f why the router is process switching. Check your config and look for problems. Configuring and Managing Switching Paths Packets that are malformed can cause a router to process-switch. I've seen Metropolitan Area Ethernet carrier equipment muck up Ethernet packets just enough that the router had to process-switch them. I've seen the same thing when an ASIC in a switch fails. My point is that external devices or events, not just events internal to the router, can cause the router to fall back on process switching. Fast Switching On an interface that is currently process-switching, the interface command ip route- cache enables fast switching: R1(config)#int s0/1 R1 (config-if)# ip route-cache This turns on fast switching without enabling CEF: R1#sho ip int s0/1 I include swi IP fast switching is enabled IP fast switching on the same interface is enabled IP Flow switching is disabled IP CEF switching is disabled IP Fast switching turbo vector IP multicast fast switching is enabled IP multicast distributed fast switching is disabled On an interface that is running CEF, turning off CEF will result in the interface running fast switching: R1 (config)#int s0/1 R1 (config-if)# no ip route-cache cef You cannot disable fast switching without also disabling CEF, but you can enable fast switching without enabling CEF. Continuing with the example in the previous section, as soon as I enable fast switching again on the process-switching router, the CPU utilization drops back down to normal levels: R1#sho proc cpu hist 2222244444444444444444444444444444444444444444 4444444444440000077777111118888899999888889999933333444446 ******************** Chapter 15: Switching Algorithms in Cisco Routers CPU% per second (last 60 seconds) CEF is enabled by default on all modern Cisco routers, but in the event that you need to enable it on an older router, or if it has been disabled, there are two places you can configure it. First, using the global command ip cef, you can enable CEF on every interface that supports it: R1(config)#ip cef Ne