Ethernet Interfaces
Almost every Cisco router has one or more Ethernet interfaces. Ethernet is a broadcast medium. Many devices can be attached to a single Ethernet network, and information transmitted by a host is broadcast across the entire Ethernet network. Almost all modern office networks are Ethernet.
Theoretically, every host on an Ethernet network sees all data transmitted by every host on that Ethernet. Switches direct transmissions to only the target system whenever possible. Even a top-of-the-line switch still sends some traffic to all the hosts on the network. If you're having trouble with your local Ethernet, a bad switch or a bad cable is the most common cause. (If you're still using a hub, that's almost certainly the problem. Please ...
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