Ospf Overview - Avaya 8800 Configuration Manual

OSPF and RIP fundamentals
in large networks, OSPF is a link-state protocol that supports IP subnets, Type of Service
(TOS)-based routing, and tagging of externally-derived routing information.
OSPF navigation
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OSPF overview

• Dijkstras algorithm
• Autonomous system and areas
• OSPF neighbors
• Router types
• OSPF interfaces
• OSPF and IP
• RIP and route redistribution
• OSPF packets
• Intra-area link-state advertisements
• ASE routes
• OSPF virtual links
• OSPF ASBRs
• OSPF metrics
• OSPF security mechanisms
• OSPF and route redistribution
• OSPF configuration considerations
OSPF overview
In an OSPF network, each router maintains a link-state database that describes the topology
of the autonomous system (AS). The database contains the local state for each router in the
AS, including its usable interfaces and reachable neighbors. Each router periodically checks
for changes in its local state and shares detected changes by flooding link-state advertisements
(LSA) throughout the AS. Routers synchronize their topological databases based on the
sharing of information from LSAs.
From the topological database, each router constructs a shortest-path tree, with itself as the
root. The shortest-path tree provides the optimal route to each destination in the AS. Routing
information from outside the AS appears on the tree as leaves.
OSPF routes IP traffic based on the destination IP address, subnet mask, and IP TOS.
34 Configuration — OSPF and RIP
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June 2011