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witching and virtual networking became the Holy Grail of man-

ufacturers and customers alike in the 1990s. High-speed, low-latency bridging at
Layer 2 provided the first inducement for administrators to purchase and install
switches. By the late 1990s, switches were no longer restricted to Layer 2, and
route- and port-based switching at Layers 3 and 4 were becoming commonplace.

Switching provides many significant advantages, including greater aggregate

bandwidth at lower cost and collision (full-duplex) control. The downside
frequently includes a forklift upgrade in the wiring closet and slightly modified
troubleshooting procedures. For example, it is not possible to simply plug a pro-
tocol analyzer into a port and see all traffic on the segment.

The Cisco Catalyst product line includes Ethernet, FDDI, Token Ring, and

ATM switching. Although this section focuses primarily on the Catalyst 5000
product line, other Catalyst products are capable of additional functions,
including voice switching and Layer 3 processing.

Switches, Bridges, and Hubs

n understanding of switches and their functions requires an under-

standing of the differences between broadcast and collision domains.

The

broadcast domain

defines the scope of broadcasts within the network.

Usually, this is equal to the diameter of the subnet because most upper-layer
protocols rely on broadcasts to function. As such, the broadcast domain is
usually controlled by routers.

Collision domains

are defined by the scope of impact that a collision may

have. With hubs, this scope is equal to all stations connected to the shared
media; as the number of nodes and traffic load increases, collisions become
a more significant problem for administrators and designers. Switches
reduce this scope to two: the switch port and the end node. By using full-
duplex Ethernet, which is an option available on most switches and newer
NICs, collisions are no longer a factor.

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