First Ignorance is really a lack of knowledge of something. It is by a knowledge that dukkha stops, contrary to some weird views invented by people, like taking vows, doing some ritual, or having some stimuli of the senses, like smelling some aroma, or hearing some sound..
Being a sotapanna is really about knowledge and being an arhant is again about this special knowledge plus the execution of this knowledge and the knowledge of the execution of this special knowledge, like here in the suttanipata http://ftp.budaedu.org/ebooks/pdf/EN391.pdf ,
728. “Sufferings in their many forms in the world
originate based on acquisition.
The ignorant dullard who creates acquisition 186
encounters suffering again and again.
Therefore, understanding, one should not create
contemplating it as the genesis and origin of suffering. (5)
199. Then its hollow head
is filled with the brain.
Led on by ignorance, the fool
conceives it as beautiful. (7)
277. “Harassing one who is self-developed,
led on by ignorance,
one does not know defilement
as the path leading to hell. (4)
It is not wrong to say that the ''travel again and again
in the saṃsāra '' is due to ignorance.
729. “Those who travel again and again
in the saṃsāra of birth and death,
with its becoming thus, becoming otherwise:
that journey is due to ignorance. (6)
730. “It is because of ignorance, this great delusion,
that one has wandered on for so long.
But those beings who have gained clear knowledge
do not come back to renewed existence. 187 (7)
731. “Whatever suffering originates
is all conditioned by volitional activities.
With the cessation of volitional activities,
there is no origination of suffering. (8)
732. “When one has known this danger,
‘Suffering is conditioned by volitional activities,’
by the stilling of all volitional activities,
by the stopping of perceptions,
the destruction of suffering occurs
when one has known this as it really is. (9)
You cannot say that nibanna is the ''stilling of ignorance'', the contrary would be weird at best.
Then the method to remove this ignorance is always the same
1025. “Bāvari asks about the head
and the splitting of the head.
Explain this, Blessed One!
Remove our doubt, O rishi!” (50)
1026. “Know ignorance to be ‘the head’;
clear knowledge is ‘head-splitting’
when conjoined with faith, mindfulness,
concentration, desire, and energy.” (51)
1106. “The abandoning of both,
(Udaya,” said the Blessed One),
“sensual desires and dejection;
the dispelling of mental dullness,
the warding off of regrets: (2)
1107. “purified by equanimity and mindfulness,
preceded by thought on the Dhamma—
I call this emancipation by final knowledge,
the breaking up of ignorance.” (3) 
1108. “By what is the world fettered?
What is its means of traveling about?
By the abandoning of what
is ‘nibbāna’ spoken of?” (4)
1109. “The world is fettered by delight;
thought is its means of traveling about.
It is by the abandoning of craving
that ‘nibbāna’ is spoken of.” (5)
342 The Suttanipāta
1110. “How does one live mindfully
for consciousness to cease?
Having come to ask the Blessed One,
let us hear that word of yours.” (6)
1111. “For one not seeking delight in feeling
internally and externally,
for one living mindfully thus,
consciousness ceases.” (7)