ip route-cache

To control the use of high-speed switching caches for IP routing, use the ip route-cache command in interface configuration mode. To disable any of these switching modes, use the no form of this command.

Syntax Description

cbus	(Optional) Enables both autonomous switching and fast switching.
same-interface	Enables fast-switching packets to back out through the interface on which they arrived.
flow	(Optional) Enables the RSP to perform flow switching on the interface.
distributed	Enables VIP distributed switching on the interface. This feature can be enabled on Cisco 7500 series routers with an RSP and Versatile Interface Processor (VIP) controllers. If both ip route-cache flow and ip route-cache distributed are configured, the VIP does distributed flow switching. If only ip route-cache distributed is configured, the VIP does distributed switching.

Defaults

IP autonomous switching is disabled.

Fast switching varies by interface and media.

Distributed switching is disabled.

Command Modes

Interface configuration

Command History

Release	Modification
10.0	This command was introduced.
11.2	The distributed keyword was added.

Usage Guidelines

Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis.

The ip route-cache command with no additional keywords enables fast switching.

Our routers generally offer better packet transfer performance when fast switching is enabled, with one exception. On networks using slow serial links (64K and below), disabling fast switching to enable the per-packet load sharing is usually the best choice.

You can enable IP fast switching when the input and output interfaces are the same interface, using the ip route-cache same-interface command. This normally is not recommended, although it is useful when you have partially meshed media, such as Frame Relay. You could use this feature on other interfaces, although it is not recommended because it would interfere with redirection.

When the Route Switch Processor (RSP) is flow switching, it uses a flow cache instead of a destination network cache to switch IP packets. The flow cache uses source and destination network address, protocol, and source and destination port numbers to distinguish entries.

The flow caching option can also be used to allow statistics to be gathered with a finer granularity. The statistics include IP subprotocols, well-known ports, total flows, average number of packets per flow, and average flow lifetime.

On Cisco 7500 series routers with RSP and Versatile Interface Processor (VIP) controllers, the VIP hardware can be configured to switch packets received by the VIP with no per-packet intervention on the part of the RSP. When VIP distributed switching is enabled, the input VIP interface tries to switch IP packets instead of forwarding them to the RSP for switching. Distributed switching helps decrease the demand on the RSP.

Not all switching methods are available on all platforms. Refer to the Cisco Product Catalog for information about features available on the platform you are using.

Examples

The following example enables both fast switching and autonomous switching:

ip route-cache cbus
 

The following example disables both fast switching and autonomous switching:

no ip route-cache
 

The following example turns off autonomous switching only:

no ip route-cache cbus
 

The following example enables VIP distributed flow switching on the interface:

interface ethernet 0/5/0
 ip address 17.252.245.2 255.255.255.0
 ip route-cache distributed
 ip route-cache flow
 

The following example returns the system to its defaults (fast switching enabled; autonomous switching disabled):

ip route-cache

Related Commands

Command	Description
exit	Leaves aggregation cache mode.
show mpoa client	Displays the routing table cache used to fast switch IP traffic.