The following figure depicts an OSPF network example. The backbone is area 0 with a backbone router. The internal routers are in area 1 and 2. The area border routers connect area 1 and 2 to the backbone.
Figure 76 OSPF Network Example
25.1.2 How OSPF Works
Layer 3 devices exchange routing information to build synchronized link state database within the same AS or area. They do this by exchanging Hello messages to confirm which neighbor (layer 3) devices exist and then they exchange database descriptions (DDs) to create the link state database. The link state database in constantly updated through LSAs (Link State Advertisements).
The link state database contains records of router IDs, their associated links and path costs. Each device can then use the link state database and Dijkstra algorithm to compute the least cost paths to network destinations.
25.1.3 Interfaces and Virtual Links
An OSPF interface is a link between a layer 3 device and an OSPF network. An interface has state information, an IP address and subnet mask associated with it. When you configure an OSPF interface, you first set an interface to transmit OSPF traffic and add the interface to an area.
You can configure a virtual link to establish/maintain connectivity between a
25.1.4 Configuring OSPF
To configure OSPF on the switch, do the following tasks
1Enable OSPF
2Create OSPF areas
3Create and associate interface(s) to an area
4Create virtual links to maintain backbone connectivity.
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