This read-write Unsigned32, ranging 1 to 20, controls how often Router Solicitations are resent after receiving a Router Advertisement, computed as Lifetime divided by (1 + Robustness). An admin can raise this value to send solicitations more frequently relative to the advertised lifetime, refreshing the router relationship more proactively for a specific configuration entry. For example, increasing this value on a config entry using a router with a short advertised lifetime would keep the device re-soliciting well before that lifetime expires.