A Question about Macbeth--the Porter?

So in Act 2, Scene 3, the Porter pretends he is at the gates of hell. An ogy is made between hell and the castle. When Macduff and Lennox enter the castle, it is as if they are entering hell. Would this be irony or dramatic irony? The audience knows that Macbeth has already killed Duncan and that Macduff and Lennox are about to figure this out too--so would that make it dramatic irony since the audience knows something the characters don't?