Editing Cisco IOS (section)

== Routing ==
In all versions of Cisco IOS, [[Routing|packet routing]] and [[packet forwarding|forwarding]] ([[Packet switching|switching]]) are distinct functions. Routing and other protocols run as Cisco IOS processes and contribute to the Routing Information Base (RIB). This is processed to generate the final IP forwarding table (FIB, Forwarding Information Base), which is used by the forwarding function of the router. On router platforms with software-only forwarding (e.g., Cisco 7200), most traffic handling, including [[access control list]] filtering and forwarding, is done at interrupt level using [[Cisco Express Forwarding]] (CEF) or dCEF (Distributed CEF). This means IOS does not have to do a process [[context switch]] to forward a packet. Routing functions such as [[Open Shortest Path First|OSPF]] or [[Border Gateway Protocol|BGP]] run at the process level. In routers with hardware-based forwarding, such as the Cisco 12000 series, IOS computes the FIB in software and loads it into the forwarding hardware (such as an [[Application-specific integrated circuit|ASIC]] or network processor), which performs the actual packet forwarding function.