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Network Working Group                                     M. SteenstrupRequest for Comments: 1477                 BBN Systems and Technologies                                                              July 1993IDPR as a Proposed StandardStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard.  Distribution of this memo is   unlimited.1.  Introduction   This document contains a discussion of inter-domain policy routing   (IDPR), including an overview of functionality and a discussion of   experiments.  The objective of IDPR is to construct and maintain   routes between source and destination administrative domains, that   provide user traffic with the services requested within the   constraints stipulated for the domains transited.   Four documents describe IDPR in detail:      M. Steenstrup.  An architecture for inter-domain policy routing.RFC 1478.  July 1993.      M. Steenstrup.  Inter-domain policy routing protocol      specification: version 1.RFC 1479.  July 1993.      H. Bowns and M. Steenstrup.  Inter-domain policy routing      configuration and usage.  Work in Progress.  July 1991.      R. Woodburn.  Definitions of managed objects for inter-domain      policy routing (version 1).  Work in Progress.  March 1993.   This is a product of the Inter-Domain Policy Routing Working Group of   the Internet Engineering Task Force (IETF).2.  The Internet Environment   As data communications technologies evolve and user populations grow,   the demand for internetworking increases.  The Internet currently   comprises over 7000 operational networks and over 10,000 registered   networks.  In fact, for the last several years, the number of   constituent networks has approximately doubled annually.  Although we   do not expect the Internet to sustain this growth rate, we must   prepare for the Internet of five to ten years in the future.Steenstrup                                                      [Page 1]

RFC 1477                         IDPR                          July 1993   Internet connectivity has increased along with the number of   component networks.  Internetworks proliferate through   interconnection of autonomous, heterogeneous networks administered by   separate authorities.  We use the term "administrative domain" (AD)   to refer to any collection of contiguous networks, gateways, links,   and hosts governed by a single administrative authority that selects   the intra-domain routing procedures and addressing schemes, specifies   service restrictions for transit traffic, and defines service   requirements for locally-generated traffic.   In the early 1980s, the Internet was purely hierarchical, with the   ARPANET as the single backbone.  The current Internet possesses a   semblance of a hierarchy in the collection of backbone, regional,   metropolitan, and campus domains that compose it.  However,   technological, economical, and political incentives have prompted the   introduction of inter-domain links outside of those in the strict   hierarchy.  Hence, the Internet has the properties of both   hierarchical and mesh connectivity.   We expect that, over the next five years, the Internet will grow to   contain O(10) backbone domains, most providing connectivity between   many source and destination domains and offering a wide range of   qualities of service, for a fee.  Most domains will connect directly   or indirectly to at least one Internet backbone domain, in order to   communicate with other domains.  In addition, some domains may   install direct links to their most favored destinations.  Domains at   the lower levels of the hierarchy will provide some transit service,   limited to traffic between selected sources and destinations.   However, the majority of Internet domains will be "stubs", that is,   domains that do not provide any transit service for any other domains   but that connect directly to one or more transit domains.   The bulk of Internet traffic will be generated by hosts in the stub   domains, and thus, the applications running in these hosts will   determine the traffic service requirements.  We expect application   diversity encompassing electronic mail, desktop videoconferencing,   scientific visualization, and distributed simulation, for example.   Many of these applications have strict requirements on loss, delay,   and throughput.   In such a large and heterogeneous Internet, the routing procedures   must be capable of ensuring that traffic is forwarded along routes   that offer the required services without violating domain usage   restrictions.  We believe that IDPR meets this goal; it has been   designed to accommodate an Internet comprising O(10,000)   administrative domains with diverse service offerings and   requirements.Steenstrup                                                      [Page 2]

RFC 1477                         IDPR                          July 19933.  An Overview of IDPR   IDPR generates, establishes, and maintains "policy routes" that   satisfy the service requirements of the users and respect the service   restrictions of the transit domains.  Policy routes are constructed   using information about the services offered by and the connectivity   between administrative domains and information about the services   requested by the users.3.1  Policies   With IDPR, each domain administrator sets "transit policies" that   dictate how and by whom the resources in its domain should be used.   Transit policies are usually public, and they specify offered   services comprising:   - Access restrictions: e.g., applied to traffic to or from certain     domains or classes of users.   - Quality: e.g., delay, throughput, or error characteristics.   - Monetary cost: e.g., charge per byte, message, or session time.   Each domain administrator also sets "source policies" for traffic   originating in its domain.  Source policies are usually private, and   they specify requested services comprising:   - Access: e.g., domains to favor or avoid in routes.   - Quality: e.g., acceptable delay, throughput, and reliability.   - Monetary cost: e.g., acceptable cost per byte, message, or session     time.3.2  Functions   The basic IDPR functions include:   - Collecting and distributing routing information, i.e., domain     transit policy and connectivity information.  IDPR uses link state     routing information distribution, so that each source domain may     obtain routing information about all other domains.   - Generating and selecting policy routes based on the routing     information distributed and on source policy information.  IDPR     gives each source domain complete control over the routes it     generates.Steenstrup                                                      [Page 3]

RFC 1477                         IDPR                          July 1993   - Setting up paths across the Internet, using the policy routes     generated.   - Forwarding messages across and between administrative domains along     the established paths.  IDPR uses source-specified message     forwarding, giving each source domain complete control over the     paths traversed by its hosts' inter-domain traffic.   - Maintaining databases of routing information, inter-domain policy     routes, forwarding information, and configuration information.3.3  Entities   Several different entities are responsible for performing the IDPR   functions:   - "Policy gateways", the only IDPR-recognized connecting points     between adjacent domains, collect and distribute routing     information, participate in path setup, maintain forwarding     information databases, and forward data messages along established     paths.   - "Path agents", resident within policy gateways, act on behalf of     hosts to select policy routes, to set up and manage paths, and to     maintain forwarding information databases.  Any Internet host can     reap the benefits of IDPR, as long as there exists a path agent     willing to act on its behalf and a means by which the host's     messages can reach that path agent.   - Special-purpose servers maintain all other IDPR databases as     follows:      o  Each "route server" is responsible for both its database of         routing information, including domain connectivity and transit         policy information, and its database of policy routes.  Also,         each route server generates policy routes on behalf of its         domain, using entries from its routing information database         and using source policy information supplied through         configuration or obtained directly from the path agents.  A         route server may reside within a policy gateway, or it may         exist as an autonomous entity.  Separating the route server         functions from the policy gateways frees the policy gateways         from both the memory intensive task of routing information         database and route database maintenance and the         computationally intensive task of route generation.      o  Each "mapping server" is responsible for its database of         mappings that resolve Internet names and addresses toSteenstrup                                                      [Page 4]

RFC 1477                         IDPR                          July 1993         administrative domains.  The mapping server function can be         easily integrated into an existing name service such as the         DNS.      o  Each "configuration server" is responsible for its database of         configured information that applies to policy gateways, path         agents, and route servers in the given administrative domain.         Configuration information for a given domain includes source         and transit policies and mappings between local IDPR entities         and their addresses.  The configuration server function can be         easily integrated into a domain's existing network management         system.3.4  Message Handling   There are two kinds of IDPR messages:   - "Data messages" containing user data generated by hosts.   - "Control messages" containing IDPR protocol-related control     information generated by policy gateways and route servers.   Within the Internet, only policy gateways and route servers must be   able to generate, recognize, and process IDPR messages.  Mapping   servers and configuration servers perform necessary but ancillary   functions for IDPR, and they are not required to execute IDPR   protocols.  The existence of IDPR is invisible to all other gateways   and hosts.  Using encapsulation across each domain, an IDPR message   tunnels from source to destination across the Internet through   domains that may employ disparate intra-domain addressing schemes and   routing procedures.4.  Security   IDPR contains mechanisms for verifying message integrity and source   authenticity and for protecting against certain types of denial of   service attacks.  It is particularly important to keep IDPR control   messages intact, because they carry control information critical to   the construction and use of viable policy routes between domains.4.1  Integrity and Authenticity   All IDPR messages carry a single piece of information, referred to in   the IDPR documentation as the "integrity/authentication value", which   may be used not only to detect message corruption but also to verify   the authenticity of the message's source IDPR entity.  The Internet   Assigned Numbers Authority (IANA) specifies the set of valid   algorithms which may be used to compute the integrity/authenticationSteenstrup                                                      [Page 5]

RFC 1477                         IDPR                          July 1993   values.  This set may include algorithms that perform only message   integrity checks such as n-bit cyclic redundancy checksums (CRCs), as   well as algorithms that perform both message integrity and source   authentication checks such as signed hash functions of message   contents.   Each domain administrator is free to select any   integrity/authentication algorithm, from the set specified by the   IANA, for computing the integrity/authentication values contained in   its domain's messages.  However, we recommend that IDPR entities in   each domain be capable of executing all of the valid algorithms so   that an IDPR message originating at an entity in one domain can be   properly checked by an entity in another domain.   IDPR control messages must carry a non-null integrity/authentication   value.  We recommend that control message integrity/authentication be   based on a digital signature algorithm applied to a one-way hash   function, such as RSA applied to MD5, which simultaneously verifies   message integrity and source authenticity.  The digital signature may   be based on either public key or private key cryptography.  However,   we do not require that IDPR data messages carry a non-null   integrity/authentication value.  In fact, we recommend that a higher   layer (end-to-end) procedure assume responsibility for checking the   integrity and authenticity of data messages, because of the amount of   computation involved.4.2  Timestamps   Each IDPR message carries a timestamp (expressed in seconds elapsed   since 1 January 1970 0:00 GMT) supplied by the source IDPR entity,   which serves to indicate the age of the message.  IDPR entities use   the absolute value of a timestamp to confirm that the message is   current and use the relative difference between timestamps to   determine which message contains the most recent information.  All   IDPR entities must possess internal clocks that are synchronized to   some degree, in order for the absolute value of a message timestamp   to be meaningful.  The synchronization granularity required by IDPR   is on the order of minutes and can be achieved manually.   Each IDPR recipient of an IDPR control message must check that the   message's timestamp is in the acceptable range.  A message whose   timestamp lies outside of the acceptable range may contain stale or   corrupted information or may have been issued by a source whose clock   has lost synchronization with the message recipient.  Such messages   must therefore be discarded, to prevent propagation of incorrect IDPR   control information.  We do not require IDPR entities to perform a   timestamp acceptability test for IDPR data messages, but instead   leave the choice to the individual domain administrators.Steenstrup                                                      [Page 6]

RFC 1477                         IDPR                          July 19935.  Size Considerations   IDPR provides policy routing among administrative domains and has   been designed to accommodate an Internet containing tens of thousands   of domains, supporting diverse source and transit policies.   In order to construct policy routes, route servers require routing   information at the domain level only; no intra-domain details need be   included in IDPR routing information.  Thus, the size of the routing   information database maintained by a route server depends on the   number of domains and transit policies and not on the number hosts,   gateways, or networks in the Internet.   We expect that, within a domain, a pair of IDPR entities will   normally be connected such that when the primary intra-domain route   fails, the intra-domain routing procedure will be able to use an   alternate route.  In this case, a temporary intra-domain failure is   invisible at the inter-domain level.  Thus, we expect that most   intra-domain routing changes will be unlikely to force inter-domain   routing changes.   Policy gateways distribute routing information when detectable   inter-domain changes occur but may also elect to distribute routing   information periodically as a backup.  Thus, policy gateways do not   often need to generate and distribute routing information messages,   and the frequency of distribution of these messages depends only   weakly on intra-domain routing changes.   IDPR entities rely on intra-domain routing procedures operating   within domains to transport inter-domain messages across domains.   Hence, IDPR messages must appear well-formed according to the intra-   domain routing procedures and addressing schemes in each domain   traversed; this requires appropriate header encapsulation of IDPR   messages at domain boundaries.  Only policy gateways and route   servers must be capable of handling IDPR-specific messages; other   gateways and hosts simply treat the encapsulated IDPR messages like   any other.  Thus, for the Internet to support IDPR, only a small   proportion of Internet entities require special IDPR software.   With domain-level routes, many different traffic flows may use not   only the same policy route but also the same path, as long their   source domains, destination domains, and requested services are   identical.  Thus, the size of the forwarding information database   maintained by a policy gateway depends on the number of domains and   source policies and not on the number of hosts in the Internet.   Moreover, memory associated with failed, expired, or disused paths   can be reclaimed for new paths, and thus forwarding information for   many paths can be accommodated.Steenstrup                                                      [Page 7]

RFC 1477                         IDPR                          July 19936.  Interactions with Other Inter-Domain Routing Procedures   We believe that many Internet domains will benefit from the   introduction of IDPR.  However, the decision to support IDPR in a   given domain is an individual one, left to the domain administrator;   not all domains must support IDPR.   Within a domain that supports IDPR, other inter-domain routing   procedures, such as BGP and EGP, can comfortably coexist.  Each   inter-domain routing procedure is independent of the others.  The   domain administrator determines the relationship among the inter-   domain routing procedures by deciding which of its traffic flows   should use which inter-domain routing procedures and by configuring   this information for use by the policy gateways.   Hosts in stub domains may have strict service requirements and hence   will benefit from the policy routing provided by IDPR.  However, the   stub domain itself need not support IDPR in order for its traffic   flows to use IDPR routes.  Instead, a "proxy domain" may perform IDPR   functions on behalf of the stub.  The proxy domain must be reachable   from the stub domain according to an inter-domain routing procedure   independent of IDPR.  Administrators of the stub and potential proxy   domains mutually negotiate the relationship.  Once an agreement is   reached, the administrator of the stub domain should provide the   proxy domain with its hosts' service requirements.   IDPR policy routes must traverse a contiguous set of IDPR domains.   Hence, the degree of IDPR deployment in transit domains will   determine the availability of IDPR policy routes for Internet users.   For a given traffic flow, if there exists no contiguous set of IDPR   domains between the source and destination, the traffic flow relies   on an alternate inter-domain routing procedure to provide a route.   However, if there does exist a contiguous set of IDPR domains between   the source and destination, the traffic flow may take advantage of   policy routes provided by IDPR.7.  Implementation Experience   To date, there exist two implementations of IDPR: one an independent   prototype and the other an integral part of the gated UNIX process.   We describe each of these implementations and our experience with   them in the following sections.7.1  The Prototype   During the summer of 1990, the IDPR development group consisting of   participants from USC, SAIC, and BBN began work on a UNIX-based   software prototype of IDPR, designed for implementation in SunSteenstrup                                                      [Page 8]

RFC 1477                         IDPR                          July 1993   workstations.  This prototype consisted of multiple user-level   processes to provide the basic IDPR functions together with kernel   modifications to speed up IDPR data message forwarding.   Most, but not all, of the IDPR functionality was captured in the   prototype.  In the interests of producing working software as quickly   as possible, we intentionally left out of the IDPR prototype support   for source policies and for multiple policy gateways connecting two   domains.  This simplified configuration and route generation without   compromising the basic functionality of IDPR.   The IDPR prototype software was extensively instrumented to provide   detailed information for monitoring its behavior.  The   instrumentation allowed us to detect events including but not limited   to:   - Change in policy gateway connectivity to adjacent domains.   - Change in transit policies configured for a domain.   - Transmission and reception of link state routing information.   - Generation of policy routes, providing a description of the actual     route.   - Transmission and reception of path control information.   - Change of path state, such as path setup or teardown.   With the extensive behavioral information available, we were able to   track most events occurring in our test networks and hence determine   whether the prototype software provided the expected functionality.7.1.1  Test Networks   In February 1991, the IDPR development group began experimenting with   the completed IDPR prototype software.  Each IDPR development site   had its own testing environment, consisting of a set of   interconnected Sun workstations, each workstation performing the   functions of a policy gateway and route server:   - USC used a laboratory test network consisting of SPARC1+     workstations, each pair of workstations connected by an Ethernet     segment.  The topology of the test network could be arbitrarily     configured.   - SAIC used Sun3 workstations in networks at Sparta and at MITRE.     These two sites were connected through Alternet using a 9.6kb SLIPSteenstrup                                                      [Page 9]

RFC 1477                         IDPR                          July 1993     link and through an X.25 path across the DCA EDN testbed.   - BBN used SPARC1+ workstations at BBN and ISI connected over both     DARTnet and TWBnet.7.1.2  Experiments   The principal goal of our experiments with the IDPR prototype   software was to provide a proof of concept.  In particular, we set   out to verify tha t the IDPR prototype software was able to:   - Monitor connectivity across and between domains.   - Update routing information when inter-domain connectivity changed     or when new transit policies were configured.   - Distribute routing information to all domains.   - Generate acceptable policy routes based on current link state     routing information.   - Set up and maintain paths for these policy routes.   - Tear down paths that contained failed components, supported stale     policies, or attained their maximum age.   Furthermore, we wanted to verify that the IDPR prototype software   quickly detected and adapted to those events that directly affected   policy routes.   The internetwork topology on which we based most of our experiments   consisted of four distinct administrative domains connected in a   ring.  Two of the four domains served as host traffic source and   destination, AD S and AD D respectively, while the two intervening   domains provided transit service for the host traffic, AD T1 and AD   T2.  AD S and AD D each contained a single policy gateway that   connected to two other policy gateways, one in each transit domain.   AD T1 and AD T2 each contained at most two policy gateways, each   policy gateway connected to the other and to a policy gateway in the   source or destination domain.  This internetwork topology provided   two distinct inter-domain routes between AD S and AD D, allowing us   to experiment with various component failure and transit policy   reconfiguration scenarios in the transit domains.   For the first set of experiments, we configured transit policies for   AD T1 and AD T2 that were devoid of access restrictions.  We then   initialized each policy gateway in our internetwork, loading in the   domain-specific configurations and starting up the IDPR processes.Steenstrup                                                     [Page 10]

RFC 1477                         IDPR                          July 1993   In our experiments, we did not use mapping servers; instead, we   configured address/domain mapping tables in each policy gateway.   After policy gateway initialization, we observed that each policy   gateway immediately determined the connectivity to policy gateways in   its own domain and in the adjacent domains.  The representative   policy gateway in each domain then generated a routing information   message that was received by all other policy gateways in the   internetwork.   To test the route generation and path setup functionality of the IDPR   prototype software, we began a telnet session between a host in AD S   and a host in AD D.  We observed that the telnet traffic prompted the   path agent resident in the policy gateway in AD S to request a policy   route from its route server.  The route server then generated a   policy route and returned it to the path agent.  Using the policy   route supplied by the route server, the path agent initiated path   setup, and the telnet session was established immediately.   Having confirmed that the prototype software satisfactorily performed   the basic IDPR functions, we proceeded to test the software under   changing network conditions.  The first of these tests showed that   the IDPR prototype software was able to deal successfully with a   component failure along a path.  To simulate a path component   failure, we terminated the IDPR processes on a policy gateway in the   transit domain, AD T1, traversed by the current path.  The policy   gateways on either side of the failed policy gateway immediately   detected the failure.  Next, these two policy gateways, representing   two different domains, each issued a routing information message   indicating the connectivity change and each initiated path teardown   for its remaining path section.   Once the path was torn down, the path agent agent in AD S requested a   new route from its route server, to carry the existing telnet   traffic.  The route server, having received the new routing   information messages, proceeded to generate a policy route through   the other transit domain, AD T2.  Then, the path agent in AD S set up   a path for the new route supplied by the route server.  Throughout   the component failure and traffic rerouting, the telnet session   remained intact.   At this point, we restored the failed policy gateway in AD T1 to the   functional state, by restarting its IDPR processes.  The restored   policy gateway connectivity prompted the generation and distribution   of routing information messages indicating the change in domain   connectivity.Steenstrup                                                     [Page 11]

RFC 1477                         IDPR                          July 1993   Having returned the internetwork topology to its initial   configuration, we proceeded to test that the IDPR prototype software   was able to deal successfully with transit policy reconfiguration.   The current policy route carrying the telnet traffic traversed AD T2.   We then reconfigured the transit policy for AD T2 to preclude access   of traffic travelling from AD S to AD D.  The transit policy   reconfiguration prompted both the distribution of routing information   advertising the new transit policy for AD T2 and the initiation of   path teardown.   Once the path was torn down, the path agent in AD S requested a new   route from its route server, to carry the existing telnet traffic.   The route server, having received the new routing information   message, proceeded to generate a policy route through the original   transit domain, AD T1.  Then, the path agent in AD S set up a path   for the new route supplied by the route server.  Throughout the   policy reconfiguration and rerouting, the telnet session remained   intact.   This set of experiments, although simple, tested all of the major   functionality of the IDPR prototype software and demonstrated that   the prototype software could quickly and accurately adapt to changes   in the internetwork.7.1.3  Performance Analysis   We (USC and SAIC members of the IDPR development group) evaluated the   performance of the path setup and message forwarding portions of the   IDPR prototype software.  For path setup, we measured the amount of   processing required at the source path agent and at intermediate   policy gateways during path setup.  For message forwarding, we   compared the processing required at each policy gateway when using   IDPR forwarding with IP encapsulation and when using only IP   forwarding.  We also compared the processing required when no   integrity/authentication value was calculated for the message and   when the RSA/MD4 algorithms were employed.   Our performance measurements were encouraging, but we have not listed   them here.  We emphasize that although we tried to produce efficient   software for the IDPR prototype, we were not able to devote much   effort to optimizing this software.  Hence, the performance   measurements for the IDPR prototype software should not be blindly   extrapolated to other implementations of IDPR.  To obtain a copy of   the performance measurements for path setup and message forwarding in   the IDPR prototype software, contact Robert Woodburn   (woody@sparta.com) and Deborah Estrin (estrin@usc.edu).Steenstrup                                                     [Page 12]

RFC 1477                         IDPR                          July 19937.2  The Gated Version   In 1992, SRI joined the IDPR development group, and together SRI,   SAIC, and BBN completed the task of integrating IDPR into the gated   UNIX process.  As a result, IDPR is now available as part of gated.   The gated version of IDPR contains the full functionality of IDPR   together with a simple yet versatile user interface for IDPR   configuration.  As a single process, the gated version of IDPR   performs more efficiently than the multiple-process prototype   version.   The gated version of IDPR is freely available to the Internet   community.  Hence, anyone with a UNIX-based machine can experiment   with IDPR, without investing any money or implementation effort.  By   making IDPR widely accessible, we can gain Internet experience by   introducing IDPR into operational networks with real usage   constraints and transporting host traffic with real service   requirements.  Currently, a pilot deployment and demonstration of   IDPR is under way in selected locations in the Internet.8.  Security Considerations   Refer tosection 4 for details on security in IDPR.9.  Author's Address   Martha Steenstrup   BBN Systems and Technologies   10 Moulton Street   Cambridge, MA 02138   Phone: (617) 873-3192   Email: msteenst@bbn.comSteenstrup                                                     [Page 13]