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My internet speed dropped from aobut 90Mb/s to 0.5-2Mb/s. Only one computer seemed affected.

So I was been looking through the device list on my Linkysys Smart Wi-Fi router and came across something unusual. The same computer is connected three times with different MAC addresses. I tried blocking the MAC addresses that did not match the ipconfig MAC and that resulted each time in the computer being unable to use the internet at all.

I've never seen this before and am dumbfounded. Please help.

migrated from serverfault.com Oct 15 '14 at 4:09

This question came from our site for system and network administrators.

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    How do you know it's the same computer? – David Schwartz Oct 15 '14 at 4:33
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    Definitely look for other devices using your IP address. Duplicate address issues will cause this type of problem. – cpt_fink Oct 15 '14 at 5:47
  • have same issue. Second unknown device in home network mimicking my computer name, but different MAC. Once I renamed my computer, that other device in network also renamed. I suspect some virtualization software on my computer, but it didn't go away even after removing all virtualization services. Did you figure out what was causing it? – Philipp Munin Jun 14 '17 at 21:06
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If you use LAN or WLAN for the computer, there will be two MAC addresses used. Although it is very unlikely to cause poor performance into internet, you can restart the router so that it will forget all MAC addresses.

  • The two mac addresses would have unique IP addresses. – cpt_fink Oct 15 '14 at 5:46
  • These two IP addresses will be linked to the same host name. – user3767013 Oct 15 '14 at 16:54
  • @user3767013: which is irrelevant. 2 devices, 2 mac addresses, 2 ip addresses. the problem pops up when you have the same ip address bound to different mac-addresses or different nic's with the same mac-address. routers/switchers will have a hard time to deliver the packets. – akira Oct 15 '14 at 19:34

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