CRONUS Virtual Local Network
RFC 824

Document Type RFC - Unknown (August 1982; No errata)
Last updated 2013-03-02
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DOS-26 Rev A                                Virtual Local Network
      RFC 824


                            William I. MacGregor
                              Daniel C. Tappan
                        Bolt Beranek and Newman Inc.

                               25 August 1982

      [The purpose of this note is to describe the CRONUS Virtual
      Local Network, especially the addressing related features.
      These features include a method for mapping between Internet
      Addresses and Local Network addresses.  This is a topic of 
      current concern in the ARPA Internet community.  This note is
      intended to stimulate discussion.  This is not a specification
      of an Internet Standard.]

      1  Purpose and Scope

           This note defines the Cronus (1) Virtual Local Network

      (VLN), a facility which provides interhost message transport to

      the Cronus Distributed Operating System.  The VLN consists of a

      'client interface specification' and an 'implementation'; the

      client interface is expected to be available on every Cronus

      host.  Client processes can send and receive datagrams using

      specific, broadcast, or multicast addressing as defined in the

      interface specification.

      (1) The Cronus Distributed Operating System is being designed  by
      Bolt  Beranek  and Newman Inc., as a component of the Distributed
      Systems Technology Program  sponsored  by  Rome  Air  Development
      Center.   This work is supported by the DOS Design/Implementation
      contract, F30602-81-C-0132.


      DOS-26 Rev A                                Virtual Local Network
      RFC 824

           From the viewpoint of other Cronus system software and

      application programs, the VLN stands in place of a direct

      interface to the physical local network (PLN).  This additional

      level of abstraction is defined to meet two major system


        *  COMPATIBILITY.  The VLN defines a communication facility
           which is compatible with the Internet Protocol (IP)
           developed by DARPA; by implication the VLN is compatible
           with higher-level protocols such as the Transmission Control
           Protocol (TCP) based on IP.

        *  SUBSTITUTABILITY.  Cronus software built above the VLN is
           dependent only upon the VLN interface and not its
           implementation.  It is possible to substitute one physical
           local network for another in the VLN implementation,
           provided that the VLN interface semantics are maintained.

           (This note assumes the reader is familiar with the concepts

      and terminology of the DARPA Internet Program; reference [6] is a

      compilation of the important protocol specifications and other

      documents.  Documents in [6] of special significance here are [5]

      and [4].)

           The compatibility goal is motivated by factors relating to

      the Cronus design and its development environment.  A large body

      of software has evolved, and continues to evolve, in the internet

      community fostered by DARPA.  For example, the compatibility goal


      DOS-26 Rev A                                Virtual Local Network
      RFC 824

      permits the Cronus design to assimilate existing software

      components providing electronic mail, remote terminal access, and

      file transfer in a straightforward manner.  In addition to the

      roles of such services in the Cronus system, they are needed as

      support for the design and development process.  The prototype

      Cronus cluster, called the Advanced Development Model (ADM), will

      be connected to the ARPANET, and it is important that the ADM

      conform to the standards and conventions of the DARPA internet


           The substitutability goal reflects the belief that different

      instances of the Cronus cluster will utilize different physical

      local networks.  Substitution may be desirable for reasons of

      cost, performance, or other properties of the physical local

      network such as mechanical and electrical ruggedness.  The

      existence of the VLN interface definition suggests a procedure

      for physical local network substitution, namely, re-

      implementation of the VLN interface on each Cronus host.  The

      implementations will be functionally equivalent but can be

      expected to differ along dimensions not specified by the VLN

      interface definition.  Since different physical local networks


      DOS-26 Rev A                                Virtual Local Network
      RFC 824

      are often quite similar, the task of "re-implementing" the VLN is
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