Cisco Packet Tracer

Cisco Packet Tracer screenshots

Packet Tracer is a networking simulation software made by Cisco
Main Window
Cisco Packet Tracer 5.1 : Main Window

Alternative downloads

Bonjour Print Services for Windows
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Bonjour Printer Wizard lets you configure printers from your computer.
Colasoft Packet Player
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Open captured packet trace files and play them back in the network.
The Tracer beta 1 - build 1-30
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The Tracer shows information about single hops and geographical locations.