Gauge theories with N=2 supersymmetry in four dimensions usually admit several different descriptions. In many cases, these dualities can be conveniently studied using the six-dimensional setup proposed by Gaiotto in 2009, which allows us to understand them in terms of simple geometric data. After reviewing this formalism, I will discuss a special class of N=2 gauge theories: although these models have a six-dimensional origin, their dualities cannot be understood in terms of the above mentioned framework.