SpiNNaker is a large-scale multi-core computing engine designed to model heavily distributed fine-grain problems. The machine is constructed hierarchically: 1 monitor and 16 worker processors form a single node of a toroidal compute `surface'. The six high-speed bi-directional links of each node are used for triangular edge connections that provide alternative routes around problematic links. The system itself is scalable from one node up to 216 resulting in a maximum of 220 worker processors. SpiNNaker is an isotropic homogeneous network of processors that deliberately includes no central overseer. A consequence of this isotropy is an absence of perimeter and hence no natural position for peripheral I/O connections. This study describes the practical techniques and details employed in two components of the system: (a) SpiNNlink is the proposed board-to-board interconnection system that multiplexes 48 separate 250 Mbps SpiNNaker links through six off-board connections without compromising the overall system bisection bandwidth, forms an isotropic meta-network on top of SpiNNaker without requiring any cooperation from system software, and remains transparent to the SpiNNaker network; and (b) SpiNNterceptor is the proposed peripheral I/O subsystem developed as a layer on top of SpiNNlink that provides over 18 Gbps of minimally disruptive communication between SpiNNaker applications and externally connected equipment.