Summaryzation or stub area

[news2010a]

Imagine I have the following:

[AS running RIP]-Router1-[OSPF Area 1]--[Area0]

Imagine that currently I am receiving 15 network advertisements type 5 LSA on my OSPF Area 1. If I need to minimize the number of Type 5 LSAs from the RIP network from 15 routes to 1 into my OSPF area, what's the correct way to do this ? Should I setup Area 1 as a stub area, or should I just do 'summary-address' on Router1 ? I think it is the stub area option, but I would like to confirm. Thanks.

[royalblues · Accepted solution]

Hi Marlon,

You cannot make AREA1 as stub as a stub area supresses all the type 5 LSA and hence would not be able to advertise the RIP redistributed routes to the baclbone.

You should use area 1 as NSSA generating type 7 LSA and the ABR will convert the type 7 LSA's to type 5 and propogate it to the backbone.

See the following link for more information

http://www.cisco.com/en/US/partner/tech/tk365/technologies_tech_note09186a0080094a88.shtml

HTH, rate if it does

Narayan

[leonvd79 · Accepted solution]

As Narayan pointed out, stub would not accept external LSA's.

Your question, which Narayan overlooked:

"If I need to minimize the number of Type 5 LSAs from the RIP network from 15 routes to 1 into my OSPF area, what's the correct way to do this ?"

Yes, a summary-route would be the way to go. Area 1 does not have to be a NSSA. Unless if you want it to be stub.

router ospf 1

redistibute rip subnets

summary-address

HTH

--Leon

* Please rate ALL posts.

[globalnettech · Accepted solution]

Hello,

assuming that you are redistributing RIP into OSPF on your Router 1, you would not be able to configure that area as a stub area anyway, since redistribution is not allowed in a stub area. Even if you configure area 1 as an NSSA, that still would not reduce the number of routes, and all the RIP routes would be leaked by the NSSA ABR. By configuring a NSSA totally stub area (area 1 nssa no-summary), a default summary route would be generated by the ABR (Router 1), so this would actually reduce the number of routes to one. If you only have a choice between a stub area and summarizing, sumarizing is the only way to achieve the desired route reduction.

HTH,

GNT

[news2010a]

Ohh, you are right. Thanks. You are amazing !