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Could you explain the characteristics and principles of operation of a Layer 3 switch?

Could you explain the characteristics and principles of operation of a Layer 3 switch and explain how the use of this switch can provide faster access/transmission compared to the use of a router?

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The basic principle of a Layer 3 switch can be explained as "route once, switch many." What this really means is that a Layer 3 switch can actually store MAC-to-IP address associations for the source and destination of the packet. So when there is a packet with a new source destination pair, it is routed (which means that the routing table is referred to for determining the best path, which is time consuming), and this source destination pair information is stored in the router cache. Now when the next packet arrives with the same source destination pair, no routing lookup is needed and the packet is directly switched (which is much, much faster). This is a principle of Layer 3 switching and that is the reason why it is faster than pure routing.

For more information, see this tip: Layer 3 switches explained by David Davis.

This was first published in July 2004

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