An OSPF Stub area is used to limit the types of LSA’s allowed to enter an area.
The types are
Intra area routes – LSA types 1 & 2
Inter area routes – LSA types 3 & 4
External routes – LSA type 5
NSSA external routes – LSA type 7
There is a great post here by packet life
http://packetlife.net/blog/2008/jun/24/ospf-area-types/
More Info
LSA Type 1 – Router – contains router links and state and is flooded into the area of origin
LSA Type 2 – Network – generated by DR – lists all attached routers – flooded into the area of origin.
LSA Type 3 – Network Summary – generated by ABR’s sent into an area to advertise prefixes to other areas – flooded throughout the Autonomous System.
LSA Type 4 – ASBR Summary – generated by ABR’s – advertises the ASBR – flooded throughout the Autonomous System
LSA Type 5 – AS External - generated by ASBR – advertises external destination – flooded throughout the Autonomous System
LSA Type 7 – NSSA External – generated by the ASBR in a not so stubby area – advertises external destination.
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