Cisco routers are specialized computers used in data networks to provide connectivity between remote computers (also called hosts) and network segments. Cisco routers operate on the third network layer of the OSI (Open Systems Interconnection) reference model and perform such functions as packet forwarding and best-path determination.

The architecture of Cisco routers is very similar to that of other computers. Routers have memory and a processor, which are used to execute the operating system and numerous processes or programs. Generally speaking, the Cisco IOS (Internetwork Operating System) is a set of processes running inside a router. Examples of such processes are the forwarding engines for network layer protocols
for example, IP, IPX, AppleTalk routing protocols RIP, OSPF, BGP data link layer protocols PPP, HDLC, Frame Relay as well as numerous other tasks.

The type of central processor used in Cisco routers varies, depending on the router model. For example, Cisco 2500-series routers use the 20MHz Motorola 68EC030, whereas the more powerful routers, such as the Gigabit Switch Router (GSR), use the 200MHz IDT R5000 RISC (reduced instruction set computer).

The internal architecture of routers also depends on the router model. The architecture can be as simple as “one bus, one CPU” in the case of the 2500 series and as complex as the switch fabric with up to 320Gbps (gigabits per second) capacity and distributed traffic processing used by the GSR 12416.