------.
| | / \ | |
| .-+--./ \.--+-. Limited |
| .---. | B + Internet + B | Domain |
| | Z | '-+--'\ /'--+-' LD3 |
| '---' | \ / | |
| | '-+-----+-' '------------'
'---------------------' | |
.-+-. .+-..---.
| X | | B ++ Y |
'---' '--''---'
Figure 1: Illustration for terms
Figure 1 illustrates the following additional terms:
Border: qualifier for network elements (B) (as in "border router"
etc.) that are situated on the boundary between a Limited Domain
and a different one and/or the general Internet.
Internally interoperable Limited Domains: Limited Domains that can
accommodate nodes that can operate as if they were in the Internet
(Z).
Globally interoperable Limited Domains: Limited Domains that can
interoperate with nodes in the global Internet (X).
Externally interoperable Limited Domains: Limited Domains that can
interoperate via the Internet (LD1), but possibly limited to
interoperation with other Limited Domains (LD3) or with specially
equipped Internet nodes (Limited Domains of size 1, Y logically
containing a B).
Internet, Global Internet, General Internet: (TBD, clarify usage
here)
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2. Desirable Communication
All the examples so far presume an environment where it is desirable
that any node can communicate with any other node. This has
certainly served well as a guiding principle for quickly improving
the value of a network: Leaving open the potential to communicate
maximizes the potential network effect [METCALFE]. However,
firewalls are then widely used to suppress some of these potential
communication paths [FIREWALL]. MUD [RFC8520] was designed to aid
routers and switches in setting up limited connectivity to this end.
In the MUD architecture, we first build a system that fundamentally
supports unlimited connectivity from everyone to everyone and then
restrict it based on self-descriptions of the nodes. An alternative
approach would be an architecture that does not provide any
connectivity unless and until that is authorized by declared
communication requirements that have in turn been authorized by some
management entity.
2.1. Example: Addressing Desirable Peers Only
There may be other reasons for pursuing an architecture that limits
itself to desirable communication only. A trivial, but maybe not
overly useful example would be to number all the addresses of
correspondent hosts allowed by the self-descriptions and replace the
IP addresses in the packets by these numbers.
If this limitation becomes part of the architecture, protocols used
inside the Limited Domains could completely get rid of IP addresses
and use just the correspondent numbers (possibly packaged in
something that looks like an IP address, but is limited in its
variability to just encapsulating that number).
The border router would become a NAT, but one that is acting based on
extensive, precomputable information about the communication
requirements inside the Limited Domain, instead of learning and
potentially losing dynamic state that becomes a single point of
failure.
Again, this is a trivial example, but it should be sufficient as a
motivation for having a look at employing knowledge about the nodes
and their communication requirements in a Limited Domain for
interconnecting this with the Internet (and thus possibly to like-
minded (Limited Domains on the other side of an Internet path).
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3. Self-Descriptions
Note that not all of the information that may be needed as a
description of Limited Domain nodes can come from MUD-like class
definitions. Limited Domain nodes are instantiations of these
classes, where the instantiations will differ between each other in
details. Different Limited Domain nodes may also be assigned a
different purpose in life, causing a need to further parameterize the
self-description.
Alongside a discussion of an interconnection architecture that can
make use of self-descriptions would therefore need to be a discussion
on how to structure self-description classes with this purpose in
mind and how to parameterize these and derive description instances.
For the Internet of Things (IoT), additional self-description
techniques have been defined that can provide information for Limited
Domain network elements. A fully instance-oriented description of an
IoT device is provided by a W3C WoT (Web of Things) Thing Description
[TD]. W3C WoT is presently in the process of adding a class-based
description technique to TDs, the Thing Model (previously called
Thing Description Template, TDT) [TD-WD]. The communication patterns
offered by the device are detailed in _Protocol Bindings_, which can
contain URIs combined with protocol-specific vocabulary ([TD-PB],
currently defined for HTTP, CoAP, MQTT). An experimental extension
to TDs that enables deriving the configuration of Time-Sensitive
Networking (TSN) networks from the self-description is described in
[TD-OPC-UA].
An IoT-oriented description technique that, unlike TD, is class-based
from the outset is the Semantic Definition Format (SDF) for Data and
Interactions of Things [I-D.ietf-asdf-sdf]. A concept similar to WoT
Protocol Bindings is not defined yet, but a combination of MUD and
SDF descriptions could provide a basic description of a device
situated in a Limited Domain.
The Constrained RESTful Environments (CoRE) architecture also
provides instance-oriented self-descriptions in the form of the CoRE
Link Format [RFC6690], an instance of which is provided by each CoAP
server under /.well-known/core. Link-format information, as well as
self-describing information in the newer CoRAL format
[I-D.ietf-core-coral], can be stored in the CoRE Resource Directory
[I-D.ietf-core-resource-directory].
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All these potential sources of (self-)description only provide meager
information about purpose-in-life, i.e., beyond the intrinsic
properties of the device. Obtaining a full description of the
communication requirements of a node (including its desirable
correspondence nodes) will therefore require additional input, beyond
the class-based self-descriptions of the devices.
4. Directions of Work
The above discussion leads us to the following interrelated areas for
further exploration:
1. Extending the self-description mechanisms to provide more
information that may be useful in a Limited Domain.
2. Merging the self-description information with other
configuration/management information (such as purpose-in-life)
that may be available for the Limited Domain.
3. Defining Limited Domain architectures that can benefit from
information made available by (1) and (2), including defining the
operation of network elements and nodes inside the Limited
Domain.
4. Defining border network element functionality that makes such a
Limited Domain a Globally Interoperable Limited Domain.
5. Defining border network element functionality that makes such a
Limited Domain an Externally Interoperable Limited Domain.
6. Discovery between Limited Domains, between Limited Domain nodes
(Rendezvous problem); establishment of communications (cf.
[RFC8445]).
7. Defining appropriate security workflows and the supporting
security mechanisms for items 1 to 6.
8. Addressing operational considerations for items 1 to 7.
9. Addressing privacy considerations for items 1 to 8.
5. IANA Considerations
This document contains no requests to IANA.
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6. Security Considerations
The security considerations of [RFC8799] apply.
Item 7 of Section 4 raises the need for security work, one example of
which might be:
Self-descriptions of nodes in many cases need to undergo an
authorization process before they can be used as the basis of network
configuration. The authorization process sketched by [RFC8520] may
be too simplistic, in particular the simplified number of
stakeholders assumed. The present document is not providing answers
in this space, but needs to raise the issue.
7. Informative References
[FIREWALL] Bellovin, S. and W. Cheswick, "Network firewalls", IEEE
Communications Magazine Vol. 32, pp. 50-57,
DOI 10.1109/35.312843, September 1994,
<https://doi.org/10.1109/35.312843>.
[I-D.ietf-asdf-sdf]
Koster, M. and C. Bormann, "Semantic Definition Format
(SDF) for Data and Interactions of Things", Work in
Progress, Internet-Draft, draft-ietf-asdf-sdf-09, 6
November 2021, <https://www.ietf.org/archive/id/draft-
ietf-asdf-sdf-09.txt>.
[I-D.ietf-core-coral]
Amsüss, C. and T. Fossati, "The Constrained RESTful
Application Language (CoRAL)", Work in Progress, Internet-
Draft, draft-ietf-core-coral-04, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-core-coral-
04.txt>.
[I-D.ietf-core-resource-directory]
Amsüss, C., Shelby, Z., Koster, M., Bormann, C., and P. V.
D. Stok, "CoRE Resource Directory", Work in Progress,
Internet-Draft, draft-ietf-core-resource-directory-28, 7
March 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-resource-directory-28.txt>.
[METCALFE] Metcalfe, B., "Metcalfe's Law after 40 Years of Ethernet",
Computer Vol. 46, pp. 26-31, DOI 10.1109/mc.2013.374,
December 2013, <https://doi.org/10.1109/mc.2013.374>.
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[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", RFC 8520,
DOI 10.17487/RFC8520, March 2019,
<https://www.rfc-editor.org/info/rfc8520>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[RFC8930] Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On
Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6
Network", RFC 8930, DOI 10.17487/RFC8930, November 2020,
<https://www.rfc-editor.org/info/rfc8930>.
[TD] "Web of Things (WoT) Thing Description", (Link errors
corrected 23 June 2020), W3C Recommendation, April 2020,
<https://www.w3.org/TR/wot-thing-description/>.
[TD-OPC-UA]
Sciullo, L., Bhattacharjee, S., and M. Kovatsch, "Bringing
deterministic industrial networking to the W3C web of
things with TSN and OPC UA", Proceedings of the 10th
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International Conference on the Internet of Things,
DOI 10.1145/3410992.3410997, October 2020,
<https://doi.org/10.1145/3410992.3410997>.
[TD-PB] "Web of Things (WoT) Binding Templates", W3C Working Group
Note, January 2020,
<https://www.w3.org/TR/wot-binding-templates/>.
[TD-WD] "Web of Things (WoT) Thing Description 1.1", W3C Editor's
Draft, May 2021,
<https://w3c.github.io/wot-thing-description/>.
[USEFUL] Carpenter, B., Crowcroft, J., and D. Trossen, "Limited
domains considered useful", ACM SIGCOMM Computer
Communication Review Vol. 51, pp. 22-28,
DOI 10.1145/3477482.3477487, July 2021,
<https://doi.org/10.1145/3477482.3477487>.
Acknowledgments
Adrian Farrel provided substantive comments as well as the basis for
Figure 1.
Author's Address
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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