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New Member

OSPF Route Scenario

Hello peoples,

I have a  scenario where I have a single router being multihomed to two different  area 0 routers. I want to turn this new multihomed router up on a new  area, say area 2. These area 0 routers will be the ABRs for the new area  2. I want to be able to redistribute / advertise all routes into the  the area 0 backbone ABRs but only receive a default route on the  multihomed area 2 router. What kind of OSPF area type should I use? I  initially tried stub area but I realized quickly it doesn't play well  with redistribution. Then I thought maybe NSSA with no-summary would be  the best but soon noticed that I had a hand full of learned E2 routes  from the directly connected ABR routers in my area 2 router. So that  threw me off a little too.

I  want to be able to just use "redistribute connected" on the multihomed  router without network commands (except maybe for the P2P links /30s).  If it matters or helps any, area 0 backbone is a ring topology and the  new router on area 2 will simply be an island spoke.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: OSPF Route Scenario

I guess the two Area 0 routers at the edge to Area 2 are the ABRs?

Then I thought maybe NSSA with no-summary would be  the best but soon  noticed that I had a hand full of learned E2 routes  from the directly  connected ABR routers in my area 2 router. So that  threw me off a  little too.

A (totally) NSSA should meet your requirements. You can use the no-redistribution option on the ABRs (which obviously are ASBRs at the same time) to avoid the translation of the extenal routes into type-7 LSAs:

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

I  want to be able to just use "redistribute connected" on the  multihomed  router without network commands (except maybe for the P2P  links /30s).

You can do that, but it is not the recommended approach, here you can find another discussion about that: https://supportforums.cisco.com/message/3970307#3971734

Do you have a special reason to inject those networks as externals instead of advertising as internals?

HTH

Rolf

5 REPLIES

OSPF Route Scenario

Can you post a diagram?

HTH,
John

*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
New Member

OSPF Route Scenario

Re: OSPF Route Scenario

I guess the two Area 0 routers at the edge to Area 2 are the ABRs?

Then I thought maybe NSSA with no-summary would be  the best but soon  noticed that I had a hand full of learned E2 routes  from the directly  connected ABR routers in my area 2 router. So that  threw me off a  little too.

A (totally) NSSA should meet your requirements. You can use the no-redistribution option on the ABRs (which obviously are ASBRs at the same time) to avoid the translation of the extenal routes into type-7 LSAs:

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

I  want to be able to just use "redistribute connected" on the  multihomed  router without network commands (except maybe for the P2P  links /30s).

You can do that, but it is not the recommended approach, here you can find another discussion about that: https://supportforums.cisco.com/message/3970307#3971734

Do you have a special reason to inject those networks as externals instead of advertising as internals?

HTH

Rolf

New Member

OSPF Route Scenario

So would the no-redistribution command be a separate command from the no-summary command or would it be added to the same command?

Also in regards to not wanting to use the network command, it's mainly due to the amount of subnets involved and making this a "cookie cutter" solution for these types of turn-ups. If not using redistribution is the best policy though, I can reconsider. Internal or external routes really does not bother me as there would be no situation where the same network could be advertised with a higher preference.

Re: OSPF Route Scenario

So would the no-redistribution command be a separate command from the  no-summary command or would it be added to the same command?

Both options can be combined:

router ospf 1

area 2 nssa no-redistribution no-summary

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