On most supercomputers, except some torus network based systems, resource managers allocate nodes to jobs without considering the sharing of network resources by different jobs. Such network-oblivious resource allocations result in link sharing among multiple jobs that can cause significant performance variability and performance degradation for individual jobs. In this paper, we explore low-diameter networks and corresponding node allocation policies that can eliminate inter-job interference. We propose a variation to n-dimensional mesh networks called express mesh. An express mesh is denser than the corresponding mesh network, has a low diameter independent of the number of routers, and is easily partitionable. We compare structural properties and performance of express mesh with other popular low-diameter networks. We present practical node allocation policies for express mesh and fat-tree networks that not only eliminate inter-job interference and performance variability, but also improve overall performance.