Network operating system. A network operating system (NOS) is a specialized operating system for a network device such as a router, switch or firewall.

Historically operating systems with networking capabilities were described as network operating systems, because they allowed personal computers (PCs) to participate in computer networks and shared file and printer access within a local area network (LAN). This description of operating systems is now largely historical, as common operating systems include a network stack to support a client–server model.

History
Packet switching networks were developed to share hardware resources, such as a mainframe computer, a printer or a large and expensive hard disk.

Historically, a network operating system was an operating system for a computer which implemented network capabilities. Operating systems with a network stack allowed personal computers to participate in a client-server architecture in which a server enables multiple clients to share resources, such as printers.

These limited client/server networks were gradually replaced by Peer-to-peer networks, which used networking capabilities to share resources and files located on a variety of computers of all sizes. A peer-to-peer network sets all connected computers equal; they all share the same abilities to use resources available on the network.

Today, distributed computing and groupware applications have become the norm. Computer operating systems include a networking stack as a matter of course. During the 1980s the need to integrate dissimilar computers with network capabilities grew and the number of networked devices grew rapidly. Partly because it allowed for multi-vendor interoperability, and could route packets globally rather than being restricted to a single building, the Internet protocol suite became almost universally adopted in network architectures. Thereafter, computer operating systems and the firmware of network devices tended to support Internet protocols.

Network device operating systems 
Network operating systems can be embedded in a router or hardware firewall that operates the functions in the network layer (layer 3). Notable network operating systems include:

Proprietary network operating systems
 Cisco IOS, a family of network operating systems used on Cisco Systems routers and network switches. (Earlier switches ran the Catalyst operating system, or CatOS)
 RouterOS by MikroTik
 ZyNOS, used in network devices made by ZyXEL

FreeBSD, NetBSD, OpenBSD, and Linux-based operating systems 
 Cisco NX-OS, IOS XE, and IOS XR; families of network operating systems used across various Cisco Systems device including the Cisco Nexus and Cisco ASR platforms
 Junos OS; a network operating system that runs on Juniper Networks platforms
 Cumulus Linux distribution, which uses the full TCP/IP stack of Linux
 DD-WRT, a Linux kernel-based firmware for wireless routers and access points as well as low-cost networking device platforms such as the Linksys WRT54G
 Dell Networking Operating System; DNOS9 is NetBSD based, while OS10 uses the Linux kernel
 Extensible Operating System runs on switches from Arista and uses an unmodified Linux kernel 
 ExtremeXOS (EXOS), used in network devices made by Extreme Networks
 FTOS (Force10 Operating System), the firmware family used on Force10 Ethernet switches
 ONOS, an open source SDN operating system (hosted by Linux Foundation) for communications service providers that is designed for scalability, high performance and high availability.
 OpenBSD, an open source operating system which includes its own implementations of BGP, RPKI, OSPF, MPLS, VXLAN, and other IETF standardized networking protocols, as well as firewall (PF) and load-balancing functionality.
 OpenWrt used to route IP packets on embedded devices
 pfSense, a fork of M0n0wall, which uses PF
 OPNsense, a fork of pfSense
 SONiC, a Linux-based network operating system developed by Microsoft
 VyOS, an open source fork of the Vyatta routing package

See also
 Distributed operating system
 FRRouting
 Interruptible operating system
 Network Computer Operating System
 Network functions virtualization
 Operating System Projects
 SONiC (operating system)

References

 
Internet Protocol based network software
Operating systems