ospf distribute-list out not work

acbennyma · ‎08-12-2011

Dear all,

I want to add distribute-list 1 out in R7, so that R8 and R9 can't learn R6's loopback address. Howerver, once I type distribute-list 1out fastEthernet 0/1 and enter. It it not work. Any one know is it distribute-list out can not be used in ospf ? Any better solution?

I know there are 2 alternate method

1) apply "distribute-list 1 in" R8 router, but this action only make R8 don't learn that route, R9 still can learn it if I don't apply distribute-list 1 in router R9

2) R7 act as ABR, use two ospf proccess ID, Process 100 face to R6, Process 200 face to R8. In R7 ospf proccess 200, redistribute ospf 100 with route-map (desire route)

Marwan ALshawi · ‎08-12-2011

The command

distribute-list out works only on the routes being redistributed by the Autonomous System Boundary Routers (ASBRs) into OSPF. It can be applied to external type 2 and external type 1 routes, but not to intra-area and interarea routes

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094704.shtml#q12

HTH

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Marwan ALshawi · ‎08-12-2011

by the way in your 2) i dont think R7 will be considered as ABR

you can make R7 as ABR by having R6 in area 6 and R7 --to R8 area 0 then in R7 use the command filter-list in the outbound direction to Area 0 this command help you to filter out OSPF Inter area route LSA3

HTH

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Jon Marshall · ‎08-12-2011

Following up on Marwan's post.

Filtering routes within an area is not a particularly scalable solution.

If you want to stop the route for the loopback being inserted into the routing table on R8 and R9 you would need to use a distribute-list in on both R8 and R9. It's important to understand what you are doing though. You are not actually stopping the LSA for that network being received. So both R8 and R9 will still have an LSA for that network. You are simply stopping them inserting a route for that network into their routing tables.

The key thing to understand is that distribute-list may stop the routers inserting the route into their routing tables but it does not stop them advertising the LSA for that network to other routers. So it's not a scalable solution if you need many routers in the same area not to use the route ie. each router you didn't want to have a route for the loopback network would need a distribute-list applied.

However you can filter routes between areas and that is generally a much better approach.

Jon

cadet alain · ‎08-12-2011

Hi,

distribute-list out in OSPF won't work because all OSP routers in the same area need to have the same topology database.What distribute-list in does is not install the route in the rib from the topology table.

You could not put the loopbacks on R6 into the OSPF process but redistribute them then on R8 and R9 put the admin distance for external routes to 255.

Regards.

Alain.

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acbennyma · ‎08-12-2011

Dear marwanshawi,

Could you tell more about how to type the configuration about the command filter-list in the outbound direction to Area 0 this command help you to filter out OSPF Inter area route LSA3