Sharing data between the processors becomes increasingly expensive as the number of cores in a system grows. In particular, the network processing overhead on larger systems can reach tens of thousands of CPU cycles per TCP packet, for just hundreds of "useful" instructions. Most of these cycles are spent waiting - when the CPU is stalled while accessing “bouncing” cache lines of network control data shared by all processors in the system - and synchronizing access to this shared state. In many cases, the resulting excessive CPU utilization limits the overall system performance. We describe an IsoStack architecture which eliminates the unnecessary sharing of network control state at all stack layers, from the low-level device access, through the transport protocol, to the socket interface layer. The IsoStack "offloads" network stack processing to a dedicated processor core; multiple applications running on the rest of the cores invoke the IsoStack services in parallel, using a thin access layer that emulates the standard sockets API, without introducing new dependencies between the processors. We present a prototype implementation of this architecture, and provide detailed performance analysis. We demonstrate the ability to scale up the number of application threads and scale down the size of messages. In particular, we show an order of magnitude performance improvement for short messages, reaching the 10Gb/s line speed at 40% CPU utilization even for 64 byte messages, while the unmodified system is choked when driving 11 times less throughput.