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Layer 3 Switching Presentation


									Layer 3 Switching Presentation
Michael DeBakey

        Layer 3 switching is an area that has been expanded upon and redefined with the

proliferation of better quality processors commonly used in network equipment. Cisco

refers to higher end routers as “switch routers” which move data across subnets from one

interface to another. Traffic routed at the layer 3 level of the OSI model is comprised of a

series of packets containing a source and a destination address, as opposed to frames that

are transmitted at the layer 2 level.

        Is layer 3 switching a threat? Hardly. It has improved network performance

drastically as routing algorithms and processor speeds improve. In addition, good

network design theory plays into this naturally. By generously segmenting your network

into partitioned network groups using Virtual LANs (VLANs) you then introduce inter-

VLAN routing at the core by default. Routing is faster than layer 2 switching.

        Routers expand upon the idea of layer 3 switching and introduce more complex

routing algorithms for use on backbone or WAN/MAN topologies. Layer 3 switching

simply means the moving of packets from source to destination. A router (or layer 3

switch) has the ability to use different types of cabling, including ethernet, token ring,

fibre optic, or even proprietary cabling used by certain vendors. Through one layer 3

device, connections can be bridged or aggregated (both of these being layer 2 operations)

and then routed, though it is always preferable to have a router do nothing but route


        Layer 3 switches come with a variety of features. They can cost anywhere from

$30 for a consumer-grade Linksys router to millions of dollars for a well-implemented

and fully redundant carrier class router such as the Cisco CRS-1. One of the biggest
differences between these two devices (besides cost) is the type of connections they can

handle. The CRS-1 handles Ethernet, but in addition it also handles fibre optic cabling,

T1 interfaces, and other advanced circuits. The CRS-1 is also expandable by using

additional blade modules for additional capacity.

       Implementation costs can run from nothing to around $2,000 for a day’s work by

a network consulting firm such as ePlus. Cisco is the leader in layer 3 switching

equipment. For what a school would need, a Cisco Catalyst 6509 switch would cost

anywhere from $40,000 – $80,000 for the right modules including gigabit copper ports,

SFP ports, and two supervisor blade modules. Typically one would want to enroll a Cisco

product in a Smartnet contract for 24/7/365 support on the product. One would most

likely implement a layer 3 switch in the MDF and collapse one building’s network into

that MDF, allowing routing to take place back to the core network. All of these concepts

are easily transferable to private industry, so there is no reason why a properly

implemented solution in a K-12 networked environment could not be implemented

equally well in a corporate environment (and vice versa).

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