what network driver routines are invoked via "ifup" and "ifdown"?

first time poking around network drivers, and i'm wondering what platform driver routines are called when invoking ifup/ifdown from user space (if any). i'm *assuming* (possibly incorrectly) that the probe() and remove() routines are invoked only on loading and unloading the driver, not simple ifup and ifdown. guidance, anyone? rday