What is route aging and invalidation in RIP timers, and what does it imply for route reliability?

• A. If no updates arrive within the invalid timer, the route is invalidated; after flush, it is removed, reducing stale routes.
• B. Routes expire after a fixed count of days regardless of updates.
• C. Aging only affects the router's own interface status, not routing tables.
• D. Invalid timer triggers immediate removal of all routes from the routing table.

Answer: (A)

RIP uses timers to keep its routing information trustworthy by avoiding reliance on stale data. Each route has an invalid timer and a flush timer. If no update for a route arrives within the invalid timer, the route is marked invalid in the table, meaning it’s considered unreachable even though it’s still present. If nothing refreshes that route before the flush timer expires, the route is removed from the table. This process reduces the presence of stale routes in the routing table, which would otherwise lead to incorrect forwarding decisions. In terms of reliability, this mechanism helps ensure that routes used for forwarding reflect current topology; you may briefly see a route flagged as invalid during a period of no updates, but once it’s flushed, it won’t be used again unless a fresh update reinstates it.