Understanding all the OSPF LSA types is one of the keys to understanding OSPF, so its definatly worth me making a few notes on them

LSA type 1 – Router LSAs are sent from a router to other routers in the same area. It contains information regarding the routers interfaces in the same area, relevant interfaces IPs, its adjacent routers on those interfaces and sub networks

LSA type 2 – Network LSAs are generated by the DR on a multi access segment, and provides similar information to an LSA type 1 for the multi access segment and subnet which it belongs

LSA type 3 – Network Summary LSAs are generated by ABRs and contain the subnets & costs but omit the topological data from all subnets in one area and sent to another area via the ABR

LSA type 4 -ASBR summary LSAs are from ASBRs and are identical in structure to a type 3 LSA and sent when crossing an AS boundary

LSA type 5 -Are AS external LSAs which are originated by ASBRs and describe external networks

LSA type 6 – Is defined as a Group Membership LSA but not used in Cisco devices

LSA type 7 -NSSA External LSAs are generated by the ASBR in an NSSA area

LSA type 8 – Is defined as a External Attribute LSA but not used in Cisco devices

LSA types 9 to 11 – Defined as Opaque LSAs and are reserved for future expansion