This field specifies the amount of time a node remains in the table of discovered nodes. Setting this field allows nodes that have not been heard from to be removed from the discovered nodes table. If this field is blank, nodes are NEVER removed from the discovered nodes table. However, if the same Network Address is used with a new MAC Address, the MAC address of the existing entry is changed and a trap is sent. The node expiration period is specified using decimal values appended by the unit: d - day, h - hour, m - minute, s - second, u - millisecond. If no unit is appended, the value is minutes. Multiple values/units are allowed (i.e. 1h45m = 1 hour, 45 minutes). The default for this field is 7d (7 days). It is a good idea to perform an active search at least as often as this node expiration time period to avoid losing nodes that are not initiating communication (e.g. file servers, bridges, hubs, etc.). However, nodes of this type that are being status checked by the status checker table will continue to exist.