IP Conflict

1,025 pts.
Tags:
DHCP
IP addressing
Microsoft Windows
Networking
Windows 2000 Server
Hello all; I am having a problem with a small network that I need help with, this has happened a few times now where two laptops receive the same IP address from my DHCP server, and it is always the same 2 laptops, I was able to fix this momentarily by excluding the IP address that was in question then both laptops received a different IP but then after a week the same problem occurred, I don't why this keeps occurring with the same 2 laptops it makes no sense to me. I now have 3 IP addresses excluded from my range because of this problem, the list will eventually get too big unless I fix the problem. Thanks in advance for your help, if you need any further info please let me know. CG._
ASKED: January 16, 2008  10:16 PM
UPDATED: January 28, 2008  7:24 PM

Answer Wiki

Thanks. We'll let you know when a new response is added.

Is it possible the two laptop have the Same MAC address? From Windows, do a “Start-Run” and enter “CMD”. At a command line on each laptop do an “ipconfig /a”. Under Physical Address, it will tell you the mac address of the Network Interface card along with your current IP address and other network setting. The MAC address on both laptops should NOT be the same. You can also do an “ipconfig /release” to dump the IP address and then a “ipconfig /renew” to get a new IP address.
If thats not it, you may want to set factory defaults on the DSL/cable modem your using as a DHCP server. Maybe that will correct the problem. Be sure to always write down your current settings before defaulting any device. Make sure you know any needed passwords as well. Hope you get it figured out.
Randy

**Buddy**
the above should be right but if the MAC addresses are different then check to see if the SID on each machine is different. were these machines imaged from the same image? if so they will have the same SID until you run newsid to randomly create a new SID for them.
**/Buddy**

Discuss This Question: 6  Replies

 
There was an error processing your information. Please try again later.
Thanks. We'll let you know when a new response is added.
Send me notifications when members answer or reply to this question.

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
  • ChazBrown
    Firstly, it is impossibole for two devices to have the same MAC address as it is assigned by the manufacturer and is not 'configurable' by the end user. Secondly, it is 'supposedly' impossible for a DHCP server to assign two like IPs on the same network. I am unsure of exactly what to check and my head is 'spinning' at the possibility. However, one easy way around this, especially on a small network, is to simply use static IPs. As you are the one assigning them, it would stand to reason that they would never conflict. The first thing I would check in this case is the network set up. You have a configuration issue somewhere. I am guessing that one of the laptops has a different domain setting or something. I have no idea how the DHCP server could assign 2 like IPs at the same time otherwise. HTH Owen
    110 pointsBadges:
    report
  • Tbitner
    Try putting a PCMCIA nic in one of the laptops and see if it fixes the problem. Use that one as your primary and disable the other one.
    510 pointsBadges:
    report
  • Squashjunkie
    There is the possibility of nic cards having the same mac address, but this will have been changed by someone after the laptops have left the manufacturers. You can check the mac address by typing "ipconfig /all" in a dos box, and make sure they are not duplicate. If they are, get the following tool which is a freeware app allowing you to change the mac address of either of the two machines. Importantly though, check the DHCP configuration on your server / router. Making sure both the reservation time in the DHCP configuration and that ip's are not being "released" from the client ahead of time (this can happen when there are drift between the clocks of the server and client) should make sure the problem doesn't re-occur.
    report
  • Squashjunkie
    Made a hash of my post, so here it is again...... :) There is the possibility of nic cards having the same mac address, but this will have been changed by someone after the laptops have left the manufacturers. You can check the mac address by typing “ipconfig /all” in a dos box, and make sure they are not duplicate. If they are, get the following tool http://tmac.technitium.com/tmac/index.html which is a freeware app allowing you to change the mac address of either of the two machines. Importantly though, check the DHCP configuration on your server / router. Making sure both the reservation time in the DHCP configuration and that ip’s are not being “released” from the client ahead of time (this can happen when there are drift between the clocks of the server and client) should make sure the problem doesn’t re-occur.
    325 pointsBadges:
    report
  • CGarcia26C
    Thank you guys for your help, the problem was actually that the dchp database was corrupted and therefore giving out the same ip to different computers, after reconciling the dchp database and then verifying it, the problem was solved, and just fo fun I added some reservations to the scope just to make sure that does not happen again. Thank you all again for your input. CG._
    1,025 pointsBadges:
    report
  • CGarcia26C
    amazing stuff thanx :)
    0 pointsBadges:
    report

Forgot Password

No problem! Submit your e-mail address below. We'll send you an e-mail containing your password.

Your password has been sent to:

To follow this tag...

There was an error processing your information. Please try again later.

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Thanks! We'll email you when relevant content is added and updated.

Following