Types of Link State Advertisemnt

Router link type 1 - lists neighbours and cost to each, flooded within an area
Network link type 2 - send by DR, lists all routers it is adjacent to, flooded within an area
Network summary link type 3 - send by ABR, lists prefixes in area, advertises summary
AS external ASBR summary link type 4 - send by ASBR, describes external route
External Link LSA type 5 - external route advertised by ASBR, type 5 can also be default-route
NSSA external type 7 -created by ASBR in not so stubby area, type 5 tunnelled through NSSA, converted to type 5 on ABR.