Ignore Target Def - How does it work?

[Zorandel]

Ignore Target Def - How does it work?

I'am wondering how does "ignore target defence" work?
Is it LITERALLY like it says (100% chance to hit) or does it simply lower the def in a way that we can't see it ?

 

[nicro tower]

it basically calculates the enemy def in as 0 so you can still miss if ur AR is really low.
and max chance to hit is 95%

 

[Nilaripper]

Check out this:
http://www.battle.net/forums/thread.aspx?fn=d2-gameplay&t=163465&p=1&#post163465

Under 26.you find the difference between ITD and always hit.