Neighbor adjacencies are automatic

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Cisco CCIE Prep v1.0—Module 7-25

Point-to-point subinterfaces on the hub router treat each connection to a spoke router as a separate IP subnet. Point-to-point subinterfaces were originally created in order to handle issues caused by split horizon when running distance vector routing protocols over NBMA networks.

A point-to-point subinterface has the same properties of a physical point-to-point interface. As far as OSPF is concerned, an adjacency is always formed over a point-to-point subinterface, with no DR/BDR election.

Point-to-point mode is the default OSPF network type for point-to-point subinterfaces. Therefore, no further configuration is required.

Table 6-7: < ip ospf network point-to-point > Command

Command

Description

ip ospf network point-to-point

Sets the OSPF network type to point-to-point. Performed from router configuration mode.

Note By default, OSPF considers loopbacks as host routes and advertises them with a /32 subnet mask. You can add the ip ospf network point-to-point command to a loopback interface and OSPF will then advertise the loopback interface's actual subnet mask. This is useful when classless-to-classful route redistribution is being performed in the network. Route redistribution is covered in Module 9: Advanced Routing Techniques.

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