OSPF filtering

Unanswered Question
Jul 17th, 2009
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I have 3 routers in three areas.

R1 ---> Area 0

R2 ---> Area 0 and 1 (ABR)

R3 ---> Area 1.

R2 is connected to R3 (in area 1)through a FR,with 'ip ospf net point-to-point' configured. I try to filter inter- area routes from area 0 from entering area 1 by applying the below command at the serial interface of R2 connecting to R3....'ip ospf database-filter all out'. Bur I am still seeing the IA routes. Please whats the reason.

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Marwan ALshawi Sat, 07/18/2009 - 04:03
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about your command database-filter

i think its not the best choice for your case

becuase, if there are two links between OSPF neighbors, this command can be used to prevent the flooding of LSAs on one of the links

in addition you using ospf network type as p2p

however, This command can be used only on a multipoint interface or an NBMA interface

ok to solve this issue easlly i would suggest you to do the following commnads ( which will let you filter area 0 routes and send only default route to r3)using totally stubby area of ospf

on r2

area 1 stub

area 1 stub no summary

on r3

area 1 stub

now router3 will see area 1 routes and default routes point to r2 link

good luck

if helpful Rate

Giuseppe Larosa Sat, 07/18/2009 - 04:18
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Hello Kennie,

in addition to what Marwan sugests for inter-area filtering you should use

router ospf 10

area area# filter-list prefix-list-name in|out

command that allows to invoke a prefix-list inside the routing process on ABR.

the command you have tried to use is not the right tool here.

in your case

area 1 filter-list only_these in


area 0 filter-list only_these out

can do the job

Hope to help



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