LSDB (Link State Database): A database that stores LSAs. This is how OSPF builds a picture of the network. A network topology map.
LSA (Link State Advertisement): A data structure that describes part of the network.
DBD or DDP (Database Description packet): A list of LSAs that a router has. This packet does not contain LSAs, just the headers. This is sent to a neighbor so it can figure out which LSAs to request.
LSU (Link State Update): A packet containing LSAs.
LSAck (Link State Acknowledgement): Confirms receipt of an LSU.
LSR (Link State Request): A packet which requests a list of LSAs that the router has found are missing or out of date based on its neighbor’s Dababase Description (DBD).
Neighbors: A relationship between routers on the same data link that, once established, allows them to exchange their LSDBs.
OSPF Areas
32-bit number, can be decimal or dotted-decimal
Area 0 (0.0.0.0)
Backbone area
All areas must connect to Area 0
Stub Area
Not-so-stubby Area (NSSA)
Totally Stubby Area
Totally Stubby NSSA
Transit Area
OSPF Router Types
IR (Internal Router)
BR (Backbone Router)
ABR (Area Border Router)
ASBR (Autonomous System Border Router)
OSPF Router Attributes
DR (Designated Router)
BDR (Backup Designated Router)
LSA Types
Type 1 - Router LSA
LSA Originator:: All routers
LSA Scope:: Same area
Advertises::
Itself
Links in the same area
Type 2 - Network LSA
LSA Originator:: DR
LSA Scope:: Same Area
Advertises::
Routers on the same segment
Type 3 - Summary LSA
LSA Originator:: ABR
LSA Scope:: Connected areas
Advertises::
Prefixes and metrics for connected area
Can optionally do route summarization
Type 4 - ASBR-Summary LSA
LSA Originator:: ABR
LSA Scope:: All except stub and NSSA
Advertises::
Location of ASBRs to other areas. ASBRs flood Type 1 LSA, which are not transmitted to other areas. When an ABR receives a Type 1 LSA form an ASBR, it creates a Type 4 LSA to send to other areas.
Type 5 - External LSA
LSA Originator:: ASBR
LSA Scope:: All except stub and NSSA
Advertises::
Information from other routing processes
Type 6 - Group Membership LSA
Meant for Multicast OSPF, Not widely used.
Type 7 - NSSA External LSA
LSA Originator:: ASBR in a NSSA
LSA Scope:: Same area
Advertises::
Mask for a Type 5 LSA in an area that blocks Type 5 LSAs. This is needed when an ASBR is inside a NSSA. When the Type 7 reaches the ABR, it’s translated to a Type 5