User`s guide

OSPF Overview
Matrix DFE Series and N-SA User’s Guide 8-3
Link-State Advertisements (LSAs)
UsingOSPF,theMatrixDFE‐PlatinumSeriessystemfloodslink‐stateadvertisement(LSA)
packetstokeepitstopologicaldatabaseupdated,andtohelpensurethedatabasesofitsneighbors
arealsocurrent.
Typesof LSAs,eachrelatingtoaparticularpartoftheOSPFroutingdomain,areasfollows.
Routerlink
advertisementsaresentbyeachDFESeriessystemconfiguredwithOSPFtodescribe
therouter’slinkswithinthearea.Therouterfloodstheseadvertisementswithinthesinglearea
only.
Networklinkadvertisementsdescribealltheroutingsystemsthatareattachedtothenetwork.
Theadvertisementsarefloodedwithinasinglearea
only.Theyaregeneratedbythedesignated
router.
Summarylinkadvertisementsdescribethe routesinotherOSPFareasthattheDFESeriessystem
knowsabout.TheDFESeriessystemmustbeconfiguredasanareaborderrouter(ABR)to
performthistypeofflooding.Theseadvertisementsarefloodedtotheareas
thatusetheroutes.
TheareasmustbewithinthesameAS.
ASexternallinkadvertisementsdescribeexternalroutesthattheDFESeriessystemknows
about.TheDFESeriessystemmustbeconfiguredasanASboundaryrouter(ASBR)tofloodthis
typeofadvertisement.Theseadvertisementsarefloodedthroughoutthe
AS,excepttostubareas.
TheDFESeries/N‐SAsystemsupportsopaqueType7LSAsfornot‐so‐stubbyareas(NSSAs).
Matrix DFE Series and N-SA Operation in OSPF Networks
EachroutingsystemwithinanOSPFASmaintainsadatabaseofthenetworktopology.Toreduce
thesizeofthedatabase,anASistypicallydividedintosmallerroutingareas,andtherouting
systemsperformdifferentroleswithintheAS.YoucanconfiguretheMatrixDFE‐PlatinumSeries
systemtoperform
anyofthethreeroutingroleswithinanOSPFautonomoussystem:internal
router,areaborderrouter(ABR),orASboundaryrouter(ASBR).
Figure 8‐1showsasampleOSPFtopology,withthedifferenttypesofrouters.
Internalrouter–Systemswithinaspecificareaarecalledinternalrouters.WhentheTN250G
functions
asaninternalrouter,allinterfacesaredirectlyconnectedtootherrouterswithinthe
samearea.
Areaborderrouter–AsanABR,theDFESeriessystemcanbelongtomultipleareas.Inthisrole,
theroutermaintainsaseparatetopologydatabaseforeachareainwhichitisamember.
TheDFE
Seriessystem’sABRsupportincludesroutesummarization,whichenablestheroutertoadvertise
aroutethatconsolidatesmultipleadvertisedaddresses.TheDFESeriessystemalsosupports
virtuallinks,enablingconnectiontoabackbonewithoutaphysicalconnection.Stubareasupport
includestheabilitytopreventABRsfromsendingsummary
link‐stateadvertisementsintothe
stubarea.
IftheDFESeriessystemhasmorethanoneareaconfigured,andatleastoneisthebackbone,the
routerautomaticallyisanABR.
ASboundaryrouter–TheDFESeriessystemcanalsobeconfiguredasanASBR.Inthisrole,the
router
exchangesexternallylearnedroutinginformationwithotherroutersthroughouttheAS.As
anASBR,therouterprovidesrouteredistribution,aswellasrouteaggregationtohelpreducethe
amountofroutinginformationinthenetwork.Theimportingandexportingofroutingpoliciesis
alsoafunctionofASBRs.ASBRsarecreated
whenyouconfigurerouteredistribution.