Network functions (such as firewalls and routing) can all be virtualized inside the hypervisor.
Network functions that operate inside a hypervisor operate just like their physical version, but we don't need to worry about power supplies failing, CPUs going bad, or anything else that can cause a physical network device to fail.
What we do have to worry about what it comes to virtualizing network function: we do have to worry about the host that runs the virtual network functions; however, redundancy is built into many hypervisors.
