Ethernet Networking

Ethernet Networking in a Nutshell:

First, we have to understand how Ethernet works. For a nicely summarized history as well as an explanation of the type of media it can run on, you can click here.

Assuming everything is on the same network....... When a computer wants to talk to another computer on your network it 'listens' to see if there is any other traffic on the wire it is attached to. If it detects that it is all clear, it will send its traffic. Sometimes (and the likelihood increases the more computers you have on your network and the more heavily it is used) two hosts will send their data at the same time. When this happens, a collision occurs. When a collision is detected, a timer starts on each of the hosts which must expire before it will attempt to send traffic again. Meanwhile, while this is happening, the user staring at the monitor is busy complaining about how slow the network is.

Now, when host 'A' tries to access a resource from host 'B' for the first time it will send a broadcast to every host on the network asking for host 'B' to tell it where it is at. All the rest of the hosts on the network will receive this broadcast, look at the request, and decide "He's not talking to me" and purge the request from its NIC memory buffer. Host 'B', however, will say "Oh, that's me!" and respond with it's MAC address. Host 'A' will then write that address into its address resolution protocol (ARP) cache, and from that point on when 'A' wants to talk to 'B', it will attempt to talk directly to 'B' by using its MAC address. If all your hosts are attached to hubs, you begin to run into a problem. Why? Because a hub broadcasts all information that it receives in a port (that's a physical port on the device, not the...

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...nnected through four repeaters, or concentrators, and only three of the five segments may contain user connections.

The Ethernet protocol requires that a signal sent out over the LAN reach every part of the network within a specified length of time. The 5-4-3 rule ensures this. Each repeater that a signal goes through adds a small amount of time to the process, so the rule is designed to minimize transmission times of the signals.

The 5-4-3 rule -- which was created when Ethernet, 10Base5, and 10Base2 were the only types of Ethernet network available -- only applies to shared-access Ethernet backbones. A switched Ethernet network should be exempt from the 5-4-3 rule because each switch has a buffer to temporarily store data and all nodes can access a switched Ethernet LAN simultaneously.

Hopefully this information will assist in starting your networks correctly.