DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
backbone through a router. OSPF allows routing information to be distributed by forwarding it into area 0, from which the information can be forwarded to all other areas (and all other routers) on the network.
In situations where an area is required, but is not possible to provide a physical connection to the backbone, a virtual link can be configured.
Virtual Links
Virtual links accomplish two purposes:
1.Linking an area that does not have a physical connection to the backbone.
2.Patching the backbone in case there is a discontinuity in area 0.
Areas Not Physically Connected to Area 0
All areas of an OSPF network should have a physical connection to the backbone, but is some cases it is not possible to physically connect a remote area to the backbone. In these cases, a virtual link is configured to connect the remote area to the backbone. A virtual path is a logical path between two border routers that have a common area, with one border router connected to the backbone.
Partitioning the Backbone
OSPF also allows virtual links to be configured to connect the parts of the backbone that are discontinuous. This is the equivalent to linking different area 0s together using a logical path between each area 0. Virtual links can also be added for redundancy to protect against a router failure. A virtual link is
136 | Switch Management and Operating Concepts |
