(Spoiler Extended) Dragons North of the Wall

So probably already mentioned... but I just finished the new book and the scene where Alysanne tries to take Silverwing over the Wall, but the dragon refuses... got me thinking does the magic of the wall work both ways? It keeps the Others from coming south, but also prevents dragons from going north... also the fact that her daughter Daenerys dies from "the shivers"... sort of hammers home the vulnerability of Targs and their dragons to ice magic. Thoughts?