Routing in wireless network is challenging because of the unpredictable behavior of the medium and the proactive effect of interference. In order to exploit all the advantages that the wireless medium offers, new routing metrics must be explored. These metrics should come from a cross-layer approach in order to make the routing layer aware of the local issues of the underling layers. In the present paper, we explore three primitive physical layer parameters: interference, packet success rate, and data rate. We define the metrics so that the routing level can correctly find paths that offer: low levels of generated interference, reliability in terms of packet success rate, and highest available transmission rate. We prove that for cross-layer based routing, if the metrics are well designed, the problem is NP-complete.