CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

Periodic Flooding

Although OSPF does not send routing updates on a periodic interval, as do distance vector protocols, OSPF does reflood each LSA every 30 minutes based on each LSA’s age variable. The router that creates the LSA sets this age to 0 (seconds). Each router then increments the age of its copy of each LSA over time. If 30 minutes pass with no changes to an LSA—meaning that no other reason existed in that 30 minutes to cause a reflooding of the LSA—the owning router increments the sequence number, resets the timer to 0, and refloods the LSA.

Because the owning router increments the sequence number and resets the LSAge every 1800 seconds (30 minutes), the output of various show ip ospf database commands should also show an age of less ...