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Community Member

Cnverting OSPF area to NSSA

What I have now is a normal OSPF area with 8 ASBRs attached (ppp links) to two ABRs and many (approx 50) RIP routers attached to the ASBRs . The ABRs also have RIP circuits/networks/routers attached to them. This area only uses a single class B address range BUT the "original design" did not summarize any of the external RIP ip addresses at the ASBRs because the ip addresses at the ASBRs are not continous and therefore can not be summarized there (at the ASBRs).

At this point I have a area range command on the ABRs and it has sucessfully summarized all the "OSPF" router links to one type-3 LSA distributed to the rest of the network. But I still have a 100 or so type-5 LSAs flooding the rest of the network. This is the reason I want to convert this area to NSSA so that I can summarize the external RIP routes (type-7) at a NSSA ABR to ONE(1) type-5 LSA along with the one type-3 LSA.

The 'area range' command will summarize all the OSPF routes in a area. But I ALSO want the ABRs to summarize ( and translate) all the EXTERNAL type-7 LSAs to one AS external type-5 to the rest of the OSPF domain. Which probably calls for a 'summary-address' statement. Correct? What I have now are approx. 100 type-5 LSA going thoughout the network from the this normal area which I want to convert to NSSA to eliminate all these external routes.

Also according to RFC1587 ... I quote

Translating Type-7 LSAs Into Type-5 LSAs

This step is performed as part of the NSSA's Dijkstra calculation

after type-5 and type-7 routes have been calculated. If the

calculating router is not an area border router this translation

algorithm should be skipped. All reachable area border routers in

the NSSA should now be examined noting the one with the highest

router ID. If this router has the highest router ID, it will be the

one translating type-7 LSAs into type-5 LSAs for the NSSA, otherwise

the translation algorithm should not be performed.

Which seems to means to me that only one ABR (the highest router-ID) does type-7 to type-5 translations. If this is the case then a second (lower router-ID) ABR in a NSSA area would never see any incoming traffic and would only do so if the primary ABR failed. Am I correct?

Basically, the main question is if BOTH or only ONE ABR would generate these summary LSAs....

I am still wondering :-(


Jim Coffey

Community Member

Re: Cnverting OSPF area to NSSA

Just to make my concerns prefectly clear...

The ABRs have directly attached RIP circuits also along with type-7 LSAs being received by OSPF links from the 8 ASBRs. In other words they are both ABRs and ASBRs. So if I use a 'summary-address' statement on the ABRs will this just summarize the directly connected RIP circuits or ALL the type-7 LSAs in the area?

Thanks for your time,

Jim Coffey

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