As per Relevance of the word autonomous, we have this rfc below:
Network Working Group S.
Request for Comments: 1136 D.
Merit/
December 1989
Administrative Domains and Routing
A Model for Routing in the
1) Status of this
This RFC proposes a model for describing routing within the Internet
The model is an adaptation of the "OSI Routeing Framework" [1].
memo does not specify an Internet standard. Comments are welcome
Distribution of this memo is unlimited
2)
The authors would like to thank Guy Almes of Rice University for
contributions and insight
3)
The "core" model of Autonomous Systems [2] formed the basis for
routing model used in the Internet. Due to massive growth
topology changes, the "core" model no longer is in harmony with
reality of today's Internet. Indeed, this situation was foreseen
the outset
"Ultimately, however, the internet may consist of a number of co
equal autonomous systems, any of which may be used...as
transport medium for traffic originating in any system
destined for any system. When this more complex
comes into being, it will be inappropriate to regard any
autonomous system as a "core" system" [2].
Furthermore, the Autonomous System concept has been outgrown
certain parts of the Internet, in which the complexity of
routing has exceeded the limits of the definition of
Systems
A model which can provide a better match to the Internet can be
in the "OSI Routeing Framework" [1].
This framework proposes a structure of Routing Domains
Administrative Domains. This paper is intended to briefly
this framework, to outline how this model better fits the reality
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the present and future Internet, and to show how the model can aid
the construction of well-engineered routing environments
4)
The following is a brief glossary of OSI terminology.
definitions can be found in the OSI Basic Reference Model [4],
Internal Organization of the Network Layer [5], and the OSI
Framework [1].
"Routeing" is the official ISO spelling of what is
commonly spelled "routing." In this paper, the ISO
will be used wherever directly quoted from ISO documents,
the common spelling used otherwise
End System (ES
An OSI system on which applications run. An End System
full seven-layer OSI functionality. Basically equivalent to
Internet Host
Intermediate System (IS
An OSI system that performs routing and relaying functions
order to provide paths between End Systems.
Systems have no functionality above the Network Layer (
a practical realization of an OSI router will have some
of End System functionality for network management functions
among other things). Basically equivalent to an
Router
Subnetwork (SN
A communications medium that provides a "direct" path
Network Layer entities. This can be realized via a point-to
point link, a LAN, a Public Data Network, and so forth.
is essentially equivalent to an Internet Subnet. It is
noting that, unlike Internet Subnets, OSI Subnetworks are
necessarily reflected in the addressing hierarchy, so
double meaning of the Internet term "Subnet" (a single IP hop
a part of the address hierarchy) does not hold in the
world
Open Systems Interconnection Environment (OSIE
The global collection of Open Systems. Basically equivalent
the Internet
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Network Service Access Point (NSAP
A conceptual point on the Network/Transport Layer boundary
an End System that is globally addressable (and the
globally unambiguous) in the OSIE. An NSAP represents
service available above the Network Layer (such as a choice
transport protocols). An End System may have multiple NSAPs
An NSAP address is roughly equivalent to the Internet [address
protocol] pair
Administrative Domain (AD
"A collection of End Systems, Intermediate Systems,
subnetworks operated by a single organization or
authority. The components which make up the domain are
to interoperate with a significant degree of mutual trust
themselves, but interoperate with other Administrative
in a mutually suspicious manner" [1].
A group of hosts, routers, and networks operated and managed
a single organization. Routing within an Administrative
is based on a consistent technical plan. An
Domain is viewed from the outside, for purposes of routing,
a cohesive entity, of which the internal structure
unimportant. Information passed by other
Domains is trusted less than information from one's
Administrative Domain
Administrative Domains can be organized into a loose
that reflects the availability and authoritativeness of
information. This hierarchy does not imply
containment, nor does it imply a strict tree topology
Routing Domain (RD
"A set of End Systems and Intermediate Systems which
according to the same routeing procedures and which is
contained within a single Administrative Domain" [1].
"A Routeing Domain is a set of ISs and ESs bound by a
routeing procedure; namely
they are using the same set of routeing metrics
they use compatible metric measurement techniques
they use the same information distribution protocol,
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they use the same path computation algorithm" [1].
The "OSI Routeing Framework" further provides a
definition of a Routing Domain, specifying that all ISs
a Routing Domain can determine whether an ES within the
is reachable, and if so can derive a path to it
Routing Domains may be divided into subdomains, not
subnetting in the Internet. This allows a
structuring of the domain, permitting containment of
topological details of a subdomain with the resultant
in distributed routing information
An intra-Routing Domain routing protocol is equivalent to
Internet Interior Gateway Protocol (IGP).
An Administrative Domain may contain multiple Routing Domains
A Routing Domain may never span multiple
Domains
An Administrative Domain may consist of only a single
Domain, in which case they are said to be Congruent.
congruent Administrative Domain and Routing Domain is
to an Internet Autonomous System
Common Domain (CD
"An Administrative Domain which is not a member of a
level domain. A common domain is the highest level in
routeing hierarchy. There is no single domain above the
domain. In this sense, the routeing hierarchy is in
multiple hierarchies, with the common domain as the
element of each hierarchy".
"Where there are multiple common domains, they cooperate
peers to make it possible to route to any NSAP in the OSIE
[1].
Common Domains have global routing information to the
necessary to route packets to the proper domain. Each of
several peer national backbones in today's Internet may
considered to be similar to a Common Domain. Note that in
Internet the hierarchical containment implied by the
of a CD does not really exist; however, there is a level
implicit ordering based on topology and policy issues (
willingness to be used as a transit network) that can be
as defining a Common Domain in the Internet
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For completeness, we offer the following definition for an
Autonomous System (AS):
"An 'autonomous system' consists of a set of gateways, each
which can reach any other gateway in the same system using
via gateways only in that system. The gateways of a
cooperatively maintain a routing data base using an
gateway protocol (IGP)..." [3]
5) Environment and
The "OSI Routeing Framework" describes the environment for
routing as well as its goals. The environment described is a
interconnected, highly heterogeneous collection of LANs and
and private networks made up of a diverse collection of
from multiple vendors. A number of goals are enumerated, including
- Support of multiple subnetwork
- Very large numbers of connected
- End System
- Multiple organizations with mutual distrust and policy/
- High
- Robust and dynamic routing in the face of topological
The environment and goals described are a good match for those in
Internet. The Internet crosses multiple types of physical media
link layer protocols, and administrative controls. Routers and
may come from many vendors. The Internet has become international
scope. Issues of security and the isolation of bad
information have become international concerns
The Internet environment, with over 900 highly connected
(and growing exponentially), is very much like the environment
OSI model aims to describe
6) Structure of Global
The "OSI Routeing Framework" classifies routing into three types
- within a Routing
- within an Administrative
- between Administrative
Routing within a Routing Domain involves a high level of
trust. This allows the use of complex, tightly-coupled
that can make the best use of dynamic, highly
environments
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Routing Domains may be recursively subdivided into Subdomains
order to reduce routing complexity. The details of a subdomain
be largely hidden from other subdomains with an attendant
in the volume of routing information exchanged
Intra-Administrative Domain routing is concerned with
multiple Routing Domains within an administration. Issues
include address administration, cost recovery, and policy concerns
A moderate level of trust is assumed. The nature of the
between Routing Domains can range from being tightly coupled (
path routing between two RDs running different routing protocols)
being more policy-based. However, inter-RD routing within
Administrative Domain is tightly coordinated and represents a
technical plan
Inter-Administrative Domain routing is concerned with managing
controlling the flow of information in a highly structured
between organizations that may require formal
agreements. The issues of concern at this level tend to
administrative in nature (legal/political constraints, security
access control, etc.). Multiple agreements between
administrations are unlikely to be implicitly transitive. This
the analysis of policy interactions very important
7) Mapping the AD/RD Model Onto the
The national network backbones (NSFNET, ARPANET, MILNET, NSN,
soon ESNET) can be viewed as Common Domains. Each may
sufficiently global routing knowledge to determine a path to
Internet address
Regional networks are clearly Administrative Domains.
policy agreements are defined between the regional networks and
backbones. On the other hand, regional networks very often
tightly coupled to individual networks and campus networks in
of routing. In this sense, a regional network could be viewed as
Routing Domain with individual campuses thought of as Subdomains
From the standpoint of routing functionality, it is most useful
view a "classic" Autonomous System as a congruent Routing Domain
Administrative Domain. An AS as defined represents both a single
and a point of policy administration. The sixteen bit value
known as the Autonomous System number may instead be viewed as
Administrative Domain number
In reality, however, many so-called Autonomous Systems today do
adhere to the strict definition of an AS. In theory, an
System is quite similar to a Routing Domain, in which a high level
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trust is made between systems, a consistent IGP is run, and
routing information is distributed. On the other hand, AS
have become an abstraction for policy groupings to backbones
Indeed, entire regional networks are viewed by the backbones as
single Autonomous System, even though they are not nearly
homogeneous as the AS model specifies. Such entities can be
as an Administrative Domain containing several Routing Domains
Although it is true that, in this interpretation,
nontechnical administrations are represented within a
Administrative Domain (in conflict with the definition of
Administrative Domain), such structures require a single approach
internal routing. Even if there is not a true
representing the collection of domains (such as a consortium),
typically is a technical committee to settle common technical issues
8) The AD/RD Model as an Engineering
Current Autonomous Systems cross administrative boundaries
impunity. This works as long as the individual
operating within the common AS agree to a common technical policy
routing and network management. Connections with other backbones
regional networks, and campus networks must be planned, implemented
and managed in a coordinated fashion
This coordination becomes more difficult, but more necessary, as
AS grows. As connectivity and policy become more complex,
Autonomous Systems start to fragment. An example of this is
network that is currently a member of an NSFNET regional network
will be adding a connection to ESNET. The administrators of
network and the regional network must carefully coordinate
changes necessary to implement this connection, including
altering the boundaries of policy and routing. A lack
coordination could result in routing loops and policy violations
A point that is being increasingly realized is that the
responsible for exterior or policy routing (be it an
System or an Administrative Domain) must have a common
policy for routing. The effects of attempting different
to policy and external routing while maintaining a single AS
been painfully evident in real instances in the Internet
Under the AD/RD model, a routing domain cannot be in
Administrative Domains. For example, if a campus network wants
set its own routing policy and enforce it via management of
routers, the campus has elected to become a separate
Domain. If that campus uses a common IGP with other campuses,
represents an attempt to split a Routing Domain (the regional
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RFC 1136 A Model for Routing in the Internet December 1989
with a common IGP) across multiple Administrative Domains (the
and the rest of the regional). Such arrangements represent
engineering practice, cause real routing problems, and are
by the AD/RD model
Under the strict Autonomous System model, only one IGP can
within an AS. However, many regional networks are successfully
multiple IGPs. The AD/RD model allows this valuable
topology. Such a topology would also be allowed by the AS model
it were to be broadened to allow multiple IGPs, in which case an
and an AD would effectively become equivalent
9) The AD/RD Model in a Dual Protocol
As the OSI protocol suite is deployed and an OSI Internet
constructed, it is very likely that significant portions of
current TCP/IP Internet will also carry OSI traffic. Many
vendors provide dual protocol capability today, or will in the
future, and the investment in network infrastructure is such that
is unlikely that a separate, parallel internet will be
for OSI traffic
It is logical to assume that, in many cases, the same technical
administrative boundaries will apply to both DoD IP and
protocols, and in some cases a single routing protocol may be used
support both protocol suites
Thus, it would be most advantageous to have a common model and
nomenclature in order to provide a more unified, manageable
environment. Given that the OSI Routeing Framework represents
model on which OSI routing is built, the use of the AD/RD model
describe the existing Internet is an appropriate step
describing and building the combined internet
10)
The AD/RD model of routing describes the current Internet better
existing models because it describes
- How Intra-Domain and Inter-Domain relationships work at
routing and policy
- How routing domains and administrative domains can
hierarchically
- The existence of multiple national
- A common model for dual protocol
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The expanding Internet has grown from the "core" model with
small attached networks to a highly interconnected environment
spans several continents. Several national peer networks serve
ever-growing set of regional networks. The AD/RD model can
Internet protocol designers abstract the functional pieces from
large Internet
The Internet grows daily. Any model of Internet routing needs
provide a way to understand and order the growth. The ISO
Framework provides a structure to handle such growth
11)
[1] ISO, "OSI Routeing Framework", ISO/TR 9575, 1989.
[2] Rosen, E., "Exterior Gateway Protocol", RFC 827, Bolt Beranek
Newman, October 1982.
[3] Mills, D., "Autonomous Confederations", RFC 975, M/A
Linkabit, February 1986.
[4] ISO, "Open Systems Interconnection--Basic Reference Model",
7498.
[5] ISO, "Internal Organization of the Network Layer", ISO 8648.
ISO documents can be obtained from the following source
American National Standards
1430
New York, NY 10018
(212) 642-4900
Additionally, a number of private firms are authorized to
ISO documents
Security
Security issues are not addressed in this memo
Authors'
Susan
Merit/
1075 Beal Ave
Ann Arbor, MI 48109
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RFC 1136 A Model for Routing in the Internet December 1989
Phone: (313) 936-3000
Email: skh@merit.
Dave
Merit/
1075 Beal Ave
Ann Arbor, MI 48109
Phone: (313) 763-4898
Email: dkatz@merit.
Hares & Katz [Page 10]
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just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
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