Explanation/Reference:
Explanation:
Before you troubleshoot any OSPF neighbor-related issues on an NBMA network, it is important to remember that an NBMA network can be configured in these modes of operation with the ip ospf network command:
Point-to-Point

Point-to-Multipoint

Broadcast

NBMA

The Hello and Dead Intervals of each mode are described in this table:

Reference: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13693-22.html