EIGRP SIA timers
Each EIGRP router manages its own SIA timer. For each route in an active state, when the timer reaches 90 seconds, it will send a SIA query to the corresponding neighbor. Any neighbor that does not respond to the SIA query by the time the original timer reaches 180 seconds will be considered SIA.
The neighbor adjacency is dropped, and any other routes learned from that neighbor are also removed.
This will occur even if hellos are still being received from the particular neighbor. Hellos ensure connectivity with neighbors while the SIA ensures timely updates of EIGRP routes.
The purpose of the SIA Query and Reply feature is not only to resolve eigrp failures due to congestion, but also due to the waiting time it takes to allow additional routers to respond to queries in larger EIGRP topologies.