What are the conditions necessary for Nibbana? This question is pretty straight forward. 

Suppose I wish to attain Nibbana then what are the conditions which I must fulfill in order to attain Nibbana?
What are the conditions necessary for Nibbana?


This answer is pretty straight forward. 

Practice and perfect the Noble Eightfold Path as laid out by the Buddha. When perfected, the Path Consciousness takes Nibbana as an object. 

It performs four distinct functions, i.e.; "fully understanding Dukkha, abandoning the origin of Dukkha, realizing Nibbana and cultivating the Noble Eightfold Path".


  Is Nibbana guaranteed after perfecting the Noble Eightfold Path ?


In the Nagara Sutta, the Buddha teaches how he discovered an ancient Path, the Noble Eightfold Path, and by following it he came to experience the cessation of aging and death (conditioned reality).


  "... So too, bhikkhus, I saw the ancient path, the ancient road travelled
  by the Perfectly Enlightened Ones of the past. And what
  is that ancient path, that ancient road? It is just this Noble
  Eightfold Path; that is, right view, right intention, right speech,
  right action, right livelihood, right effort, right mindfulness, right
  concentration. I followed that path and by doing so I have directly
  known aging-and-death, its origin, its cessation,and the way leading to its cessation ..."
  
  -- SN 12.65: The City, p. 603, Bodhi transl.