This read-write value, in seconds, sets how long an aged-out RIPng route is retained in the IPv6 routing table, typically marked unreachable, before being permanently deleted, defaulting to 120 seconds. This hold time gives neighboring routers a chance to learn the route is now unreachable before it disappears entirely, preventing routing black holes from premature deletion. For example, with the default 120-second garbage-collection time, a route that expired at time T remains visible as unreachable until roughly T+120 seconds.