Juniper IGP - CONFIGURATION GUIDE V11.1.X, Configuration Manual

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Figure 17: Optimizing OSPF Area Aggregate Costs
In this example, the router IDs of the OSPF routers in area 1 are announced by OSPF
into area 0. ABR 1 and ABR 2 aggregates the 10.1.1.x networks in area 1 at the
border. Each individual OSPF link has a cost of 1.
ABR 1 calculates the following costs:
■
A cost of 5 to reach Router 6:
ABR 1-->Router 4-->Router 5--> ABR 2-->Router 6
■
A cost of 3 to reach Router 5:
ABR 1-->Router 4-->Router 5
■
A cost of 2 to reach Router 4:
ABR 1->Router 4
The highest individual cost is 5. ABR 1 subsequently advertises a cost of 5 for the
aggregate 10.1.1.0 to be announced into area 0.
ABR 2 calculates the following costs:
■
A cost of 2 to reach Router 6:
ABR 2-->Router 6
■
A cost of 2 to reach Router 5:
ABR 2-->Router 5
■
A cost of 3 to reach Router 4:
Optimizing the Cost to Reach a Range of OSPF Routers Within an Area
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Chapter 5: Configuring OSPF