The White Council assaults Dol Guldur?

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I was wondering about the White Counsil the other day, regarding the Hobbit movies...

I was thinking about the time when the White Counsil ousted the Necromancer from Dul Guldur. How did they manage this? I know that Sauron just feigned resistance and then pulled back to give his enemies a false sense of security and to return to Mordor. But with which forces did the WC attack Dol Guldur with? For all they knew they were in for a very difficult siege with uncertain outcome, and must have brought a strong host with siege capabilities and materiel, if we presume Dol Guldur was a fortified stronghold with plenty of men and god knows what to defend it. Or maybe Dol Guldur wasn't a strong fortress at all?

So who do you reckon partook in this attack? The elves of Lorien? The elves of Rivendell? The Elves of Mirkwood? The rangers? Other men than the dunedain is out of the question I think, and their numbers are surely too small to pose a serious military theat anyway. And I find it hard to believe that Gandalf, Galadriel, Elrond and Cirdan could or would dare threaten Sauron's stronghold unaided.

Any thoughts?