See NSSA Configuration, Summary Address Configuration, and Area Default-Cost for the topology for this procedure.
SEFOS# configure terminal
SEFOS(config)# router ospf
SEFOS(config-router)# router-id 10.10.2.1
SEFOS(config-router)# network 10.4.0.1 area 0.0.0.0 SEFOS(config-router)# network 10.10.2.1 area 0.0.0.6
SEFOS(config-router)# area 0.0.0.6 nssa
SEFOS(config-router)# summary-address 90.0.0.0 255.0.0.0 0.0.0.6