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My LAN is really slow

markflexman asked

We have a 10 user network that for the last few weeks has been really slow, not all the time, but most of it. The first sign was slow internet, but if we disconnected the LAN and plugged a laptop straight into the router it worked fine. We have a Draytek router so we enabled syslog, this did not show anything obvious - it seems that the problem causing the slowness is within the lan - ie the traffic never gets to the router.
We replaced the switches, had no effect.

We have run Wireshark to try and see what is happening on the LAN - but again nothing obvious.

Any other tools/tricks anyone can suggest?

Watch Question

How does your laptopconnect to the LAN?  Wired or wireless?

You could try disconnecting all but one of the machines on the LAN - is it still slow?  If so disconnect that machine and plug in another one.  

Do this for all of the machines.  If they all seem fine plug a second one in and test again.  Do this until all of the machines are plugged in or you identify the machine that is causing the slowdown.

Or if it is wireless consider other sources of interference.  Any new kit bought recently that may be affecting the signal?  Have you moved the AP?  Or built a new wall?  That last one is pretty unlikely I'll grant you... :)

Of course it may be that someone has set up a new wireless network near you that is interfereing with yours.  Have you noticed any new wireless networks?  (there are analyzers available if required)


Thanks for the response, the connections are all wired.

I have tried turning the machines on/off one at a time, but there is no consistency, i can have all the machines on and it runs fine for a couple of hours and then nose dives
Lavi ShiffmanConsultant

Run iperf between pairs of machines.  This is going to take some time, but will show you if the paths between the machines is working as expected and if you get the expected bandwidth.


r u using Switches, i hope there isnt loop in your network, if u sure that switch and lan cables r fine,
then you have to look up on the systems on lan for viruses, there might be trojans or any other viruses which broadcast in your network , uses ur bandwidths , slows down, and even can turn ur internet down since the router is not capable of holding that much request and when u restart that it will be fine for some time,

check all the systems and make sure your lan is virus free,


I think it is solved; i noticed that the internet problem was way worse when machines were accessing the 'server' actually a win 7 machine with raid 1, so not running dhcp, dns etc, i tried changing the name of the server and the internet problem went away, but access to the server was still slow - we updated the nic driver and all is fine now.

I understand why the nic change helped the lan, but why the server name change helped the internet, i have no idea!