The principal objective of DEISA 1, 2, a consortium of major national supercomputing centres in Europe, is to advance computational science in leading scientific and industrial disciplines by deploying an innovative Grid-empowered infrastructure to enhance and reinforce High-performance Computing in Europe. The infrastructure, based on the tight coupling of homogeneous national supercomputers, provides a distributed supercomputing platform operating in multi-cluster mode. The production capability and capacity of the distributed platform will provide a substantial European added-value to the existing national infrastructures and will, in turn, be integrated into a larger heterogeneous Grid. The DEISA service activity “Network operation and support” defines, deploys and operates the network interconnect required by this infrastructure during the project lifetime and beyond. The paper will give an overview about the activities performed in this service activity, the experiences that have been gathered and the future tasks which have to be performed.