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Strange IP Addresses being picked up

Posted on 2012-03-16
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Last Modified: 2012-03-31
The last few days , a number of our desktops have acquired strange IP addresses , outside our range . They pick up an address in the range 192.168.11.xx . To reset I have to go into CMD and ipconfig /release then ipconfig/renew . Is there any way this can be prevented ?
All help gratefully received .

regards ,
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Question by:TomTierney
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by:John-Charles-Herzberg
ID: 37728832
Have you scanned you network for another DHCP server?

Thanks
JC
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by:IanTh
IanTh earned 500 total points
ID: 37728853
when it has a 192.168.11.x in the ipconfig get the gateway ip address as thats the device that has the dhcp  server role for 192.168.11.x when you have the gateway that may show you whats going on

as 192.168.x.x is a home ip range I bet somebody has put their home router with dhcp running onto your lan imho
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Author Comment

by:TomTierney
ID: 37728917
How can I fix it ??
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Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

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Expert Comment

by:John-Charles-Herzberg
ID: 37728929
This software might help.

DhcpExplorer allows you to discover DHCP servers on your local subnet or LAN

http://www.softpedia.com/get/Network-Tools/Network-IP-Scanner/DHCPExplorer.shtml
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by:John-Charles-Herzberg
ID: 37728933
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by:John-Charles-Herzberg
ID: 37729523
This video might help if you are OK with using linix to help find the DHCP server(s)

3hacks : Rogue DHCP Server Detection (dhcp_probe)

http://www.youtube.com/watch?v=bc1m4Npoyik

Thanks
JC
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Author Comment

by:TomTierney
ID: 37736984
Still got the problem . Downloaded DHcP explorer but that only shows our subnet . I viewed the video but didn't 'get it' . I can see no visible signs of a 'home' address so difficult to remove . I really am struggling with this one . Anyone ?
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by:IanTh
ID: 37737124
can yu ping the rogue ip addres I mean does it actually exist
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Author Comment

by:TomTierney
ID: 37737395
I tried pinging one of the addresses I have seen and it just timed out .... 192.168.11.11
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Author Comment

by:TomTierney
ID: 37737837
Our RAS server has an address of 192.168.11.14 ?? I don't recall this . Does this sound correct ?
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by:IanTh
ID: 37738198
whats your lan ip address range ? 10.0.0.x or someting
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Author Comment

by:TomTierney
ID: 37738339
192.168.16.x
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Accepted Solution

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TomTierney earned 0 total points
ID: 37747205
Hi , it appears that my problem was caused by a Buffalo router that we have deployed at one of our satellite sites . We spotted this on a tech forum and now , having disabled this equipment , normality has been restored .
Thanks for all the input .

regards ,
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Author Comment

by:TomTierney
ID: 37747435
I've requested that this question be closed as follows:

Accepted answer: 0 points for TomTierney's comment #37747205

for the following reason:

It appears to have done the trick . It would appear to be a common occurrence .<br /><br />regards ,
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by:IanTh
ID: 37747436
I would like to point to my second post where I stated

as 192.168.x.x is a home ip range I bet somebody has put their home router with dhcp running onto your lan imho

and your cooment

Hi , it appears that my problem was caused by a Buffalo router that we have deployed at one of our satellite sites . We spotted this on a tech forum and now , having disabled this equipment , normality has been restored

how is that different I stated it was another router and your fix is another router
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by:IanTh
ID: 37790865
thanks
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