IP forwarding cache

The IP forwarding cache provides a fast-path mechanism for forwarding IP packets. The cache contains entries for IP destinations. When a routing switch has completed processing and addressing for a packet and is ready to forward the packet, the device checks the IP forwarding cache for an entry to the packet's destination.

• If the cache contains an entry with the destination IP address, the device uses the information in the entry to forward the packet out the ports listed in the entry. The destination IP address is the address of the packet's final destination. The port numbers are the ports through which the destination can be reached.

• If the cache does not contain an entry, the software can create an entry in the forwarding cache.

Each entry in the IP forwarding cache has an age timer. The age interval depends on the number of entries in the table. The age timer ranges from 12 seconds (full table) to 36 seconds (empty table.) Entries are aged only if they are not being used by traffic. If you have an entry that is always being used in hardware, it will never age. If there is no traffic, it will age in 12 to 36 seconds. The age timer is not configurable.