User`s manual

autonomous system must be connected to the backbone. This backbone area allows summary
information to be exchanged between Area Border Routers. When designing an OSPF network, you
should start with Area 0.
Stub Areas
A stub area is an area that is only connected to one area, often this is the backbone area. Route
information is not advertised into stub areas. By creating stub areas, you reduce the router's memory use
and processing requirements.
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Not-so-Stubby Areas (NSSA)
A not-so-stubby area is the same as a stub area except that external routes learned by an Autonomous
System Border Router can be advertised within the NSSA. Likewise, external routes learned in an NSSA
can be advertised to other areas.
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OSPF routers
OSPF classifies different types of routers depending on the area in which they reside and what their tasks are.
An Internal Router (IR) is one with all of its routing interfaces in the same OSPF area.
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An Area Border Router (ABR) has interfaces in more than one OSPF area. Every ABR listens and
exchanges information with other ABRs. By examining the advertisements from other ABRs, an ABR
creates its link state database
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An Autonomous System Border Router (ASBR) is a gateway between OSPF and other routing
protocols or other autonomous systems.
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Link State Database
A Link State Database is used to create the OSPF routing table. This database contains all the Link State
Announcements (LSA) that it has issued and received. All routers within an area have exactly the same Link
State Database.
Link State Announcements (LSA)
When OSPF is configured on a routing interface on a BitStorm L3S Switch, the Switch sends a Link State
Advertisement (LSA) over the routing interface. This LSA tells neighboring routers the state of the routing
information in that routing interface's Link State Database.
Configuring OSPF
To configure OSPF, see:
OSPF Configuration Basics●
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