The MTU does not match on both interfaces

OSPF is not enabled on one of the routers

The Router ID is the same on both routers

A OSPF Hello has not been received from the neighbor

89

87

85

83

Area Border Router

Autonomous System Boundary Router

Designated Router

All routers within an OSPF area.

The age for newly created link state information is set to 0 for OSPF and 1200 for IS-IS

The age for newly created link state information is set to 1200 for OSPF and 0 for IS-IS

The age is incremented or decremented as it is flooded from router to router and as it is held in the topological database.

The age is incremented or decremented only as it is held in the topological database and not as it is flooded router to router.

The system ID

The loopback address

The sequence number of the hello packet

The device that first initiated communication becomes the DIS

config>filter# default-action XXX

config>filter>ip-filter# default-action XXX

config>filter# default-mode XXX

config>filter>ip-filter# default-mode XXX

The router with the lowest priority is the DR.

The router with the highest priority is the DR.

If priorities are the same, the DR is chosen based on the lowest RID.

If priorities are the same, the DR is chosen based on the highest RID.