CompTIA® Network+ : Ospf
Routing & Spanning Tree Protocol
OSPF(Open Shortest Path First) Routing Protocol:
OSPF is a link state technology that uses Dijkstra
algorithm to compute routing information.
An OSPF area is a collection of networks and routers
that have the same area identification.OSPF process
identifier is locally significant.
OSPF Area Types
Backbone Area (Area 0) - The backbone area is
the central area to which all other areas in OSPF
Standard Area : Default OSPF area type -Standard
areas are defined as areas that can accept intra-area,
inter-area and external routes. Intra-area routes
refer to updates that are passed within the area.
Inter-area routes refer to updates that are passed
between areas. External routes refer to updates
passed from another routing protocol into the OSPF
domain by the Autonomous System Border Router (ASBR).
Stub Area : These areas do not accept routes
belonging to external autonomous systems (AS); however,
these areas have inter-area and intra-area routes.
In order to reach the outside networks, the routers
in the stub area use a default route which is injected
into the area by the Area Border Router (ABR). A
stub area is typically configured in situations
where the branch office need not know about all
the routes to every other office, instead it could
use a default route to the central office and get
to other places from there. Hence the memory requirements
of the leaf node routers is reduced, and so is the
size of the OSPF database.
Totally Stubby Area : These areas do not allow
routes other than intra-area and the default routes
to be propagated within the area. The ABR injects
a default route into the area and all the routers
belonging to this area use the default route to
send any traffic outside the area.
Not So Stubby Area (NSSA) : This type of area
allows the flexibility of importing a few external
routes into the area while still trying to retain
the stub characteristic.