Multilayer switch - Wikipedia

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.

MultiLayer Switch (MLS) - OSI layer 3 and/or 4

A Multilayer Switch (MLS) can priorties packets by the 6 bits in IP DSCP (differentiated services CodePoint). These 6 bits was used in the "old days" for Type of Service (ToS).

The following 4 mappings are normally available in a MLS:

From OSI layer 2, 3 og 4 to IP DSCP (if IP packet) and/or VLAN IEEE 802.1p.
From VLAN IEEE 802.1p to IP DSCP.
From IP DSCP to VLAN IEEE 802.1p.
From VLAN IEEE 802.1p to port queue.

Many MLS implements QoS differentiated services and/or integrated services in hardware.

Some MLS are also able to route between VLAN and/or ports like a common router. The routing are normally as quick as switching (with wirespeed).

Layer 7 switch, web-switch, content-switch

Some switches can use up to OSI layer 7 packet information, they are called layer 7 switches, content-switch or web-switch.

Some of the applications areas are load-balancing among HTTP, HTTPS and/or VPN servers. Load-balancing can be made by using NAT. Some of the layer 7 switches can NAT at wirespeed.

Sources/references

Danish wikipedia (http://www.wikipedia.dk)

External addresses

Google: Layer 3 Switching (http://directory.google.com/Top/Computers/Internet/Protocols/Transmission_Protocols/Networking_Resources/Routing/Layer_3_Switching/)
Multilayer Switching Reference Guide (http://www.bcr.com/bcrmag/mlsreference.asp)
Quality of Service: Delivering QoS on the Internet and in Corporate Networks (http://www.employees.org/~ferguson/QoS.html)
Cisco White Paper: DiffServ-The Scalable End-to-End QoS Model (http://www.cisco.com/warp/public/cc/pd/iosw/ioft/iofwft/prodlit/difse_wp.htm)
Survey of QoS Routing (http://citeseer.nj.nec.com/544755.html)
Network Magazine 04/01/1999, Multilayer Switching: Between the Lines (http://www.networkmagazine.com/article/NMG20000509S0010) Vendors are touting switches and routers with features at layer 2, layer 3, layer 4, and beyond. Here?s how to separate fact from fiction.
Siemens, The Solution Provider Lexikon: Web-Switch (http://w3.siemens.de/solutionprovider/_online_lexikon/0/f011680.htm)