rfc1126.txt

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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.






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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.



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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



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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.




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RFC 1126            Inter-Autonomous System Routing         October 1989


      a) Ubiquity

         It is not a goal to design a routing environment in which any
         participating autonomous system can obtain a routing service to
         any other participating autonomous system in a ubiquitous
         fashion.  Within a policy sensitive routing environment, the
         cooperation of intermediate resources will be necessary and
         cannot be guaranteed to all participants.  The concept of
         ubiquitous connectivity will not be a valid one.

      b) Congestion control

         The ability for inter-autonomous system routing to perform
         congestion control is a non-requirement.  Additional study is
         necessary to determine what mechanisms are most appropriate and
         if congestion control is best realized within the inter-AS
         and/or intra-AS environments, and if both, what the dynamics of
         the interactions between the two are.

      c) Load splitting

         The functional capability to distribute the flow of datagrams,
         from a source to a destination, across two or more distinct
         paths through route synthesis and/or forwarding is a non-
         requirement.

      d) Maximizing the utilization of resources

         There is no goal or requirement for the inter-autonomous system
         routing environment to be designed such that it attempts to
         maximize the utilization of available resources.

      e) Schedule to deadline service

         The ability to support a schedule to deadline routing service
         is a non-requirement for the inter-autonomous routing
         environment at this point in time.

      f) Non-interference policies of resource utilization

         The ability to support routing policies based upon the concept
         of non-interference is a not a requirement.  An example of such
         a policy is one where an autonomous system allows the
         utilization of excess bandwidth by external users as long as
         this does not interfere with local usage of the link.






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