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Network Working Group M. Little
Request for Comments: 1126 SAIC
October 1989
Goals and Functional Requirements for
Inter-Autonomous System Routing
Status of this Memo
This document describes the functional requirements for a routing
protocol to be used between autonomous systems. This document is
intended as a necessary precursor to the design of a new inter-
autonomous system routing protocol and specifies requirements for the
Internet applicable for use with the current DoD IP, the ISO IP, and
future Internet Protocols. It is intended that these requirements
will form the basis for the future development of a new inter-
autonomous systems routing architecture and protocol. This document
is being circulated to the IETF and Internet community for comment.
Comments should be sent to: "open-rout-editor@bbn.com". This memo
does not specify a standard. Distribution of this memo is unlimited.
1. Introduction
The development of an inter-autonomous systems routing protocol
proceeds from those goals and functions seen as both desirable and
obtainable for the Internet environment. This document describes
these goals and functional requirements. The goals and functional
requirements addressed by this document are intended to provide a
context within which an inter-autonomous system routing architecture
can be developed which will meet both current and future Internet
routing needs. The goals presented indicate properties and general
capabilities desired of the Internet routing environment and what the
inter-autonomous system routing architecture is to accomplish as a
whole.
The goals are followed by functional requirements, which address
either detailed objectives or specific functionality to be achieved
by the architecture and resulting protocol(s). These functional
requirements are enumerated for clarity and grouped so as to map
directly to areas of architectural consideration. This is followed
by a listing and description of general objectives, such as
robustness, which are applicable in a broad sense. Specific
functions which are not reasonably attainable or best left to future
efforts are identified as non-requirements.
The intent of this document is to provide both the goals and
functional requirements in a concise fashion. Supporting arguments,
Little [Page 1]
RFC 1126 Inter-Autonomous System Routing October 1989
tradeoff considerations and the like have been purposefully omitted
in support of this. An appendix has been included which addresses
this omission to a limited extent and the reader is directed there
for a more detailed discussion of the issues involved.
The goals and functional requirements contained in this document are
the result of work done by the members of the Open Routing Working
Group. It is our intention that these goals and requirements reflect
not only those foreseen in the Internet community but are also
similar to those encountered in environments proposed by ANSI, ECMA
and ISO. It is expected that there will be some interaction and
relationship between this work and the product of these groups.
2. Overall Goals
In order to derive a set functional requirements there must be one or
more principals or overall goals for the routing environment to
satisfy. These high level goals provide the basis for each of the
functional requirements we have derived and will guide the design
philosophy for achieving an inter-autonomous system routing solution.
The overall goals we are utilizing are described in the following
sections.
2.1 Route to Destination
The routing architecture will provide for the routing of datagrams
from a single source to one or more destinations in a timely manner.
The larger goal is to provide datagram delivery to an identifiable
destination, one which is not necessarily immediately reachable by
the source. In particular, routing is to address the needs of a
single source requiring datagram delivery to one or more
destinations. The concepts of multi-homed hosts and multicasting
routing services are encompassed by this goal. Datagram delivery is
to be provided to all interconnected systems when not otherwise
constrained by autonomous considerations.
2.2 Routing is Assured
Routing services are to be provided with assurance, where the
inability to provide a service is communicated under best effort to
the requester within an acceptable level of error. This assurance is
not to be misconstrued to mean guaranteed datagram delivery nor does
it imply error notification for every lost datagram. Instead,
attempts to utilize network routing services when such service cannot
be provided will result in requester notification within a reasonable
period given persistent attempts.
Little [Page 2]
RFC 1126 Inter-Autonomous System Routing October 1989
2.3 Large System
The design of the architecture, and the protocols within this
architecture, should accommodate a large number of routing entities.
The exact order of magnitude is a relative guess and the best designs
would provide for a practical level of unbounded growth.
Nevertheless, the routing architecture is expected to accommodate the
growth of the Internet environment for the next 10 years.
2.4 Autonomous Operation
The routing architecture is to allow for stable operation when
significant portions of the internetworking environment are
controlled by disjoint entities. The future Internet environment is
envisioned as consisting of a large number of internetworking
facilities owned and operated by a variety of funding sources and
administrative concerns. Although cooperation between these
facilities is necessary to provide interconnectivity, it is viewed
that both the degree and type of cooperation will vary widely.
Additionally, each of these internetworking facilities desires to
operate as independently as possible from the concerns and activities
of other facilities individually and the interconnection environment
as a whole. Those resources used by (and available for) routing are
to be allowed autonomous control by those administrative entities
which own or operate them. Specifically, each controlling
administration should be allowed to establish and maintain policies
regarding the use of a given routing resource.
2.5 Distributed System
The routing environment developed should not depend upon a data
repository or topological entity which is either centralized or
ubiquitous. The growth pattern of the Internet, coupled with the
need for autonomous operation, dictates an independence from the
topological and administrative centralization of both data and
control flows. Past experience with a centralized topology has shown
that it is both impractical for the needs of the community and
restrictive of administrative freedoms. A distributed routing
environment should not be restrictive of either redundancy or
diversity. Any new routing environment must allow for arbitrary
interconnection between internetworks.
2.6 Provide A Credible Environment
The routing environment and services should be based upon mechanisms
and information that exhibit both integrity and security. The
routing mechanisms should operate in a sound and reliable fashion
while the routing information base should provide credible data upon
Little [Page 3]
RFC 1126 Inter-Autonomous System Routing October 1989
which to base routing decisions. The environment can be unreliable
to the extent that the resulting effect on routing services is
negligible. The architecture and protocol designs should be such
that the routing environment is reasonably secure from unwanted
modification or influence.
2.7 Be A Managed Entity
Provide a manger insight into the operation of the inter-autonomous
system routing environment to support resource management, problem
solving, and fault isolation. Allow for management control of the
routing system and collect useful information for the internetwork
management environment. Datagram events as well as the content and
distribution characteristics of relevant databases are of particular
importance.
2.8 Minimize Required Resources
Any feasible design should restrain the demand for resources required
to provide inter-autonomous systems routing. Of particular interest
are those resources required for data storage, transmission, and
processing. The design must be practical in terms of today's
technology. Specifically, do not assume significant upgrades to the
existing level of technology in use today for data communication
systems.
3. Functional Requirements
The functional requirements we have identified have been derived from
the overall goals and describe the critical features expected of
inter-autonomous system routing. To an extent, these functions are
vague in terms of detail. We do not, for instance, specify the
quantity or types for quality-of-service parameters. This is
purposeful, as the functional requirements specified here are
intended to define the features required of the inter-autonomous
system routing environment rather than the exact nature of this
environment. The functional requirements identified have been
loosely grouped according to areas of architectural impact.
3.1 Route Synthesis Requirements
Route synthesis is that functional area concerned with both route
selection and path determination (identification of a sequence of
intermediate systems) from a source to a destination. The functional
requirements identified here provide for path determination which is
adaptive to topology changes, responsive to administrative policy,
cognizant of quality-of-service concerns, and sensitive to an
interconnected environment of autonomously managed systems.
Little [Page 4]
RFC 1126 Inter-Autonomous System Routing October 1989
a) Route around failures dynamically
Route synthesis will provide a best effort attempt to detect
failures in those routing resources which are currently being
utilized. Upon detection of a failed resource, route synthesis
will provide a best effort to utilize other available routing
resources in an attempt to provide the necessary routing
service.
b) Provide loop free paths
The path provided for a datagram, from source to destination,
will be free of circuits or loops most of the time. At those
times a circuit or loop exists, it occurs with both negligible
probability and duration.
c) Know when a path or destination is unavailable
Route synthesis will be capable of determining when a path
cannot be constructed to reach a known destination.
Additionally, route synthesis will be capable of determining
when a given destination cannot be determined because the
requested destination is unknown (or this knowledge is
unavailable).
d) Provide paths sensitive to administrative policies
Route synthesis will accommodate the resource utilization
policies of those administrative entities which manage the
resources identified by the resulting path. However, it is
inconceivable to accommodate all policies which can be defined
by a managing administrative entity. Specifically, policies
dependent upon volatile events of great celerity or those which
are non-deterministic in nature cannot be accommodated.
e) Provide paths sensitive to user policies
Paths produced by route synthesis must be sensitive to policies
expressed by the user. These user policies are expressed in
terms relevant to known characteristics of the topology. The
path achieved will meet the requirements stated by the user
policy.
f) Provide paths which characterize user quality-of-service
requirements
The characteristics of the path provided should match those
indicated by the quality-of-service requested. When
Little [Page 5]
RFC 1126 Inter-Autonomous System Routing October 1989
appropriate, utilize only those resources which can support the
desired quality-of-service (e.g., bandwidth).
g) Provide autonomy between inter- and intra-autonomous system
route synthesis
The inter- and intra-autonomous system routing environments
should operate independent of one another. The architecture
and design should be such that route synthesis of either
routing environment does not depend upon information from the
other for successful functioning. Specifically, the inter-
autonomous system route synthesis design should minimize the
constraints on the intra-autonomous system route synthesis
decisions when transiting (or delivering to) the autonomous
system.
3.2 Forwarding Requirements
The following requirements specifically address the functionality of
the datagram forwarding process. The forwarding process transfers
datagrams to intermediate or final destinations based upon datagram
characteristics, environmental characteristics, and route synthesis
decisions.
a) Decouple inter- and intra-autonomous system forwarding
decisions
The requirement is to provide a degree of independence between
the inter-autonomous system forwarding decision and the intra-
autonomous system forwarding decision within the forwarding
process. Though the forwarding decisions are to be independent
of each other, the inter-autonomous system delivery process may
necessarily be dependent upon intra-autonomous system route
synthesis and forwarding.
b) Do not forward datagrams deemed administratively inappropriate
Forward datagrams according to the route synthesis decision if
it does not conflict with known policy. Policy sensitive route
synthesis will prevent normally routed datagrams from utilizing
inappropriate resources. However, a datagram routed abnormally
due to unknown events or actions can always occur and the only
way to prohibit unwanted traffic from entering or leaving an
autonomous system is to provide policy enforcement within the
forwarding function.
Little [Page 6]
RFC 1126 Inter-Autonomous System Routing October 1989
c) Do not forward datagrams to failed resources
A datagram is not to be forwarded to a resource known to be
unavailable, notably an intermediate system such as a gateway.
This implies some ability to detect and react to resource
failures.
d) Forward datagram according to its characteristics
The datagram forwarding function is to be sensitive to the
characteristics of the datagram in order to execute the
appropriate route synthesis decision. Characteristics to
consider are the destination, quality-of-service, precedence,
datagram (or user) policy, and security. Note that some
characteristics, precedence for example, affect the forwarding
service provided whereas others affect the path chosen.
3.3 Information Requirements
This functional area addresses the general information requirements
of the routing environment. This encompasses both the nature and
disbursal of routing information. The characteristics of the routing
information and its disbursal are given by the following functional
requirements.
a) Provide a distributed and descriptive information base
The information base must not depend upon either centralization
or exact replication. The content of the information base must
be sufficient to support all provided routing functionality,
specifically that of route synthesis and forwarding.
Information of particular importance includes resource
characteristics and resource utilization policies.
b) Determine resource availability
Provide a means of determining the availability of any utilized
resource in a timely manner. The timeliness of this
determination is dependent upon the routing service(s) to be
supported.
c) Restrain transmission utilization
The dynamics of routing information flow should be such that a
significant portion of transmission resources are not consumed.
Routing information flow should adjust to the demands of the
environment, the capacities of the distribution facilities
utilized, and the desires of the resource manager.
Little [Page 7]
RFC 1126 Inter-Autonomous System Routing October 1989
d) Allow limited information exchange
Information distribution is to be sensitive to administrative
policies. An administrative policy may affect the content or
completeness of the information distributed. Additionally,
administrative policy may determine the extent of information
distributed.
3.4 Environmental Requirements
The following items identify those requirements directly related to
the nature of the environment within which routing is to occur.
a) Support a packet-switching environment
The routing environment should be capable of supporting
datagram transfer within a packet-switched oriented networking
environment.
b) Accommodate a connection-less oriented user transport service
The routing environment should be designed such that it
accommodates the model for connection-less oriented user
transport service.
c) Accommodate 10K autonomous systems and 100K networks
This requirement identifies the scale of the internetwork
environment we view as appearing in the future. A routing
design which does not accommodate this order of magnitude is
viewed as being inappropriate.
d) Allow for arbitrary interconnection of autonomous systems
The routing environment should accommodate interconnectivity
between autonomous systems which may occur in an arbitrary
manner. It is recognized that a practical solution is likely
to favor a given structure of interconnectivity for reasons of
efficiency. However, a design which does not allow for and
utilize interconnectivity of an arbitrary nature would not be
considered a feasible design.
3.5 General Objectives
The following are overall objectives to be achieved by the inter-
autonomous routing architecture and its protocols.
a) Provide routing services in a timely manner
Little [Page 8]
RFC 1126 Inter-Autonomous System Routing October 1989
Those routing services provided, encapsulated by the
requirements stated herein, are to be provided in a timely
manner. The time scale for this provision must be reasonable
to support those services provided by the internetwork
environment as a whole.
b) Minimize constraints on systems with limited resources
Allow autonomous systems, or gateways, of limited resources to
participate in the inter-autonomous system routing
architecture. This limited participation is not necessarily
without cost, either in terms of responsiveness, path
optimization, or other factor(s).
c) Minimize impact of dissimilarities between autonomous systems
Attempt to achieve a design in which the dissimilarities
between autonomous systems do not impinge upon the routing
services provided to any autonomous system.
d) Accommodate the addressing schemes and protocol mechanisms of
the autonomous systems
The routing environment should accommodate the addressing
schemes and protocol mechanisms of autonomous systems, where
these schemes and mechanisms may differ among autonomous
systems.
e) Must be implementable by network vendors
This is to say that the algorithms and complexities of the
design must be such that they can be understood outside of the
research community and implementable by people other than the
designers themselves. Any feasible design must be capable of
being put into practice.
4. Non-Goals
In view of the conflicting nature of many of the stated goals and the
careful considerations and tradeoffs necessary to achieve a
successful design, it is important to also identify those goals or
functions which we are not attempting to achieve. The following
items are not considered to be reasonable goals or functional
requirements at this time and are best left to future efforts. These
are non-goals, or non-requirements, within the context of the goals
and requirements previously stated by this document as well as our
interpretation of what can be practically achieved.
Little [Page 9]
RFC 1126 Inter-Autonomous System Routing October 1989
a) Ubiquity
It i
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cmr8.1500-13 @sf
1293 1828 p 54 c
22 r 55 c
cmr10.1643-34 @sf
71 1940 p (Complications) s
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0 2093 p 780 2 ru
cmr6.1500-4 @sf
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cmr9.1500-18 @sf
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(er) s
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11 r 98 c
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13 r (tra\016c) s
13 r (\(i.e.,) s
13 r (pac) s
0 r 107 c
-1 r (ets) s
12 r (sourced) s
cmti9.1500-21 @sf
13 r (and) s
cmr9.1500-18 @sf
14 r (destined) s
13 r (for) s
0 2272 p (mem) s
0 r 98 c
(ers) s
14 r (of) s
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14 r (same) s
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14 r (tra) s
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cmr6.1500-4 @sf
52 2348 p 55 c
cmr9.1500-18 @sf
69 2364 p (Economies) s
16 r (of) s
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26 r 70 c
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21 r 87 c
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12 r (of) s
12 r 112 c
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0 r 116 c
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16 r (See) s
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13 r (more) s
13 r (discussion.) s
cmr10.1643-34 @sf
0 2678 p (Estrin) s
1669 r ([P) s
0 r (age) s
14 r (4]) s
@eop
3 @bop0
cmbx12.1500-48 @sf
[<FFFF800FF8FFFF807FFC07F000FF1E07F001FE0E07F001FC0607F001FC0007F001FC0007F001FC0007F001FC0007F001FC00
07F001FC0007F001FC0007F003FC0007F003F80007F007F80007F01FF00007FFFFC00007FFFFC00007F007F00007F001F800
07F000FC0007F0007E0007F0007F0007F0007F0007F0007F0007F0007F0007F0007F0007F0007F0007F0007E0007F000FC00
07F001F80007F007F000FFFFFFC000FFFFFE0000> 40 34 -2 0 41.798] 82 @dc
[<03FC7FC00FFF7FC00FC3FE001F81FE001F80FE001F80FE001F807E001F807E001F807E001F807E001F807E001F807E001F80
7E001F807E001F807E001F807E001F807E001F807E001F807E001F807E00FF83FE00FF83FE00> 32 22 -2 0 31.133] 117 @dc
cmr8.1500-13 @sf
[<03FE03FE0070007000700070FFFEFFFEE0707070307018701C700E700670077003F001F000F000F00070> 16 21 -1 0 17.642] 52 @dc
[<1F807FE0F0F0E070E038E038003800380038607078F07FE06FC060006000600060007FC07FE07FF07030> 16 21 -2 0 17.642] 53 @dc
cmr6.1500-4 @sf
[<1FE01FE0030003000300FFE0FFE0E300630033003B001B001F000F0007000700> 16 16 -1 0 15.220] 52 @dc
[<3F00FFC0E1C0E0E0E0E000E070E079E07FC06F80600060007C007F007F806180> 16 16 -1 0 15.220] 53 @dc
cmr9.1500-18 @sf
[<C000C000E000600060007000300030003800180018001C000C000C000E00060006000700030003800180018001C000C000C0
00E000600060007000300030003800180018001C000C000C> 16 37 -2 9 19.198] 47 @dc
3 @bop1
cmsl10.1643-38 @sf
0 -99 p (RF) s
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518 r 80 c
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15 r (1989) s
cmbx12.1500-48 @sf
0 45 p (3.1) s
56 r 80 c
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18 r (Routing) s
cmr10.1643-34 @sf
0 170 p (Previous) s
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0 r 104 c
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0 r 51 c
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13 r (bac) s
0 r (kb) s
0 r (one) s
13 r (and/or) s
12 r (regional) s
13 r (net) s
0 r 119 c
-2 r (orks) s
12 r (in) s
13 r (the) s
0 1128 p (researc) s
0 r 104 c
14 r (in) s
0 r (ternet,) s
14 r (i.e.,) s
15 r (priv) s
-2 r (ate) s
15 r 118 c
-1 r (ertical) s
14 r 98 c
0 r (ypass) s
14 r (links.) s
71 1224 p (Implicit) s
16 r (in) s
16 r (this) s
16 r (complex) s
16 r (top) s
1 r (ology) s
17 r (are) s
16 r (organizational) s
16 r 98 c
1 r (oundaries.) s
23 r (These) s
17 r 98 c
1 r (oundaries) s
16 r (de\014ne) s
16 r (Ad-) s
0 1280 p (ministrativ) s
0 r 101 c
16 r (Domains) s
18 r (\(ADs\)) s
17 r (whic) s
0 r 104 c
16 r (preclude) s
18 r (the) s
18 r (imp) s
1 r (osition) s
17 r (of) s
18 r 97 c
17 r (single,) s
18 r (cen) s
0 r (tralized) s
17 r (set) s
17 r (of) s
18 r 112 c
1 r (olicies) s
0 1337 p (on) s
15 r (all) s
15 r (resources.) s
21 r (The) s
15 r (sub) s
3 r (ject) s
15 r (of) s
15 r (this) s
15 r (pap) s
1 r (er) s
16 r (is) s
15 r (the) s
15 r 112 c
1 r (olicy) s
16 r (requiremen) s
-1 r (ts) s
15 r (for) s
15 r (resource) s
15 r (usage) s
15 r (con) s
0 r (trol) s
14 r (in) s
0 1393 p (the) s
15 r (Researc) s
0 r 104 c
14 r (In) s
0 r (ternet.) s
71 1489 p (In) s
16 r (the) s
16 r (remainder) s
16 r (of) s
16 r (this) s
15 r (section) s
16 r 119 c
0 r 101 c
15 r (describ) s
1 r 101 c
16 r (the) s
16 r 112 c
2 ticularly difficult to
achieve stability in multi-vendor environments, in large internets,
and in environments characterized by a large variation in network
characteristics. For these reasons, we believe that it would be a
mistake to attempt to achieve effective load-based routing in an
Inter-AS Routing scheme.
A.6.5 Non-Interference Policies
There are policies which are in effect, or desired to be in effect,
which are based upon the concept of non-interference. These policies
state that the utilization of a given resource is permissible by one
party as long as that utilization does not disrupt the current or
future utilization of another party. These policies are often of the
kind "you may use the excess capacity of my link" without
guaranteeing any capacity will be available. The expectation is to
be able to utilize the link as needed, perhaps to the exclusion of
the other party. The problem with supporting such a policy is the
need to be cognizant of highly dynamic state information and the
implicit requirement to adapt to these changes. Rapid, persistent,
and non-deterministic state changes would lead to routing
oscillations and looping. We do not believe it is feasible to
support policies based on these considerations in a large
internetworking environment based on the current design of IP.
Security Considerations
Security issues are not addressed in this memo.
Little [Page 24]
RFC 1126 Inter-Autonomous System Routing October 1989
Author's Address
Mike Little
Science Applications International Corporation (SAIC)
8619 Westwood Center Drive
Vienna, Virginia 22182
Phone: 703-734-9000
EMail: little@SAIC.COM
Little [Page 25]