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Network Working Group                                          D. EstrinRequest for Comments:  1125              USC Computer Science Department                                                           November 1989POLICY REQUIREMENTS FOR INTER ADMINISTRATIVE DOMAIN ROUTING1  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 sharedEstrin                                                          [Page 1]

RFC 1125                  Policy Requirements              November 1989   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   inSection 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 planEstrin                                                          [Page 2]

RFC 1125                  Policy Requirements              November 1989   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 inSection 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 ofEstrin                                                          [Page 3]

RFC 1125                  Policy Requirements              November 1989   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)Estrin                                                          [Page 4]

RFC 1125                  Policy Requirements              November 1989   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). SeeSection 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 inSection 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 associateEstrin                                                          [Page 5]

RFC 1125                  Policy Requirements              November 1989   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 anEstrin                                                          [Page 6]

RFC 1125                  Policy Requirements              November 1989   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 notEstrin                                                          [Page 7]

RFC 1125                  Policy Requirements              November 1989   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; seeSection 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 someEstrin                                                          [Page 8]

RFC 1125                  Policy Requirements              November 1989   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; seeSection8.Estrin                                                          [Page 9]

RFC 1125                  Policy Requirements              November 1989   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 passedEstrin                                                         [Page 10]

RFC 1125                  Policy Requirements              November 1989   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 inSection 6.3 an AD can express its charging andEstrin                                                         [Page 11]

RFC 1125                  Policy Requirements              November 1989   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 bilateralEstrin                                                         [Page 12]

RFC 1125                  Policy Requirements              November 1989   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.Estrin                                                         [Page 13]

RFC 1125                  Policy Requirements              November 1989NATIONAL 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 ofEstrin                                                         [Page 14]

RFC 1125                  Policy Requirements              November 1989   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. SeeSection 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 theEstrin                                                         [Page 15]

RFC 1125                  Policy Requirements              November 1989   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.Estrin                                                         [Page 16]

RFC 1125                  Policy Requirements              November 19896.3.4  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 forEstrin                                                         [Page 17]

RFC 1125                  Policy Requirements              November 1989      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   betweenRFC1102 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.)Estrin                                                         [Page 18]

RFC 1125                  Policy Requirements              November 19899  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,RFC791, 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.Estrin                                                         [Page 19]

RFC 1125                  Policy Requirements              November 1989   [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.EDUEstrin                                                         [Page 20]

RFC 1125                  Policy Requirements              November 1989Estrin                                                         [Page 21]