In the past, switches used one of the following forwarding methods for switching data between network ports:

Figure 1 highlights differences between these two methods.

In store-and-forward switching, when the switch receives the frame, it stores the data in buffers until the complete frame has been received. During the storage process, the switch analyzes the frame for information about its destination. In this process, the switch also performs an error check using the Cyclic Redundancy Check (CRC) trailer portion of the Ethernet frame.

CRC uses a mathematical formula, based on the number of bits (1s) in the frame, to determine whether the received frame has an error. After confirming the integrity of the frame, the frame is forwarded out the appropriate port toward its destination. When an error is detected in a frame, the switch discards the frame. Discarding frames with errors reduces the amount of bandwidth consumed by corrupt data. Store-and-forward switching is required for Quality of Service (QoS) analysis on converged networks where frame classification for traffic prioritization is necessary. For example, voice over IP data streams need to have priority over web-browsing traffic.

In Figure 2, play the animation for a demonstration of the store-and-forward process. Store-and-forward is the sole forwarding method used on current models of Cisco Catalyst switches.