10mbps vs 100mbps

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Oct 5th, 2007
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All, I have a situation where some ports are statically set to 10mbps but communicates to devices on ports that are Auto Negotiate, but Operate at 100mbps.

With the Speed of packets being sent from each port, does this cause collisions because port 1 (running at 10mb) is send to Port 2 (running at 100) and visa versa?

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scottmac Fri, 10/05/2007 - 06:20
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The ports must operate at the same speed, or no traffic will pass in either direction.

Hopefully, the 100M ports set to "Auto" are downshifting their speed to match the 10M ports. This arrangement doesn't work sometimes because th eolder 10M ports do not respond, or do not respond properly because the do not understand the protocol.

It's usually best to force the 10/100 ports down to 10M, half duplex.

Ports with duplex mismatches will talk and get *some* traffic through (just with lots of collisions), ports that are not the same speed will not talk at all.

Good Luck


rwamstutz Fri, 10/05/2007 - 06:27
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thank you for your reply. I am not getting duplex mismatches on the switches.

The ports running 10/half mb are terminals and they are sending data to a server running 100/full mbps. There are also terminals running 100/full that send data to the server. Does the terminals running 10/half still cause problems?

Kevin Dorrell Fri, 10/05/2007 - 06:25
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With a switch, it does not matter if one port is running at 10 and another at 100. They do not interfere at all. The receiving port receives the complete frame at the rate appropriate to its connected host, stores it in the switch memory, and only once it has finished receiving it does it start to transmit it (from memory) on the outgoing port at the rate appropriate to its connected host.

Is that OK?

Kevin Dorrell



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