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I've got a problem with my Internet modem. When I connect the modem directly to my computer and run a speed test, I got 15 mbps when it should be 25 mbps. I then set the LAN card to use "100BaseTX Full_Duplex", which increased the speed to 22 mbps, which is acceptable.

However, when I then put my Linksys WRT54G into the mix, so that the Internet goes to the modem, then my router, and then my desktop (all wired), then the speeds drop back down to 15 mbps, even though I still have "100BaseTX Full_Duplex" in use.

Do I have to enable 100 Full Duplex on the router somehow? If so, how do I do that?

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migrated from serverfault.com Sep 11 '10 at 22:57

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There typically is not the ability to do that with most stock SOHO NAT routers. You might check with see if your particular Linksys model can be updated to run the DD-WRT or Tomato firmware alternatives, but that may render the unit out of warranty or support from Linksys. It may also come down to the actual NAT router hardware being underpowered - which occurs pretty frequently too.

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The product is advertised as "There's also a built-in four-port full-duplex 10/100 switch to connect your wired-Ethernet devices." but that doesn't seem to be the case. Or, does this description mean something else, for some reason? –  Gary Sep 12 '10 at 16:40
    
I can confirm that DD-WRT firmware works on the WRT54G. –  myopic.bones Jul 27 '11 at 3:43
    
That is the case. The switch is capable of full-duplex under the appropriate conditions. The problem is, the software doesn't allow you to force full-duplex under these particular conditions, not that the switch isn't capable of full-duplex. Different firmware will allow you to force a port into full-duplex. –  David Schwartz Sep 16 '11 at 2:44

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