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In Figure
Area 3 does not have a direct physical connection to the backbone,
Area 0, which is an OSPF requirement. This is because the backbone is
a collection point for LSAs. ABRs forward summary LSAs to the
backbone, which in turn forwards the traffic to all areas. All
interarea traffic transits the backbone.
To provide connectivity to the
backbone, a virtual link must be configured between R2 and R1. Area 1
will be the transit area and R1 will be the entry point into Area 0.
R2 will have a logical connection to the backbone through the transit
area.
Both sides of the virtual link must be
configured, as follows:
- R2(config-router)#area 1
virtual-link 10.3.10.5 – With
this command, Area 1 is defined to be the transit area and the
router ID of the other side of the virtual link is configured.
- R1(config-router)#area 1
virtual-link 10.7.20.123 –
With this command, Area 1 is defined to be the transit area and the
router ID of the other side of the virtual link is configured.
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