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The growth of the Internet has
prompted the IT industry to look at mechanisms that improve the
efficiency of packet forwarding. The bus architecture found within
traditional routers fails to scale beyond a maximum load of about 1
Gb/s. Gigabit routers have been developed to achieve speeds far
greater than this by replacing the bus architecture with a switch
fabric to interconnect various components within the router. Here,
the switching fabric is used as a very fast interconnect, and is
essentially "hidden" from the outside world, with the IP processing
functionality maintained within the interfaces to the fabric.
The term
multilayer routing covers approaches to the integration of layer 3
datagram forwarding and layer 2 switching that go beyond the use of
the techniques found within gigabit routing/switching. The approach
uses label lookups to allow more efficient packet classification,
and the potential to engineer the network and manage the impact of
data flows. A number of vendor-specific approaches to multilayer
routing appeared between 1994 and 1997, including
- IP Switching,
- Cell Switch
Router (CSR),
- ARIS,
- Tag
Switching, and
- IPSOFACTO.
The fact that
these approaches were proprietary, and produced incompatible
solutions, led to the formation of the Internet Engineering Task
Force (IETF) Multi Protocol Label Switching working group.
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