An interface, or link, is the connection between a router and one of its attached networks. Its associated state information is obtained from the underlying lower level protocols and the routing protocol itself. An interface to a network has a single IP address and mask.
When you enable an OSPF interface, you designate it as one of the following types:
Note:
When an OSPF interface is enabled, you cannot change its interface type. You must first disable the interface, change its type, and then re-enable it.