ISO/IEC TR 9575:1990
(Main)Information technology — Telecommunications and information exchange between systems — OSI Routeing Framework
Information technology — Telecommunications and information exchange between systems — OSI Routeing Framework
Technologies de l'information — Communication de données et échange d'information entre systèmes — Cadre général de routage OSI
General Information
Relations
Standards Content (Sample)
ISOIIEC
TECHNICAL
TR 9575 '*
REPORT
First edition
1990-06-01
I n f o r m at i on tech no Io g y - Tel eco m m u n i ca t i o n s
and information exchange between systems -
OS1 Routeing Framework
Technologies de l'information - Communication de données et échange
d'information entre systèmes - Cadre général de routage OS1
Reference number
ISO/IEC/TR 9575 : 1990 (E)
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ISO/IEC/TR 9575 : 1990 (E)
Con teii ts
...
Foreword. . tit
Introduction . iv
Scope . 1
Normative References . 1
Definitions .
Symbols and abbreviations .
Routeing Concepts . . 2
Environment for OS1 routeing .
Goals for OS1 Routeing . 6
Structure of global OS1 Routeing . 8
O ISO/IEC 1990
All rights resewed. No part of this publication may be reproduced or utilized in
any form by any means, electronic or mechanical, including photocopying and
microfilm, withour permission in writing from the publisher
ISO/IEC Copyri ht Office, P.O. Box 56, 121 1 Geneva 20, Switzerland
Printed in SwitzeJand.
ii
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ISOIIECITR 9575 : 1990 (E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the International
Electrotechnical Commission) together form a system for worldwide standardization
as a whole. National bodies that are members of IS0 or IEC participate in the
development of International Standards through technical committees established by
the respective organization to deal with particular fields of technical activity. IS0 and
IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with IS0 and IEC, also
take part in the work.
In the field of information technology, IS0 and IEC have established a joint technical
committee, ISO/IEC JTC 1.
The main task of a technical committee is to prepare International Standards but
in exceptional circumstances, the publication of a Technical Report of one of the
following types may be proposed:
-
type 1, when the required support cannot be obtained for the publication of
an International Standard, despite repeated efforts;
- type 2, when the subject is still under technical development or where for
any other reason there is the future but not immediate possibility of an agree-
ment on an International Standard;
- type 3, when a technical committee has collected data of a different kind
from that which is normally published as an International Standard ("state of the
art", for example).
1 and 2 are subject to review within three years of publica-
Technical Reports of types
tion, to decide whether they can be transformed into International Standards.
Technical Reports of type 3 do not necessarily have to be reviewed until the data they
provide are considered to be no longer valid or useful.
ISO/IEC/TR 9575, which is a Technical Report of type 3, was prepared by ISO/IEC
JTCl , information technology.
iii
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ISO/IEC/TR 9575 : 1990 (E)
Introduction
in the OS1 environment (OSE), the possibility exists for any End Syatem (ES) to
communicate with my other ES. The physical path (or paths) over which this com-
munication takes place may
-
include multiple Intermediate Systems (IS):
- include multiple subnetwork types; and
- traverse multiple. independent organisations.
a different path from an-
Furthermore, one instance of conmiunications may follow
other instance of commiinicaiionu.
Within the Network Layer. the hirerriul Urgariisutioir of tlie Nmwk Layc~ (IS0
8648) identifies two functions, Routeing and Relaying. as being central to the ability
for End Systems to communicate through an arbitrary concateiiation of subnetworks
and Intermediate Systems.
Part of the overall function of routeing and relaying is to allow ESs and ISs to find an
appropriate path between two or more ESs for a given instance of communications.
Relaying is concerned primarily with the actual transformation and manipulation of
Network Protocol Data Units (NPDUs) as they transit Intermediate Systems.
Routeing, on the other hand, is primarily concerned with the maintenance and selec-
tion of paths through multiple subnetworks and Intermediate Systems which allow
NPDUs to flow smoothly between End Systems.
There are four important aspects to routeing. i.e.:
a) the information required by ESs and ISs ( 5.1.1).
b) the techniques used by ESs and ISs to collect that information (5.1.2),
c) the techniques used by ESs and ISs to distribute that information (5.1.3). and
d) the functions executed by ESs and ISs on that information to determine the
paths over which NPDI.Js flow between pairs of NSAPs (5.1.4).
This Technical Report discusscs thcsc aspects of routeing. xiti tli:scribt.s how various
protocols may be employed to effect the OS1 routeing fiinctioris. It does not discus<
relaying. except where rclaying functions are closely allied with roiiteing functions.
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lSO/lEC/TR 9575 : 1990 (E)
TECHNICAL REPORT
Iii for in at i o 11 t ecli 110 1 o gy - Tel eco in in uni ca t i oiis aiid in for in at io II
exchange between systems - OS1 Roiiteing Framework
e1 Scope
This Technical Report piovide. '1 Ciaiiizwork in which OS1 pro-
tocols for routeing inay bc dcvelopetl aiid to expedite the pro-
gression of roiitemg protocols tliiougli the \taridardisiition pioc-
es<.
2 Norinative References
The following stmuitlards contain provisioiis which, though ref-
erence in this text. constitute provisions of this Technical Rc-
port. At the tirne of publication. tlic editions indicated were
valid. All standards are subject to revision. atid parlies to agree-
3 Definitions
ments based on this Technical Repor! :iIc encoiiragcd to investi-
gate the possibility of applying tlie niosî recent editions of tlie
standards listed below. Members of IEC mid IS0 imiiiit:iin reg-
3.1 Refereiice Mociel definitions
isters of currently valid Interiiatiorial Standards.
This Techiiical Report makes use of the following tenns defined
in IS0 7498:
a) Network Layer
h) Network Service ~~CCSS point
c) Network Service awes\ point addreîs
ci) Network entity
e) Routemg
n Nctwork protocd
F) Netwoih rclq
11) Netnork protocol ciat'i unit
I) Sy\tcin tiian,igemeiit
1 ) L'iycl in,in'i~"~neiit
3.2 Nct wo i*k I ,ajw architect il re
clef in it i oil s
Thi\ Technical Report mike\ uw of the following terril5 defined
in IS0 8648.
a) Subnetwork
b) End system
c) Jntenriediate system
ci) Suhiictwot k sewice
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ISO/IEC/TR 9575 : 1990 (E)
acts as a repository for, and source of. routeing
3.3 Network Layer addressing
information for that subnetwork.
definitions
This Technical Report makes use of the following terms de-
4 Symbols and abbreviations
fied in IS0 8348/Add.2:
a) Subnetwork address
ES End System
b) Subnetwork point of attachment
IS Intermediate System
Local Area Network
LAN
3.4 Rout eing f rainew o r k de fin it i om
NPDU Network Protocol Data Unit
Network Service Access Point
NSAP
For the purpose of this Technical Report the following defini-
OSIE Open System Interconnection Environment
tions apply.
Protocol Data Unit
PDU
QoS Quality of Service
3.4.1 Administrative Domain: A collection of End
SN Subnetwork
systems, Intermediate systems. and subnetworks
operated by a single organisation or administrative SNARE Subnetwork Address Resolution Entity
aut horit y.
Subnetwork Point of Attachment
SNPA
OSIE Open Systems Interconnection Environn:eiit
The components whicli make up the domain are assumed to
Wide Area Network
WAN
interoperate with a significant degree of mutual trust among
themselves, but interoperate with other Administrative Do-
mains in a mutually suspicious manner.
5 Routeing Concepts
NOTE - The terni Aili,ii>iisri.ntii,<, Dorm7in is not intended to
have any particular relatioiisliip to an Administrafion as de-
5.1 Fiin c t i on al de coin posit ion of
fined by the CCITT. A CCITT Adniinistration niay in fact
operate an Administrative Doniniii, but this would be no dif-
routeing
ferent from an Administrative Doiiiiuii operated by any or-
ganisation from the point of view of this Kouteiiig Frariie-
OS1 Routeing can be decomposed into four different but inter-
work.
related aspects. The purposes of this division are to
3.4.2 routeing domain: A set of End Systems and
-
conceptually clarify the functions of routeing;
Intermediate System4 which operate according to the
same routeing procedures and which is wholly
-
simplify the design of routeing protocols by breaking
contained within a single Administrative Doniain.
routeing into its component parts; and
See 8.2.1 for a precise forinal definition of this concept.
-
make the rouîeing functions as flexible as is practical by
allowing for degrees of freedom in each aspect.
3.4.3 common domain: An Administrative Domain
which is not a member of a higher level domain.
The four aspects are described in the following clauses. Figure
1 below illustrates the relationship among these four aspects of
A common domain is the highest level in the routeing hierar-
routeing
chy. 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 hier-
5.1.1 Rout eiii g hi fornia t ion Rase
archy.
The Routeing irifonnatiori Base coniprise.; thc coinplcte infor-
Where there are multiple common domains. they co-operate as
mation required by a particular ES or IS to accomplish
peers to make it possible to route to any NSAP in the OSIE.
routeing. Such information might include:
hop: The traversal of a single subnetwork by a PDIJ.
3.4.4
Next hop i-outeinp tahles. Theïe are tables \\.hich rclate
destination NSAPs to thc potential next subnctu.ork hopv
3.4.5 black hole: A situation in which an Inte~inediate
(e.g. local and remote SNPAS) \vhich might bc used to
System. due to 21 breakdown of the routehg
forward the PDU cloïer to it? dedmtion.
procedures. malicious intent, or lack of information.
.
discards or otherwise refuses to forward all tralfk Lists of neighbour ESs and 1Ss. Tlieqe lists enable tlli ES
directed to it.
or IS to ascertain the local topology.
A black hole may also be formed 011 a connectiorile\\ - Measured QoS characteristics of a dataliiik or
subnetwork when the intendcd iecipieiit of traffic IF unavail- subnetwork path. These measurements allow the routehg
functions to adapt to QoS changes.
able.
-
Network maps. 'These are complete topological graphs of
3.4.6 subnetwork address resolution entity: A
a portion of' the global network. Such maps can be used
network layer entity available on a subnetwork which
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ISOllEClTR 9575 : 1990 (E)
Infornirition Base
Decision
I
Fipire 1 - Decomposition of the routeing function
to cornpute shortest paths to destination NSMs ushg
5.1.4.1 Functions F1 and F2
my of a nuinkr of ioiiteiiig metric\.
The functions F1 and F2 are two functions required by every
5.1.2 Inforniaiioii collectioii
ES and IS to route an NPDU. The inputs to F1 are
ESs and ISs build up their routeiiig infonnation bases by col-
a) the called or destination NSAP address:
lecting information from their local environment and froin
other systems. Sonic exaiiiple sources of information arc:
b) the calling or source NSAP address:
measurement protocols, policy input from System Maiiage-
I)
ment. directory lookup functions. and routcing protocols. The
a source route (optional). A source route is a sequence of
c)
information collection function is illustrated in figure 1 by tlie
network entity titles which identify Network relay sys-
box labelled Update Rcc(~ii~c.
tems. See, for example. the source routing funci.ion of
IS0 8473. In a complete source route the next nzttwork
5. I .3 Inf'orinatioii Dis1 rihution
cntity title in the secpicnce i.; tlic output of F1. h :I partial
sourcc route. the next netnwk entity title in the wluerice
Systems may inforin otlicr systcnis of pertinent information in
is iised to detennine the net\vork entity title ofa Netwjrk
base by clistribu t ing this in for-
their local route irig information
relay system used to rrach the Network relay identified
mation. Some cxatiipleï of iriforiiiiitioii distribution techniqiic.
by tlie source roiitt'.
include: routeing protocol< and interactions through the man
agenient information bases. Tlir inforiiiiition distribution func
tion is illustrated in fisL1tc: I b!, tlie box lalxllcci l/pckifc ,Scr/d.
C) the Forwiirding information RM
5. i .J Roil te C;I I CII I a 1 i ( )II a II d it ia i ti 1 cria II CC'
For each NPL>U that i\ touted. FI deternime\
These are the internal functions executed by ES'; and ]Ss 011
the routeing infoimat ion base to accomplish roiiteiiig. The 11ii1-
f) The Network entity title of a Network relay \y\teni on
jor function in this category is tlic generation of tlie forwarding
the path to the destination NSAP or CIW.
information base which ' iiscd to actually relay NPD1.Js. This
function is illiiçtr:ited in iprc I by tlie box labelled Docisior,.
Other cxaniples of these internal functions include: timirig g) The title of the destination Network entity. if no relay
functions such as ageing old routcirig iiifonnatioti base entries. function is necessary to reach the destination. The title
and the functioiis Fi aiid F2 described below. may be the sanie as the destination NSAP address.
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ISOllEClTR 9575 : 1990 (E)
The inputs to F2 are
5.2 Relatioilship of routeing to OS1
Man age in eii t
h) The network entity title of thc Network relay or destina-
tion End system determined by F1.
Operation of the Network Layer. in fulfilment of the role as-
i) QoS.
signed to it in the OS1 Reference Model, requires shared
knowledge coricernhg the location of NSAPs ancl routes
j) the Forwarding information hase
through the available subnetworks.
This function is performed after F1 to determine which
As shown in figures 2 and 1, the routeing function intersects
subnetwork point of attachment (SNPA) to use when sending
with OS1 management through information stored in. arid re-
an NPDU to the Network IC~~IJ or destination network entity.
trieved from. the management information base (the boxes la-
The information yielded by ihis function is
belled Lo(~i1 hlfovmition Base in the figures). Routeing infor-
mation is placed in the management information base either
k) identification of the selected SNPA.
through interaction with Network Layer entities or through in-
teraction with System Management (the box labelled 0.51
1) values of parameters which are input to the subnetwork
Murragcnierrt Applii~irioit).
service provider associated with that SNPA.
It may be desirable to collect and distiibute routeinç informa-
tion automatically through the operation of OS1 Routeing pro-
i.
tocols: these protocols may be located at the Network Layer
11111111111111111111111111
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I Local Systeiii I
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I System I
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: Application I
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Figure I. - Koiiteing Escliange using Network layer protocols
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ISOIIECITR 9575 : 1990 (E)
context negotiation and the establishment of mmagenient
(Layer managernent) or ihe appliciii ion layer (System manage-
associations over a reliable end-to-end transport service
ment).
is possible.
The use of a "network laye1 routeirig information exchnngi.
Figure 1 illustrates the use of a system management protocol to
protocol" lias (among otheri) the followmg advantages:
exchange roiiteing information.
-
it confines the generation. cxchaiige, and synchronisation
In general. it is likely that a complete and realistic solution to
of routeing infotiniltion within the Network layer. This
the global routeing problem in the OS1 environment will re-
keeps routeirig a "closcd system" and avoids difficult is-
quire a combination of techniques. involving both Network
sues in cross-layer co-ordination.
layer management protocols and System management proto-
cols.
-
capabilitie\ existing in ttic lower layer.; but noi available
m the upper layet.;. can bc iircd (e g multicait).
6 Environment for OS1 routeing
Figure 2 illustraies thc iiic of a layei nianagenient plotocol to
exchangc roiiteing infoniiat ion
OS1 Routeing shall be capable of operating effectively in a va-
riety of environments, which when considered together rewlt
Use of an "application Iayci routehg iriforniation excliaigc
in a number of difficult goals for any Routeing scheme to sat-
protocol" has (among othcri) the following advantage:
a
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Remote End
LOC~ System I
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8 I or Intermediate
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I I I
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I M aiiri~cineii t Routeing Infomiation Management
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mmmmmmmmmmmmmm
Application
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Local
Information
RilW
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ISO/IEC/TR 9575 : 1990 (E)
isfy. This clause discuses some of the environmcnts envi- rest of OS1 has enabled systems from multiple vendors to
interoperate.
sioned for OS1 routeing and points out some of their salient
features from the point of view of routeing.
6.1 Interconnection of LANs
7 Goals for OS1 Routeing
LANs may be connected either locally through an
The environment identified for OS1 routeing in clause 6 results
Interworking IJnit. or across larger distances via point-to-point
in soine difficult goals for any OS1 routeing scheme. These
subnetworks, private leased-line networks, or public data net-
goals are discussed in the following subclauses.
works. In all cases routeing functions are needed to determine
paths through the WAN that nieet connectivity and/or QoS re-
quirements. These routeing fiinct ions may be arbitrcarily com-
7.1 Multiple Subnetwork Types
plex, depending on whether organisational boundaries are be-
ing crossed, the need for optimal routes. resilience from fail-
ure. etc. In addition. the routeing functions for LAN-WAN The routeing functions defined within this framework shall he
interconnection need to take account of the wide disparity of designed to operate without regard to my specific underlying
transmiss ion bandwidth between the t WO environments. technology or transmission medium, to the extent that the,y do
not rely upon any technolo_ry specific service for their correct
operation. These functions shall also be designed to operate
6.2 Yu Mi c/Private Net \YOI'I~
of the geographic distribution of ESs and
correctly irrespective
Iii t e rcon n e c t i o n ISs which comprise the global routeing domain (i.e. they are
not iopology dependent).
Many organisations already operate private data networks. In
order to communicate with other organisations their private 7.2 Very large iiuiiiber of ESs and ISs
networks may be interconnected using public network facili-
ties. Routeing functions shall be capable of efficient routeing
The global OSE in which End System data are to be trans-
within both the private and public domains, while providing
ferred is assumed to consist of a very large number of NSAPs
the organisational isolation necessary for the separate rnanage-
7
ment of these domains. Further. the routeing methods. nietrks. (>LO ) which, hi the most general situation. may he logically
interconnected by means of paths consisting of concatenated
and policies may be very different hi the public domain than in
intermediate system. The total number of intermediate sys-
the private domain. Routebig functions shall be capable of suc-
tems is assumed to be one to two orders of magnitude fewer
cessfully dealing with the limited control and data flow across
these sorts of boundaries. than the number of NSAPs (or End Systems), but very large as
well. Any routeing scheme adopted for OS1 shell be capable of
indefinite scaling.
6.3 Factory and cainpris networks
7.2.1 Eiid Systems slioiild be kept simple
The use of networks in factories and campus envirorunents
such as universities, corporate heüdquarters, goverrunent min-
A consequence of the preponderance of End-systems over In-
istries, and research establishments is growing rapidly. These
termediate systems is the desire to keep the ESs simple. even
environments are characterised by large numbers of systems
at the expense of making the ISs more complicatecl. This
(sometimes in the thousands) connected by rich topologies. Zn
makes sense also because Intermediate systems are often dedi-
these environments. the confipration of the neiwork tends to
cated to routehg and relaying. End-systems, on the other hand.
change rapidly and the exercise of centralised control over thç
perfonii routeing as an overhead function necessary to enable
installation and operat ion of systems inhimal. Routeinp
them to do their real job of executing applications.
schemes for this kind of environment need to be robust against
unanticipated configuration changes and he able to adapt to
changes in network usage, applications. and traffic patterns
7.3 it1 u It i p le o I- gai1 i sa t i on s
without the need for the extensive intervention of a centrulised
administrative function.
The presence of multiple orsaniwtionr: \iiih the OS1 environ-
inent \vil1 requirc the follon.iris iitttibiiteï of OS1 roiiieing.
6.4 Mu1 t i -11 en do r s U II n e t WO I' lis
Networks are inherently a mulii--vendor environment. It is ex-
tremely rare for a consumer to acquirç an entire subnctwork
C;lobul touteing shall by necessity ix ablc. to operate correctlj,
(LAN or WAN) from a singlc vendor. since systems are pur--
under the distdwted control of iiiuliiple orgmisaiionï. Fur-
chased cl1 different tbncq for (liflcrcrnt applic~~iio~is. In niany
tlieniiorc, thc control 01' roiiteirig withi~i ;I siiiglc orpariisniinti
cases hnwcvel-, operaiors of' ptiv;itc (atid in SOIII~ ciiscs public,
may be distributed for reasons of efficiency. economy. per-
netwiorks are forced to acquire a11 of their ISs from a single
formance, etc.
source because of the lack of routeing standards. This situation
litnits the ability of organisations to build cost-effective net-
7.3.2 'ïrrist, firewalls, aiid secririt!
works and severely constrains the ways in which their iiet-
works can be interconnected with those of other organisations.
l'lie exchange of routehg iiifonnation between ISs has the ef-
An effective set of OS1 routeiiip standards will enable the con-
fect? of
struction of practical multi-vendor subnetworks. much as the
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lSO/lEC/TR 9575 : 1990 (E)
a) allowing one IS to unpact the routcing decisions niade by
7.4 Pe r f o I- 111 aii ce
mother IS; and
Peiforxmnce IV characterised by the efficiency and robustne\s
b) providuig 011~ IS with mlorni'ition 'iboiit anothei IS
of tlic Network Sçrvicc rls scen by participating systems. It is
important that tlie5e sy\teni\ rlvoid
Of specific concern here is
-
introducing a high degree of overhead (control) traffic:
c) the effect of bxl roiiieing infomiat ion exchanged ht: -
and
tween ISs in diffcrcni administrative domains. and
concentrating traffic on a few paths when other paths are
relatively free. thus causing iiiiiiecessary congestion.
ci) the implicit or explicit exchange of private, proprietary,
or secret information iicross aclministrativc domains.
OS1 routehg is expected to be "fair" to all participating Net-
work entities in the sense of providing equitable access that is
The exchange of roiiteirig infoimation across adiriiiiisiraiivc
only constrained by the bandwidths of the connected SNPAS.
boundaries should tmixiiiiisc thç uscfiilness of that infomiion
Measures sliall be taken to avoid service denitil and to allow
while rniriitnising the potential adverse effects of that idorinci
for a "reasonable" throughput and response time to all systems.
tion. Examples of ;idvcrsc roiiteing effects are routeing loops
Good performance also requires a dynamic adaptive capability
and "black holes" (both of which cm severely degrade net-
in the Network entities to respond to various types of failures.
work performance). incorrect routeing, and illegal roiiteing (es-
The routeing scheme should be able to adapt appropriately to
pecially with regard to iiaiioiinl boundaries). Furthermore, the
changes in topology. including partitions.
routeing information exchanged should provide a tniiiiriiuin of
ancillary infoimat ion while providing a mixiniiim of routeing
functionality. Exiiiiiples of Luicillmy iiiformatiori about the in-
7.S Existing Network Layer protocols
ternals of an atlininistr:iiivo
Any scheme adopted for OS1 Routeing should not have an ex-
- topology information.
cessive impact on existing Network Layer Protocols. An ideal
- size. roiiteing scheme would not require any rnodificationi to cur-
rent network layer protocol standards nor necessitate their re-
- level of activity.
implementation to accommodate the routeing functions.
- reliability.
-
quality and/or typc OF srrvicc. ;uid
7.6 C o in in un i ca t i on t ype iii cle p eii deil ce
- tariff structure.
Routeirig procedures should accoinmodate both Connection-
Organisations operat ing ;itliniiiistrative domains should he able
mode and Connectioniess-mode communication. However.
t O control t lie "leak ay " of in fornint ion out side f heir aclrriiri i.;
Routcing procedures inay vary for the two types. For iristance.
trative doinain(s). That is. iticy should be able io control tlic
routeiiig loops are easier to tolerate for a few connectionleas-
amount and kind of iiilonrintion which ciiters or leaves their
inode PDUs than for an entire Network Layer connection. Op-
administrative boundaries whiic still providing and receiving
timisations may be made by taking advantage of the character-
some rihiniiiin global roiiteirig c:ipability.
istics of either form of communication. however. these opthi-
zations may be at the expense of cornrniinication type inde-
pendence.
)When establishing adtiiiniitr'itivç bouiidaine\ and exchmgiiiy
routeing infortnation across tliosc boundaries. strong iiuthenti-
cation of Network entities inay he rcquired. Authentication of
7.7 Resilience
Network entities is nec iiy to prevent ari IS belonging to one
administrative domain in claiming io be a differeiit IS bc-
longing to anothcr (possibly the local) administrative domain. The Roiiteing procediires should lie able to rty.xi
Without ~iutliciiticiitiori. iidriiiiiistr;itivc doniaim may be sus- or logical cniincctivity friiiurcu h> firiding toute.: nroiind thow
fi'[ i IIIL .>, i. A triideoff tiîiiut 17c iii;idc bct\vrcn speedy ;riid ïohii\t
ceptible to a vrir-iety of cxtcrnnl attacks. inciudijig ilie deiiiiil of
recovery from coriiiecti\-ity friiltirt!\ rliicl routring overherid niitl
service to Iarsc iiuiiibers of .:y.:icms.
coiiiplcsiiy. A coniiccii\.it) failiitc wliich results in a patiit ion
cult to rcc'oi'c'r irorii tti:iii :I l'iiiliirc wliich doe.: riot
7.3.3 Ko LI 1 e i 11 1: ti o ni ;I i I 15
caiisc~ ii partition.
The routciiig fiirictions shdl be dcsigricd to o~xr:iiç ;icross mu!-
7.8 Koiitcing pi'oc.etlrir-e diagnosis
tipie routeiiig dotriain.: (see X.2, I IOr dctailed inforniaiion on
routeuig domiins). Tlieic ioiiiciiig dotmiii.: iiiiiy hc privatc. 111
Roiiteing procetlureq should be diapiosiihle. This cli;ignosi<
the senw that :I given roiiteirig dotiiiiin niay iiiake iisc of tion-
ranges from solving wvere prohletriç in ihc routeiiip proce-
stnndard roiiteing functions :itit1 protocols intcrn:illy while sup-
pwîing standard roiitcing lïiiiciioiiii ml protocols exieriinlly. A diires which cause them to fail. to optimising the roiiteing pro-
routeing domain imy. Iioucvci, makc use of standard roiiieirii; cedures for a particular environment. Creating roiitcing proce-
functions and protocols both internally and externally. Ttit- dures which arc diagnosable inay involve avoiding certain al-
routeing fiinctioiis shall be iiblc to ticconitnodate neiwork to gorithms. adding error md probing YlXJs to a protocol. and
pologies consisting of both 01' these routeùig domain types. maintaining trace and error state in systenis.
7
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ISOIIECITR 9575 : 1990 (E)
each subnetwork to wluch the ES i5 attached. and each IS
8 Structure of global OS1 Routeing
knows about every End System reachable on each subnetwork
to which the IS is attached.
8.1 Categories of routeiiig
4
...
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