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Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — LSA Types and Area Border Routers:

“Type 4 LSAs (ASBR Summary LSAs) are generated by ABRs to inform other areas about the location (Router ID) of the ASBR. Each ABR generates a Type 4 LSA for its directly connected non-backbone areas.”

R3 generates Type 4 LSA into Area 0.

R6 generates Type 4 LSA into Area 2.

This allows routers in all areas to reach external destinations advertised by R1.