Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Multilayer switching is an evolution of LAN and internetworking technologies. Multilayer devices combine aspects of OSI layer 2 (the data link layer) and OSI layer 3 (the network layer) into hybrid switches that can route packets at wire speed. A basic switch is a multiport bridge. These switches were developed to allow microsegmentation of LANs into large broadcast domains with small collision domains. See "Switching and Switched Networks" for an overview of the evolution of switches.

As the technology developed, hardware-based routing functions were also added, then higher-level functions such as the ability to look deep inside packets for information that could aid in the packet-forwarding process. Thus, multilayer switches are devices that examine layer 2 through layer 7 information.

This topic continues in "The Encyclopedia of Networking and Telecommunications" with a discussion of the following:

• Layer 1 through Layer 7 functionality
• Use of ASICs and network processors in multilayer switches
• Layer 2/Layer 3 switching functionality
• Cut-through routing versus label switching
• Silicon-based routing
• Deep packet classification
• Server load balancing
• Bandwidth managers
• QoS (quality of service) and CoS (class of service) support
• Policy-based management and DEN (directory-enabled networks)

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