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Problem when I reboot one of the computers on our network, the other computers drop their Internet connection for a couple of minutes!

Posted on 2012-04-08
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Last Modified: 2012-04-14
Hi guys, hoping you can assist with this we are problem we are having.

We are running a standard network with a D-Link router, which has DHCP disabled.  We don't have a server.  We have set up static IP addresses on all of our machines.

When we reboot one of the desktops ( could be either of them - there are 3 on the network ); the other 2 desktops drop their network connection!

Configuration is:

10.1.1.xxx IP addresses
255.255.255.0 - subnet
Router - 10.1.1.1

DNS - Have tried both options, being the router to distribute the DNS, or Google's 8.8.8.8

Would appreciate any thoughts and support you could give!

Please see below for some screen grabs of the network connection on 1 machine; thanks in advance for someone's assistance!

Screen Shot 1
Screen Shot 2
Screen Shot 3
Screen Shot 4
Screen Shot 5
Screen Shot 61.jpg
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Question by:troy_g
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by:Anuroopsundd
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can you try nslookup on the machine
and see if it connects to the dns server. if it does does it provide response for the queries

below is what you have to do in command prompt

nslookp

yahoo.com
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Author Comment

by:troy_g
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thanks Anuroopsundd, yes, it did provide the following response:

nslookup results
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by:Anuroopsundd
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ok. that means you are able to properly resolve the DNS.
in browser just put http://72.30.38.140/ and see if it opens yahoo.com
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by:Anuroopsundd
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also on the client machine try below commands. to check if the traffic is going out

tracert yahoo.com
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Author Comment

by:troy_g
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thanks, confirming :

http://72.30.38.140/

resolved ok to yahoo.com

sorry for the delay in responding this now, as would you believe that it just happened again!

Can clarify as well, that have all 3 desktops connected via the one switch / hub at the moment, whereas previously one of the desktops was cabled differently.

and below is the successful tracert from client machine :tracert from client machine
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Expert Comment

by:Anuroopsundd
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Ok... so you mean it does not happen always.. and only sometimes the internet is effected when you shutdown one of the machine..

am i right?
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Author Comment

by:troy_g
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good question, sorry for not clarifying, but yes, i am pretty sure that every time one of these machines get shutdown ( and the problem only arises when it reboots Windows and connects to the network ) that yes, we get this annoying issue!
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by:Anuroopsundd
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OK.. so this can be due to some virus or application on those machine which are doing arp spoffing on your network.
 so ones those machine are up than all the traffic is being going through that machine..

to check you can run arp -a on the client machine and see what mac addresses it has for default gateway...

if  it getting arp spoffing then you may see wrong gateway mac address or 2 mac address for your gateway ip....
switch of the problematic machine and then again check the client with the above command.
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Author Comment

by:troy_g
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thanks, have done, please see below for screenshot.

Also, clarifying that the problem isn't actually just with the Internet, it actually appears to drop the whole network connection, as my NAS becomes unreachable during the period when it is off.  It is so weird, as it then takes a minute or two to come back on and then everything works again!

arp -a screenshots...
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Assisted Solution

by:Anuroopsundd
Anuroopsundd earned 250 total points
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right now is everything working fine?
 check the machine with antivirus and antispyware first which when booted up makes the problem
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Accepted Solution

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TimotiSt earned 250 total points
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That "deterministic network enhancer" on the first screenshot looks like a possible culprit to me...
According to the Citrix docs, it can cause some problems:
http://www.citrix.com/lang/English/lp/lp_1680845.asp

Tamas
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Author Closing Comment

by:troy_g
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thanks so much guys, worked a treat!  Troy
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