In this video we explore how stub and totally stub areas (stub no-summary) work, what OSPF LSA they filter and how OSPF provide connectivity to the routes that are lost with this LSA filtering

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Video Description

Filtering type 4/5 LSAs
The ABR originates a default route with a type 3 LSA
It's not permitted to inject information about other routing domains in this area type. 

Logic inside this area:
The routers know how to reach the ABR, the ABR knows how to reach to the ASBR and the ASBR knows how to reach external routes. If all of the traffic is sent to the ABR, the more specific information is not needed.

Totally Stub (no-summary)
Same behavior as stub areas but type 3 LSAs are also filtered.

Logic inside this area:
Uses the logic of stub areas with the exception that now it applies to all of the traffic that goes outside the area. The ABR know how to reach any point of the network and because of that, all of the traffic is sent to them, more specific information is not needed.



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