store-and-forward

Resets the switching method for forwarding packets from cut-through to store-and-forward.
Syntax
store-and-forward
no store-and-forward
Command Default

The switching method is cut-through.

Modes

Global configuration mode

Usage Guidelines

Ethernet devices support two basic switching methods for packet forwarding: store-and-forward and cut-through.

Note: You must save the configuration and reload for the change to take effect.

A store-and-forward device does not make a forwarding decision on a data packet until it has received the whole frame and checked its integrity; a cut-through device starts the forwarding process soon after it makes the forwarding decision on an incoming frame that is, it might start forwarding before the entire packet is received. This reduces forwarding latency, especially for longer packets. However, there are many factors to consider when selecting which switching method is best for your environment and in some cases it is desirable to change from the default method and configure a device to store-and-forward.

The following table describes some of the differences in how packets are handled depending on the switching method.

Feature Cut-through Store-and-forward
Forwarding Data forwarding starts before an entire packet is received Device waits for entire packet received before processing.
Latency Low latency, less than 1 micro second. Higher latency; latency depends on frame size.
FCS Errors FCS errors may be propagated from one device to another. FCS errors are checked and error packets are discarded in the MAC receive.
MTU size MTU size is validated by MAC receive. Oversize packets are marked as error packets but not dropped in the MAC receive. MTU size is validated by MAC receive. Oversize packets are dropped at the MAC layer.

The no form of this command restores the default packet-forwarding method to cut-through.

Examples

This example globally enables store-and-forward packet switching and saves the configuration. 

Device(config)# store-and-forward
Device(config)# write memory
Device(config)# end
History
Release version Command history
08.0.10b This command was introduced.
Parent topic: Commands Si - Z