Independent Submission B. Carpenter
Request for Comments: 8799
Univ. of Auckland
Category: Informational B. Liu
ISSN: 2070-1721 Huawei Technologies
Limited Domains and Internet Protocols
There is a noticeable trend towards network behaviors and semantics
that are specific to a particular set of requirements applied within
a limited region of the Internet. Policies, default parameters, the
options supported, the style of network management, and security
requirements may vary between such limited regions. This document
reviews examples of such limited domains (also known as controlled
environments), notes emerging solutions, and includes a related
taxonomy. It then briefly discusses the standardization of protocols
for limited domains. Finally, it shows the need for a precise
definition of "limited domain membership" and for mechanisms to allow
nodes to join a domain securely and to find other members, including
This document is the product of the research of the authors. It has
been produced through discussions and consultation within the IETF
but is not the product of IETF consensus.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see Section 2 of RFC 7841
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8799
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) in effect on the date of
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Table of Contents 1.
Failure Modes in Today's Internet 3.
Examples of Limited Domain Requirements 4.
Examples of Limited Domain Solutions 5.
The Scope of Protocols in Limited Domains 6.
Functional Requirements of Limited Domains 7.
Security Considerations 8.
IANA Considerations 9.
Informative References Appendix A
. Taxonomy of Limited Domains A.1.
Domain as a Whole A.2.
Individual Nodes A.3.
Domain Boundary A.4.
Connection to the Internet A.7.
Security, Trust, and Privacy Model A.8.
Making Use of This Taxonomy
As the Internet continues to grow and diversify, with a realistic
prospect of tens of billions of nodes being connected directly and
indirectly, there is a noticeable trend towards network-specific and
local requirements, behaviors, and semantics. The word "local"
should be understood in a special sense, however. In some cases, it
may refer to geographical and physical locality -- all the nodes in a
single building, on a single campus, or in a given vehicle. In other
cases, it may refer to a defined set of users or nodes distributed
over a much wider area, but drawn together by a single virtual
network over the Internet, or a single physical network running in
parallel with the Internet. We expand on these possibilities below.
To capture the topic, this document refers to such networks as
"limited domains". Of course, a similar situation may arise for a
network that is completely disconnected from the Internet, but that
is not our direct concern here. However, it should not be forgotten
that interoperability is needed even within a disconnected network.
Some people have concerns about splintering of the Internet along
political or linguistic boundaries by mechanisms that block the free
flow of information. That is not the topic of this document, which
does not discuss filtering mechanisms (see [RFC7754
]) and does not
apply to protocols that are designed for use across the whole
Internet. It is only concerned with domains that have specific
The word "domain" in this document does not refer to naming domains
in the DNS, although in some cases, a limited domain might
incidentally be congruent with a DNS domain. In particular, with a
"split horizon" DNS configuration [RFC6950
], the split might be at
the edge of a limited domain. A recent proposal for defining
definite perimeters within the DNS namespace [DNS-PERIMETER] might
also be considered to be a limited domain mechanism.
Another term that has been used in some contexts is "controlled
environment". For example, [RFC8085
] uses this to delimit the
operational scope within which a particular tunnel encapsulation
might be used. A specific example is GRE-in-UDP encapsulation
], which explicitly states that "The controlled environment
has less restrictive requirements than the general Internet." For
example, non-congestion-controlled traffic might be acceptable within
the controlled environment. The same phrase has been used to delimit
the useful scope of quality-of-service protocols [RFC6398
]. It is
not necessarily the case that protocols will fail to operate outside
the controlled environment, but rather that they might not operate
optimally. In this document, we assume that "limited domain" and
"controlled environment" mean the same thing in practice. The term
"managed network" has been used in a similar way, e.g., [RFC6947
In the context of secure multicast, a "group domain of
interpretation" is defined by [RFC6407
Yet more definitions of types of domains are to be found in the
routing area, such as [RFC4397
], and [RFC4655
conclude that the notion of a limited domain is very widespread in
many aspects of Internet technology.
The requirements of limited domains will depend on the deployment
scenario. Policies, default parameters, and the options supported
may vary. Also, the style of network management may vary between a
completely unmanaged network, one with fully autonomic management,
one with traditional central management, and mixtures of the above.
Finally, the requirements and solutions for security and privacy may
This document analyzes and discusses some of the consequences of this
trend and how it may impact the idea of universal interoperability in
the Internet. First, we list examples of limited domain scenarios
and of technical solutions for limited domains, with the main focus
being the Internet layer of the protocol stack. An appendix provides
a taxonomy of the features to be found in limited domains. With this
background, we discuss the resulting challenge to the idea that all
Internet standards must be universal in scope and applicability. To
the contrary, we assert that some protocols, although needing to be
standardized and interoperable, also need to be specifically limited
in their applicability. This implies that the concepts of a limited
domain, and of its membership, need to be formalized and supported by
secure mechanisms. While this document does not propose a design for
such mechanisms, it does outline some functional requirements.
This document is the product of the research of the authors. It has
been produced through discussions and consultation within the IETF
but is not the product of IETF consensus.
2. Failure Modes in Today's Internet
Today, the Internet does not have a well-defined concept of limited
domains. One result of this is that certain protocols and features
fail on certain paths. Earlier analyses of this topic have focused
either on the loss of transparency of the Internet [RFC2775
] or on the middleboxes responsible for that loss [RFC3234
]. Unfortunately, the problems persist both in
application protocols and even in very fundamental mechanisms. For
example, the Internet is not transparent to IPv6 extension headers
], and Path MTU Discovery has been unreliable for many years
]. IP fragmentation is also unreliable
[FRAG-FRAGILE], and problems in TCP MSS negotiation have been
On the security side, the widespread insertion of firewalls at domain
boundaries that are perceived by humans but unknown to protocols
results in arbitrary failure modes as far as the application layer is
concerned. There are operational recommendations and practices that
effectively guarantee arbitrary failures in realistic scenarios
Domain boundaries that are defined administratively (e.g., by address
filtering rules in routers) are prone to leakage caused by human
error, especially if the limited domain traffic appears otherwise
normal to the boundary routers. In this case, the network operator
needs to take active steps to protect the boundary. This form of
leakage is much less likely if nodes must be explicitly configured to
handle a given limited-domain protocol, for example, by installing a
specific protocol handler.
Investigations of the unreliability of IP fragmentation
[FRAG-FRAGILE] and the filtering of IPv6 extension headers [RFC7872
strongly suggest that at least for some protocol elements,
transparency is a lost cause and middleboxes are here to stay. In
the following two sections, we show that some application
environments require protocol features that cannot, or should not,
cross the whole Internet.
3. Examples of Limited Domain Requirements
This section describes various examples where limited domain
requirements can easily be identified, either based on an application
scenario or on a technical imperative. It is, of course, not a
complete list, and it is presented in an arbitrary order, loosely
from smaller to bigger. 1.
A home network. It will be mainly unmanaged, constructed by a
non-specialist. It must work with devices "out of the box" as
shipped by their manufacturers and must create adequate security
by default. Remote access may be required. The requirements
and applicable principles are summarized in [RFC7368
A small office network. This is sometimes very similar to a
home network, if whoever is in charge has little or no
specialist knowledge, but may have differing security and
privacy requirements. In other cases, it may be professionally
constructed using recommended products and configurations but
operate unmanaged. Remote access may be required. 3.
A vehicle network. This will be designed by the vehicle
manufacturer but may include devices added by the vehicle's
owner or operator. Parts of the network will have demanding
performance and reliability requirements with implications for
human safety. Remote access may be required to certain
functions but absolutely forbidden for others. Communication
with other vehicles, roadside infrastructure, and external data
sources will be required. See [IPWAVE-NETWORKING] for a survey
of use cases. 4.
Supervisory Control And Data Acquisition (SCADA) networks and
other hard real-time networks. These will exhibit specific
technical requirements, including tough real-time performance
targets. See, for example, [RFC8578
] for numerous use cases.
An example is a building services network. This will be
designed specifically for a particular building but using
standard components. Additional devices may need to be added at
any time. Parts of the network may have demanding reliability
requirements with implications for human safety. Remote access
may be required to certain functions but absolutely forbidden
for others. An extreme example is a network used for virtual
reality or augmented reality applications where the latency
requirements are very stringent. 5.
Sensor networks. The two preceding cases will all include
sensors, but some networks may be specifically limited to
sensors and the collection and processing of sensor data. They
may be in remote or technically challenging locations and
installed by non-specialists. 6.
Internet-of-Things (IoT) networks. While this term is very
flexible and covers many innovative types of networks, including
ad hoc networks that are formed spontaneously and some
applications of 5G technology, it seems reasonable to expect
that IoT edge networks will have special requirements and
protocols that are useful only within a specific domain, and
that these protocols cannot, and for security reasons should
not, run over the Internet as a whole. 7.
Constrained Networks. An important subclass of IoT networks
consists of constrained networks [RFC7228
] in which the nodes
are limited in power consumption and communications bandwidth
and are therefore limited to using very frugal protocols. 8.
Delay-tolerant networks. These may consist of domains that are
relatively isolated and constrained in power (e.g., deep space
networks) and are connected only intermittently to the outside,
with a very long latency on such connections [RFC4838
Clearly, the protocol requirements and possibilities are very
specialized in such networks. 9.
"Traditional" enterprise and campus networks, which may be
spread over many kilometers and over multiple separate sites,
with multiple connections to the Internet. Interestingly, the
IETF appears never to have analyzed this long-established class
of networks in a general way, except in connection with IPv6
deployment (e.g., [RFC7381
10. Unsuitable standards. A situation that can arise in an
enterprise network is that the Internet-wide solution for a
particular requirement may either fail locally or be much more
complicated than is necessary. An example is that the
complexity induced by a mechanism such as Interactive
Connectivity Establishment (ICE) [RFC8445
] is not justified
within such a network. Furthermore, ICE cannot be used in some
cases because candidate addresses are not known before a call is
established, so a different local solution is essential
11. Managed wide-area networks run by service providers for
enterprise services such as Layer 2 (Ethernet, etc.) point-to-
point pseudowires, multipoint Layer 2 Ethernet VPNs using
Virtual Private LAN Service (VPLS) or Ethernet VPN (EVPN), and
Layer 3 IP VPNs. These are generally characterized by service-
level agreements for availability, packet loss, and possibly
multicast service. These are different from the previous case
in that they mostly run over MPLS infrastructures, and the
requirements for these services are well defined by the IETF.
12. Data centers and hosting centers, or distributed services acting
as such centers. These will have high performance, security,
and privacy requirements and will typically include large
numbers of independent "tenant" networks overlaid on shared
13. Content Delivery Networks (CDNs), comprising distributed data
centers and the paths between them, spanning thousands of
kilometers, with numerous connections to the Internet.
14. Massive Web Service Provider Networks. This is a small class of
networks with well-known trademarked names, combining aspects of
distributed enterprise networks, data centers, and CDNs. They
have their own international networks bypassing the generic
carriers. Like CDNs, they have numerous connections to the
Internet, typically offering a tailored service in each economy.
Three other aspects, while not tied to specific network types, also
strongly depend on the concept of limited domains: 1.
Many of the above types of networks may be extended throughout
the Internet by a variety of virtual private network (VPN)
techniques. Therefore, we argue that limited domains may overlap
each other in an arbitrary fashion by use of virtualization
techniques. As noted above in the discussion of controlled
environments, specific tunneling and encapsulation techniques may
be tailored for use within a given domain. 2.
Intent-Based Networking. In this concept, a network domain is
configured and managed in accordance with an abstract policy
known as "Intent" to ensure that the network performs as required
[IBN-CONCEPTS]. Whatever technologies are used to support this
will be applied within the domain boundary, even if the services
supported in the domain are globally accessible. 3.
Network Slicing. A network slice is a form of virtual network
that consists of a managed set of resources carved off from a
larger network [ENHANCED-VPN]. This is expected to be
significant in 5G deployments [USER-PLANE-PROTOCOL]. Whatever
technologies are used to support slicing will require a clear
definition of the boundary of a given slice within a larger
While it is clearly desirable to use common solutions, and therefore
common standards, wherever possible, it is increasingly difficult to
do so while satisfying the widely varying requirements outlined
above. However, there is a tendency when new protocols and protocol
extensions are proposed to always ask the question "How will this
work across the open Internet?" This document suggests that this is
not always the best question. There are protocols and extensions
that are not intended to work across the open Internet. On the
contrary, their requirements and semantics are specifically limited
(in the sense defined above).
A common argument is that if a protocol is intended for limited use,
the chances are very high that it will in fact be used (or misused)
in other scenarios including the so-called open Internet. This is
undoubtedly true and means that limited use is not an excuse for bad
design or poor security. In fact, a limited use requirement
potentially adds complexity to both the protocol and its security
design, as discussed later.
Nevertheless, because of the diversity of limited domains with
specific requirements that is now emerging, specific standards (and
ad hoc standards) will probably emerge for different types of
domains. There will be attempts to capture each market sector, but
the market will demand standardized solutions within each sector. In
addition, operational choices will be made that can in fact only work
within a limited domain. The history of RSVP [RFC2205
that a standard defined as if it could work over the open Internet
might not in fact do so. In general, we can no longer assume that a
protocol designed according to classical Internet guidelines will in
fact work reliably across the network as a whole. However, the "open
Internet" must remain as the universal method of interconnection.
Reconciling these two aspects is a major challenge.
4. Examples of Limited Domain Solutions
This section lists various examples of specific limited domain
solutions that have been proposed or defined. It intentionally does
not include Layer 2 technology solutions, which by definition apply
to limited domains. It is worth noting, however, that with recent
developments such as Transparent Interconnection of Lots of Links
] or Shortest Path Bridging [SPB], Layer 2 domains
may become very large. 1.
Differentiated Services. This mechanism [RFC2474
] allows a
network to assign locally significant values to the 6-bit
Differentiated Services Code Point field in any IP packet.
Although there are some recommended code point values for
specific per-hop queue management behaviors, these are
specifically intended to be domain-specific code points with
traffic being classified, conditioned, and mapped or re-marked
at domain boundaries (unless there is an inter-domain agreement
that makes mapping or re-marking unnecessary). 2.
Integrated Services. Although it is not intrinsic in the design
of RSVP [RFC2205
], it is clear from many years' experience that
Integrated Services can only be deployed successfully within a
limited domain that is configured with adequate equipment and
Network function virtualization. As described in [RFC8568
this general concept is an open research topic in which virtual
network functions are orchestrated as part of a distributed
system. Inevitably, such orchestration applies to an
administrative domain of some kind, even though cross-domain
orchestration is also a research area. 4.
Service Function Chaining (SFC). This technique [RFC7665
assumes that services within a network are constructed as
sequences of individual service functions within a specific SFC-
enabled domain such as a 5G domain. As that RFC states:
"Specific features may need to be enforced at the boundaries of
an SFC-enabled domain, for example to avoid leaking SFC
information". A Network Service Header (NSH) [RFC8300
] is used
to encapsulate packets flowing through the service function
chain: "The intended scope of the NSH is for use within a single
provider's operational domain." 5.
Firewall and Service Tickets (FAST). Such tickets would
accompany a packet to claim the right to traverse a network or
request a specific network service [FAST]. They would only be
meaningful within a particular domain. 6.
Data Center Network Virtualization Overlays. A common
requirement in data centers that host many tenants (clients) is
to provide each one with a secure private network, all running
over the same physical infrastructure. [RFC8151
various use cases for this, and specifications are under
development. These include use cases in which the tenant
network is physically split over several data centers, but which
must appear to the user as a single secure domain. 7.
Segment Routing. This is a technique that "steers a packet
through an ordered list of instructions, called segments"
]. The semantics of these instructions are explicitly
local to a segment routing domain or even to a single node.
Technically, these segments or instructions are represented as
an MPLS label or an IPv6 address, which clearly adds a semantic
interpretation to them within the domain. 8.
Autonomic Networking. As explained in [REF-MODEL], an autonomic
network is also a security domain within which an autonomic
control plane [ACP] is used by autonomic service agents. These
agents manage technical objectives, which may be locally
defined, subject to domain-wide policy. Thus, the domain
boundary is important for both security and protocol purposes. 9.
Homenet. As shown in [RFC7368
], a home networking domain has
specific protocol needs that differ from those in an enterprise
network or the Internet as a whole. These include the Home
Network Control Protocol (HNCP) [RFC7788
] and a naming and
discovery solution [HOMENET-NAMING].
10. Creative uses of IPv6 features. As IPv6 enters more general
use, engineers notice that it has much more flexibility than
IPv4. Innovative suggestions have been made for:
* The flow label, e.g., [RFC6294
* Extension headers, e.g., for segment routing [RFC8754
Operations, Administration, and Maintenance (OAM) marking
* Meaningful address bits, e.g., [EMBEDDED-SEMANTICS]. Also,
segment routing uses IPv6 addresses as segment identifiers
with specific local meanings [RFC8402
* If segment routing is used for network programming
[SRV6-NETWORK], IPv6 extension headers can support rather
complex local functionality.
The case of the extension header is particularly interesting,
since its existence has been a major "selling point" for IPv6,
but new extension headers are notorious for being virtually
impossible to deploy across the whole Internet [RFC7045
]. It is worth noting that extension header filtering
is considered an important security issue [IPV6-EXT-HEADERS].
There is considerable appetite among vendors or operators to
have flexibility in defining extension headers for use in
limited or specialized domains, e.g., [IPV6-SRH], [BIGIP], and
[APP-AWARE]. Locally significant hop-by-hop options are also
envisaged, that would be understood by routers inside a domain
but not elsewhere, e.g., [IN-SITU-OAM].
11. Deterministic Networking (DetNet). The Deterministic Networking
] and encapsulation [DETNET-DATA-PLANE] aim
to support flows with extremely low data loss rates and bounded
latency but only within a part of the network that is "DetNet
aware". Thus, as for Differentiated Services above, the concept
of a domain is fundamental.
12. Provisioning Domains (PvDs). An architecture for Multiple
Provisioning Domains has been defined [RFC7556
] to allow hosts
attached to multiple networks to learn explicit details about
the services provided by each of those networks.
13. Address Scopes. For completeness, we mention that, particularly
in IPv6, some addresses have explicitly limited scope. In
particular, link-local addresses are limited to a single
physical link [RFC4291
], and Unique Local Addresses [RFC4193
are limited to a somewhat loosely defined local site scope.
Previously, site-local addresses were defined, but they were
obsoleted precisely because of "the fuzzy nature of the site
]. Multicast addresses also have explicit
14. As an application-layer example, consider streaming services
such as IPTV infrastructures that rely on standard protocols,
but for which access is not globally available.
All of these suggestions are only viable within a specified domain.
Nevertheless, all of them are clearly intended for multivendor
implementation on thousands or millions of network domains, so
interoperable standardization would be beneficial. This argument
might seem irrelevant to private or proprietary implementations, but
these have a strong tendency to become de facto standards if they
succeed, so the arguments of this document still apply.
5. The Scope of Protocols in Limited Domains
One consequence of the deployment of limited domains in the Internet
is that some protocols will be designed, extended, or configured so
that they only work correctly between end systems in such domains.
This is to some extent encouraged by some existing standards and by
the assignment of code points for local or experimental use. In any
case, it cannot be prevented. Also, by endorsing efforts such as
Service Function Chaining, Segment Routing, and Deterministic
Networking, the IETF is in effect encouraging such deployments.
Furthermore, it seems inevitable, if the Internet of Things becomes
reality, that millions of edge networks containing completely novel
types of nodes will be connected to the Internet; each one of these
edge networks will be a limited domain.
It is therefore appropriate to discuss whether protocols or protocol
extensions should sometimes be standardized to interoperate only
within a limited-domain boundary. Such protocols would not be
required to interoperate across the Internet as a whole. Various
scenarios could then arise if there are multiple domains using the
limited-domain protocol in question: A.
If a domain is split into two parts connected over the Internet
directly at the IP layer (i.e., with no tunnel encapsulating the
packets), a limited-domain protocol could be operated between
those two parts regardless of its special nature, as long as it
respects standard IP formats and is not arbitrarily blocked by
firewalls. A simple example is any protocol using a port number
assigned to a specific non-IETF protocol.
Such a protocol could reasonably be described as an "inter-
domain" protocol because the Internet is transparent to it, even
if it is meaningless except in the two limited domains. This is,
of course, nothing new in the Internet architecture.
B. If a limited-domain protocol does not respect standard IP formats
(for example, if it includes a non-standard IPv6 extension
header), it could not be operated between two domains connected
over the Internet directly at the IP layer.
Such a protocol could reasonably be described as an "intra-
domain" protocol, and the Internet is opaque to it.
C. If a limited-domain protocol is clearly specified to be invalid
outside its domain of origin, neither scenario A nor B applies.
The only solution would be a single virtual domain. For example,
an encapsulating tunnel between two domains could be used to
create the virtual domain. Also, nodes at the domain boundary
must drop all packets using the limited-domain protocol.
D. If a limited-domain protocol has domain-specific variants, such
that implementations in different domains could not interoperate
if those domains were unified by some mechanism as in scenario C,
the protocol is not interoperable in the normal sense. If two
domains using it were merged, the protocol might fail
unpredictably. A simple example is any protocol using a port
number assigned for experimental use. Related issues are
discussed in [RFC5704
], including the complex example of
To provide a widespread example, consider Differentiated Services
]. A packet containing any value whatsoever in the 6 bits of
the Differentiated Services Code Point (DSCP) is well formed and
falls into scenario A. However, because the semantics of DSCP values
are locally significant, the packet also falls into scenario D. In
fact, Differentiated Services are only interoperable across domain
boundaries if there is a corresponding agreement between the
operators; otherwise, a specific gateway function is required for
meaningful interoperability. Much more detailed discussion is found
] and [RFC8100
To provide a provocative example, consider the proposal in [IPV6-SRH]
that the restrictions in [RFC8200
] should be relaxed to allow IPv6
extension headers to be inserted on the fly in IPv6 packets. If this
is done in such a way that the affected packets can never leave the
specific limited domain in which they were modified, scenario C
applies. If the semantic content of the inserted headers is locally
defined, scenario D also applies. In neither case is the Internet
outside the limited domain disturbed. However, inside the domain,
nodes must understand the variant protocol. Unless it is
standardized as a formal version, with all the complexity that
], the nodes must all be non-standard to the extent
of understanding the variant protocol. For the example of IPv6
header insertion, that means non-compliance with [RFC8200
] within the
domain, even if the inserted headers are themselves fully compliant.
Apart from the issue of formal compliance, such deviations from
documented standard behavior might lead to significant debugging
issues. The possible practical impact of the header insertion
example is explored in [IN-FLIGHT-IPV6].
The FAST proposal mentioned in Section 4
, Paragraph 2, Item 5 is also
an interesting case study. The semantics of FAST tickets [FAST] have
limited scope. However, they are designed in a way that, in
principle, allows them to traverse the open Internet, as standardized
IPv6 hop-by-hop options or even as a proposed form of IPv4 extension
header [IPV4-EXT-HEADERS]. Whether such options can be used reliably
across the open Internet remains unclear [IPV6-EXT-HEADERS].
We conclude that it is reasonable to explicitly define limited-domain
protocols, either as standards or as proprietary mechanisms, as long
as they describe which of the above scenarios apply and they clarify
how the domain is defined. As long as all relevant standards are
respected outside the domain boundary, a well-specified limited-
domain protocol need not damage the rest of the Internet. However,
as described in the next section, mechanisms are needed to support
domain membership operations.
Note that this conclusion is not a recommendation to abandon the
normal goal that a standardized protocol should be global in scope
and able to interoperate across the open Internet. It is simply a
recognition that this will not always be the case.
6. Functional Requirements of Limited Domains
Noting that limited-domain protocols have been defined in the past,
and that others will undoubtedly be defined in the future, it is
useful to consider how a protocol can be made aware of the domain
within which it operates and how the domain boundary nodes can be
identified. As the taxonomy in Appendix A
shows, there are numerous
aspects to a domain. However, we can identify some generally
required features and functions that would apply partially or
completely to many cases.
Today, where limited domains exist, they are essentially created by
careful configuration of boundary routers and firewalls. If a domain
is characterized by one or more address prefixes, address assignment
to hosts must also be carefully managed. This is an error-prone
method, and a combination of configuration errors and default routing
can lead to unwanted traffic escaping the domain. Our basic
assumption is therefore that it should be possible for domains to be
created and managed automatically, with minimal human configuration.
We now discuss requirements for automating domain creation and
First, if we drew a topology map, any given domain -- virtual or
physical -- will have a well-defined boundary between "inside" and
"outside". However, that boundary in itself has no technical
meaning. What matters in reality is whether a node is a member of
the domain and whether it is at the boundary between the domain and
the rest of the Internet. Thus, the boundary in itself does not need
to be identified, but boundary nodes face both inwards and outwards.
Inside the domain, a sending node needs to know whether it is sending
to an inside or outside destination, and a receiving node needs to
know whether a packet originated inside or outside. Also, a boundary
node needs to know which of its interfaces are inward facing or
outward facing. It is irrelevant whether the interfaces involved are
physical or virtual.
To underline that domain boundaries need to be identifiable, consider
the statement from the Deterministic Networking Problem Statement
] that "there is still a lack of clarity regarding the limits
of a domain where a deterministic path can be set up". This remark
can certainly be generalized.
With this perspective, we can list some general functional
requirements. An underlying assumption here is that domain
membership operations should be cryptographically secured; a domain
without such security cannot be reliably protected from attack. 1.
Domain Identity. A domain must have a unique and verifiable
identifier; effectively, this should be a public key for the
domain. Without this, there is no way to secure domain
operations and domain membership. The holder of the
corresponding private key becomes the trust anchor for the
Nesting. It must be possible for domains to be nested (see, for
example, the network-slicing example mentioned above). 3.
Overlapping. It must be possible for nodes and links to be in
more than one domain (see, for example, the case of PvDs
mentioned above). 4.
Node Eligibility. It must be possible for a node to determine
which domain(s) it can potentially join and on which
Secure Enrollment. A node must be able to enroll in a given
domain via secure node identification and to acquire relevant
security credentials (authorization) for operations within the
domain. If a node has multiple physical or virtual interfaces,
individual enrollment for each interface may be required. 6.
Withdrawal. A node must be able to cancel enrollment in a given
Dynamic Membership. Optionally, a node should be able to
temporarily leave or rejoin a domain (i.e., enrollment is
persistent but membership is intermittent). 8.
Role, implying authorization to perform a certain set of
actions. A node must have a verifiable role. In the simplest
case, the role choices are "interior node" and "boundary node".
In a boundary node, individual interfaces may have different
roles, e.g., "inward facing" and "outward facing".
9. Peer Verification. A node must be able to verify whether
another node is a member of the domain.
10. Role Verification. A node should be able to learn the verified
role of another node. In particular, it should be possible for
a node to find boundary nodes (interfacing to the Internet).
11. Domain Data. In a domain with management requirements, it must
be possible for a node to acquire domain policy and/or domain
configuration data. This would include, for example, filtering
policy to ensure that inappropriate packets do not leave the
These requirements could form the basis for further analysis and
Another aspect is whether individual packets within a limited domain
need to carry any sort of indicator that they belong to that domain
or whether this information will be implicit in the IP addresses of
the packet. A related question is whether individual packets need
cryptographic authentication. This topic is for further study.
7. Security Considerations
As noted above, a protocol intended for limited use may well be
inadvertently used on the open Internet, so limited use is not an
excuse for poor security. In fact, a limited use requirement
potentially adds complexity to the security design.
Often, the boundary of a limited domain will also act as a security
boundary. In particular, it will serve as a trust boundary and as a
boundary of authority for defining capabilities. For example,
segment routing [RFC8402
] explicitly uses the concept of a "trusted
domain" in this way. Within the boundary, limited-domain protocols
or protocol features will be useful, but they will in many cases be
meaningless or harmful if they enter or leave the domain.
The boundary also serves to provide confidentiality and privacy for
operational parameters that the operator does not wish to reveal.
Note that this is distinct from privacy protection for individual
users within the domain.
The security model for a limited-scope protocol must allow for the
boundary and in particular for a trust model that changes at the
boundary. Typically, credentials will need to be signed by a domain-
8. IANA Considerations
This document has no IANA actions.9.
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in Progress, Internet-Draft, draft-jiang-semantic-prefix-
06, 15 July 2013, <https://tools.ietf.org/html/draft-
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Networks (VPN+)
Service", Work in Progress, Internet-Draft, draft-ietf-
teas-enhanced-vpn-06, 13 July 2020,
[FAST] Herbert, T., "Firewall and Service Tickets", Work in
Progress, Internet-Draft, draft-herbert-fast-04, 10 April
Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile", Work
in Progress, Internet-Draft, draft-ietf-intarea-frag-
fragile-17, 30 September 2019,
Lemon, T., Migault, D., and S. Cheshire, "Homenet Naming
and Service Discovery Architecture", Work in Progress,
Internet-Draft, draft-ietf-homenet-simple-naming-03, 23
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Clemm, A., Ciavaglia, L., Granville, L., and J. Tantsura,
"Intent-Based Networking - Concepts and Definitions", Work
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definitions-01, 9 March 2020,
Smith, M., Kottapalli, N., Bonica, R., Gont, F., and T.
Herbert, "In-Flight IPv6 Extension Header Insertion
Considered Harmful", Work in Progress, Internet-Draft,
draft-smith-6man-in-flight-eh-insertion-harmful-02, 30 May
Bhandari, S., Brockners, F., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Kfir, A., Gafni, B.,
Lapukhov, P., Spiegel, M., Krishnan, S., and R. Asati,
"In-situ OAM IPv6 Options", Work in Progress, Internet-
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Herbert, T., "IPv4 Extension Headers and Flow Label", Work
in Progress, Internet-Draft, draft-herbert-ipv4-eh-01, 2
Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
Pang, "IPv6 Application of the Alternate Marking Method",
Work in Progress, Internet-Draft, draft-ietf-6man-ipv6-
alt-mark-01, 22 June 2020, <https://tools.ietf.org/html/
Gont, F. and W. LIU, "Recommendations on the Filtering of
IPv6 Packets Containing IPv6 Extension Headers", Work in
Progress, Internet-Draft, draft-ietf-opsec-ipv6-eh-
filtering-06, 2 July 2018, <https://tools.ietf.org/html/
[IPV6-SRH] Voyer, D., Filsfils, C., Dukes, D., Matsushima, S., Leddy,
J., Li, Z., and J. Guichard, "Deployments With Insertion
of IPv6 Segment Routing Headers", Work in Progress,
insertion-09, 19 May 2020, <https://tools.ietf.org/html/
Andrews, M., "TCP Fails To Respect IPV6_USE_MIN_MTU", Work
in Progress, Internet-Draft, draft-andrews-tcp-and-ipv6-
use-minmtu-04, 18 October 2015,
Jeong, J., "IPv6 Wireless Access in Vehicular Environments
(IPWAVE): Problem Statement and Use Cases", Work in
Progress, Internet-Draft, draft-ietf-ipwave-vehicular-
networking-16, 7 July 2020, <https://tools.ietf.org/html/
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
and J. Nobre, "A Reference Model for Autonomic
Networking", Work in Progress, Internet-Draft, draft-ietf-
anima-reference-model-10, 22 November 2018,
] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205
, DOI 10.17487/RFC2205
September 1997, <https://www.rfc-editor.org/info/rfc2205
] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474
, December 1998,
] Carpenter, B., "Internet Transparency", RFC 2775
, February 2000,
] Lahey, K., "TCP Problems with Path MTU Discovery", RFC 2923
, DOI 10.17487/RFC2923
, September 2000,
] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234
, DOI 10.17487/RFC3234
, February 2002,
] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879
, DOI 10.17487/RFC3879
] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193
, DOI 10.17487/RFC4193
, October 2005,
] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291
, DOI 10.17487/RFC4291
] Bryskin, I. and A. Farrel, "A Lexicography for the
Interpretation of Generalized Multiprotocol Label
Switching (GMPLS) Terminology within the Context of the
ITU-T's Automatically Switched Optical Network (ASON)
Architecture", RFC 4397
, DOI 10.17487/RFC4397
] Mannie, E., Ed. and D. Papadimitriou, Ed., "Recovery
(Protection and Restoration) Terminology for Generalized
Multi-Protocol Label Switching (GMPLS)", RFC 4427
, March 2006,
] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655
, August 2006,
] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821
, DOI 10.17487/RFC4821
, March 2007,
] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838
, DOI 10.17487/RFC4838
April 2007, <https://www.rfc-editor.org/info/rfc4838
] Aboba, B., Ed. and E. Davies, "Reflections on Internet
Transparency", RFC 4924
, DOI 10.17487/RFC4924
, July 2007,
] Bryant, S., Ed., Morrow, M., Ed., and IAB, "Uncoordinated
Protocol Development Considered Harmful", RFC 5704
, November 2009,
] Hu, Q. and B. Carpenter, "Survey of Proposed Use Cases for
the IPv6 Flow Label", RFC 6294
, DOI 10.17487/RFC6294
] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325
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, July 2011,
] Le Faucheur, F., Ed., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398
, DOI 10.17487/RFC6398
] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407
, DOI 10.17487/RFC6407
October 2011, <https://www.rfc-editor.org/info/rfc6407
] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709
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] Boucadair, M., Kaplan, H., Gilman, R., and S.
Veikkolainen, "The Session Description Protocol (SDP)
Alternate Connectivity (ALTC) Attribute", RFC 6947
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] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in
the DNS", RFC 6950
, DOI 10.17487/RFC6950
, October 2013,
] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045
, December 2013,
] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228
, May 2014,
] Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
Weil, "IPv6 Home Networking Architecture Principles", RFC 7368
, DOI 10.17487/RFC7368
, October 2014,
] Chittimaneni, K., Chown, T., Howard, L., Kuarsingh, V.,
Pouffary, Y., and E. Vyncke, "Enterprise IPv6 Deployment
Guidelines", RFC 7381
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, October 2014,
] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556
, DOI 10.17487/RFC7556
, June 2015,
] Trammell, B., Ed. and M. Kuehlewind, Ed., "Report from the
IAB Workshop on Stack Evolution in a Middlebox Internet
(SEMI)", RFC 7663
, DOI 10.17487/RFC7663
, October 2015,
] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665
, October 2015,
] Barnes, R., Cooper, A., Kolkman, O., Thaler, D., and E.
Nordmark, "Technical Considerations for Internet Service
Blocking and Filtering", RFC 7754
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March 2016, <https://www.rfc-editor.org/info/rfc7754
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Control Protocol", RFC 7788
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"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872
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] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085
, DOI 10.17487/RFC8085
March 2017, <https://www.rfc-editor.org/info/rfc8085
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in-UDP Encapsulation", RFC 8086
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March 2017, <https://www.rfc-editor.org/info/rfc8086
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Classes and Practice", RFC 8100
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March 2017, <https://www.rfc-editor.org/info/rfc8100
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"Use Cases for Data Center Network Virtualization Overlay
Networks", RFC 8151
, DOI 10.17487/RFC8151
, May 2017,
] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200
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] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300
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] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402
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July 2018, <https://www.rfc-editor.org/info/rfc8402
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Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445
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] Dolson, D., Ed., Snellman, J., Boucadair, M., Ed., and C.
Jacquenet, "An Inventory of Transport-Centric Functions
Provided by Middleboxes: An Operator Perspective", RFC 8517
, DOI 10.17487/RFC8517
, February 2019,
] Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", RFC 8557
, DOI 10.17487/RFC8557
, May 2019,
] Bernardos, CJ., Rahman, A., Zuniga, JC., Contreras, LM.,
Aranda, P., and P. Lynch, "Network Virtualization Research
Challenges", RFC 8568
, DOI 10.17487/RFC8568
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] Grossman, E., Ed., "Deterministic Networking Use Cases", RFC 8578
, DOI 10.17487/RFC8578
, May 2019,
] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655
, October 2019,
] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754
, DOI 10.17487/RFC8754
, March 2020,
[SPB] "IEEE Standard for Local and metropolitan area networks -
Bridges and Bridged Networks",
DOI 10.1109/IEEESTD.2018.8403927, IEEE 802.1Q-2018, July
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
Work in Progress, Internet-Draft, draft-ietf-spring-srv6-
network-programming-16, 27 June 2020,
Homma, S., Miyasaka, T., Matsushima, S., and D. Voyer,
"User Plane Protocol and Architectural Analysis on 3GPP 5G
System", Work in Progress, Internet-Draft, draft-ietf-dmm-
5g-uplane-analysis-03, 3 November 2019,
Appendix A. Taxonomy of Limited Domains
This appendix develops a taxonomy for describing limited domains.
Several major aspects are considered in this taxonomy:
* The domain as a whole
* The individual nodes
* The domain boundary
* The domain's topology
* The domain's technology
* How the domain connects to the Internet
* The security, trust, and privacy model
The following sub-sections analyze each of these aspects.
A.1. Domain as a Whole
* Why does the domain exist? (e.g., human choice, administrative
policy, orchestration requirements, technical requirements such as
operational partitioning for scaling reasons)
* If there are special requirements, are they at Layer 2, Layer 3,
or an upper layer?
* Where does the domain lie on the spectrum between completely
managed by humans and completely autonomic?
* If managed, what style of management applies? (Manual
configuration, automated configuration, orchestration?)
* Is there a policy model? (Intent, configuration policies?)
* Does the domain provide controlled or paid service or open access?
A.2. Individual Nodes
* Is a domain member a complete node or only one interface of a
* Are nodes permanent members of a given domain, or are join and
leave operations possible?
* Are nodes physical or virtual devices?
* Are virtual nodes general purpose or limited to specific
functions, applications, or users?
* Are nodes constrained (by battery, etc.)?
* Are devices installed "out of the box" or pre-configured?
A.3. Domain Boundary
* How is the domain boundary identified or defined?
* Is the domain boundary fixed or dynamic?
* Are boundary nodes special, or can any node be at the boundary?
* Is the domain a subset of a Layer 2 or 3 connectivity domain?
* Does the domain overlap other domains? (In other words, is a node
allowed to be a member of multiple domains?)
* Does the domain match physical topology, or does it have a virtual
* Is the domain in a single building, vehicle, or campus? Or is it
* If distributed, are the interconnections private or over the
* In IP addressing terms, is the domain Link local, Site local, or
* Does the scope of IP unicast or multicast addresses map to the
* What routing protocol(s) or different forwarding mechanisms (MPLS
or other non-IP mechanism) are used?
* In an overlay domain, what overlay technique is used (L2VPN,
* Are there specific QoS requirements?
* Link latency - Normal or long latency links?
* Mobility - Are nodes mobile? Is the whole network mobile?
* Which specific technologies, such as those in Section 4
A.6. Connection to the Internet
* Is the Internet connection permanent or intermittent? (Never
connected is out of scope.)
* What traffic is blocked, in and out?
* What traffic is allowed, in and out?
* What traffic is transformed, in and out?
* Is secure and privileged remote access needed?
* Does the domain allow unprivileged remote sessions?
A.7. Security, Trust, and Privacy Model
* Must domain members be authorized?
* Are all nodes in the domain at the same trust level?
* Is traffic authenticated?
* Is traffic encrypted?
* What is hidden from the outside?
* Safety level - Does the domain have a critical (human) safety
* Reliability requirement - Normal or 99.999%?
* Environment - Hazardous conditions?
* Installation - Are specialists needed?
* Service visits - Easy, difficult, or impossible?
* Software/firmware updates - Possible or impossible?
A.9. Making Use of This Taxonomy
This taxonomy could be used to design or analyze a specific type of
limited domain. For the present document, it is intended only to
form a background to the scope of protocols used in limited domains
and the mechanisms required to securely define domain membership and
Useful comments were received from Amelia Andersdotter, Edward
Birrane, David Black, Ron Bonica, Mohamed Boucadair, Tim Chown,
Darren Dukes, Donald Eastlake, Adrian Farrel, Tom Herbert, Ben Kaduk,
John Klensin, Mirja Kuehlewind, Warren Kumari, Andy Malis, Michael
Richardson, Mark Smith, Rick Taylor, Niels ten Oever, and others.
Q14, Huawei Campus
No. 156 Beiqing Road
Hai-Dian District, Beijing
The University of Auckland
School of Computer Science
University of Auckland
Q14, Huawei Campus
No. 156 Beiqing Road
Hai-Dian District, Beijing