IP forwarding cache

The IP forwarding cache contains entries for IP destinations, and provides a fast-path mechanism for forwarding IP packets.

When a Brocade Layer 3 device has completed the 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 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 final destination. The port numbers are the ports through which the destination can be reached.
  • If the cache does not contain an entry and the traffic does not qualify for an entry in the session table instead, the software can create an entry in the forwarding cache.

Each entry in the IP forwarding cache has an age timer. If the entry remains unused for ten minutes, the software removes the entry. The age timer is not configurable.

Each entry in the IP forwarding cache has an age timer. The age timer is not configurable.

Here is an example of an entry in the IP forwarding cache. 

IP Address     Next Hop   MAC             Type  Port  Vlan  Pri
192.168.1.11   DIRECT     0000.0000.0000  PU    n/a   0     1

Each IP forwarding cache entry contains the IP address of the destination, and the IP address and MAC address of the next-hop router interface to the destination. If the destination is actually an interface configured on the Layer 3 device itself, as shown here, then next-hop information indicates this. The port through which the destination is reached is also listed, as well as the VLAN and Layer 4 QoS priority associated with the destination if applicable.

NOTE
You cannot add static entries to the IP forwarding cache. You can increase the number of entries the cache can contain.
Parent topic: IP packet flow through a Layer 3 device