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I have a network with a router and a switch. At first my ISP's optical fiber is connected with media converter input port. Than Ethernet cable (output port of Media converter) is connected with the switch. Then an output Ethernet cable is connected with our inner Microtik router. Then this router is connected with another LAN switch. From this switch we have got every connection other switch. It is our total network structure.

Our bandwidth is 2 Mbps. From the 11th of March our MRTG graph shows high all the time even when my all switch is switched off except LAN switch. That's why our line is breaking up (Voice call).

How could be it possible? My all PC's bandwidth is limited but when connected PC with media converter directly then the graph shows normal. That's why I can't blame my ISP.

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Could you add an image from MRTG for the last month? – Ladadadada Mar 30 '12 at 17:06

Check the speed and duplex of all connections. Where possible, set the speed and duplex manually. While Auto/Auto should work in most cases, I have seem many cases where it does not. Some vendors even specify what shold be used. Our ISP insists on a specific speed and duplex as does our WAN accelerator vendor.

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+1 for setting speed/duplex manually. Horribly cheesy line to remember: when applicable, you "auto not" use auto-negotiation. (*cue comedic drum riff). – Mike B Mar 30 '12 at 17:41

I think you should check :

  1. Speed between 2 devices between the switch when you transfer files between them (that way you can see if the issue it's at the switch.
  2. If the speed is the same (2mbs) then check the router configuration if it limits the port speed .
  3. If you observe no real speed improvement then check cables connectors because somewhere you have a bottleneck .
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The short answer to your question is "yes". The most common way would be if one of its ports is connected to another one of its ports (either directly or through another switch) and spanning tree is not enabled. Under those conditions, it can receive a single packet and repeat it out all of its ports hundreds of times.

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