Network Working Group                                          D. Estrin
Request for Comments:  1125              USC Computer Science Department
                                                           November 1989


      POLICY REQUIREMENTS FOR INTER ADMINISTRATIVE DOMAIN ROUTING

1  STATUS OF THIS MEMO

   The purpose of this memo is to focus discussion on particular
   problems in the Internet and possible methods of solution.  No
   proposed solutions in this document are intended as standards for the
   Internet.  Rather, it is hoped that a general consensus will emerge
   as to the appropriate solution to such problems, leading eventually
   to the development and adoption of standards.  Distribution of this
   memo is unlimited.

2  ABSTRACT

   Efforts are now underway to develop a new generation of routing
   protocol that will allow each Administrative Domain (AD) in the
   growing Internet (and internets in general) to independently express
   and enforce policies regarding the flow of packets to, from, and
   through its resources. (FOOTNOTE 1: The material presented here
   incorporates discussions held with members of the IAB Autonomous
   Networks Research Group and the Open Routing Working Group.)  This
   document articulates the requirements for policy based routing and
   should be used as input to the functional specification and
   evaluation of proposed protocols.

   Two critical assumptions will shape the type of routing mechanism
   that is devised: (1) the topological organization of ADs, and (2) the
   type and variability of policies expressed by ADs.  After justifying
   our assumptions regarding AD topology we present a taxonomy, and
   specific examples, of policies that must be supported by a PR
   protocol.  We conclude with a brief discussion of policy routing
   mechanisms proposed in previous RFCs (827, 1102, 1104, 1105).  Future
   RFCs will elaborate on the architecture and protocols needed to
   support the requirements presented here.

3  BACKGROUND

   The Research Internet has evolved from a single backbone wide area
   network with many connected campus networks, to an internet with
   multiple cross-country backbones, regional access networks, and a
   profusion of campus networks. (FOOTNOTE 2: The term Research Internet
   refers to a collection of government, university, and some private
   company, networks that are used by researchers to access shared

   computing resources (e.g., supercomputers), and for research related
   information exchange (e.g., distribution of software, technical
   documents, and email). The networks that make up the Research
   Internet run the DOD Internet Protocol [1].)  At times during its
   development the Research Internet topology appeared somewhat chaotic.
   Overlapping facilities and lateral (as opposed to hierarchical)
   connections seemed to be the rule rather than the exception.  Today
   the Research Internet topology is becoming more regular through
   coordination of agency investment and adoption of a hierarchy similar
   to that of the telephone networks'.  The result is several
   overlapping wide area backbones connected to regional networks, which
   in turn connect to campus networks at universities, research
   laboratories, and private companies. However, the telephone network
   has lateral connections only at the highest level, i.e., between long
   haul carriers.  In the Research Internet there exist lateral
   connections at each level of the hierarchy, i.e., between campus (and
   regional) networks as well.

   Additional complexity is introduced in the Research Internet by
   virtue of connections to private networks. Many private companies are
   connected to the Research Internet for purposes of research or
   support activities. These private companies connect in the same
   manner as campuses, via a regional network or via lateral links to
   other campuses. However, many companies have their own private wide
   area networks which physically overlap with backbone and/or regional
   networks in the research internet, i.e., private vertical bypass
   links.

   Implicit in this complex topology are organizational boundaries.
   These boundaries define Administrative Domains (ADs) which preclude
   the imposition of a single, centralized set of policies on all
   resources.  The subject of this paper is the policy requirements for
   resource usage control in the Research Internet.

   In the remainder of this section we describe the policy routing
   problem in very general terms. Section 4 examines the constraints and
   requirements that makes the problem challenging, and leads us to
   conclude that a new generation of routing and resource control
   protocols are needed. Section 5 provides more detail on our
   assumptions as to the future topology and configuration of
   interconnected ADs. We return to the subject of policy requirements
   in Section 7 and categorize the different types of policies that ADs
   in the research internet may want to enforce.  Included in this
   section are examples of FRICC policy statements.  (FOOTNOTE 3: The
   Federal Research Internet Coordinating Committee (FRICC) is made up
   of representatives of each of the major agencies that are involved in
   networking. They have been very effective in coordinating their
   efforts to eliminate inefficient redundancy and have proposed a plan

   for the next 10 years of internetworking for the government,
   scientific, and education community [2].)  Section 7 identifies types
   of policy statements that are problematic to enforce due to their
   dynamics, granularity, or performance implications. Several proposed
   mechanisms for supporting PR (including RFCs 827, 1102, 1104, 1105)
   are discussed briefly in Section 8. Future RFCs will elaborate on the
   architecture and protocols needed to support the requirements
   presented here.

3.1  POLICY ROUTING

   Previous protocols such as the Exterior Gateway Protocol (EGP)[3]
   embodied a limited notion of policy and ADs. In particular,
   autonomous system boundaries constrained the flow of routing database
   information, and only indirectly affected the flow of packets
   themselves.  We consider an Administrative Domain (AD) to be a set of
   hosts and network resources (gateways, links, etc.) that is governed
   by common policies.  In large internets that cross organization
   boundaries, e.g., the Research Internet, inter-AD routes must be
   selected according to policy-related parameters such as cost and
   access rights, in addition to the traditional parameters of
   connectivity and congestion. In other words, Policy Routing (PR) is
   needed to navigate through the complex web of policy boundaries
   created by numerous interconnected ADs. Moreover, each AD has its own
   privileges and perspective and therefore must make its own evaluation
   of legal and preferred routes.  Efforts are now underway to develop a
   new generation of routing protocol that will allow each AD to
   independently express and enforce policies regarding the flow of
   packets to, from, and through its resources [4].  (FOOTNOTE 4:  These
   issues are under investigation by the IAB Autonomous Networks
   Research Group and the IAB Open Routing Working Group. For further
   information contact the author.)

   The purpose of this paper is to articulate the requirements for such
   policy based routing. Two critical assumptions will shape the type of
   routing mechanism that is devised:

   * The topological organization of ADs, and
   * The type and variability of policies expressed by ADs.

   We make use of the policies expressed by owners of current Research
   Internet resources and private networks connected to the Research
   Internet to generalize types of policies that must be supported. This
   top down effort must be done with attention to the technical
   implications of the policy statements if the result is to be useful
   in guiding technical development. For example, some ADs express the
   desire to enforce local constraints over how packets travel to their
   destination. Other ADs are only concerned with preventing use of

   their own network resources by restricting transit.  Still other ADs
   are concerned primarily with recovering the expense of carrying
   traffic and providing feedback to users so that users will limit
   their own data flows; in other words they are concerned with
   charging.  We refer to ADs whose primary concern is communication to
   and from hosts within their AD as stub and to ADs whose primary
   concern is carrying packets to and from other ADs as transit}.  If we
   address control of transit alone, for example, the resulting
   mechanisms will not necessarily allow an AD to control the flow of
   its packets from source to destination, or to implement flexible
   charging schemes.  (FOOTNOTE 5: Gene Tsudik uses the analogy of
   international travel to express the need for source and transit
   controls. Each country expresses its own policies about travel to and
   through its land.  Travel through one country enroute to another is
   analogous to transit traffic in the network world. A traveler
   collects policy information from each of the countries of interest
   and plans an itinerary that conforms to those policies as well as the
   preferences of the traveler and his/her home nation.  Thus there is
   both source and transit region control of routing.)  Our purpose is
   to articulate a comprehensive set of requirements for PR as input to
   the functional specification, and evaluation, of proposed protocols.

4  WHY THE PROBLEM IS DIFFICULT

   Before proceeding with our description of topology and policy
   requirements this section outlines several assumptions and
   constraints, namely: the lack of global authority, the need to
   support network resource sharing as well as network interconnection,
   the complex and dynamic mapping of users to ADs and privileges, and
   the need for accountability across ADs.  These assumptions limit the
   solution space and raise challenging technical issues.

   The purpose of policy based routing is to allow ADs to interconnect
   and share computer and network resources in a controlled manner.
   Unlike many other problems of resource control, there is no global
   authority. Each AD defines its own policies with respect to its own
   traffic and resources. However, while we assume no global authority,
   and no global policies, we recognize that complete autonomy implies
   no dependence and therefore no communication.  The multi-organization
   internets addressed here have inherent regions of autonomy, as well
   as requirements for interdependence. Our mechanisms should allow ADs
   to design their boundaries, instead of requiring that the boundaries
   be either impenetrable or eliminated.

   One of the most problematic aspects of the policy routing
   requirements identified here is the need to support both network
   resource sharing and interconnection across ADs. An example of
   resource sharing is two ADs (e.g., agencies, divisions, companies)

   sharing network resources (e.g., links, or gateways and links) to
   take advantage of economies of scale.  Providing transit services to
   external ADs is another example of network resource sharing.
   Interconnection is the more common example of ADs interconnecting
   their independently used network resources to achieve connectivity
   across the ADs, i.e., to allow a user in one AD to communicate with
   users in another AD. In some respects, network resource control is
   simpler than network interconnection control since the potential
   dangers are fewer (i.e., denial of service and loss of revenue as
   compared with a wide range of attacks on end systems through network
   interconnection). However, controlled network resource sharing is
   more difficult to support.  In an internet a packet may travel
   through a number of transit ADs on its way to the destination.
   Consequently, policies from all transit ADs must be considered when a
   packet is being sent, whereas for stub-AD control only the policies
   of the two end point ADs have to be considered. In other words,
   controlled network resource sharing and transit require that policy
   enforcement be integrated into the routing protocols themselves and
   can not be left to network control mechanisms at the end points.
   (FOOTNOTE 6&7: Another difference is that in the interconnect case,
   traffic traveling over AD A's network resources always has a member
   of AD A as its source or destination (or both).  Under resource
   sharing arrangements members of both AD A and B are connected to the
   same resources and consequently intra-AD traffic (i.e., packets
   sourced and destined for members of the same AD) travels over the
   resources. This distinction is relevant to the writing of policies in
   terms of principal affiliation.  Economies of scale is one motivation
   for resource sharing. For example, instead of interconnecting
   separately to several independent agency networks, a campus network
   may interconnect to a shared backbone facility.  Today,
   interconnection is achieved through a combination of AD specific and
   shared arrangements. We expect this mixed situation to persist for
   "well-connected" campuses for reasons of politics, economics, and
   functionality (e.g., different characteristics of the different
   agency-networks). See Section 5 for more discussion.)

   Complications also result from the fact that legitimate users of an
   AD's resources are not all located in that AD. Many users (and their
   computers) who are funded by, or are affiliated with, a particular
   agency's program reside within the AD of the user's university or
   research laboratory.  They reside in a campus AD along with users who
   are legitimate users of other AD resources.  Moreover, any one person
   may be a legitimate user of multiple AR resources under varying
   conditions and constraints (see examples in Section 6). In addition,
   users can move from one AD to another. In other words, a user's
   rights can not be determined solely based on the AD from which the
   user's communications originate.  Consequently, PR must not only
   identify resources, it must identify principals and associate

   different capabilities and rights with different principals.  (The
   term principal is taken from the computer security community[7].)

   One way of reducing the compromise of autonomy associated with
   interconnection is to implement mechanisms that assure
   accountability} for resources used. Accountability may be enforced a
   priori, e.g., access control mechanisms applied before resource usage
   is permitted.  Alternatively, accountability may be enforced after
   the fact, e.g., record keeping or metering that supports detection
   and provides evidence to third parties (i.e., non-repudiation).
   Accountability mechanisms can also be used to provide feedback to
   users as to consumption of resources. Internally an AD often decides
   to do away with such feedback under the premise that communication is
   a global good and should not be inhibited. There is not necessarily a
   "global good" across AD boundaries. Therefore, it becomes more
   appropriate to have resource usage visible to users, whether or not
   actual charging for usage takes place.  Another motivation that
   drives the need for accountability across AD boundaries is the
   greater variability in implementations. Different implementations of
   a single network protocol can vary greatly as to their efficiency
   [8].  We can not assume control over implementation across AD
   boundaries.  Feedback mechanisms such as metering (and charging in
   some cases) would introduce a concrete incentive for ADs to employ
   efficient and correct implementations.  PR should allow an AD to
   advertise and apply such accounting measures to inter-AD traffic.

   In summary, the lack of global authority, the need to support network
   resource sharing as well as network interconnection, the complex and
   dynamic mapping of users to ADs and rights, and the need for
   accountability across ADs, are characteristics of inter-AD
   communications which must be taken into account in the design of both
   policies and supporting technical mechanisms.

5  TOPOLOGY MODEL OF INTERNET

   Before discussing policies per se, we outline our model of inter-AD
   topology and how it influences the type of policy support required.
   Most members of the Internet community agree that the future Internet
   will connect on the order of 150,000,000 termination points and
   100,000 ADs. However, there are conflicting opinions as to the AD
   topology for which we must design PR mechanisms.  The informal
   argument is described here.

   SIMPLE AD TOPOLOGY AND POLICY MODEL Some members of the Internet
   community believe that the current complex topology of interconnected
   ADs is a transient artifact resulting from the evolutionary nature of
   the Research Internet's history.  (FOOTNOTE 9: David Cheriton of
   Stanford University articulated this side of the argument at an

   Internet workshop in Santa Clara, January, 1989). The critical points
   of this argument relate to topology and policy. They contend that in
   the long term the following three conditions will prevail:

   * The public carriers will provide pervasive, competitively
     priced, high speed data services.

   * The resulting topology of ADs will  be
     stub (not transit) ADs connected to regional
     backbones, which in turn interconnect via multiple,
     overlapping long haul backbones, i.e., a  hierarchy with
     no lateral connections between stub-ADs or regionals,
     and no vertical bypass links.

   * The policy requirements of the backbone and stub-ADs
     will be based only on charging for resource usage at the
     stub-AD to backbone-AD boundary, and to settling accounts
     between neighboring backbone providers (regional to long haul,
     and long haul to long haul).

   Under these assumptions, the primary requirement for general AD
   interconnect is a metering and charging protocol. The routing
   decision can be modeled as a simple least cost path with the metric
   in dollars and cents. In other words, restrictions on access to
   transit services will be minimal and the functionality provided by
   the routing protocol need not be changed significantly from current
   day approaches.

   COMPLEX AD TOPOLOGY AND POLICY MODEL The counter argument is that a
   more complex AD topology will persist. (FOOTNOTE 10:  Much of the
   remainder of this paper attempts to justify and provide evidence for
   this statement.) The different assumptions about AD topology lead to
   the significantly different assumptions about AD policies.

   This model assumes that the topology of ADs will in many respects
   agree with the previous model of increased commercial carrier
   participation and resulting hierarchical structure. However, we
   anticipate unavoidable and persistent exceptions to the hierarchy.
   We assume that there will be a relatively small number of long haul
   transit ADs (on the order of 100), but that there may be tens of
   thousands of regional ADs and hundreds of thousands of stub ADs
   (e.g., campuses, laboratories, and private companies).  The competing
   long haul offerings will differ, both in the services provided and in
   their packaging and pricing.  Regional networks will overlap less and
   will connect campus and private company networks. However, many
   stub-ADs will retain some private lateral links for political,
   technical, and reliability reasons.  For example, political
   incentives cause organizations to invest in bypass links that are not

   always justifiable on a strict cost comparison basis; specialized
   technical requirements cause organizations to invest in links that
   have characteristics (e.g., data rate, delay, error, security) not
   available from public carriers at a competitive rate; and critical
   requirements cause organizations to invest in redundant back up links
   for reliability reasons.  These exceptions to the otherwise regular
   topology are not dispensible. They will persist and must be
   accommodated, perhaps at the expense of optimality; see Section 5 for
   more detail.  In addition, many private companies will retain their
   own private long haul network facilities. (FOOTNOTE 11:  While
   private voice networks also exist, private data networks are more
   common.  Voice requirements are more standardized because voice
   applications are more uniform than are data applications, and
   therefore the commercial services more often have what the voice
   customer wants at a price that is competitive with the private
   network option. Data communication requirements are still more
   specialized and dynamic.  Thus, there is less opportunity for economy
   of scale in service offerings and it is harder to keep up to date
   with customer demand. For this reason we expect private data networks
   to persist for the near future. As the telephone companies begin to
   introduce the next generation of high speed packet switched services,
   the scenario should change. However, we maintain that the result will
   be a predominance, but not complete dominance, of public carrier use
   for long haul communication.  Therefore, private data networks will
   persist and the routing architecture must accommodate controlled
   interconnection.)  Critical differences between the two models follow
   from the difference in assumptions regarding AD topology. In the
   complex case, lateral connections must be supported, along with the
   means to control the use of such connections in the routing
   protocols.

   The different topologies imply different policy requirements.  The
   first model assumes that all policies can be expressed and enforced
   in terms of dollars and cents and distributed charging schemes. The
   second model assumes that ADs want more varied control over their
   resources, control that can not be captured in a dollars and cents
   metric alone. We describe the types of policies to be supported and
   provide examples in the following section, Section 6. In brief, given
   private lateral links, ADs must be able to express access and
   charging related restrictions and privileges that discriminate on an
   AD basis.  These policies will be diverse, dynamic, and new
   requirements will emerge over time, consequently support must be
   extensible.  For example, the packaging and charging schemes of any
   single long haul service will vary over time and may be relatively
   elaborate (e.g., many tiers of service, special package deals, to
   achieve price discrimination).

   Note that these assumptions about complexity do not preclude some

   collection of ADs from "negotiating away" their policy differences,
   i.e., forming a federation, and coordinating a simplified inter-AD
   configuration in order to reduce the requirements for inter-AD
   mechanisms.  However, we maintain that there will persist collections
   of ADs that will not and can not behave as a single federation; both
   in the research community and, even more predominantly, in the
   broader commercial arena.  Moreover, when it comes to interconnecting
   across these federations, non-negotiable differences will arise
   eventually.  It is our goal to develop mechanisms that are applicable
   in the broader arena.

   The Internet community developed its original protocol suite with
   only minimal provision for resource control [9].  This was
   appropriate at the time of development based on the assumed community
   (i.e., researchers) and the ground breaking nature of the technology.
   The next generation of network technology is now being designed to
   take advantage of high speed media and to support high demand traffic
   generated by more powerful computers and their applications [10].  As
   with TCP/IP we hope that the technology being developed will find
   itself applied outside of the research community. This time it would
   be inexcusable to ignore resource control requirements and not to pay
   careful attention to their specification.

   Finally, we look forward to the Internet structure taking advantage
   of economies of scale offered by enhanced commercial services.
   However, in many respects the problem that stub-ADs may thus avoid,
   will be faced by the multiple regional and long haul carriers
   providing the services. The carriers' charging and resource control
   policies will be complex enough to require routing mechanisms similar
   to ones being proposed for the complex AD topology case described
   here.  Whether the network structure is based on private or
   commercial services, the goal is to construct policy sensitive
   mechanisms that will be transparent to end users (i.e., the
   mechanisms are part of the routing infrastructure at the network
   level, and not an end to end concern).

6  POLICY TYPES

   This section outlines a taxonomy of internet policies for inter-AD
   topologies that allow lateral and bypass links.  The taxonomy is
   intended to cover a wide range of ADs and internets. Any particular
   PR architecture we design should support a significant subset of
   these policy types but may not support all of them due to technical
   complexity and performance considerations.  The general taxonomy is
   important input to a functional specification for PR. Moreover, it
   can be used to evaluate and compare the suitability and completeness
   of existing routing architectures and protocols for PR; see Section
   8.

   We provide examples from the Research Internet of the different
   policy types in the form of resource usage policy statements. These
   statements were collected through interviews with agency
   representatives, but they do not represent official policy. These
   sample policy statements should not} be interpreted as agency policy,
   they are provided here only as examples.

   Internet policies fall into two classes, access and charging.  Access
   policies specify who can use resources and under what conditions.
   Charging policies specify the metering, accounting, and billing
   implemented by a particular AD.

6.1  TAXONOMY OF ACCESS POLICIES

   We have identified the following types of access policies that ADs
   may wish to enforce. Charging policies are described in the
   subsequent section. Section 6.3 provides more specific examples of
   both access and charging policies using FRICC policy statements.

   Access policies typically are expressed in the form: principals of
   type x can have access to resources of type y under the following
   conditions, z. The policies are categorized below according to the
   definition of y and z.  In any particular instance, each of the
   policy types would be further qualified by definition of legitimate
   principals, , x, i.e., what characteristics x must have in order to
   access the resource in question.

   We refer to access policies described by stub and transit ADs.  The
   two roles imply different motivations for resource control, however
   the types of policies expressed are similar; we expect the supporting
   mechanisms to be common as well.

   Stub and transit access policies may specify any of the following
   parameters:

   * SOURCE/DESTINATION
   Source/Destination policies prevent or restrict communication
   originated by or destined for particular ADs (or hosts or user
   classes within an AD).

   * PATH
   Path sensitive policies specify which ADs may or may not be passed
   through en route to a destination. The most general path sensitive
   policies allow stub and transit ADs to express policies that depend
   on any component in the AD path. In other words, a stub AD could
   reject a route based on any AD (or combination of ADs) in the route.
   Similarly, a transit AD could express a packet forwarding policy that
   behaves differently depending upon which ADs a packet has passed

   through, and is going to pass through, en route to the destination.
   Less ambitious (and perhaps more reasonable) path sensitive policies
   might only discriminate according to the immediate neighbor ADs
   through which the packet is traveling (i.e., a stub network could
   reject a route based on the first transit AD in the route, and a
   transit AD could express a packet forwarding policy that depends upon
   the previous, and the subsequent, transit ADs in the route.)

   * QUALITY/TYPE OF SERVICE(QOS OR TOS)
   This type of policy restricts access to special resources or
   services.  For example, a special high throughput, low delay link may
   be made available on a selective basis.

   * RESOURCE GUARANTEE
   These policies provide a guaranteed percentage of a resource on a
   selective, as needed basis.  In other words, the resource can be used
   by others if the preferred-AD's offered load is below the guaranteed
   level of service.  The guarantee may be to always carry intra-AD
   traffic or to always carry inter-AD traffic for a specific AD.

   *  TEMPORAL
   Temporal policies restrict usage based on the time of day or other
   time related parameters.

   *  HIGH LEVEL PROTOCOL
   Usage may be restricted to a specific high level protocol such as
   mail or file transfer. (Alternatively, such policies can be
   implemented as source/destination policies by configuring a host(s)
   within an AD as an application relay and composing policy terms that
   allow inter-AD access to only that host.)

   *  RESOURCE LIMIT
   There may be a limit on the amount of traffic load a source may
   generate during a particular time interval, e.g., so many packets in
   a day, hour, or minute.

   *  AUTHENTICATION REQUIREMENTS
   Conditions may be specified regarding the authenticability of
   principal identifying information. Some ADs might require some form
   of cryptographic proof as to the identity and affiliations of the
   principal before providing access to critical resources.

   The above policy types usually exist in combination for a particular
   AD, i.e., an AD's policies might express a combination of transit,
   source/destination, and QOS restrictions. This taxonomy will evolve
   as PR is applied to other domains.

   As will be seen in Section 6.3 an AD can express its charging and

   access policies in a single syntax. Moreover, both stub and transit
   policies can co-exist. This is important since some ADs operate as
   both stub and transit facilities and require such hybrid control.

6.2 TAXONOMY OF CHARGING POLICIES

   Stub and transit charging policies  may specify the following
   parameters:

   *  UNIT OF ACCOUNTING (e.g., dollars or credits).
   *  BASIS FOR CHARGING (e.g., per Kbyte or per Kpkt).
   *  ACTUAL CHARGES (e.g., actual numbers such as $.50/Mbyte).
   *  WHO IS CHARGED OR PAID (e.g., originator of packet,
      immediate neighbor from whom packet was received, destination
      of packet, a third party collection agent).
   *  WHOSE PACKET COUNT is used (e.g., source, destination, the
      transit AD's own count, the count of some upstream or
      downstream AD).
   *  BOUND ON CHARGES (e.g., to limit the  amount that a stub
      AD is willing to spend, or the amount that a transit AD is
      willing to carry.)

   The enforcement of these policies may be carried out during route
   synthesis or route selection [4].

6.3  EXAMPLE POLICY STATEMENTS

   The following policy statements were collected in the fall of 1988
   through interviews with representatives of the federal agencies most
   involved in supporting internetworking. Once again we emphasize that
   these are not official policy statements. They are presented here to
   provide concrete examples of the sort of policies that agencies would
   like to enforce.

   Expressing policies as Policy Terms (PTs)

   Each policy is described in English and then expressed in a policy
   term (PT) notation suggested by Dave Clark in [4].  Each PT
   represents a distinct policy of the AD that synthesized it.  The
   format of a PT is:

    [(H{src},AD{src},AD{ent}),(H{dst},AD{dst},AD{exit}),UCI, Cg,Cb]

   Hsrc stands for source host, ADsrc for source AD, ADent for entering
   AD (i.e., neighboring AD from which traffic is arriving directly),
   Hdst for destination host, ADdst for destination AD, ADexit for exit
   AD (i.e.,neighboring AD to which traffic is going directly), UCI for
   user class identifier, and Cg and Cb for global and bilateral

   conditions, respectively. The purpose of a PT is to specify that
   packets from some host, H{src}, (or a group of hosts) in a source AD,
   AD{src}, are allowed to enter the AD in question via some directly
   connected AD, AD{ent}, and exit through another directly connected
   AD, AD{exit}, on its way to a host, H{dst}, (or a group of hosts) in
   some destination AD, AD{dst}.  User Class Identifier (UCI) allows for
   distinguishing between various user classes, e.g., Government,
   Research, Commercial, Contract, etc.  Global Conditions (Cg)
   represent billing and other variables.  Bilateral Conditions (Cb)
   relate to agreements between neighboring ADs, e.g., related to
   metering or charging.  In the example policy terms provided below we
   make use of the following abbreviations: Fricc for
   {DOE,NASA,DCA,NSF}, F for Federal Agency, Re for Regional, U for
   University, Co for Commercial Corporation, and Cc for Commercial
   Carrier. A hyphen, -, means no applicable matches.

   By examining a PT we can identify the type of policy represented, as
   per the taxonomy presented earlier.

   *  If an AD specifies a policy term that has a null (-) entry for
      the ADexit, then it is disallowing transit for some group of users,
      and it is a transit policy.

   *  If an AD specifies a  policy term that lists itself
      explicitly as ADsrc or ADdst, it is expressing restrictions on who
      can access particular resources within its boundaries, or on who inside
      can obtain external access. In other words the AD is expressing a
      source/destination policy.

   *  If ADexit or ADentr is specified then the policy expressed is an
      exit/entrance path policy.

   *  If the global conditions include charging, QOS, resource
      guarantee,  time of day, higher level application, resource limit, or
      authentication related information it is obviously a charging, QOS,
      resource guarantee, temporal, higher level application, resource
      limit, or authentication policy, respectively.

   As seen below, any one PT typically incorporates a combination of
   policy types.

6.3.1  THE FRICC

   In the following examples all policies (and PTs) are symmetrical
   under the assumption that communication is symmetrical.

NATIONAL SCIENCE FOUNDATION (NSF)

   1.  NSF will carry traffic for any host connected to a F/Re network
   talking to any other host connected to a F/Re via any F/Re entry and
   exit network, so long as there is it is being used for research or
   support. There is no authentication of the UCI and no per packet
   charging.  NSFnet is a backbone and so does not connect directly to
   universities or companies...thus the indication of {F/Re} instead of
   {F/Re/U/Co} as ADent and ADexit.

   [NSF1:  (*, {F/Re}, {F/Re})(*, {F/Re}, {F/Re}){research,support}
   {unauthenticated UCI,no-per-pkt charge}{}]

   2.  NSF will carry traffic to user and expert services hosts in NSF
   AD to/from any F/Re AD, via any F/Re AD. These are the only things
   that directly connect to NSFnet.

   [NSF2: ({User svcs, Expert Svcs},{NSF},{F/Re})(*,{F/Re},{-}){}{}{}]

DEPARTMENT OF ENERGY (DOE)

   1.  DOE will carry traffic to and from any host directly connected to
   DOE so long as it is used for research or support. There is no
   authentication of the UCI and no per packet charging.

   [DOE1: (*,DOE,-)(*,*,*){research,support}
   {unauthenticated UCI,no-per-packet charge}{}]

   2.  DOE will carry traffic for any host connected to a F/Re network
   talking to any other host connected to a F/Re via any F/Re entry and
   exit network without regard to the UCI. There is no authentication of
   the UCI and no per packet charging. (in other words DOE is more
   restrictive with its own traffic than with traffic it is carrying as
   part of a resource sharing arrangement.)

   [DOE2: (*,{F/Re},{F/Re})(*,{F/Re},{F/Re}){}
   {unauthenticated UCI, no-per-pkt charge}{}]

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION (NASA)

   1.  Nasa will accept any traffic to/from members of the Nasa AD. But
   no transit. No UCI authentication and no per packet charge.

   [NASA1: (*,*,*)(*,Nasa,-){Nasa-research, support}
   {unauthenticated UCI,no-per-packet-charge}{}]

   2.  Nasa will carry transit traffic to/from other federal agency
   networks if it is in support of research, and if the total use of

   available BW by non-nasa Federal agencies is below n%. NOTE THAT this
   non-interference policy type needs some more work in terms of
   integrating it into the routing algorithms. See Section 7.

   [NASA2: (*,{F},*)(*,{F},*){research,support}
   {per-packet accounting, limited to n% of available BW}{}]

   3.  NASA will carry commercial traffic to federal and regional and
   university ADs for nasa research or support. But it will not allow
   transit. The particular entry AD is not important.

   [NASA3: (*,{Co},*} (*,{F/R/U},*) {NASA research,support}
    {unauthenticated UCI, no per packet charge}{}]

   4.  On a case by case basis NASA may provide access to its resources
   on a cost reimbursed basis. Transit traffic will not be carried on
   this basis.

    [NASA4: (*,*,-)(*,*,-){}
    {per-packet-charge, limited to n% of available BW} {}]

DEFENSE ADVANCED RESEARCH PROJECTS AGENCY (DARPA)

   1.  DARPA will carry traffic to/from any host in DARPA AD from any
   external host that can get it there so long as UCI is research or
   support. No UCI authentication or per packet charge.

   [DARPA1: (*,*,*)(*,DARPA,-){research,support}
   {unauthenticated-UCI, no per packet charge}{}]

   2.  DARPA will carry traffic for any host connected to a F/Re/U/Co
   network talking to any other host connected to a F/Re/U/Co via any
   F/Re/U/Co entry and exit network, so long as there is it is being
   used for research or support, and the network is not heavily
   congested!!.  There is no authentication of the UCI and no per packet
   charging.  NOTE: Darpa would like to say something about the need to
   enter the Darpa AD at the point closest to the destination...but i
   don't know how to express this...

   DARPA2: (*,{F/R/U/Co},{F/R/U/Co})(*,{F/R/U/Co},{F/R/U/Co})
   {research,support}{unauthenticated-UCI,no per packet charge,
   non-interference basis}{}]

DEFENSE COMMUNICATIONS AGENCY (DCA)

   1.  DCA will not carry any transit traffic. It will only accept and
   send traffic to and from its mailbridge(s) and only from and to hosts
   on other F/Re nets. All packets are marked and charged for by the

   kilopacket.

   [DCA1:(mailbridge,DCA,-)(*,{F/Re},{F/Re}){research,support}
   {unauthenticated UCI, all incoming packets marked, per-kilopacket
   charge}{}]

6.3.2 THE REGIONALS

   Interviews with regional network administrations are now underway. In
   general their policies are still in formation due to the relatively
   recent formation of these regional networks. However, for the sake of
   illustration we provide an example of a hypothetical regional's
   network policies.

REGIONAL A

   1.  Regional A will carry traffic from/to any directly connected
   F/Re/U network to any F/Re/U network via NSF if it is for a research
   or support UCI. (NSF requires that all Regional networks only pass it
   traffic that complies with its, NSF's, policies!)

   [Regional A:(*,{F/Re/U},{F/Re/U})(*,{F/Re/U},NSF){research,support}
   {unauthenticated UCI, no-per-packet charge}{}]

REGIONAL B

   1.  Regional B will carry traffic from/to any directly connected
   F/Re/U network to any F/Re/U network via a commercial carrier
   regardless of its UCI. In this case the packets are charged for since
   the commercial carrier charges per kilopacket.

   [Regional B:(*,{F/Re/U},{F/Re/U})(*,{F/Re/U},Cc){}
   {unauthenticated UCI, per-kilopacket charge}{}]

6.3.3 CAMPUS AND PRIVATE NETWORKS

   Similar interviews should be conducted with administrators of campus
   and private networks. However, many aspects of their policies are
   contingent on the still unresolved policies of the regionals and
   federal agencies.  In any event, transit policies will be critical
   for campus and private networks to flexibly control access to lateral
   links and private wide area networks, respectively. For example, a
   small set of university and private laboratories may provide access
   to special gigabit links for particular classes of researchers.  On
   the other hand, source/destination policies should not be used in
   place of network level access controls for these end ADs.

6.3.4  COMMERCIAL SERVICES

   Currently commercial communication services play a low level role in
   most parts of today's Research Internet; they provide the
   transmission media, i.e.,leased lines. In the future we expect
   commercial carriers to provide increasingly higher level and enhanced
   services such as high speed packet switched backbone services.
   Because such services are not yet part of the Research Internet
   infrastructure there exist no policy statements.

   Charging and accounting are certain to be an important policy type in
   this context.  Moreover, we anticipate the long haul services market
   to be highly competitive. This implies that competing service
   providers will engage in significant gaming in terms of packaging and
   pricing of services. Consequently, the ability to express varied and
   dynamic charging policies will be critical for these ADs.

7  PROBLEMATIC REQUIREMENTS

   Most of this paper has lobbied for articulation of relatively
   detailed policy statements in order to help define the technical
   mechanisms needed for enforcement.  We promoted a top down design
   process beginning with articulation of desired policies.  Now we feel
   compelled to mention requirements that are clearly problematic from
   the bottom up perspective of technical feasibility.

   *  Non-interference policies are of the form "I will provide
      access for principals x to resources y so long as it does not
      interfere with my internal usage." The problem with such policies
      is that access to an AD at any point in time is contingent upon a
      local, highly dynamic, parameter that is not globally available.
      Therefore such a policy term could well result in looping,
      oscillations, and excessive route (re)computation overhead,
      both unacceptable. Consequently, this is one type of policy that
      routing experts suggest would be difficult to support in a very
      large decentralized internetwork.

   *  Granularity can also be problematic, but not as devistating as
      highly dynamic PR contingencies. Here the caution is less specific.
      Very fine grain policies, which restrict access to particular
      hosts, or are contingent upon very fine grain user class
      identification, may be achieved more efficiently with network
      level access control [11] or end system controls instead of
      burdening the inter-AD routing mechanism.

   *  Security  is expensive, as always. Routing protocols are subject
      to fraud through impersonation, data substitution, and denial of
      service. Some of the proposed mechanisms provide some means for

      detection and non-repudiation. However, to achieve a priori
      prevention of resource misuse is expensive in terms of per
      connection or per packet cryptographic overhead. For some
      environments we firmly believe that this will be necessary and
      we would prefer an architecture that would accommodate such
      variability [12].

   In general, it is difficult to predict the impact of any particular
   policy term. Tools will be needed to assist people in writing and
   validating policy terms.

8  PROPOSED MECHANISMS

   Previous routing protocols have addressed a narrower definition of
   PR, as appropriate for the internets of their day. In particular, EGP
   [3], DGP[13], and BGP[6] incorporate a notion of policy restrictions
   as to where routing database information travels. None are intended
   to support policy based routing of packets as described here.  More
   recent routing proposals such as Landmark [14] and Cartesian [15]
   could be used to restrict packet forwarding but are not suited to
   source/destination, and some of the condition-oriented, policies. We
   feel these policy types are critical to support. We note that for
   environments (e.g., within an AD substructure) in which the simple-
   AD-topology conjecture holds true, these alternatives may be
   suitable.

   RFC 1104 [5] provides a good description of shorter term policy
   routing requirements. Braun classifies three types of mechanisms,
   policy based distribution of route information, policy based packet
   forwarding, and policy based dynamic allocation of network resources.
   The second class is characterized by Dave Clark's PR architecture,
   RFC 1102 [4]. With respect to the longer term requirements laid out
   in this document, only this second class is expressive and flexible
   enough to support the multiplicity of stub and transit policies. In
   other words, the power of the PR approach (e.g., RFC1102) is not just
   in the added granularity of control pointed out by Braun, i.e., the
   ability to specify particular hosts and user classes. Its power is in
   the ability to express and enforce many types of stub and transit
   policies and apply them on a discriminatory basis to different ADs.
   In addition, this approach provides explicit support for stub ADs to
   control routes via the use of source routing.  (FOOTNOTE 12:
   Moreover, the source routing approach loosens the requirements for
   every AD to share a complete view of the entire internet by allowing
   the source to detect routing loops.)  (FOOTNOTE 13:  The match
   between RFC1102 and the requirements specified in this document is
   hardly a coincidence since Clark's paper and discussions with him
   contributed to the requirements formulation presented here. His work
   is currently being evaluated and refined by the ANRG and ORWG.)

9  SUMMARY

   Along with the emergence of very high speed applications and media,
   resource management has become a critical issue in the Research
   Internet and internets in general. A fundamental characteristic of
   the resource management problem is allowing administratively ADs to
   interconnect while retaining control over resource usage. However, we
   have lacked a careful articulation of the types of resource
   management policies that need to be supported.  This paper addresses
   policy requirements for the Research Internet.  After justifying our
   assumptions regarding AD topology we presented a taxonomy and
   examples of policies that must be supported by a PR protocol.

10  ACKNOWLEDGMENTS

   Members of the Autonomous Networks Research Group and Open Routing
   Working Group have contributed significantly to the ideas presented
   here, in particular, Guy Almes, Lee Breslau, Scott Brim, Dave Clark,
   Marianne Lepp, and Gene Tsudik. In addition, Lee Breslau and Gene
   Tsudik provided detailed comments on a previous draft. David Cheriton
   inadvertently caused me to write this document.  Sharon Anderson's
   contributions deserve special recognition.  The author is supported
   by research grants from National Science Foundation, AT&T, and GTE.

11   REFERENCES

   [1] J. Postel, Internet Protocol,  Network Information Center, RFC
       791, September 1981.

   [2] G. Vaudreuil, The Federal Research Internet Coordinating
       Committee and National Research Network, ACM SIG Computer
       Communications Review,April 1988.

   [3] E. Rosen, Exterior Gateway Protocol (EGP), Network Information
       Center, RFC 827, October 1982.

   [4] D. Clark, Policy Routing in Internet Protocols, Network
       Information Center, RFC 1102, May 1989.

   [5] H.W.Braun, Models of Policy Based Routing, Network Information
       Center, RFC 1104, June 1989.

   [6] K. Lougheed, Y. Rekhter, A Border Gateway Protocol, Network
       Information Center, RFC 1105, June 1989.

   [7] J. Saltzer, M. Schroeder, The Protection of Information in
       Computer Systems, Proceedings of the IEEE, 63, 9 September 1975.

   [8] V. Jacobson, Congestion Avoidance and Control.  Proceedings of
       ACM Sigcomm, pp. 106-114, August 1988, Palo Alto, CA.

   [9] David Clark, Design Philosophy of the DARPA Internet Protocols,
       Proceedings of ACM Sigcomm, pp. 106-114, August 1988, Palo Alto,
       CA.

  [10] Gigabit Networking Group, B. Leiner, Editor. Critical Issues in
       High Bandwidth Networking, Network Information Center, RFC 1077,
       November 1988.

  [11] D. Estrin, J. Mogul and G. Tsudik, Visa Protocols for Controlling
       Inter-Organizational Datagram Flow, To appear in IEEE Journal on
       Selected Areas in Communications, Spring 1989.

  [12] D. Estrin and G. Tsudik, Security Issues in Policy Routing, IEEE
       Symposium on Research in Security and Privacy, Oakland, CA.  May
       1-3 1989.

  [13]  M. Little, The Dissimilar Gateway Protocol,  Technical report

  [14] P. Tsuchiya, The Landmark Hierarchy: A new hierarchy for routing
       in very large networks, IEEE SIGCOMM 88, Palo Alto, CA. September
       1988.

  [15] G. Finn, Reducing the Vulnerability of Dynamic Computer Networks
       USC/Information Sciences Institute, Technical Report, ISI/RR-88-
       201 July 1988.

  [16] A. Nakassis Routing Algorithm for Open Routing, Unpublished
       paper, Available from the author at the National Institute of
       Standards and Technology (formerly NBS), Washington D.C.

11  SECURITY CONSIDERATIONS

       This memo does not address the security aspects of the issues
       discussed.

AUTHOR'S ADDRESS:

       Deborah Estrin
       University of Southern California
       Computer Science Department
       Los Angeles, CA 90089-0782

       Phone: (213) 743-7842

       EMail: Estrin@OBERON.USC.EDU