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Posted by waqasahmad
Multilayer switching
Multilayer switching is simply the combination of traditional Layer 2 switching with Layer 3 routing in a single product. Multilayer switching is new, and there is no industry standard yet on nomenclature. Vendors, analysts, and editors don’t agree about the specific meaning of terms such as multilayer switch, Layer 2 router, Layer 3 switch, IP switch, routing switch, switching router, and wirespeed router. The term multilayer switch seems to be the best and most widely used description of this class of product that performs both Layer 3 routing and Layer 2 switching functions.
Multilayer switching is usually implemented through a fast hardware such as a higher-density ASICs (Application-Specific Integrated Circuits), which allow real-time switching and forwarding with wirespeed performance, and at lower cost than traditional software-based routers built around general-purpose CPUs.
The following are some basic architecture approaches for the multiplayer switches:
Generic Cut-Through Routing: In the multi-layer switching architecture Layer 3 routing calculations are done on the first packet in a data flow. Following packets belonging to the same flow are switched at Layer 2 along the same route. In other words, route calculation and frame forwarding are handled very differently here.
ATM-Based Cut-Through Routing - This is a variation of generic cut-through routing which is based on ATM cells rather than frames. ATM-based cut-through routing offers several advantages such as improved support of LAN emulation and multi-vendor support in the form of the Multiprotocol Over ATM (MPOA) standard. Products referred to as IP switches and tag switches generally fall into this category.
Layer 3 Learning Bridging CIn this architecture, routing is not provided. Instead, it uses IP “snooping” techniques to learn the MAC/IP address relationships of endstations from true routers that must exist elsewhere in the network. Then it redirects traffic away from the routers and switches it based on its Layer 2 addresses.
Wirespeed Routing - Wirespeed architecture routes every packet individually. It is often referred to as packet-by-packet Layer 3 switching. Using advanced ASICs to perform Layer 3 routing in hardware, it implements dynamic routing protocols such as OSPF and RIP. In addition to basic IP routing, it supports IP multicast routing, VLAN segregation, and multiple priority levels to assist in quality of service.
Posted by stephen
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