This is not an Internet standard. Distribution of this memo is unlimited. The official document is the PostScript file, which has the diagrams in place. Please use the PostScript version of this memo. The set of standards covers the services and protocols re quired to achieve such interconnection.

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This is not an Internet standard. Distribution of this memo is unlimited. The official document is the PostScript file, which has the diagrams in place. Please use the PostScript version of this memo. The set of standards covers the services and protocols re quired to achieve such interconnection.

This Protocol is positioned with respect to other related standards by the layers defined in the ISO and by the structure defined in the ISO In particular, it is a protocol of the Network Layer. This protocol permits Intermediate Systems within a routeing Domain to exchange configuration and routeing information to facilitate the operation of the route ing and relaying functions of the Network Layer.

Data is carried by ISO The related algo rithms for route calculation and maintenance are also described. The intra-domain ISIS routeing protocol is intended to support large routeing domains consisting of combinations of many types of subnetworks. This includes point-to-point links, multipoint links, X. In order to support large routeing domains, provision is made for Intra-domain routeing to be organised hierarchically.

A large domain may be administratively divided into areas. Each system resides in exactly one area. Routeing within an area is referred to as Level 1 routeing. Routeing between areas is referred to as Level 2 routeing. Level 2 Intermediate systems keep track of the paths to destination areas. Level 1 Intermediate systems keep track of the routeing within their own area. Then the NPDU travels via level 2 routeing to the destination area, where it again travels via level 1 routeing to the destination End System.

Information technology Telecommunications and information exchange between systems Intermediate system to Intermediate system Intra-Domain routeing exchange protocol for use in Conjunction with the Protocol for providing the Connectionless-mode Network Service ISO 1 Scope and Field of Application This International Standard specifies a protocol which is used by Network Layer entities operating ISO in In termediate Systems to maintain routeing information for the purpose of routeing within a single routeing domain.

The protocol herein described relies upon the provision of a connectionless-mode underlying service. This Standard specifies: a procedures for the transmission of configuration and routeing information between network entities resid ing 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 infor mation; 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 un derlying service provider through the exchange of subnetwork service primitives.

At the time of publication, the editions in dicated were valid. All standards are subject to revision, and parties to agreements based on this International Stan dard are encouraged to investigate the possibility of apply ing the most recent editions of the standards listed below.

ISO , Information processing systems Data communications Protocol for providing the connectionless-mode network service. ISO , Information processing systems Tele communications and information exchange between sys tems End system to Intermediate system Routeing ex change protocol for use in conjunction with the protocol for providing the connectionless -mode network service ISO It corresponds to the Level 1 subdomain.

Adjacencies are used as input to the Decision Proc ess 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.

The pseudonode has links to each of the n Interme diate systems and each of the ISs has a single link to the pseudonode rather than n-1 links to each of the other Intermediate systems. This is depicted below in figure 1. The first word is lower case, with the first character of subsequent words capitalised; c Protocol field names appear in San Serif type with each word capitalised.

They route directly to systems within their own area, and route towards a level 2 Interme diate system when the destination system is in a dif ferent area. Level 2 Intermediate Systems: These systems act as Level 1 Intermediate systems in addition to acting as a sys tem in the subdomain consisting of level 2 ISs. Sys tems in the level 2 subdomain route towards a desti nation area, or another routeing domain. There are several generic types of general topology subnetworks: 1 multipoint links: These are links between more than two systems, where one system is a primary system, and the remaining systems are secondary or slave systems.

The primary is capable of direct communication with any of the secondaries, but the secondaries cannot communicate directly among themselves. Dynamically established data links can be used in one of two ways: i static point-to-point Static : The call is estab lished upon system management action and cleared only on system management action or failure. The ad dress to which the call is to be established is determined dynamically from information in the arriving NPDU s.

All subnetwork types are treated by the Subnetwork Inde pendent functions as though they were connectionless subnetworks, using the Subnetwork Dependent Conver gence functions of ISO where necessary to provide a connectionless subnetwork service. The Subnetwork De pendent functions do, however, operate differently on connectionless and connection-oriented subnetworks. Furthermore, it is desirable for an intra-domain routeing protocol to aid in the operation of an inter-domain routeing protocol, where such a protocol exists for interconnecting multiple administrative domains.

In order to facilitate the construction of such multi-domain topologies, provision is made for the entering of static inter-domain routeing information. This information is pro vided by a set of Reachable Address Prefixes entered by System Management at the ISs which have links which cross routeing domain boundaries. Where the subnetwork to which this SNPA is con nected is a general topology subnetwork supporting dy namically established data links, the prefix also has associ ated with it the required subnetwork addressing information, or an indication that it may be derived from the destination NSAP address for example, an X.

The Address Prefixes are handled by the level 2 routeing al gorithm in the same way as information about a level 1 area within the domain. NPDUs with a destination address matching any of the prefixes present on any Level 2 Inter mediate System within the domain can therefore be relayed using level 2 routeing by that IS and delivered out of the domain.

It is assumed that the routeing functions of the other domain will then be able to deliver the NPDU to its destination. Within such a domain it is still possible for some End Systems to have addresses assigned which do not conform to 7.

They are independent of the specific subnetwork or data link service operating below them, except for recognis ing two generic types of subnetworks: -General Topology Subnetworks, which include HDLC point-to-point, HDLC multipoint, and dynami cally established data links such as X. The following Subnetwork Independent Functions are iden tified -Routeing. The routeing function determines NPDU paths. A path is the sequence of connected systems and links between a source ES and a destination ES.

The combined knowledge of all the Network Layer entities of all the Intermediate systems within a route ing domain is used to ascertain the existence of a path, and route the NPDU to its destination. If a sys tem or link fails on a path, it finds an alternate route. Congestion control manages the resources used at each Intermediate system. See clause 7. It adapts to topological changes within the routeing domain, but not to traffic changes, except potentially as indicated by local queue lengths.

It splits traffic load on multiple equivalent paths. The period of adaptation to topological changes in the domain is a reasonable function of the domain diameter that is, the maximum logical dis tance between End Systems within the domain and Data link speeds.

It is both processing and memory effi cient. It does not create excessive routeing traffic overhead. It recovers from transient errors such as lost or temporarily incorrect routeing PDUs. It toler ates imprecise parameter settings. It stabilises in finite time to good routes, provided no continuous topological changes or con tinuous data base corruptions occur.

System Management can control many routeing functions via parameter changes, and inspect parameters, counters, and routes. It will not, however, depend on system management action for correct behaviour.

It is sufficiently simple to permit perform ance tuning and failure isolation. It provides mechanisms to detect, isolate, and repair most common errors that may affect the routeing computation and data bases.

It operates over a mixture of network and system types, communication technologies, and topologies. It accommodates increased routeing functions, leaving earlier functions as a subset. It allows orderly transition from algorithm to algorithm without shutting down an entire domain. The congestion control compo nent prevents buffer deadlock. With hierarchical routeing, and a very large address space, domains of essentially un limited size can be supported.

It permits the utilisation of level 2 paths to repair areas which become partitioned due to failing level 1 links or ISs. Routes are a function only of the physi cal topology, and not of history. In other words, the same topology will always converge to the same set of routes. The probability of mis-delivering a NPDU, i. For domain topologies with cut set greater than one, no single point of failure will parti tion the domain. The service classes of transit delay, expense22Expense is referred to as cost in ISO The latter term is not used here because of possible confusion with the more general usage of the term to indicate path cost according to any routeing metric.

The protocol is capable of carrying information to be used for the authentication of Inter mediate systems in order to increase the security and robustness of a routeing domain. The specific mecha nism supported in this International Standard how ever, only supports a weak form of authentication us ing passwords, and thus is useful only for protection against accidental misconfiguration errors and does not protect against any serious security threat. In the future, the algorithms may be enhanced to provide stronger forms of authentication than can be provided with passwords without needing to change the PDU encoding or the protocol exchange machinery.

It does not automatically modify routes based on global traffic load. It does not determine routes by source as well as destination. It does not guarantee delivery of all offered NPDUs. It will not util ise Level 1 paths to repair a level 2 subdomain parti tion. For full logical connectivity to be available, a connected level 2 subdomain is required. The End system poll function defined in 8. An End sys tem which does not implement this option may experi ence a temporary loss of connectivity following cer tain types of topology changes on its local subnetwork.

The required local environment guarantees are: a Resource allocation such that the certain minimum re source guarantees can be met, including 1 memory for code, data, and buffers 2 processing; See The required subnetwork guarantees for point-to-point links are: a Provision that both source and destination systems complete start-up before PDU exchange can occur; b Detection of remote start-up; c Provision that no old PDUs be received after start-up is complete; d Provision that no PDUs transmitted after a particular startup is complete are delivered out of sequence; e Provision that failure to deliver a specific subnetwork SDU will result in the timely disconnection of the subnetwork connection in both directions and that this failure will be reported to both systems; and f Reporting of other subnetwork failures and degraded subnetwork conditions.

The required subnetwork guarantees for broadcast links are: a Multicast capability, i. The following services are assumed to be not available from broadcast links: a Reporting of failures and degraded subnetwork condi tions that result in NPDU loss, for instance receiver failure.

The routeing functions are designed to account for these failures. These are de scribed briefly in this sub-clause and in detail in clause 7.



Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. This RFC is available in both postscript and text versions. Where possible, use of the postscript version is recommended. For example, this text version may have figures which are less informative or missing. This allows a single routing protocol to be used to support pure IP environments, pure OSI environments, and dual environments.


Updated by: Network Working Group H. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. This information describes additional details regarding the state of the network that are useful for traffic engineering computations. Such tuples are commonly known as TLVs, and are a good way of encoding information in a flexible and extensible format. The characteristics described in this document are needed for Traffic Engineering [ 4 ] TE. Mechanisms and procedures to migrate to the new TLVs are not discussed in this document.

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