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[OT] Interesting Windows IP issue

From: ninurta2005 <ninurta2005-/E1597aS9LQAvxtiuMwx3w at>
To: Mark Komarinski <mkomarinski-GqRSzq0LZOzYtjvyW6yDsg at>
Sent: Sat, January 22, 2011 3:51:15 PM
Subject: Re: [OT] Interesting Windows IP issue

A rogue DHCP server crossed my mine too. It was odd that under Linux, it grabbed 
a IP address from the Lan-10 subnet, but under Windows, it went with a address 
from the subnet; I am guessing using the same Ethernet cable. As 
a rule, you can't have DHCP addresses issued from two different private address 
range subnets on the same ethernet cable via the same subnet. Since Cat5E was 
mentioned, I suspected that it wasn't getting a wireless IP. Laptops will have 
two ethernet connections, one for wireless and one for cabled Ethernet. 

Disable the wireless radio to be sure, it is only way to assure the host is 
receiving a wired DHCP request response.

If you have a testbed that is also using the Lan-10 Private range, attach the 
laptop to that network and see if the  problem follows the laptop. I created one 
using Openwall with DHCP enabled. Ditto for IPCOP and Smoothwall which works 
just as well.

Best of luck,

From: Mark Komarinski <mkomarinski-GqRSzq0LZOzYtjvyW6yDsg at>
To: discuss-mNDKBlG2WHs at
Sent: Sat, January 22, 2011 3:21:01 PM
Subject: Re: [OT] Interesting Windows IP issue

On 1/22/2011 10:30 AM, Jerry Feldman wrote:
> Yesterday at work, one of my coworkers wanted to make a presentation
> from his company laptop (Windows XP). For some reason his IP address was
> showing 192.168.x.x, not the internal company 10. address. I used my
> Ubuntu netbook to make sure the CAT5E cable was ok, and I certainly got
> a valid 10. address. We moved to another office because the lighting was
> better, and the same thing. We even rebooted his computer. Somehow it
> wanted to remain at 192.168. Our cables are plugged directly into a
> switch that plugs into our firewall. After a while we finally got the
> thing up and running on the corporate network. Note that I had even done
> a IPCONFIG /release and IPCONFIG /renew. I've seen this before on his
> previous laptop. Apparently he does something at home, but when I look
> at properties it shows DHCP.
Use  ipconfig /all to verify that a lease is actually getting assigned.  
If it is, you may have a rogue DHCP server on your hands.

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