Multilayer switch

A multilayer switch (MLS) is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers.

A layer-3 switch incorporates routing capability in addition to the layer-2 bridging found in a standard switch. The major difference between the packet forwarding operation of a router and that of a layer-3 switch is the actual implementation. In general-purpose routers, forwarding is usually implemented in software that runs on a microprocessor or a network processor, whereas a layer-3 switch performs the same operation using dedicated application-specific integrated circuit (ASIC) hardware.

A multilayer switch (MLS) can prioritize packets by the 6 bits in DSCP (differentiated services CodePoint). These 6 bits were used in the "old days" for Type of Service (ToS).

The following 4 mappings are normally available in an MLS:

Many MLSs implement QoS differentiated services and/or integrated services in hardware.

Some MLSs are also able to route between VLANs and/or ports like a common router. The routing is normally as quick as switching (at wirespeed). According to Cisco, Layer 3 switches are basically routers that switch based on Layer 3 information, the basic difference being processing speed and/or the way they do the switching; Layer 3 switches use ASICs/hardware instead of the CPU/software that a router would.

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