You can assemble a server from off the shelf components that will be able to sent and receive traffic in multi Gigabit speed. Here is an example of an 10Gps net card from Intel.
But can we turn this server into a high performance network appliance? Do we still need a dedicated hardware like for example ASIC, FPGA, low latency RAM and TCAM RAM in network devise so they can efficiently switch and forward packets with maximum wire speed.
Router hardware design plan
Looking at this presentation from 2012 https://ripe64.ripe.net/presentations/18-ripe-64-router-architecture-challenges.pdf you would think that yes. These would be the obvious reasons (screenshots taken from the presentation):
Network processing unit (NPU) and new hardware design
The key points listed above still hold. But the next generation network appliances will be rather build with a help of a multicore generic NPU using the power of parallel processing than expensive and purposely design ASIC. With the right software (OS - often Linux, drivers, firmware, SDK, and API libraries) you will be able to turn a conventional x86 server with a modern PCIe data bus into a high performance, low latency and high speed network appliance.
Netronome Network Cards Accelerate SDN and NFV Designs
100Gps FlowNIC-6xxx network card
Hardware reference designs for FlowProcessor NPU chips