What are the Sunnahs of Wudu’, and does forgetting them invalidate it, or does it refer to the number of times a limb is washed?

The Sunan (recommended acts) of Wudu' are actions for which the doer is rewarded, but their omission does not invalidate the Wudu'. These are: mentioning the name of Allah (Tasmiyah), using the Siwak (tooth-stick), washing the hands three times at the beginning of Wudu', exaggerating in rinsing the mouth and nose for one who is not fasting, running fingers through a thick beard and between the fingers and toes, starting with the right before the left, repeating the washing of each limb two or three times, and performing the remembrance (Dhikr) after completing Wudu'.