Most switch&#x2F;router dataplane processing is done in hardware, with control by custom drivers in the control-plane OS.<p>Cisco IOS is variously hosted on a proprietary real-time OS, QNX or Linux.
Juniper JunOS is FreeBSD-based.
Arista AOS is Linux-based.<p>With the advent of SDN, the packet-rate limitations of a general-purpose OS lead to things like DPDK and Snabb, but they both run within a Linux host environment (DPDK can use FreeBSD as well; not sure re: Snabb).