Multilayer switch
From Free net encyclopedia
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 that of a Layer 3 switch is the physical implementation. In general-purpose routers, packet switching takes place using a 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 that switch based on Layer 3 information, the basic difference being processing speed and/or the way they do the 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-switches, or web-switches.
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
- Network Magazine 1 April 1999, Multilayer Switching: Between the Lines 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.da:Multilayer switch