"OSPF is a link-state intra-domain routing protocol used in IP networks. OSPF behavior over demand circuits (DC) is optimized in RFC 1793 to minimize the amount of overhead traffic. A part of the OSPF demand circuit extensions is the Hello suppression mechanism. This technique allows a demand circuit to go down when no interesting traffic is going through the link. However@ it also introduces a problem@ where it becomes impossible to detect an OSPF-inactive neighbor over such a link. This memo introduces a new mechanism called ""neighbor probing"" to address the above problem."
RFC 3883-2004 history
2004RFC 3883-2004 Detecting Inactive Neighbors over OSPF Demand Circuits (DC)