Hi

I have 4 routers running ospf with each others and all the internal interfaces are OSPF passive interfaces to make their subnets to be shared between all routers.

R1, R2, and R4 are in area 0.0.0.0, while R3 is in area 0.0.01

The ABR is R2

The case is that I need a specific direct subnet on R2 (which its interface is an OSPF passive interface in area 0.0.0.0), I need this subnet to be advertised to all neighbors except R3.

How can that be achived?

(R1)------- Area 0.0.0.0------------ (R2) --------- Area 0.0.0.1--------(R3)

                           /

                         /

                       /

                   (R4)

           Area 0.0.0.0

Thanks in advance 🙂

I believe you would need to make area 1 a totally stubby area and then configure to ABR to inject a default route into area 1. That will prevent external routes going into the area while allowing external reachability via the default route. Remember that for consistency, OSPF needs to send LSAs to update all neighbors with advertised routes whether by being directly in the area or via NET summary LSA's.

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@lyndidon wrote:

I believe you would need to make area 1 a totally stubby area and then configure to ABR to inject a default route into area 1. That will prevent external routes going into the area while allowing external reachability via the default route. Remember that for consistency, OSPF needs to send LSAs to update all neighbors with advertised routes whether by being directly in the area or via NET summary LSA's.

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Thanks for reply

I still need other routes to be advertised to R3, and when I will make area1 to be totally stubby area I will prevent these routes to be advertised to it.

Maybe you can use network-summary-export on R2.

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@mihaigabriel wrote:

Maybe you can use network-summary-export on R2.

 

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Thanks mihaigabriel,

that worked just fine 🙂

But what about if there's a network in R3 I also do not need to advertise to any other router? how can this be done.

Thanks for support

Hello,

If R3 is the R2' "one and only" area 1 neighbor then You can use either "area-range restrict" or "network-summary-export" on R2.

If R3 has other area 1 neighbors which need to know about said prefix, then there is no way to achieve that with  "area-range restrict" or "network-summary-export".

Then You have the following options:

1/ export said prefix as Type-5 and use OSPF import policy on R3 to suppress said prefix installation in R3' route table, or

2/ make sure every R2' neighbor currently in area 1 resides in own separate area and only then use "network-summary-export" on R3, or

3/ bring up iBGP, suppress said prefix in iBGP export policy from R2 towards R3 and announce said prefix in iBGP export policy from R2 towards every other router.

HTH

Thanks

Alex

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@aarseniev wrote:

Hello,

If R3 is the R2' "one and only" area 1 neighbor then You can use either "area-range restrict" or "network-summary-export" on R2.

If R3 has other area 1 neighbors which need to know about said prefix, then there is no way to achieve that with  "area-range restrict" or "network-summary-export".

Then You have the following options:

1/ export said prefix as Type-5 and use OSPF import policy on R3 to suppress said prefix installation in R3' route table, or

2/ make sure every R2' neighbor currently in area 1 resides in own separate area and only then use "network-summary-export" on R3, or

3/ bring up iBGP, suppress said prefix in iBGP export policy from R2 towards R3 and announce said prefix in iBGP export policy from R2 towards every other router.

HTH

Thanks

Alex

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aarseniev .. Thanks for your more than complete several solutions 🙂    very valuable information indeed 🙂

 I will be glad if you had a look at thie topic:

http://forums.juniper.net/t5/Routing/OSPF-not-advertising-a-passive-interface-network-to-specific/td-p/215473