Network Working Group                                     D. Oran, EditorRequest for Comments: 1142                        Digital Equipment Corp.                                                            February 1990	        OSI IS-IS Intra-domain Routing Protocol Status of this Memo   This RFC is a republication of ISO DP 10589 as a service to the   Internet community.  This is not an Internet standard.   Distribution of this memo is unlimited.	NOTE:  This is a bad ASCII version of this document.  The officialdocument is the PostScript file, which has the diagrams in place.Please use the PostScript version of this memo.ISO/IEC DIS 10589 Information technology Telecommunications and information exchangebetween systems Interme diate system to Intermediate systemIntra-Domain routeing exchange protocol for use in Conjunction withthe Protocol for providing the Connectionless- mode Network Service(ISO 8473) Technologies de l'information Communication de donnies etichange d'information entre systhmes Protocole intra-domain de routaged'un systhme intermediare ` un systhme intermediare ` utiliserconjointement avec le protocole fournissant le service de riseau enmode sans connexion (ISO 8473) UDC 00000.000 : 000.0000000000Descriptors: Contents	Introduction		iv	1 	Scope and Field of Application	1	2 	References	1	3 	Definitions	2	4 	Symbols and Abbreviations 	3	5 	Typographical Conventions	4	6 	Overview of the Protocol	4	7 	Subnetwork Independent Functions	9	8 	Subnetwork Dependent Functions	35	9 	Structure and Encoding of PDUs	47	10 	System Environment	65	11 	System Management 	67	12 	Conformance	95	Annex A 	PICS Proforma	99	Annex B 	Supporting Technical Material	105	Annex C 	Implementation Guidelines and Examples	109	Annex D 	Congestion Control and Avoidance	115 IntroductionThis Protocol is one of a set of International Standards produced tofacilitate the interconnection of open systems. The set of standardscovers the services and protocols re quired to achieve suchinterconnection.  This Protocol is positioned with respect to otherrelated standards by the layers defined in the ISO 7498 and by thestructure defined in the ISO 8648. In particular, it is a protocol ofthe Network Layer. This protocol permits Intermediate Systems within arouteing Domain to exchange configuration and routeing information tofacilitate the operation of the route ing and relaying functions ofthe Network Layer.  The protocol is designed to operate in closeconjunction with ISO 9542 and ISO 8473.  ISO 9542 is used to establishconnectivity and reachability between End Systems and Inter mediateSystems on individual Subnetworks. Data is carried by ISO 8473.  Therelated algo rithms for route calculation and maintenance are alsodescribed.  The intra-domain ISIS routeing protocol is intended tosupport large routeing domains consisting of combinations of manytypes of subnetworks. This includes point-to-point links, multipointlinks, X.25 subnetworks, and broadcast subnetworks such as ISO 8802LANs.  In order to support large routeing domains, provision is madefor Intra-domain routeing to be organised hierarchically. A largedomain may be administratively divided into areas.  Each systemresides in exactly one area. Routeing within an area is referred to asLevel 1 routeing. Routeing between areas is referred to as Level 2routeing.  Level 2 Intermediate systems keep track of the paths todestination areas. Level 1 Intermediate systems keep track of therouteing within their own area. For an NPDU destined to another area,a Level 1 Intermediate system sends the NPDU to the nearest level 2 ISin its own area, re gardless of what the destination area is. Then theNPDU travels via level 2 routeing to the destination area, where itagain travels via level 1 routeing to the destination End System. Information technologyTelecommunications and information exchange between systemsIntermediate system to Intermediate system Intra-Domain routeingexchange protocol for use in Conjunction with the Protocol forproviding the Connectionless-mode Network Service (ISO 8473) 1 Scope and Field of ApplicationThis International Standard specifies a protocol which is used byNetwork Layer entities operating ISO 8473 in In termediate Systems tomaintain routeing information for the purpose of routeing within asingle routeing domain. The protocol herein described relies upon theprovision of a connectionless-mode underlying service.11See ISO 8473and its Addendum 3 for the mechanisms necessary to realise thisservice on subnetworks based on ISO 8208, ISO 8802, and the OSI DataLink Service. This Standard specifies: a)procedures for the transmission of configuration and routeing information between network entities residing in Intermediate Systems within a single routeing domain; b)the encoding of the protocol data units used for the transmission of the configuration and routeing information; c)procedures for the correct interpretation of protocol control information; and d)the functional requirements for implementations claiming conformance to this Standard.The procedures are defined in terms of: a)the interactions between Intermediate system Network entities through the exchange of protocol data units; and b)the interactions between a Network entity and an underlying service provider through the exchange of subnetwork service primitives.c)the constraints on route determination which must be observed by each Intermediate system when each has a routeing information base which is consistent with the others. 2 References2.1  Normative ReferencesThe following standards contain provisions which, through reference inthis text, constitute provisions of this Interna tional Standard.  Atthe time of publication, the editions in dicated were valid. Allstandards are subject to revision, and parties to agreements based onthis International Stan dard are encouraged to investigate thepossibility of apply ing the most recent editions of the standardslisted below.  Members of IEC and ISO maintain registers of currentlyvalid International Standards.  ISO 7498:1984, Information processingsystems Open Systems Interconnection Basic Reference Model.  ISO7498/Add.1:1984, Information processing systems Open SystemsInterconnection Basic Reference Model Addendum 1: Connectionless-modeTransmission.  ISO 7498-3:1989, Information processing systems OpenSystems Interconnection Basic Reference Model Part 3: Naming andAddressing.  ISO 7498-4:1989, Information processing systems OpenSystems Interconnection Basic Reference Model Part 4: ManagementFramework.  ISO 8348:1987, Information processing systems Datacommunications Network Service Definition.  ISO 8348/Add.1:1987,Information processing systems Data communications Network ServiceDefinition Addendum 1: Connectionless-mode transmission.  ISO8348/Add.2:1988, Information processing systems Data communicationsNetwork Service Definition Addendum 2: Network layer addressing.  ISO8473:1988, Information processing systems Data communications Protocolfor providing the connectionless-mode network service.  ISO8473/Add.3:1989, Information processing systems Telecommunications andinformation exchange betweensystems  Protocol for providing the connectionless-mode network service  Addendum 3: Provision of the underlying service assumed by ISO 8473 over subnetworks which provide the OSI data link service.ISO 8648:1988,  Information processing systems  Open Systems Interconnection  Internal organisation of the Network Layer.ISO 9542:1988, Information processing systems  Telecommunications and information exchange between systems  End system to Intermediate system Routeing exchange protocol for use in conjunction with the protocol for providing the connectionless -mode network service (ISO 8473).ISO 8208:1984, Information processing systems  Data communications  X.25 packet level protocol for Data terminal equipmentISO 8802:1988, Information processing systems  Telecommunications and information exchange between systems  Local area networks.ISO/TR 9575:1989, Information technology   Telecommunications and information exchange between systems  OSI Routeing Framework.ISO/TR 9577:1990, Information technology   Telecommunications and information exchange between systems  Protocol Identification in the Network Layer.ISO/IEC DIS 10165-4:, Information technology  Open systems interconnection  Management Information Services  Structure of Management Information Part 4: Guidelines for the Definition of Managed Objects.ISO/IEC 10039:1990, IPS-T&IEBS  MAC Service Definition.2.2 Other ReferencesThe following references are helpful in describing some of the routeing algorithms: McQuillan, J. et. al., The New Routeing Algorithm for the ARPANET, IEEE Transactions on Communications, May 1980.Perlman, Radia, Fault-Tolerant Broadcast of Routeing Information, Computer Networks, Dec. 1983. Also in IEEE INFOCOM 83, April 1983.Aho, Hopcroft, and Ullman, Data Structures and Algorithms, P204208  Dijkstra algorithm. 3 Definitions3.1 Reference Model definitionsThis International Standard  makes use of the following terms defined in ISO 7498:a)Network Layerb)Network Service access pointc)Network Service access point addressd)Network entitye)Routeingf)Network protocolg)Network relayh)Network protocol data unit3.2 Network Layer architecture definitionsThis International Standard makes use of the following terms defined in ISO 8648:a)Subnetworkb)End systemc)Intermediate systemd)Subnetwork servicee)Subnetwork Access Protocol f)Subnetwork Dependent Convergence Protocol g)Subnetwork Independent Convergence Protocol3.3 Network Layer addressing definitionsThis International Standard makes use of the following terms defined in ISO 8348/Add.2:a)Subnetwork addressb)Subnetwork point of attachmentc)Network Entity Title3.4 Local Area Network Definitions This International Standard makes use of the following terms defined in ISO 8802: a)Multi-destination address b)Media access controlc)Broadcast medium3.5 Routeing Framework Definitions This document makes use of the following terms defined in ISO/TR 9575: a)Administrative Domain b)Routeing Domain c)Hop d)Black hole   3.6 Additional DefinitionsFor the purposes of this International Standard, the following definitions apply: 3.6.1   Area: A routeing subdomain which maintains detailed routeing information about its own internal composition, and also maintains routeing information which allows it to reach other routeing subdomains. It corresponds to the Level 1 subdomain. 3.6.2   Neighbour: An adjacent system reachable by traversal of a single subnetwork by a PDU. 3.6.3   Adjacency: A portion of the local routeing information which pertains to the reachability of a single neighbour ES or IS over a single circuit.Adjacencies are used as input to the Decision Process for forming paths through the routeing domain.A separate adjacency is created for each neighbour on a circuit, and for each level of routeing (i.e. level 1 and level 2) on a broadcast circuit.3.6.4   Circuit: The subset of the local routeing information base pertinent to a single local SNPA. 3.6.5   Link: The communication path between two neighbours. A Link is up when communication is possible between the two SNPAs.3.6.6   Designated IS: The Intermediate system on a LAN which is designated to perform additional duties. In particular it generates Link State PDUs on behalf of the LAN, treating the LAN as a pseudonode. 3.6.7   Pseudonode: Where a broadcast subnetwork has n connected Intermediate systems, the broadcast subnetwork itself is considered to be a pseudonode.