A novel trend in mobile networks is to co-locate the base stations with virtualized core network functions, such as session management and routing. The goal is to lose the long-standing physical dependency between the radio access and the core network, and improve network resiliency. In this work, we focus on the placement of virtualized core functions within a network of multiple base stations interconnected via a potentially limited backhaul. Since all data and signaling traffic are exchanged on the links interconnecting the base stations, the placement of these functions deeply impacts the backhaul load. We compare centralized and distributed placement strategies, with respect to the overall backhaul bandwidth consumption. Results show that distributing instances of the core functions (e.g., routing) in the network is significantly less costly from a backhaul point of view, and can economize backhaul consumption by 86%.