Must Remember Cisco Commands

The 'no ip route-cache' command enables process switching on an interface. Cisco layer 3 devices have three switching modes, Process Switching, Fast Switching, and Cisco Express Forwarding switching. Most current Cisco models have CEF enabled by default because of the amount of information it caches and how efficient it switches traffic. Seeing the 'no ip route-cache' command means that all packets entering the layer-3 interface will be process switched by the CPU instead of hardware. This can possibly over-burden the CPU when high amounts of traffic is needing to be switched.

“ip route-cache” controls the use of switching methods for forwarding IP packets:

ip route-cache [same-interface | flow | distributed | cef | policy]
  • same-interface – Enables fast-switching packets to forward IP packets back out through the interface on which they arrived.
  • flow – Enables NetFlow accounting for packets that are received by the interface.
  • distributed – Enables distributed switching on the interface.
  • cef – Enables Cisco Express Forwarding (CEF) operation on an interface.
  • policy – Enables fast-switching for packets that are forwarded using Policy Based Routing (PBR).

The NetFlow Subinterface Support feature provides the ability to enable NetFlow on a per-subinterface basis. In a scenario in which your network contains thousands of subinterfaces and you want to collect export records from only a few subinterfaces, you can fine-tune your collection of data to only specified subinterfaces. The result is lower bandwidth requirements for NetFlow Data Export (NDE) and reduced platform requirements for NetFlow data-collection devices.
Using the NetFlow Subinterface Support feature, you can enable NetFlow on selected subinterfaces using the ip flow ingress command. If you configure the ip flow ingress command on a few selected subinterfaces and then configure the ip route-cache flow command on the main interface, enabling the main interface will overwrite the ip flow ingress command and data collection will start from the main interface as well as all the subinterfaces. In a scenario in which you configure the ip flow ingress command and then configure the ip route-cache flow command on the main interface, you can restore subinterface data collection by using the no ip route-cache flow command. This configuration will disable data collection from the main interface and restore data collection to the subinterfaces you originally configured with the ip flow ingress command.

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