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Stub Area

An area in which there are no Type 4 and 5 LSA sent by ABR. Stubby Area needs to be configured on ABRs, so that they agree on this flag and form adjacency. By default, Stub Area ABR will generate a Default Route pointing to itself.

Configuration:

conf t

router ospf 1

area 1 stub

end

!

Totally Stubby Area

An Area where there are no Type 4 and Type 5 LSA and also now there is no Type 3 LSA sent by ABR. Totally Stubby Area needs to be configured on ABRs, so that they agree on this flag and form adjacency. By default, Stub Area ABR will generate a Default Route pointing to itself.

Configuration:

conf t

router ospf 1

area 1 stub no-summary

end

!

Not So Stubby Area (NSSA)

In NSSA we are allowing the redistribution unlike other Areas, but in the meantime we also stop external routes, no Type 4 and 5 LSAs. Instead the ASBR sends external routes to the ABR via Type 7 LSA. ABR converts the Type 7 LSA external routes and send them as a Type 5 LSA to the OSPF Areas. NSSA needs to be configured on ASBR and ABR, so that they agree on this flag. By default, the ABR does not generate a Default Route pointing to itself, you have to configure it to inject a Default Route manually by using the keyword “default-information-originate” under the OSPF process on the ABR.

Configuration:

conf t

router ospf 1

area 1 nssa

end

!

To inject a Default Route back to NSSA use the following:

conf t

router ospf 1

area 1 nssa default-information-originate

end

!

Totally Not So Stubby Area (Totally NSSA) – Cisco Proprietary

In Totally NSSA we do the same thing like in NSSA but we also stop Type 3 LSA from being sent to the OSPF domain. So, in other words: No Type 3, 4, 5 LSAs, but allow redistribution. By default, the ABR does generate a Default Route pointing to itself.

Configuration:

conf t

router ospf 1

area 1 nssa no-summary

end

!

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