What is OSPF?

September 8, 2014 — Leave a comment

Rasesh Patel

Open Shortest Path First (OSPF) = Link State Routing Protocol

Each router builds it’s own topology database and routing table.
On network change: New LSA’s are Flooded & all routers recompute their routing table.

OSPF Router Types & Locations
1) Internal Router (IR) is inside an area.
2) Backbone Router (BR) has at least one interface in backbone area0.
3) Area Border Router (ABR) is between two or more areas.
4) Autonomous System Boundary Router (ASBR) connects to a different routing administration [Routes are redistributed into OSPF]

Segmenting an OSPF topology into multiple area is the main tool to make OSPF scale. Flooding is limited to the area so
there are fewer LSAs.

Types of Link State Advertisements (LSAs)
Type1 = Router Link
Type2 = Network Link
Type3 = Network Summary
Type4 = ASBR Summary
Type5 = External
Type6 = NSSA External

OSPF Area’s

1) Normal Area
In a regular area…

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