Cisco Switching

Cisco Switching Modes

To pass the CCNA exam and earn this important certification, you've got to know switching inside and out. While you're learning all the basic switching theory, make sure to spend some time with the one of three switching modes Cisco routers can use.You may want to check out here for more.Click Here


Store-and-Forward is exactly what it sounds like. The entire frame will be stored before it is forwarded. This mode allows for the greatest amount of error checking, since a CRC (Cyclical Redundancy Check) is run against the frame before it is forwarded. If the frame contains an error, it is discarded. If there's no problem with the frame, the frame is then forwarded to its proper destination.


While store-and-forward does perform error checking, the delay in processing the frame while this error check is run results in higher latency than the other modes you're about to read about. The latency time can also vary, since not all frames are the same size.

Cut-through switching copies only the destination MAC address into its memory before beginning to forward the frame. Since the frame is being forwarded as soon as the destination MAC is read, there is less latency than store-and-forward. The drawback is that there is no error checking.


There is a middle ground, fragment-free switching. Only part of the frame is copied to memory before it is forwarded, but it's the first 64 bytes of the frame, not just the destination MAC. (Why? Because if there is a problem with the frame, it's most likely in the first 64 bytes.) There is a little more error checking than cut-through, but not as much latency as with store-and-forward.



Note that the latency of both cut-through and fragment-free is fixed; these modes always look at the first six or 64 bytes, respectively. Store-and-forward's latency depends on the size of the frame.

It might not be possible to determine if the purchase of used cisco equipment was a wise business decision or a beneficial financial investment until well after the sales process.  Once the parts have been shipped, delivered and installed they should be tested, from the Ethernet cable all the way to the hard drive to make sure they are functional, operational and compatible with each other or any other existing equipment.


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