[quote=Оля]
Quote Originally Posted by "Полуношник":14pcxk76
All four variants is possible in different situations:

Да, не знаю
Да, знаю
Нет, не знаю
Нет, знаю
Of course, all these variants are possible, but in this case we are talking about the concrete context:

А: Вы не знаете Ивана Петрова?
Б: Да, я его знаю.

The answer sounds unnatural for me.[/quote:14pcxk76]

The whole dialogue sounds a bit unnaturally. May be we have imagined different contexts. How would you answer the question "Вы не знаете, как лучше проехать на станцию?" I would say "Да, знаю".