Over the years middleboxes have become a fundamental part of today’s networks. Despite their usefulness, they come with a number of problems, many of which arise from the fact that they are hardware-based: they are costly, difficult to manage, and their functionality is hard or impossible to change, to name a few.

To address these issues, there is a recent trend towards network function virtualization (NFV), in essence proposing to turn these middleboxes into software-based, virtualized entities. Towards this goal we introduce ClickOS, a high-performance, virtualized software middlebox platform. ClickOS virtual machines are small (5MB), boot quickly (about 30 milliseconds), add little delay (45 microseconds) and over one hundred of them can be concurrently run while saturating a 10Gb pipe on a commodity server. We further implement a wide range of middleboxes including a firewall, a carrier-grade NAT and a load balancer and show that ClickOS can handle packets in the millions per second.