This period of time is the Hold-down time. Defined in RFC 1388 Version number field is 2. After all these problems you might ask this question. Rather than using the fake network 0.0.0.0 to indicate the default network, IGRP allows a real network to be flagged as the default network. Periodically, IGRP scans the routes offering a path to this flagged network and selects the path with the lowest metric.
Default gateways help to keep the size of local routing tables smaller.
Uses the distance-vector technology of IGRP, but changes the way routes are advertised and the calculation of entries for the routing table. OSPF version 2 defined in RFC 1247 OSPF is a link-state protocol. The OSPF messages tell the status of links of each of its neighbors and propagates this info to its neighbors. Each router uses the link-state information to build a complete routing table. OSPF networks generally divided into areas such that cross-area communication is minimal.