Multilayer switch
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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.
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Layer 3 Switching
The major difference between the packet switching operation of a router and a Layer 3 switch is the physical implementation. In general-purpose routers, packet switching takes place using microprocessor, whereas a Layer 3 switch performs this using application specific integrated circuit (ASIC) hardware.
MultiLayer Switch (MLS) - OSI layer 3 and/or 4
A Multilayer Switch (MLS) can prioritize packets by the 6 bits in IP 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 a MLS:
- From OSI layer 2, 3 or 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 MLSs implement QoS differentiated services and/or integrated services in hardware.
Some MLSs are also able to route between VLAN and/or ports like a common router. The routing is normally as quick as switching (at wirespeed). According to Cisco, Level 3 switches are basically routers, and switch based on Layer 3 information, the difference being basically processing-speed and/or the way they do switching: Level 3 switches use ASICs/hardware instead of the CPU/software that a router would.
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.
External links
- Open Directory Project: Layer 3 Switching (http://www.dmoz.org/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.
- Cisco - Layer 3 Switching Demystified (http://www.cisco.com/warp/public/cc/so/neso/lnso/cpso/l3c85_wp.htm), 2000