D-Link DES-3326SR User Manual page 235

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
Figure 6 - 56. OSPF Interface Configuration − Monitor
Virtual Interface Configuration
Virtual Interfaces are used by OSPF to link areas that do not
have a physical connection to the backbone (also called Area 0)
or to link areas of the backbone itself that are discontinuous.
This allows routing information to flow from an area that is
physically disconnected from area 0 into area 0 by configuring
an interface across one of the areas previously defined above.
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