<pre>Network Working Group                                           D. Clark
Request for Comments: 1287                                           MIT
                                                               L. Chapin
                                                                     BBN
                                                                 V. Cerf
                                                                    CNRI
                                                               R. Braden
                                                                     ISI
                                                                R. Hobby
                                                                UC Davis
                                                           December 1991


                <span class="h1">Towards the Future Internet Architecture</span>

Status of this Memo

   This informational RFC discusses important directions for possible
   future evolution of the Internet architecture, and suggests steps
   towards the desired goals.  It is offered to the Internet community
   for discussion and comment.  This memo provides information for the
   Internet community.  It does not specify an Internet standard.
   Distribution of this memo is unlimited.

Table of Contents

   <a href="#section-1">1</a>.  INTRODUCTION .................................................  <a href="#page-2">2</a>

   <a href="#section-2">2</a>.  ROUTING AND ADDRESSING .......................................  <a href="#page-5">5</a>

   <a href="#section-3">3</a>.  MULTI-PROTOCOL ARCHITECTURES .................................  <a href="#page-9">9</a>

   <a href="#section-4">4</a>.  SECURITY ARCHITECTURE ........................................ <a href="#page-13">13</a>

   <a href="#section-5">5</a>   TRAFFIC CONTROL AND STATE .................................... <a href="#page-16">16</a>

   <a href="#section-6">6</a>.  ADVANCED APPLICATIONS ........................................ <a href="#page-18">18</a>

   <a href="#section-7">7</a>.  REFERENCES ................................................... <a href="#page-21">21</a>

   APPENDIX A. Setting the Stage .................................... <a href="#page-22">22</a>

   APPENDIX B. Group Membership ..................................... <a href="#page-28">28</a>

   Security Considerations .......................................... <a href="#page-29">29</a>

   Authors' Addresses ............................................... <a href="#page-29">29</a>




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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  INTRODUCTION</span>

   1.1 The Internet Architecture

      The Internet architecture, the grand plan behind the TCP/IP
      protocol suite, was developed and tested in the late 1970s by a
      small group of network researchers [1-4].  Several important
      features were added to the architecture during the early 1980's --
      subnetting, autonomous systems, and the domain name system [<a href="#ref-5" title="&quot;Internet Standard Subnetting Procedure&quot;">5</a>,<a href="#ref-6" title="&quot;Domain Names - Concepts and Facilities&quot;">6</a>].
      More recently, IP multicasting has been added [<a href="#ref-7" title="&quot;Host Extensions for IP Multicasting&quot;">7</a>].

      Within this architectural framework, the Internet Engineering Task
      Force (IETF) has been working with great energy and effectiveness
      to engineer, define, extend, test, and standardize protocols for
      the Internet.  Three areas of particular importance have been
      routing protocols, TCP performance, and network management.
      Meanwhile, the Internet infrastructure has continued to grow at an
      astonishing rate.  Since January 1983 when the ARPANET first
      switched from NCP to TCP/IP, the vendors, managers, wizards, and
      researchers of the Internet have all been laboring mightily to
      survive their success.

      A set of the researchers who had defined the Internet architecture
      formed the original membership of the Internet Activities Board
      (IAB).  The IAB evolved from a technical advisory group set up in
      1981 by DARPA to become the general technical and policy oversight
      body for the Internet.  IAB membership has changed over the years
      to better represent the changing needs and issues in the Internet
      community, and more recently, to reflect the internationalization
      of the Internet, but it has retained an institutional concern for
      the protocol architecture.

      The IAB created the Internet Engineering Task Force (IETF) to
      carry out protocol development and engineering for the Internet.
      To manage the burgeoning IETF activities, the IETF chair set up
      the Internet Engineering Steering Group (IESG) within the IETF.
      The IAB and IESG work closely together in ratifying protocol
      standards developed within the IETF.

      Over the past few years, there have been increasing signs of
      strains on the fundamental architecture, mostly stemming from
      continued Internet growth.  Discussions of these problems
      reverberate constantly on many of the major mailing lists.

   1.2  Assumptions

      The priority for solving the problems with the current Internet
      architecture depends upon one's view of the future relevance of



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      TCP/IP with respect to the OSI protocol suite.  One view has been
      that we should just let the TCP/IP suite strangle in its success,
      and switch to OSI protocols.  However, many of those who have
      worked hard and successfully on Internet protocols, products, and
      service are anxious to try to solve the new problems within the
      existing framework.  Furthermore, some believe that OSI protocols
      will suffer from versions of many of the same problems.

      To begin to attack these issues, the IAB and the IESG held a one-
      day joint discussion of Internet architectural issues in January
      1991.  The framework for this meeting was set by Dave Clark (see
      <a href="#appendix-A">Appendix A</a> for his slides).  The discussion was spirited,
      provocative, and at times controversial, with a lot of soul-
      searching over questions of relevance and future direction.  The
      major result was to reach a consensus on the following four basic
      assumptions regarding the networking world of the next 5-10 years.

      (1)  The TCP/IP and OSI suites will coexist for a long time.

           There are powerful political and market forces as well as
           some technical advantages behind the introduction of the OSI
           suite.  However, the entrenched market position of the TCP/IP
           protocols means they are very likely to continue in service
           for the foreseeable future.

      (2)  The Internet will continue to include diverse networks and
           services, and will never be comprised of a single network
           technology.

           Indeed, the range of network technologies and characteristics
           that are connected into the Internet will increase over the
           next decade.

      (3)  Commercial and private networks will be incorporated, but we
           cannot expect the common carriers to provide the entire
           service.  There will be mix of public and private networks,
           common carriers and private lines.

      (4)  The Internet architecture needs to be able to scale to 10**9
           networks.

           The historic exponential growth in the size of the Internet
           will presumably saturate some time in the future, but
           forecasting when is about as easy as forecasting the future
           economy.  In any case, responsible engineering requires an
           architecture that is CAPABLE of expanding to a worst-case
           size.  The exponent "9" is rather fuzzy; estimates have
           varied from 7 to 10.



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   1.3  Beginning a Planning Process

      Another result of the IAB and IESG meeting was the following list
      of the five most important areas for architectural evolution:

      (1)  Routing and Addressing

           This is the most urgent architectural problem, as it is
           directly involved in the ability of the Internet to continue
           to grow successfully.

      (2)  Multi-Protocol Architecture

           The Internet is moving towards widespread support of both the
           TCP/IP and the OSI protocol suites.  Supporting both suites
           raises difficult technical issues, and a plan -- i.e., an
           architecture -- is required to increase the chances of
           success.  This area was facetiously dubbed "making the
           problem harder for the good of mankind."

           Clark had observed that translation gateways (e.g., mail
           gateways) are very much a fact of life in Internet operation
           but are not part of the architecture or planning.  The group
           discussed the possibility of building the architecture around
           the partial connectivity that such gateways imply.

      (3)  Security Architecture

           Although military security was considered when the Internet
           architecture was designed, the modern security issues are
           much broader, encompassing commercial requirements as well.
           Furthermore, experience has shown that it is difficult to add
           security to a protocol suite unless it is built into the
           architecture from the beginning.

      (4)  Traffic Control and State

           The Internet should be extended to support "real-time"
           applications like voice and video.  This will require new
           packet queueing mechanisms in gateways -- "traffic control"
           -- and additional gateway state.

      (5)  Advanced Applications

           As the underlying Internet communication mechanism matures,
           there is an increasing need for innovation and
           standardization in building new kinds of applications.




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      The IAB and IESG met again in June 1991 at SDSC and devoted three
      full days to a discussion of these five topics.  This meeting,
      which was called somewhat perversely the "Architecture Retreat",
      was convened with a strong resolve to take initial steps towards
      planning evolution of the architecture.  Besides the IAB and IESG,
      the group of 32 people included the members of the Research
      Steering Group (IRSG) and a few special guests.  On the second
      day, the Retreat broke into groups, one for each of the five
      areas.  The group membership is listed in <a href="#appendix-B">Appendix B</a>.

      This document was assembled from the reports by the chairs of
      these groups.  This material was presented at the Atlanta IETF
      meeting, and appears in the minutes of that meeting [<a href="#ref-8" title="&quot;Proceedings of the Twenty-First Internet Engineering Task Force&quot;">8</a>].

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  ROUTING AND ADDRESSING</span>

   Changes are required in the addressing and routing structure of IP to
   deal with the anticipated growth and functional evolution of the
   Internet.  We expect that:

   o    The Internet will run out of certain classes of IP network
        addresses, e.g., B addresses.

   o    The Internet will run out of the 32-bit IP address space
        altogether, as the space is currently subdivided and managed.

   o    The total number of IP network numbers will grow to the point
        where reasonable routing algorithms will not be able to perform
        routing based upon network numbers.

   o    There will be a need for more than one route from a source to a
        destination, to permit variation in TOS and policy conformance.
        This need will be driven both by new applications and by diverse
        transit services.  The source, or an agent acting for the
        source, must control the selection of the route options.

   2.1  Suggested Approach

      There is general agreement on the approach needed to deal with
      these facts.

      (a)  We must move to an addressing scheme in which network numbers
           are aggregated into larger units as the basis for routing.
           An example of an aggregate is the Autonomous System, or the
           Administrative Domain (AD).

           Aggregation will accomplish several goals: define regions
           where policy is applied, control the number of routing



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           elements, and provide elements for network management.  Some
           believe that it must be possible to further combine
           aggregates, as in a nesting of ADs.

      (b)  We must provide some efficient means to compute common
           routes, and some general means to compute "special" routes.

           The general approach to special routes will be some form of
           route setup specified by a "source route".

      There is not full agreement on how ADs may be expected to be
      aggregated, or how routing protocols should be organized to deal
      with the aggregation boundaries.   A very general scheme may be
      used [ref. Chiappa], but some prefer a scheme that more restricts
      and defines the expected network model.

      To deal with the address space exhaustion, we must either expand
      the address space or else reuse the 32 bit field ("32bf") in
      different parts of the net.  There are several possible address
      formats that might make sense, as described in the next section.

      Perhaps more important is the question of how to migrate to the
      new scheme.  All migration plans will require that some routers
      (or other components inside the Internet) be able to rewrite
      headers to accommodate hosts that handle only the old or format or
      only the new format.  Unless the need for such format conversion
      can be inferred algorithmically, migration by itself will require
      some sort of setup of state in the conversion element.

      We should not plan a series of "small" changes to the
      architecture.  We should embark now on a plan that will take us
      past the exhaustion of the address space.  This is a more long-
      range act of planning than the Internet community has undertaken
      recently, but the problems of migration will require a long lead
      time, and it is hard to see an effective way of dealing with some
      of the more immediate problems, such as class B exhaustion, in a
      way that does not by itself take a long time.  So, once we embark
      on a plan of change, it should take us all the way to replacing
      the current 32-bit global address space.  (This conclusion is
      subject to revision if, as is always possible, some very clever
      idea surfaces that is quick to deploy and gives us some breathing
      room.  We do not mean to discourage creative thinking about
      short-term actions.  We just want to point out that even small
      changes take a long time to deploy.)

      Conversion of the address space by itself is not enough.  We must
      at the same time provide a more scalable routing architecture, and
      tools to better manage the Internet.  The proposed approach is to



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      ADs as the unit of aggregation for routing.  We already have
      partial means to do this.  IDPR does this.  The OSI version of BGP
      (IDRP) does this.  BGP could evolve to do this.  The additional
      facility needed is a global table that maps network numbers to
      ADs.

      For several reasons (special routes and address conversion, as
      well as accounting and resource allocation), we are moving from a
      "stateless" gateway model, where only precomputed routes are
      stored in the gateway, to a model where at least some of the
      gateways have per-connection state.

   2.2  Extended IP Address Formats

      There are three reasonable choices for the extended IP address
      format.

      A)   Replace the 32 bit field (32bf) with a field of the same size
           but with different meaning.  Instead of being globally
           unique, it would now be unique only within some smaller
           region (an AD or an aggregate of ADs).  Gateways on the
           boundary would rewrite the address as the packet crossed the
           boundary.

           Issues: (1) addresses in the body of packets must be found
           and rewritten; (2) the host software need not be changed; (3)
           some method (perhaps a hack to the DNS) must set up the
           address mappings.

           This scheme is due to Van Jacobson.  See also the work by
           Paul Tsuchiya on NAT.

      B)   Expand the 32bf to a 64 bit field (or some other new size),
           and use the field to hold a global host address and an AD for
           that host.

           This choice would provide a trivial mapping from the host to
           the value (the AD) that is the basis of routing.  Common
           routes (those selected on the basis of destination address
           without taking into account the source address as well) can
           be selected directly from the packet address, as is done
           today, without any prior setup.

      3)   Expand the 32bf to a 64 bit field (or some other new size),
           and use the field as a "flat" host identifier.  Use
           connection setup to provide routers with the mapping from
           host id to AD, as needed.




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           The 64 bits can now be used to simplify the problem of
           allocating host ids, as in Ethernet addresses.

      Each of these choices would require an address re-writing module
      as a part of migration.  The second and third require a change to
      the IP header, so host software must change.

   2.3  Proposed Actions

      The following actions are proposed:

      A)   Time Line

           Construct a specific set of estimates for the time at which
           the various problems above will arise, and construct a
           corresponding time-line for development and deployment of a
           new addressing/routing architecture.  Use this time line as a
           basis for evaluating specific proposals for changes.  This is
           a matter for the IETF.

      B)   New Address Format

           Explore the options for a next generation address format and
           develop a plan for migration.  Specifically, construct a
           prototype gateway that does address mapping.  Understand the
           complexity of this task, to guide our thinking about
           migration options.

      C)   Routing on ADs

           Take steps to make network aggregates (ADs) the basis of
           routing.  In particular, explore the several options for a
           global table that maps network numbers to ADs.  This is a
           matter for the IETF.

      D)   Policy-Based Routing

           Continue the current work on policy based routing. There are
           several specific objectives.

           -    Seek ways to control the complexity of setting policy
                (this is a human interface issue, not an algorithm
                complexity issue).

           -    Understand better the issues of maintaining connection
                state in gateways.

           -    Understand better the issues of connection state setup.



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      E)   Research on Further Aggregation

           Explore, as a research activity, how ADs should be aggregated
           into still larger routing elements.

           -    Consider whether the architecture should define the
                "role" of an AD or an aggregate.

           -    Consider whether one universal routing method or
                distinct methods should be used inside and outside ADs
                and aggregates.

      Existing projects planned for DARTnet will help resolve several of
      these issues: state in gateways, state setup, address mapping,
      accounting and so on.  Other experiments in the R&amp;D community also
      bear on this area.

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  MULTI-PROTOCOL ARCHITECTURE</span>

   Changing the Internet to support multiple protocol suites leads to
   three specific architectural questions:

   o    How exactly will we define "the Internet"?

   o    How would we architect an Internet with n&gt;1 protocol suites,
        regardless of what the suites are?

   o    Should we architect for partial or filtered connectivity?

   o    How to add explicit support for application gateways into the
        architecture?

   3.1  What is the "Internet"?

      It is very difficult to deal constructively with the issue of "the
      multi-protocol Internet" without first determining what we believe
      "the Internet" is (or should be).   We distinguish "the Internet",
      a set of communicating systems, from "the Internet community", a
      set of people and organizations.  Most people would accept a loose
      definition of the latter as "the set of people who believe
      themselves to be part of the Internet community".  However, no
      such "sociological" definition of the Internet itself is likely to
      be useful.

      Not too long ago, the Internet was defined by IP connectivity (IP
      and ICMP were - and still are - the only "required" Internet
      protocols).  If I could PING you, and you could PING me, then we
      were both on the Internet, and a satisfying working definition of



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      the Internet could be constructed as a roughly transitive closure
      of IP-speaking systems.  This model of the Internet was simple,
      uniform, and - perhaps most important - testable.  The IP-
      connectivity model clearly distinguished systems that were "on the
      Internet" from those that were not.

      As the Internet has grown and the technology on which it is based
      has gained widespread commercial acceptance, the sense of what it
      means for a system to be "on the Internet" has changed, to
      include:

      *    Any system that has partial IP connectivity, restricted by
           policy filters.

      *    Any system that runs the TCP/IP protocol suite, whether or
           not it is actually accessible from other parts of the
           Internet.

      *    Any system that can exchange <a href="./rfc822">RFC-822</a> mail, without the
           intervention of mail gateways or the transformation of mail
           objects.

      *    Any system with e-mail connectivity to the Internet, whether
           or not a mail gateway or mail object transformation is
           required.

      These definitions of "the Internet", are still based on the
      original concept of connectivity, just "moving up the stack".

      We propose instead a new definition of the Internet, based on a
      different unifying concept:

      *    "Old" Internet concept:  IP-based.

           The organizing principle is the IP address, i.e., a common
           network address space.

      *    "New" Internet concept:  Application-based.

           The organizing principle is the domain name system and
           directories, i.e., a common - albeit necessarily multiform -
           application name space.

      This suggests that the idea of "connected status", which has
      traditionally been tied to the IP address(via network numbers,
      should instead be coupled to the names and related identifying
      information contained in the distributed Internet directory.




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      A naming-based definition of "the Internet" implies a much larger
      Internet community, and a much more dynamic (and unpredictable)
      operational Internet.  This argues for an Internet architecture
      based on adaptability (to a broad spectrum of possible future
      developments) rather than anticipation.

   3.2  A Process-Based Model of the Multiprotocol Internet

      Rather than specify a particular "multi-protocol Internet",
      embracing a pre-determined number of specific protocol
      architectures, we propose instead a process-oriented model of the
      Internet, which accommodates different protocol architectures
      according to the traditional "things that work" principle.

      A process-oriented Internet model includes, as a basic postulate,
      the assertion that there is no *steady-state* "multi-protocol
      Internet".  The most basic forces driving the evolution of the
      Internet are pushing it not toward multi-protocol diversity, but
      toward the original state of protocol-stack uniformity (although
      it is unlikely that it will ever actually get there).  We may
      represent this tendency of the Internet to evolve towards
      homogeneity as the most "thermodynamically stable" state by
      describing four components of a new process-based Internet
      architecture:

      Part 1: The core Internet architecture

           This is the traditional TCP/IP-based architecture.  It is the
           "magnetic center" of Internet evolution, recognizing that (a)
           homogeneity is still the best way to deal with diversity in
           an internetwork, and (b) IP connectivity is still the best
           basic model of the Internet (whether or not the actual state
           of IP ubiquity can be achieved in practice in a global
           operational Internet).

      "In the beginning", the Internet architecture consisted only of
      this first part.  The success of the Internet, however, has
      carried it beyond its uniform origins;  ubiquity and uniformity
      have been sacrificed in order to greatly enrich the Internet "gene
      pool".

      Two additional parts of the new Internet architecture express the
      ways in which the scope and extent of the Internet have been
      expanded.

      Part 2: Link sharing

           Here physical resources -- transmission media, network



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           interfaces, perhaps some low-level (link) protocols -- are
           shared by multiple, non-interacting protocol suites.  This
           part of the architecture recognizes the necessity and
           convenience of coexistence, but is not concerned with
           interoperability;  it has been called "ships in the night" or
           "S.I.N.".

           Coexisting protocol suites are not, of course, genuinely
           isolated in practice;  the ships passing in the night raise
           issues of management, non-interference, coordination, and
           fairness in real Internet systems.

      Part 3: Application interoperability

           Absent ubiquity of interconnection (i.e., interoperability of
           the "underlying stacks"), it is still possible to achieve
           ubiquitous application functionality by arranging for the
           essential semantics of applications to be conveyed among
           disjoint communities of Internet systems.  This can be
           accomplished by application relays, or by user agents that
           present a uniform virtual access method to different
           application services by expressing only the shared semantics.

           This part of the architecture emphasizes the ultimate role of
           the Internet as a basis for communication among applications,
           rather than as an end in itself.  To the extent that it
           enables a population of applications and their users to move
           from one underlying protocol suite to another without
           unacceptable loss of functionality, it is also a "transition
           enabler".

      Adding parts 2 and 3 to the original Internet architecture is at
      best a mixed blessing.  Although they greatly increase the scope
      of the Internet and the size of the Internet community, they also
      introduce significant problems of complexity, cost, and
      management, and they usually represent a loss of functionality
      (particularly with respect to part 3).  Parts 2 and 3 represent
      unavoidable, but essentially undesirable, departures from the
      homogeneity represented by part 1.  Some functionality is lost,
      and additional system complexity and cost is endured, in order to
      expand the scope of the Internet.  In a perfect world, however,
      the Internet would evolve and expand without these penalties.

      There is a tendency, therefore, for the Internet to evolve in
      favor of the homogeneous architecture represented by part 1, and
      away from the compromised architectures of parts 2 and 3.  Part 4
      expresses this tendency.




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      Part 4: Hybridization/Integration.

           Part 4 recognizes the desirability of integrating similar
           elements from different Internet protocol architectures to
           form hybrids that reduce the variability and complexity of
           the Internet system.  It also recognizes the desirability of
           leveraging the existing Internet infrastructure to facilitate
           the absorption of "new stuff" into the Internet, applying to
           "new stuff" the established Internet practice of test,
           evaluate, adopt.

           This part expresses the tendency of the Internet, as a
           system, to attempt to return to the original "state of grace"
           represented by the uniform architecture of part 1.  It is a
           force acting on the evolution of the Internet, although the
           Internet will never actually return to a uniform state at any
           point in the future.

      According to this dynamic process model, running X.400 mail over
      <a href="./rfc1006">RFC 1006</a> on a TCP/IP stack, integrated IS-IS routing, transport
      gateways, and the development of a single common successor to the
      IP and CLNP protocols are all examples of "good things".  They
      represent movement away from the non-uniformity of parts 2 and 3
      towards greater homogeneity, under the influence of the "magnetic
      field" asserted by part 1, following the hybridization dynamic of
      part 4.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  SECURITY ARCHITECTURE</span>

   4.1  Philosophical Guidelines

      The principal themes for development of an Internet security
      architecture are simplicity, testability, trust, technology and
      security perimeter identification.

      *    There is more to security than protocols and cryptographic
           methods.

      *    The security architecture and policies should be simple
           enough to be readily understood.  Complexity breeds
           misunderstanding and poor implementation.

      *    The implementations should be testable to determine if the
           policies are met.

      *    We are forced to trust hardware, software and people to make
           any security architecture function.  We assume that the
           technical instruments of security policy enforcement are at



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           least as powerful as modern personal computers and work
           stations; we do not require less capable components to be
           self-protecting (but might apply external remedies such as
           link level encryption devices).

      *    Finally, it is essential to identify security perimeters at
           which protection is to be effective.

   4.2  Security Perimeters

      There were four possible security perimeters: link level,
      net/subnet level, host level, and process/application level.  Each
      imposes different requirements, can admit different techniques,
      and makes different assumptions about what components of the
      system must be trusted to be effective.

      Privacy Enhanced Mail is an example of a process level security
      system; providing authentication and confidentiality for SNMP is
      another example.  Host level security typically means applying an
      external security mechanism on the communication ports of a host
      computer.  Network or subnetwork security means applying the
      external security capability at the gateway/router(s) leading from
      the subnetwork to the "outside".  Link-level security is the
      traditional point-to-point or media-level (e.g., Ethernet)
      encryption mechanism.

      There are many open questions about network/subnetwork security
      protection, not the least of which is a potential mismatch between
      host level (end/end) security methods and methods at the
      network/subnetwork level.  Moreover, network level protection does
      not deal with threats arising within the security perimeter.

      Applying protection at the process level assumes that the
      underlying scheduling and operating system mechanisms can be
      trusted not to prevent the application from applying security when
      appropriate.  As the security perimeter moves downward in the
      system architecture towards the link level, one must make many
      assumptions about the security threat to make an argument that
      enforcement at a particular perimeter is effective.  For example,
      if only link-level encryption is used, one must assume that
      attacks come only from the outside via communications lines, that
      hosts, switches and gateways are physically protected, and the
      people and software in all these components are to be trusted.

   4.3  Desired Security Services

      We need authenticatable distinguished names if we are to implement
      discretionary and non-discretionary access control at application



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      and lower levels in the system.  In addition, we need enforcement
      for integrity (anti-modification, anti-spoof and anti-replay
      defenses), confidentiality, and prevention of denial-of-service.
      For some situations, we may also need to prevent repudiation of
      message transmission or to prevent covert channels.

      We have some building blocks with which to build the Internet
      security system.  Cryptographic algorithms are available (e.g.,
      Data Encryption Standard, RSA, El Gamal, and possibly other public
      key and symmetric key algorithms), as are hash functions such as
      MD2 and MD5.

      We need Distinguished Names (in the OSI sense) and are very much
      in need of an infrastructure for the assignment of such
      identifiers, together with widespread directory services for
      making them known.  Certificate concepts binding distinguished
      names to public keys and binding distinguished names to
      capabilities and permissions may be applied to good advantage.

      At the router/gateway level, we can apply address and protocol
      filters and other configuration controls to help fashion a
      security system.  The proposed OSI Security Protocol 3 (SP3) and
      Security Protocol 4 (SP4) should be given serious consideration as
      possible elements of an Internet security architecture.

      Finally, it must be observed that we have no good solutions to
      safely storing secret information (such as the secret component of
      a public key pair) on systems like PCs or laptop computers that
      are not designed to enforce secure storage.

   4.4  Proposed Actions

      The following actions are proposed.

      A)   Security Reference Model

           A Security Reference Model for the Internet is needed, and it
           should be developed expeditiously.  This model should
           establish the target perimeters and document the objectives
           of the security architecture.

      B)   Privacy-Enhanced Mail (PEM)

           For Privacy Enhanced Mail, the most critical steps seem to be
           the installation of (1) a certificate generation and
           management infrastructure, and (2) X.500 directory services
           to provide access to public keys via distinguished names.
           Serious attention also needs to be placed on any limitations



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           imposed by patent and export restrictions on the deployment
           of this system.

      C)   Distributed System Security

           We should examine security methods for distributed systems
           applications, in both simple (client/server) and complex
           (distributed computing environment) cases.  For example, the
           utility of certificates granting permissions/capabilities to
           objects bound to distinguished names should be examined.

      D)   Host-Level Security

           SP4 should be evaluated for host-oriented security, but SP3
           should also be considered for this purpose.

      E)   Application-Level Security

           We should implement application-level security services, both
           for their immediate utility (e.g., PEM, SNMP authentication)
           and also to gain valuable practical experience that can
           inform the refinement of the Internet security architecture.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  TRAFFIC CONTROL AND STATE</span>

   In the present Internet, all IP datagrams are treated equally.  Each
   datagram is forwarded independently, regardless of any relationship
   it has to other packets for the same connection, for the same
   application, for the same class of applications, or for the same user
   class.  Although Type-of-Service and Precedence bits are defined in
   the IP header, these are not generally implemented, and in fact it is
   not clear how to implement them.

   It is now widely accepted that the future Internet will need to
   support important applications for which best-effort is not
   sufficient -- e.g., packet video and voice for teleconferencing.
   This will require some "traffic control" mechanism in routers,
   controlled by additional state, to handle "real-time" traffic.

   5.1  Assumptions and Principles


      o    ASSUMPTION: The Internet will need to support performance
           guarantees for particular subsets of the traffic.

      Unfortunately, we are far from being able to give precise meanings
      to the terms "performance", "guarantees", or "subsets" in this
      statement.  Research is still needed to answer these questions.



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      o    The default service will continue to be the current "best-
           effort" datagram delivery, with no service guarantees.

      o    The mechanism of a router can be separated into (1) the
           forwarding path and (2) the control computations (e.g.,
           routing) which take place in the background.

           The forwarding path must be highly optimized, sometimes with
           hardware-assist, and it is therefore relatively costly and
           difficult to change.  The traffic control mechanism operates
           in the forwarding path, under the control of state created by
           routing and resource control computations that take place in
           background.  We will have at most one shot at changing the
           forwarding paths of routers, so we had better get it right
           the first time.

      o    The new extensions must operate in a highly heterogeneous
           environment, in which some parts will never support
           guarantees.  For some hops of a path (e.g., a high-speed
           LAN), "over-provisioning" (i.e., excess capacity) will allow
           adequate service for real-time traffic, even when explicit
           resource reservation is unavailable.

      o    Multicast distribution is probably essential.

   5.2  Technical Issues

      There are a number of technical issues to be resolved, including:

      o    Resource Setup

           To support real-time traffic, resources need to be reserved
           in each router along the path from source to destination.
           Should this new router state be "hard" (as in connections) or
           "soft" (i.e., cached state)?

      o    Resource binding vs. route binding

           Choosing a path from source to destination is traditionally
           performed using a dynamic routing protocol.  The resource
           binding and the routing might be folded into a single complex
           process, or they might be performed essentially
           independently.  There is a tradeoff between complexity and
           efficiency.

      o    Alternative multicast models

           IP multicasting uses a model of logical addressing in which



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           targets attach themselves to a group.  In ST-2, each host in
           a multicast session includes in its setup packet an explicit
           list of target addresses.  Each of these approaches has
           advantages and drawbacks; it is not currently clear which
           will prevail for n-way teleconferences.

      o    Resource Setup vs. Inter-AD routing

           Resource guarantees of whatever flavor must hold across an
           arbitrary end-to-end path, including multiple ADs.  Hence,
           any resource setup mechanism needs to mesh smoothly with the
           path setup mechanism incorporated into IDPR.

      o    Accounting

           The resource guarantee subsets ("classes") may be natural
           units for accounting.

   5.3  Proposed Actions

      The actions called for here are further research on the technical
      issues listed above, followed by development and standardization
      of appropriate protocols.  DARTnet, the DARPA Research Testbed
      network, will play an important role in this research.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  ADVANCED APPLICATIONS</span>

   One may ask: "What network-based applications do we want, and why
   don't we have them now?"  It is easy to develop a large list of
   potential applications, many of which would be based on a
   client/server model.  However, the more interesting part of the
   question is: "Why haven't people done them already?"  We believe the
   answer to be that the tools to make application writing easy just do
   not exist.

   To begin, we need a set of common interchange formats for a number of
   data items that will be used across the network.  Once these common
   data formats have been defined, we need to develop tools that the
   applications can use to move the data easily.

   6.1  Common Interchange Formats

      The applications have to know the format of information that they
      are exchanging, for the information to have any meaning.   The
      following format types are to concern:

      (1)  Text - Of the formats in this list, text is the most stable,
           but today's international Internet has to address the needs



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           of character sets other than USASCII.

      (2)  Image -  As we enter the "Multimedia Age", images will become
           increasingly important, but we need to agree on how to
           represent them in packets.

      (3)  Graphics - Like images, vector graphic information needs a
           common definition. With such a format we could exchange
           things like architectural blueprints.

      (4)  Video - Before we can have a video window running on our
           workstation, we need to know the format of that video
           information coming over the network.

      (5)  Audio/Analog - Of course, we also need the audio to go with
           the video, but such a format would be used for representation
           of all types of analog signals.

      (6)  Display - Now that we are opening windows on our workstation,
           we want to open a window on another person's workstation to
           show her some data pertinent to the research project, so now
           we need a common window display format.

      (7)  Data Objects - For inter-process communications we need to
           agree on the formats of things like integers, reals, strings,
           etc.

      Many of these formats are being defined by other, often several
      other, standards organizations.  We need to agree on one format
      per category for the Internet.

   6.2  Data Exchange Methods

      Applications will require the following methods of data exchange.

      (1)  Store and Forward

           Not everyone is on the network all the time.  We need a
           standard means of providing an information flow to
           sometimes-connected hosts, i.e., we need a common store-and-
           forward service.  Multicasting should be included in such a
           service.

      (2)  Global File Systems

           Much of the data access over the network can be broken down
           to simple file access. If you had a real global file system
           where you access any file on the Internet (assuming you have



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           permission), would you ever need FTP?

      (3)  Inter-process Communications

           For a true distributed computing environment, we need the
           means to allow processes to exchange data in a standard
           method over the network.  This requirement encompasses RPC,
           APIs, etc.

      (4)  Data Broadcast

           Many  applications need to send the same information to many
           other hosts.  A standard and efficient method is needed to
           accomplish this.

      (5)  Database Access

           For good information exchange, we need to have a standard
           means for accessing databases. The Global File System can get
           you to the data, but the database access methods will tell
           you about its structure and content.

      Many of these items are being addressed by other organizations,
      but for Internet interoperability, we need to agree on the methods
      for the Internet.

      Finally, advanced applications need solutions to the problems of
      two earlier areas in this document.  From the Traffic Control and
      State area, applications need the ability to transmit real-time
      data.  This means some sort of expectation level for data delivery
      within a certain time frame.  Applications also require global
      authentication and access control systems from the Security area.
      Much of the usefulness of today's Internet applications is lost
      due to the lack of trust and security.  This needs to be solved
      for tomorrow's applications.
















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<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  REFERENCES</span>

   [<a id="ref-1">1</a>]  Cerf, V. and R. Kahn, "A Protocol for Packet Network
        Intercommunication," IEEE Transactions on Communication, May
        1974.

   [<a id="ref-2">2</a>]  Postel, J., Sunshine, C., and D. Cohen, "The ARPA Internet
        Protocol," Computer Networks, Vol. 5, No. 4, July 1981.

   [<a id="ref-3">3</a>]  Leiner, B., Postel, J., Cole, R., and D. Mills, "The DARPA
        Internet Protocol Suite," Proceedings INFOCOM 85, IEEE,
        Washington DC, March 1985.  Also in: IEEE Communications
        Magazine, March 1985.

   [<a id="ref-4">4</a>]  Clark, D., "The Design Philosophy of the DARPA Internet
        Protocols", Proceedings ACM SIGCOMM '88, Stanford, California,
        August 1988.

   [<a id="ref-5">5</a>]  Mogul, J., and J. Postel, "Internet Standard Subnetting
        Procedure", <a href="./rfc950">RFC 950</a>, USC/Information Sciences Institute, August
        1985.

   [<a id="ref-6">6</a>]  Mockapetris, P., "Domain Names - Concepts and Facilities", <a href="./rfc1034">RFC</a>
        <a href="./rfc1034">1034</a>, USC/Information Sciences Institute, November 1987.

   [<a id="ref-7">7</a>]  Deering, S., "Host Extensions for IP Multicasting", <a href="./rfc1112">RFC 1112</a>,
        Stanford University, August 1989.

   [<a id="ref-8">8</a>]  "Proceedings of the Twenty-First Internet Engineering Task
        Force", Bell-South, Atlanta, July 29 - August 2, 1991.





















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APPENDIX A: Setting the Stage


   Slide 1
                           WHITHER THE INTERNET?

                         OPTIONS FOR ARCHITECTURE



                           IAB/IESG -- Jan 1990



                              David D. Clark



   __________________________________________________________________
   Slide 2

                      SETTING THE TOPIC OF DISCUSSION

   Goals:

       o Establish a common frame of understanding for
         IAB, IESG and the Internet community.

       o Understand the set of problems to be solved.

       o Understand the range of solutions open to us.

       o Draw some conclusions, or else
         "meta-conclusions".

















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   __________________________________________________________________
   Slide 3

                        SOME CLAIMS -- MY POSITION

   We have two different goals:
      o Make it possible to build "The Internet"
      o Define a protocol suite called Internet

   Claim: These goals have very different implications.
     The protocols are but a means, though a powerful one.

   Claim: If "The Internet" is to succeed and grow, it will
     require specific design efforts.  This need will continue
     for at least another 10 years.

   Claim: Uncontrolled growth could lead to chaos.

   Claim: A grass-roots solution seems to be the only
     means to success.  Top-down mandates are powerless.


   __________________________________________________________________
   Slide 4

                          OUTLINE OF PRESENTATION

   1) The problem space and the solution space.

   2) A set of specific questions -- discussion.

   3) Return to top-level questions -- discussion.

   4) Plan for action -- meta discussion.

   Try to separate functional requirements from technical approach.

   Understand how we are bounded by our problem space and our
     solution space.

   Is architecture anything but protocols?










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   __________________________________________________________________
   Slide 5

                        WHAT IS THE PROBLEM SPACE?

   Routing and addressing:
      How big, what topology, and what routing model?

   Getting big:
      User services, what technology for host and nets?

   Divestiture of the Internet:
      Accounting, controlling usage and fixing faults.

   New services:
      Video? Transactions? Distributed computing?

   Security:
      End node or network?  Routers or relays?

   __________________________________________________________________
   Slide 6

                        BOUNDING THE SOLUTION SPACE

   How far can we migrate from the current state?
      o Can we change the IP header (except to OSI)?
      o Can we change host requirements in mandatory ways?
      o Can we manage a long-term migration objective?
         -  Consistent direction vs. diverse goals, funding.

   Can we assume network-level connectivity?
      o Relays are the wave of the future (?)
      o Security a key issue; along with conversion.
      o Do we need a new "relay-based" architecture?

   How "managed" can/must "The Internet" be?
      o Can we manage or constrain connectivity?

   What protocols are we working with? One or many?











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   __________________________________________________________________
   Slide 7

                        THE MULTI-PROTOCOL INTERNET

   "Making the problem harder for the good of mankind."

   Are we migrating, interoperating, or tolerating multiple protocols?
      o Not all protocol suites will have same range of functionality
        at the same time.
      o "The Internet" will require specific functions.

   Claim: Fundamental conflict (not religion or spite):
      o Meeting aggressive requirements for the Internet
      o Dealing with OSI migration.

   Conclusion: One protocol must "lead", and the others must follow.
      When do we "switch" to OSI?

   Consider every following slide in this context.

   __________________________________________________________________
   Slide 8

                          ROUTING and ADDRESSING

   What is the target size of "The Internet"?
      o How do addresses and routes relate?
      o What is the model of topology?
      o What solutions are possible?

   What range of policy routing is required?
      o BGP and IDRP are two answers.  What is the question?
      o Fixed classes, or variable paths?
      o Source controlled routing is a minimum.

   How seamless is the needed support for mobile hosts?
      o New address class, rebind to local address, use DNS?

   Shall we push for Internet multicast?











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   __________________________________________________________________
   Slide 9

                        GETTING BIG -- AN OLD TITLE

   (Addressing and routing was on previous slide...)

   What user services will be needed in the next 10 years?
      o Can we construct a plan?
      o Do we need architectural changes?

   Is there a requirement for dealing better with ranges in
      speed, packet sizes, etc.
      o Policy to phase out fragmentation?

   What range of hosts (things != Unix) will we support?


   _________________________________________________________________
   Slide 10

                         DEALING WITH DIVESTITURE

   The Internet is composed of parts separately managed and
   controlled.

   What support is needed for network charging?
      o No architecture implies bulk charges and re-billing, pay
          for lost packets.
      o Do we need controls to supply billing id or routing?

   Requirement: we must support links with controlled sharing.
      (Simple form is classes based on link id.)
      o How general?

   Is there an increased need for fault isolation? (I vote yes!)
      o How can we find managers to talk to?
      o Do we need services in hosts?













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   _________________________________________________________________
   Slide 11

                               NEW SERVICES

   Shall we support video and audio? Real time? What %?
      o Need to plan for input from research.  What quality?
      o Target date for heads-up to vendors.

   Shall we "better" support transactions?
      o Will TCP do? VMTP? Presentation? Locking?

   What application support veneers are coming?
      o Distributed computing -- will it actually happen?
      o Information networking?

   __________________________________________________________________
   Slide 12

                                 SECURITY

   Can we persist in claiming the end-node is the only line of defense?
      o What can we do inside the network?
      o What can ask the host to do?

   Do we tolerate relays, or architect them?
   Can find a better way to construct security boundaries?

   Do we need global authentication?

   Do we need new host requirements:
      o Logging.
      o Authentication.
      o Management interfaces.
         - Phone number or point of reference.

   __________________________________________________________________














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APPENDIX B: Group Membership

   Group 1: ROUTING AND ADDRESSING

       Dave Clark, MIT  [Chair]
       Hans-Werner Braun, SDSC
       Noel Chiappa, Consultant
       Deborah Estrin, USC
       Phill Gross, CNRI
       Bob Hinden, BBN
       Van Jacobson, LBL
       Tony Lauck, DEC.

   Group 2: MULTI-PROTOCOL ARCHITECTURE

       Lyman Chapin, BBN  [Chair]
       Ross Callon, DEC
       Dave Crocker, DEC
       Christian Huitema, INRIA
       Barry Leiner,
       Jon Postel, ISI

   Group 3: SECURITY ARCHITECTURE

       Vint Cerf, CNRI  [Chair]
       Steve Crocker, TIS
       Steve Kent, BBN
       Paul Mockapetris, DARPA

   Group 4: TRAFFIC CONTROL AND STATE

       Robert Braden, ISI  [Chair]
       Chuck Davin,  MIT
       Dave Mills, University of Delaware
       Claudio Topolcic, CNRI

   Group 5: ADVANCED APPLICATIONS

       Russ Hobby, UCDavis  [Chair]
       Dave Borman, Cray Research
       Cliff Lynch, University of California
       Joyce K. Reynolds, ISI
       Bruce Schatz, University of Arizona
       Mike Schwartz, University of Colorado
       Greg Vaudreuil, CNRI.






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Security Considerations

   Security issues are discussed in <a href="#section-4">Section 4</a>.

Authors' Addresses

   David D. Clark
   Massachusetts Institute of Technology
   Laboratory for Computer Science
   545 Main Street
   Cambridge, MA 02139

   Phone: (617) 253-6003
   EMail: ddc@LCS.MIT.EDU

   Vinton G. Cerf
   Corporation for National Research Initiatives
   1895 Preston White Drive, Suite 100
   Reston, VA 22091

   Phone: (703) 620-8990
   EMail: vcerf@nri.reston.va.us

   Lyman A. Chapin
   Bolt, Beranek &amp; Newman
   Mail Stop 20/5b
   150 Cambridge Park Drive
   Cambridge, MA 02140

   Phone: (617) 873-3133
   EMail: lyman@BBN.COM

   Robert Braden
   USC/Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292

   Phone: (310) 822-1511
   EMail: braden@isi.edu

   Russell Hobby
   University of California
   Computing Services
   Davis, CA 95616

   Phone: (916) 752-0236
   EMail: rdhobby@ucdavis.edu




Clark, Chapin, Cerf, Braden, &amp; Hobby                           [Page 29]
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