OSPF LSA type

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

ref.: http://communitystring.com/2008/07/ospf-lsa-types/

Area Type	Type 1 & 2 (within area)	Type 3 (from other areas)	Type 4	Type 5	Type 7
Standard & backbone	Yes	Yes	Yes	Yes	No
Stub	Yes	Yes	No	No	No
Totally stubby	Yes	No	No	No	No
NSSA	Yes	Yes	No	No	Yes
Totally stubby NSSA	Yes	No	No	No	Yes

ref.: https://learningnetwork.cisco.com/docs/DOC-7924

OSPF - Normal, Stub, Totally Stub and NSSA Area Differences

ref.: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094aaa.shtml#definestub

Normal	None
Stub	No Type 5 AS-external LSA allowed
Totally Stub	No Type 3, 4 or 5 LSAs allowed except the default summary route
NSSA	No Type 5 AS-external LSAs allowed, but Type 7 LSAs that convert to Type 5 at the NSSA ABR can traverse
NSSA Totally Stub	No Type 3, 4 or 5 LSAs except the default summary route, but Type 7 LSAs that convert to Type 5 at the NSSA ABR are allowed

more information about LSA type:

http://raycheang.blogspot.com/2012/03/ospf-lsa-type.html

OSPF

1. Hello - Hello packets are used to establish and maintain adjacency with other OSPF routers. The hello protocol is discussed in detail in the next topic.

2. DBD - The Database Description (DBD) packet contains an abbreviated list of the sending router's link-state database and is used by receiving routers to check against the local link-state database.

3. LSR - Receiving routers can then request more information about any entry in the DBD by sending a Link-State Request (LSR).

4. LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information. LSUs contain seven different types of Link-State Advertisements (LSAs). LSUs and LSAs are briefly discussed in a later topic.

5. LSAck - When an LSU is received, the router sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU.

OSPF router initial procedure

1. Sending Hello packets on all OSPF-enabled interfaces to determine if there are any neighbors on those links. OSPF Hello packets are sent as multicast to an address reserved for ALLSPFRouters at 224.0.0.5 (By default, OSPF Hello packets are sent every 10 seconds on multiaccess and point-to-point segments and every 30 seconds on non-broadcast multiaccess (NBMA) segments (Frame Relay, X.25, ATM). )
   
2. Before two routers can form an OSPF neighbor adjacency, they must agree on three values: Hello interval, Dead interval, and network type.
3. Send Link-state updates (LSUs) to advertise routing information. An LSU packet can contain 11 different types of Link-State Advertisements (LSAs).
•  LSA type: 1    Router LSAs
• type 2             Network LSAs
• type 3 or 4      Summary LSAs
• type 5             Autonomous System Extrenal LSAs
• type 6             Multicast OSPF LSAs
• type 7             Defined for Not-So-Stubby Areas
• type 8             External Attributes LSA for BGP
• type 9,10,11   Opaque LSAs
  
4. Each OSPF router maintains a link-state database containing the LSAs received from all other routers. Once a router has received all of LSAs and built its local link-state database.
   
5. OSPF uses Dijkstra's shortest path first (SPF) algorithm to create an SPF tree. 
6. The SPF tree is then used to populate the IP routing table with the best paths to each network.