As large grid infrastructures, such as Enabling Grids for E-sciencE, mature, they are being used by scientists around the world in their daily work, running thousands of concurrent computational jobs and transferring large amounts of data. The successful and sustainable operation of such grid infrastructures is only possible through the use of monitoring tools. The underlying networks upon which grid infrastructures are built are critical to their operation; therefore, network monitoring becomes an important part of the overall grid monitoring strategy. In this paper, the design and implementation of a set of tools for providing access to federated network monitoring data are presented, based on standards developed within the Open Grid Forum Network Measurements Working Group (NM-WG). These tools give access to data collected by heterogeneous, NM-WG compliant network monitoring tools.