The word “sunnah” generally means the example or practice of the Prophet (peace and blessings be upon him). When we talk about sunnahPrayers*, *we mean those ritual Prayers (salah](http://www.islamonline.net/english/introducingislam/Worship/Prayers/article02.shtml)) that the Prophet prayed in addition to the *fard *(obligatory) Prayers. They are optional, but it is highly recommended to perform these Prayers. Following the example of the Prophet brings its own reward, and further, if one has any missing fard Prayers on Judgment Day, the missing Prayers will be made up with the sunnah Prayers that were performed.
The sunnah *mu’akkadah *(confirmed sunnah) are those optional Prayers that the Prophet always performed. There are other optional Prayers that he performed less regularly, such as the one before Asr. This accounts for the variance in the number of *rakahs *before certain Prayers.
**Fajr (Subh) (Dawn Prayer): **Two *rak`ahs *of sunnah before the *fard *Prayers
rest read here Islam Online
regarding zobia’s post, two sunnah before maghrib prayer are non mu’akkadah.