From 4bfd864f10b68b71482b35c818559068ef8d5797 Mon Sep 17 00:00:00 2001 From: Thomas Voss Date: Wed, 27 Nov 2024 20:54:24 +0100 Subject: doc: Add RFC documents --- doc/rfc/rfc1136.txt | 563 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 563 insertions(+) create mode 100644 doc/rfc/rfc1136.txt (limited to 'doc/rfc/rfc1136.txt') diff --git a/doc/rfc/rfc1136.txt b/doc/rfc/rfc1136.txt new file mode 100644 index 0000000..04bb529 --- /dev/null +++ b/doc/rfc/rfc1136.txt @@ -0,0 +1,563 @@ + + + + + + +Network Working Group S. Hares +Request for Comments: 1136 D. Katz + Merit/NSFNET + December 1989 + + + Administrative Domains and Routing Domains + A Model for Routing in the Internet + + +1) Status of this Memo + + This RFC proposes a model for describing routing within the Internet. + The model is an adaptation of the "OSI Routeing Framework" [1]. This + memo does not specify an Internet standard. Comments are welcome. + Distribution of this memo is unlimited. + +2) Acknowledgement + + The authors would like to thank Guy Almes of Rice University for his + contributions and insight. + +3) Overview + + The "core" model of Autonomous Systems [2] formed the basis for the + routing model used in the Internet. Due to massive growth and + topology changes, the "core" model no longer is in harmony with the + reality of today's Internet. Indeed, this situation was foreseen at + the outset: + + "Ultimately, however, the internet may consist of a number of co- + equal autonomous systems, any of which may be used...as a + transport medium for traffic originating in any system and + destined for any system. When this more complex configuration + comes into being, it will be inappropriate to regard any one + autonomous system as a "core" system" [2]. + + Furthermore, the Autonomous System concept has been outgrown in + certain parts of the Internet, in which the complexity of regional + routing has exceeded the limits of the definition of Autonomous + Systems. + + A model which can provide a better match to the Internet can be found + in the "OSI Routeing Framework" [1]. + + This framework proposes a structure of Routing Domains within + Administrative Domains. This paper is intended to briefly describe + this framework, to outline how this model better fits the reality of + + + +Hares & Katz [Page 1] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + the present and future Internet, and to show how the model can aid in + the construction of well-engineered routing environments. + +4) Terminology + + The following is a brief glossary of OSI terminology. Formal + definitions can be found in the OSI Basic Reference Model [4], the + Internal Organization of the Network Layer [5], and the OSI Routeing + Framework [1]. + + "Routeing" is the official ISO spelling of what is more + commonly spelled "routing." In this paper, the ISO spelling + will be used wherever directly quoted from ISO documents, and + the common spelling used otherwise. + + End System (ES) + + An OSI system on which applications run. An End System has + full seven-layer OSI functionality. Basically equivalent to an + Internet Host. + + Intermediate System (IS) + + An OSI system that performs routing and relaying functions in + order to provide paths between End Systems. Intermediate + Systems have no functionality above the Network Layer (although + a practical realization of an OSI router will have some amount + of End System functionality for network management functions, + among other things). Basically equivalent to an Internet + Router. + + Subnetwork (SN) + + A communications medium that provides a "direct" path between + Network Layer entities. This can be realized via a point-to- + point link, a LAN, a Public Data Network, and so forth. This + is essentially equivalent to an Internet Subnet. It is worth + noting that, unlike Internet Subnets, OSI Subnetworks are not + necessarily reflected in the addressing hierarchy, so the + double meaning of the Internet term "Subnet" (a single IP hop; + a part of the address hierarchy) does not hold in the OSI + world. + + Open Systems Interconnection Environment (OSIE) + + The global collection of Open Systems. Basically equivalent to + the Internet. + + + + +Hares & Katz [Page 2] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + Network Service Access Point (NSAP) + + A conceptual point on the Network/Transport Layer boundary in + an End System that is globally addressable (and the address + globally unambiguous) in the OSIE. An NSAP represents a + service available above the Network Layer (such as a choice of + transport protocols). An End System may have multiple NSAPs. + An NSAP address is roughly equivalent to the Internet [address, + protocol] pair. + + Administrative Domain (AD) + + "A collection of End Systems, Intermediate Systems, and + subnetworks operated by a single organization or administrative + authority. The components which make up the domain are assumed + to interoperate with a significant degree of mutual trust among + themselves, but interoperate with other Administrative Domains + in a mutually suspicious manner" [1]. + + A group of hosts, routers, and networks operated and managed by + a single organization. Routing within an Administrative Domain + is based on a consistent technical plan. An Administrative + Domain is viewed from the outside, for purposes of routing, as + a cohesive entity, of which the internal structure is + unimportant. Information passed by other Administrative + Domains is trusted less than information from one's own + Administrative Domain. + + Administrative Domains can be organized into a loose hierarchy + that reflects the availability and authoritativeness of routing + information. This hierarchy does not imply administrative + containment, nor does it imply a strict tree topology. + + Routing Domain (RD) + + "A set of End Systems and Intermediate Systems which operate + according to the same routeing procedures and which is wholly + contained within a single Administrative Domain" [1]. + + "A Routeing Domain is a set of ISs and ESs bound by a common + routeing procedure; namely: + + they are using the same set of routeing metrics, + + they use compatible metric measurement techniques, + + they use the same information distribution protocol, and + + + + +Hares & Katz [Page 3] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + they use the same path computation algorithm" [1]. + + The "OSI Routeing Framework" further provides a formal + definition of a Routing Domain, specifying that all ISs within + a Routing Domain can determine whether an ES within the domain + is reachable, and if so can derive a path to it. + + Routing Domains may be divided into subdomains, not unlike + subnetting in the Internet. This allows a hierarchical + structuring of the domain, permitting containment of the + topological details of a subdomain with the resultant reduction + in distributed routing information. + + An intra-Routing Domain routing protocol is equivalent to an + Internet Interior Gateway Protocol (IGP). + + An Administrative Domain may contain multiple Routing Domains. + A Routing Domain may never span multiple Administrative + Domains. + + An Administrative Domain may consist of only a single Routing + Domain, in which case they are said to be Congruent. A + congruent Administrative Domain and Routing Domain is analogous + to an Internet Autonomous System. + + Common Domain (CD) + + "An Administrative Domain which is not a member of a higher + level domain. A common domain is the highest level in the + routeing hierarchy. There is no single domain above the common + domain. In this sense, the routeing hierarchy is in fact + multiple hierarchies, with the common domain as the highest + element of each hierarchy". + + "Where there are multiple common domains, they cooperate as + peers to make it possible to route to any NSAP in the OSIE" + [1]. + + Common Domains have global routing information to the extent + necessary to route packets to the proper domain. Each of the + several peer national backbones in today's Internet may be + considered to be similar to a Common Domain. Note that in the + Internet the hierarchical containment implied by the definition + of a CD does not really exist; however, there is a level of + implicit ordering based on topology and policy issues (the + willingness to be used as a transit network) that can be viewed + as defining a Common Domain in the Internet. + + + + +Hares & Katz [Page 4] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + For completeness, we offer the following definition for an Internet + Autonomous System (AS): + + "An 'autonomous system' consists of a set of gateways, each of + which can reach any other gateway in the same system using paths + via gateways only in that system. The gateways of a system + cooperatively maintain a routing data base using an interior + gateway protocol (IGP)..." [3] + +5) Environment and Goals + + The "OSI Routeing Framework" describes the environment for OSI + routing as well as its goals. The environment described is a highly + interconnected, highly heterogeneous collection of LANs and public + and private networks made up of a diverse collection of equipment + from multiple vendors. A number of goals are enumerated, including: + + - Support of multiple subnetwork types + - Very large numbers of connected systems + - End System simplicity + - Multiple organizations with mutual distrust and policy/legal + restrictions + - High performance + - Robust and dynamic routing in the face of topological changes + + The environment and goals described are a good match for those in the + Internet. The Internet crosses multiple types of physical media, + link layer protocols, and administrative controls. Routers and hosts + may come from many vendors. The Internet has become international in + scope. Issues of security and the isolation of bad routing + information have become international concerns. + + The Internet environment, with over 900 highly connected networks + (and growing exponentially), is very much like the environment the + OSI model aims to describe. + +6) Structure of Global Routing + + The "OSI Routeing Framework" classifies routing into three types: + + - within a Routing Domain + - within an Administrative Domain + - between Administrative Domains + + Routing within a Routing Domain involves a high level of mutual + trust. This allows the use of complex, tightly-coupled procedures + that can make the best use of dynamic, highly interconnected + environments. + + + +Hares & Katz [Page 5] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + Routing Domains may be recursively subdivided into Subdomains in + order to reduce routing complexity. The details of a subdomain may + be largely hidden from other subdomains with an attendant reduction + in the volume of routing information exchanged. + + Intra-Administrative Domain routing is concerned with interconnecting + multiple Routing Domains within an administration. Issues may + include address administration, cost recovery, and policy concerns. + A moderate level of trust is assumed. The nature of the interactions + between Routing Domains can range from being tightly coupled (best + path routing between two RDs running different routing protocols) to + being more policy-based. However, inter-RD routing within an + Administrative Domain is tightly coordinated and represents a unified + technical plan. + + Inter-Administrative Domain routing is concerned with managing and + controlling the flow of information in a highly structured way + between organizations that may require formal multilateral + agreements. The issues of concern at this level tend to be + administrative in nature (legal/political constraints, security, + access control, etc.). Multiple agreements between multiple + administrations are unlikely to be implicitly transitive. This makes + the analysis of policy interactions very important. + +7) Mapping the AD/RD Model Onto the Internet + + The national network backbones (NSFNET, ARPANET, MILNET, NSN, and + soon ESNET) can be viewed as Common Domains. Each may have + sufficiently global routing knowledge to determine a path to any + Internet address. + + Regional networks are clearly Administrative Domains. Multilateral + policy agreements are defined between the regional networks and the + backbones. On the other hand, regional networks very often are + tightly coupled to individual networks and campus networks in terms + of routing. In this sense, a regional network could be viewed as a + Routing Domain with individual campuses thought of as Subdomains. + + From the standpoint of routing functionality, it is most useful to + view a "classic" Autonomous System as a congruent Routing Domain and + Administrative Domain. An AS as defined represents both a single IGP + and a point of policy administration. The sixteen bit value now + known as the Autonomous System number may instead be viewed as an + Administrative Domain number. + + In reality, however, many so-called Autonomous Systems today do not + adhere to the strict definition of an AS. In theory, an Autonomous + System is quite similar to a Routing Domain, in which a high level of + + + +Hares & Katz [Page 6] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + trust is made between systems, a consistent IGP is run, and full + routing information is distributed. On the other hand, AS numbers + have become an abstraction for policy groupings to backbones. + Indeed, entire regional networks are viewed by the backbones as a + single Autonomous System, even though they are not nearly as + homogeneous as the AS model specifies. Such entities can be viewed + as an Administrative Domain containing several Routing Domains. + + Although it is true that, in this interpretation, multiple + nontechnical administrations are represented within a single + Administrative Domain (in conflict with the definition of an + Administrative Domain), such structures require a single approach to + internal routing. Even if there is not a true administration + representing the collection of domains (such as a consortium), there + typically is a technical committee to settle common technical issues. + +8) The AD/RD Model as an Engineering Tool + + Current Autonomous Systems cross administrative boundaries with + impunity. This works as long as the individual administrations + operating within the common AS agree to a common technical policy for + routing and network management. Connections with other backbones, + regional networks, and campus networks must be planned, implemented, + and managed in a coordinated fashion. + + This coordination becomes more difficult, but more necessary, as the + AS grows. As connectivity and policy become more complex, current + Autonomous Systems start to fragment. An example of this is a + network that is currently a member of an NSFNET regional network but + will be adding a connection to ESNET. The administrators of the + network and the regional network must carefully coordinate the + changes necessary to implement this connection, including possibly + altering the boundaries of policy and routing. A lack of + coordination could result in routing loops and policy violations. + + A point that is being increasingly realized is that the entity + responsible for exterior or policy routing (be it an Autonomous + System or an Administrative Domain) must have a common technical + policy for routing. The effects of attempting different approaches + to policy and external routing while maintaining a single AS have + been painfully evident in real instances in the Internet. + + Under the AD/RD model, a routing domain cannot be in two + Administrative Domains. For example, if a campus network wants to + set its own routing policy and enforce it via management of their + routers, the campus has elected to become a separate Administrative + Domain. If that campus uses a common IGP with other campuses, it + represents an attempt to split a Routing Domain (the regional network + + + +Hares & Katz [Page 7] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + with a common IGP) across multiple Administrative Domains (the campus + and the rest of the regional). Such arrangements represent dubious + engineering practice, cause real routing problems, and are disallowed + by the AD/RD model. + + Under the strict Autonomous System model, only one IGP can exist + within an AS. However, many regional networks are successfully using + multiple IGPs. The AD/RD model allows this valuable routing + topology. Such a topology would also be allowed by the AS model if + it were to be broadened to allow multiple IGPs, in which case an AS + and an AD would effectively become equivalent. + +9) The AD/RD Model in a Dual Protocol Internet + + As the OSI protocol suite is deployed and an OSI Internet is + constructed, it is very likely that significant portions of the + current TCP/IP Internet will also carry OSI traffic. Many router + vendors provide dual protocol capability today, or will in the near + future, and the investment in network infrastructure is such that it + is unlikely that a separate, parallel internet will be established + for OSI traffic. + + It is logical to assume that, in many cases, the same technical and + administrative boundaries will apply to both DoD IP and OSI + protocols, and in some cases a single routing protocol may be used to + support both protocol suites. + + Thus, it would be most advantageous to have a common model and common + nomenclature in order to provide a more unified, manageable routing + environment. Given that the OSI Routeing Framework represents the + model on which OSI routing is built, the use of the AD/RD model to + describe the existing Internet is an appropriate step toward + describing and building the combined internet. + +10) Conclusions + + The AD/RD model of routing describes the current Internet better than + existing models because it describes: + + - How Intra-Domain and Inter-Domain relationships work at both + routing and policy level + + - How routing domains and administrative domains can be + hierarchically related + + - The existence of multiple national peers + + - A common model for dual protocol internets + + + +Hares & Katz [Page 8] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + The expanding Internet has grown from the "core" model with several + small attached networks to a highly interconnected environment that + spans several continents. Several national peer networks serve an + ever-growing set of regional networks. The AD/RD model can help + Internet protocol designers abstract the functional pieces from the + large Internet. + + The Internet grows daily. Any model of Internet routing needs to + provide a way to understand and order the growth. The ISO Routeing + Framework provides a structure to handle such growth. + +11) References + + [1] ISO, "OSI Routeing Framework", ISO/TR 9575, 1989. + + [2] Rosen, E., "Exterior Gateway Protocol", RFC 827, Bolt Beranek and + Newman, October 1982. + + [3] Mills, D., "Autonomous Confederations", RFC 975, M/A COM + Linkabit, February 1986. + + [4] ISO, "Open Systems Interconnection--Basic Reference Model", ISO + 7498. + + [5] ISO, "Internal Organization of the Network Layer", ISO 8648. + + ISO documents can be obtained from the following source: + + American National Standards Institute + 1430 Broadway + New York, NY 10018 + (212) 642-4900 + + Additionally, a number of private firms are authorized to distribute + ISO documents. + +Security Considerations + + Security issues are not addressed in this memo. + +Authors' Addresses + + Susan Hares + Merit/NSFNET + 1075 Beal Ave. + Ann Arbor, MI 48109 + + + + + +Hares & Katz [Page 9] + +RFC 1136 A Model for Routing in the Internet December 1989 + + + Phone: (313) 936-3000 + + Email: skh@merit.edu + + + Dave Katz + Merit/NSFNET + 1075 Beal Ave. + Ann Arbor, MI 48109 + + Phone: (313) 763-4898 + + Email: dkatz@merit.edu + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Hares & Katz [Page 10] + \ No newline at end of file -- cgit v1.2.3