Section 3 - OSPF

OSPF link-state database (LSDB)

A table that lists all the LSAs that an OSPF router is aware of.

link-state advertisement (LSA)

A class of OSPF data structures that holds topology information.

backbone area

The OSPF Area 0 that connects to all other OSPF areas. It is the area that should provide connectivity between all other OSPF areas

area border router (ABR)

A router that connects an OSPF area to Area 0 (that is, the backbone area).

autonomous system border router (ASBR)

A router that redistributes external routes into an OSPF routing domain.

router LSAs

A Type 1 LSA that is a fundamental building block and represents all OSPF-enabled interfaces. Type 1 LSAs remain within the OSPF area of origination.

network LSA

A Type 2 LSA that advertises the routers connected to the DR pseudonode on a multiaccess network. Type 2 LSA remains within the OSPF area of origination.

summary LSA

A Type 3 LSA that contains the routes learned from another area. Type 3 LSAs are generated on ABRs.

ASBR summary LSA

A Type 4 LSA that allows routers to locate an ASBR that is in a different OSPF area.

external LSA

A Type 5 LSA that advertises an external route into a routing domain and indicates the router acting as the ASBR for that route.

NSSA external LSA

A Type 7 LSA that allows for an external route to exist in an OSPF totally NSSA or NSSA.

OSPF stub area

An OSPF area that does not allow for external routes (Type 4 or Type 5 LSAs) in it. A default route is advertised by the ABR in lieu of the blocked prefixes.

OSPF totally stubby area

An OSPF area that does not allow for interarea or external routes (Type 3, Type 4, or Type 5 LSAs) in it. A default route is advertised by the ABR in lieu of the block prefixes.

OSPF not-so-stubby area (NSSA)

An OSPF area that does not allow external routes (Type 4 or Type 5 LSAs) in it. This area allows for routes to be redistributed into it (i.e., it can have an ASBR).

OSPF totally NSSA

An OSPF area that does not allow for interarea or external routes (Type 3, Type 4, or Type 5 LSAs) in it. A default route is advertised by the ABR in lieu of the blocked prefixes. This area allows for routes to be redistributed into this area (i.e., it can have an ASBR).

internal router

A router with all interfaces in the same area.

backup designated router (BDR)

A backup pseudonode that maintains the network segment's state to replace the DR in the event of its failure.

designated router (DR)

A pseudonode to manage the adjacency state with other routers on a multiaccess network segment. Using this pseudonode decreases the amount of flooding that needs to occur on a multiaccess network segment.

dead interval

The maximum amount of time to wait for a hello packet to be received from a neighbor before that neighbor is declared unreachable. Upon receipt, the value resets and decrements toward zero.

hello interval

The frequency at which hello packets are advertised out an interface.

interface priority

The reference value for an interface to determine preference for being elected as the designated router.

passive interface

An interface that has been enabled with a routing protocol to advertise its associated interfaces into its RIB, but that does not establish neighbor relationships with other routers associated to that interface.

interarea route

An OSPF route learned from an ABR from another area. These routes are built based on type 3 LSAs.

intra-area route

An OSPF route learned from a router within the same area. These routes are built based on type 1 and type 2 LSAs.

shortest path tree (SPT)

A router's view of the topology to reach all destinations in the topology, where the router is the top of the tree, and all of the destinations are the branches of the tree.

OSPF area

A grouping of contiguous networks and routers, where all of the routers within have the same link-state database.

backbone router

A router with at least one interface attached to Area 0.

LSA Sequence Number

A 32-bit number attached to an LSA, which increases each time the LSA is modified or reflooded. This value allows the receiver to determine if the LSA contains newer information.

maxage timer

An OSPF timer that determines how long an LSA can remain in the LSDB without having heard a reflooded copy of the LSA (defaults to 3600 seconds).

OSPF cost

The metric used by OSPF. The value is inversely proportional to the bandwidth of the interface

virtual link

A virtual tunnel that allows Area 0 to be extended further into the network and that is often used to resolve discontiguous networks.