IP address conflict on network when laptop tries to connect to it

  1. I set up a MAC address access list a couple of weeks back on my Wireless Internet Network and when I try to connect my laptop to it an Error message appears saying that:

    Network Error
    Windows has detected an IP address conflict

    Another computer on this network (i.e. this computer) has the same IP address as this computer (i.e. the laptop). Contact your network administrator for help resolving this issue. More details are available in the Windows System event Log.

    The laptop connects but it can't access that Internet. Please help. By the way the MAC address list does include the Laptop's MAC.

    Thanks for your help.
  2. Rick

    Rick TechSpot Staff Posts: 6,304   +52 Staff Member

    I don't know your skill level with networking, but forgive me in advance if I go over the super obvious to you.

    Things you should know:

    - DHCP - The protocol used by your router to give your devices automatic IP addresses.
    - Static IP - IP addresses assigned to certain devices that never change


    You could mean two things regarding "MAC address access list"

    1.) MAC address filtering - Only computers with certain MACs are allowed to connect to your network. All unidentified MACs not on that list are denied access to your network.

    2.) DHCP IP reservation - Certain IP addresses are reserved for particular MAC address. For example, 00:11:22:33:44 will always be 192.168.0.100


    Assuming you are using MAC address filtering (#1), there are two possibilities that I see...

    A.) The MAC address for your laptop is incorrect, disabled or not working as intended for some reason. Causes include a typo, using your *wired* network card MAC address instead of your wireless network card MAC address, a router firmware bug (not working as intended) or that MAC address is somehow not whitelisted (read: disabled or not enabled).

    B.) Your laptop's IP address has been manually set on the computer as a static IP which always stays the same.


    If you are actually using MAC addresses to assign static IPs through DHCP (#2), then consider these things...

    A.) You have assigned two different MACs the same IP address in your router configuration

    B.) You have mistakenly assigned a static IP to your laptop's MAC which was already in use by another device.. perhaps already given out by DHCP or even assigned manually on the device itself. In this case, make sure each IP reservation is unique.

    C.) You have used MAC-based DHCP reservation to assign a static IP to your laptop's MAC address... which falls within the router's DHCP range. Example: 00:11:22:33:44 has been assigned an address of 192.168.0.100. A badly designed router may allow you to also have it configured in such a way that it gives out IP addresses starting at 192.168.0.100 via DHCP. Due to numerous reasons, it is possible that 192.168.0.100 was given to another device before you connected with your laptop, ultimately causing an IP conflict. Restarting your router, updating the firmware or changing the the DHCP range so they do not overlap could fix this problem.

    D.) Your laptop's IP address has been set as a static IP on the laptop itself, in which case it ignores the information it gets from the router in regards to what IPs are in use. Make sure your laptop is set to lease an automatic DHCP address.



    Some more information could be valuable here -- What brand/model of router do you have? What's your current IP address? Is it DHCP or static? How many other computers do you have on your network? Are you connecting wirelessly or using a cable? When did this start happening? Did it ever work properly? Have you tried any troubleshooting steps like ipconfig /release, restarting equipment etc..?

    The more info you can provide, the more likely it is we'll be able to narrow down your issue. :)
  3. secretassasin69

    secretassasin69 Newcomer, in training Topic Starter Posts: 80

    Thank you so much

    I am using MAC address filtering and the list consists 4 addresses, a printer, a PSP, the laptop and my desktop. I was trying to make my Router have a Static IP address but I couldn't find out how to do it. When i Set up the MAC address filtering list the laptop was connected to the router and it gave me the pc name and MAC address, so i don't think that it's a typo.

    Furthermore which method is safer DHCP Reservation or Static IP against use by others who shouldn't use it. I also have a question that If i change the TCP/IPv4 to use one IP that I've assigned does that make it fully static. and am i right in saying that having static IP's that are different would mean no conflicts between them. But when i tried this it said I have changed the IPv4's on my desktop and laptop to different addresses.
  4. robin_bga

    robin_bga Newcomer, in training Posts: 258

    Hello,
    All i think could be your problems is that you have some device that has an IP so all have to do is to make sure that now machine accept the printer should have any IP address statically/manually assigned.
    That means that you will have to go to you LAN settings of you router and set it up to give IPs using DHCP Server option.
    Hope that helps...
  5. secretassasin69

    secretassasin69 Newcomer, in training Topic Starter Posts: 80

    Thanks Rick I have finally managed to fix this problem turned out that all I had to do was change the two computer's IP's to different ones and it now works
    Thanks again
  6. Rick

    Rick TechSpot Staff Posts: 6,304   +52 Staff Member

    Glad you figured it out. :)
  7. jobeard

    jobeard TS Ambassador Posts: 13,026   +221

    when using Mac filtering with address reservations,
    make sure that the DHCP range will assign a limited range
    (say 100-110) and the MAC addresses do not fall within that range
    (say 10-20, or 120-140)


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