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What Happens If Two Computers Have the Same IP Address?

What happens if two computers have the same IP address?

An IP address uniquely identifies every computer on the internet.

The key word there is unique.

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If two computers on the same network have the same IP address … well, the results are unpredictable. It depends on how all the other equipment on the network handles the problem. In general it could be as bad as both machines not being able to communicate at all. More likely only one will not be able to, or perhaps there will simply be intermittent problems on both.

In short: don’t do it.

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72 comments on “What Happens If Two Computers Have the Same IP Address?”

  1. So, if both computers have the same ip adress, do they both have the same privacy, I mean can the other computer view the other computer’s privacy, cookies, cache and history too?
    Thankyou.

    Reply
      • It’s not a yes or no. The IP address has little to nothing to do with it. On the other hand if they’re on the same network, and have the same accounts, then it’s possible the second computer can see what’s on the hard disk of the first.

        Reply
  2. So, the other computer cannot view my history or privacy even if it is the same internet connection on both right? 🙂
    Thankyou

    Reply
  3. Two computers with same IP address IS POSSIBLE. Believe it or not; Right now I am working on my pc having same IP address as my friend’s in the same network (collission domain) & its not conflicting. He has an IBM NIC & I got realtek (We both have XP). What I’ve done is.. changed my MAC address to what my friend have & everything goes out smoothly.. just my bandwidth meter shows data transfer even when I am not using that when he is using too..

    Why this happens? >> on a collission domain, devices communicate with datalink layer, so they need MAC address (not the ip address). MY LAN is single collission domain on an /24 routable ip address network in class A; so it works fine for me. Experiment with other network scenarios & update this archive.

    For other answers like if you have same internet connection thingy… NO that’s not possible as such.

    Reply
  4. Hi,

    I’m a member of an internet and forum and was accidentally banned by the administrator. The problem occurred because the administrator, in attempting to ban an idle member, accidentally banned me too – because I have the exact same IP address as the other member. This is somewhat baffling to me. Is it possible? Should I be worried? What can I do to rectify the problem?

    Any information on why this might be the case, and what can be done would be received gratefully.

    Thank you.

    Reply
  5. You could both have the same IP address if you’re both behind the same router. Either in a home, a business, a school, some other provider, or if you both use certain ISPs (AOL, for example) that put everyone behind a proxy server.

    Reply
  6. I have got an Internet router and I have connected my computer and two laptops to the router. I was just wondering do all 3 of the computers have the same IP Address or will they all be different?

    Reply
  7. They will all have their own IP address on the local network you’ve created with your router, but will all share the same IP address out on the internet.

    Reply
  8. Thanks for your quick reply.

    My ISP is NTL and I am not part of a LAN. It’s my own PC and I’m the only person that uses it. The user that the administrator tried to ban I am not in contact with – I’ve no idea who she is; she posted once or twice and was idle for a good while. Yet I apparently have an identical IP address to her.

    I’ve checked my system for viruses and it’s clear. The duplicate IP addresses are still somewhat disconcerting though. Any other theories?

    Reply
  9. I have 3 computers in a network thru a router. All of my computers have their own IP address on the local network behind my router. Is there anyway I can have seperate ips for each computer for the web, without using a proxy server?

    Reply
  10. We’ve just encountered this problem – but when you have a large site and a lot of PCs how do you find the rogue machine? It seems intermittent (may be a portable PC or even a PDA) so don’t have much time to track it down… suggestions more than welcome!!

    Ian (UK)

    Reply
  11. Hi, I have a router with two computers, a laptop, and two xboxes hooked up together. 1 computer and a laptop are on wifi, and the rest are hard wired. when i have both of the xboxes on at the same time, i get the same ip address on both of them. when i try to change them using static ip, they don’t connect to the internet. i need help because this is very frustrating. thanks.

    Reply
  12. Hi, i have a wireless router for 2 pc. Each PC has own ip address. But when i create eMule in Virtual Server List, only 1 ip address allow to key the eMule port (TCP and UDP). What should i do?
    Thanks

    Reply
  13. hi, my mate and i want to play together on the same poker tables except when we try and sit down on the same table, we get the same message, ”you cannot sit down at this table because somebosy is already sat down with the same ip address as you” now, we live 3 miles apart, so how do we get around this strange problem, any ideas welcome, thanks

    Reply
  14. CAN TWO DIFFERENT COMPUTERS HAVE THE SAME IP ADDRESS.I HAVE RECIEVED HARASSING EMAILS AND THE IP ADDRESS FOR THESE MATCH MY FRIENDS IP ADDRESS. COULD THESE OR ARE THESE COMING FROM HER COMPUTER? I THINK THEY ARE!

    Reply
  15. Hey!
    I’m sitting on a very special modem (special in my country). It uses satellite power to download, but regular 56k-technology to upload.

    Don’t know if this makes any difference, but every other time i try to download something from rapidshare it says that im already downloading something from rapidshare-servers..

    The problem here is…IM NOT DOWNLOADING ANYTHING!

    There is only one computer in my house and it is mine, so why is it that someone can use my IP while I’m using it?

    Reply
  16. Hi, I have two computers running from the same broadband modem. One is connected wireless the other by a cable connection. Both machines connect fine together to the net. Their is NO NETWORKING connection between the two pc’s.
    My question is – is it possible for someone to use either pc out of the two and be able to track or ‘see’ where the other computer user has been???

    Also is it possible for the master pc user to ‘see’ or ‘divert’ email going to the 2nd pc?
    Both pc’s use the same log on name and password as they both have to connect to the same network but both the pcs work independently of each other with seperate email accounts – basically from this scenario is it possible for one user to hack or see what the other is doing via the other computer? And if so how far regarding this can they go?

    Reply
  17. —–BEGIN PGP SIGNED MESSAGE—–
    Hash: SHA1

    1) I’m not sure what you mean by “no networking connection” between the
    two. Obviously they are joinced to the same broadband modem, and that,
    therefore provides some type of physical networking connection between
    them. *Depending on the modem* it may be possible for either computer to
    see or “sniff” the network traffic happening on the other. This is the
    case if the modem acts as a simple hub. More commonly it does not,
    acting more like a router, in which case they should not see each
    other’s traffic.

    Unfortunately it’s not really all that easy to tell or confirm exactly
    hwo your modem is operating.

    2) It’s just as possible as with any computer elsewhere on the internet.
    Accounts do get hacked, but I don’t see anything here that makes it more
    likely because of your network setup, UNLESS the traffic can be sniffed,
    which depends on the answer to your first question. If the traffic can
    be sniffed, then absolutely the account could quite easily be hacked.

    Leo
    —–BEGIN PGP SIGNATURE—–
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    Zmia0HJe2BTfTHwxBoQn/bg=
    =eGLh
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    Reply
  18. Referring back to the 2 computers 1 ip address.
    I would like to elaborate on this.

    Two computers and one modem.
    Both computers connect to the same router modem.
    Both computers are usually connected at the same time. Can this situation be regarded, treated like or become a network situation like you would find in an office environment?

    Unlike an office both computers run independently from each other and only use the same router for internet access.
    Is it possible for one computer to ‘spy’ on the other computer when both are connected to the net?
    as if in a networking scenario?.

    Reply
  19. —–BEGIN PGP SIGNED MESSAGE—–
    Hash: SHA1

    It depends entirely on the functionality provided by that modem. If it’s
    acting like a full NAT router (which it might be), then I’d expect that
    to be very similar to a standard home network.

    Leo
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    qVEcQEjTywSbxk3NCF/YTUc=
    =HPl+
    —–END PGP SIGNATURE—–

    Reply
  20. Dear Leo,

    i just purchased a laptop. i connected a router to the other computer i have at home, and then networked the laptop to that. it worked for the first two days, but now it says that two computers on the network have the same IP. so now my laptop can’t connect to the internet.

    it also says a network cable is unpluggged ( but i checked and nothing is.) maybe its caused by the IP conflict? please help.

    Reply
  21. Hi,

    One of my computers IP address matches with another IP address of a bad website in a different location?

    Why is that? Is someone misusing my IP address?

    Reply
  22. I have a little different scenario …
    We have a Novell network here ..
    and tonight for the 1st time ever we had a duplicate IP address issue ..
    What happened is our main server … say FS1 was stating that some one else on our network had the same static IP address as it (FS1) did ..
    The big problem was it was the router for our Internet/Phones/Email …etc …
    and all access to these apps died with this issue.
    Question is … does someone with the same IP address as a server (say) steal that IP address when they insert into the network ?? (ie Last 1 gets the address ..) ??
    Cause it caused our server to loose access to the Ip functionality .. and so drop all incoming access to it ..
    We did find the culprit, but were down for 2hrs doing so …
    When we turned the offending station off … everything came back to life again ..

    thx paul j.

    Reply
  23. I know nothing about computers, But a couple of days ago, a window popped up on my computer while no programs were running. I wouldn’t up the internet because it said that someone has the same IP address as I. Does that mean someone is hacking my computer?

    Reply
  24. I am really confused, i have been banned from an online game because I am suppose to have made an account on this IP address, But until 2 week ago I had NEVER been on the site before. I have checked the locotion of my Ip adress and it says i am somewhere on the other side of the country! How can this happern? And is there anyway of sorting this problem out? Would this also be the reason why my internet doesnt connect properly sometimes? It would be great If you could help, because is causing some problems.

    Reply
  25. hi leo
    I have 2 laptops using the samke router.
    My children has there own with password and username.
    Is it possible to see what they are up to.
    Just a bit worried but I dont want to intrude

    Reply
  26. Hi Leo,
    I have one internet connection on a home computer. I unconnect and reconnect to a laptop and perform internet searches. I reconnect my home computer.
    Can the laptop search history affect my home computer use in any way?

    Not that I can think of.
    -Leo

    Reply
  27. Hi Leao,
    I just want to know what happens if I register two cable Modems(Motorola SURFboard SB5120) on the same computer? Since I already have one registered(for the computer), is it possible to register the other one(for my xbox) using the same computer without affecting the first one??

    Reply
  28. hey i need help with sumthin. if me n my brother have the same ip address can he see what im doing. like say im on aim n he see the messages im sending n the messages im recieving???PLZ HELP ty

    Reply
  29. I’m trying to play video games on my two computers.
    one is connected straight to the internet the other is accessing it via wifi to the router next to my upstairs computer. but it says that they both have the same ip address and due to this any game that involves entering the other IP address to play is useless.
    please help me!!!

    Reply
  30. hi, we have recently got a new modem for our home computer, i used to be able to connect up to the internet from my laptop wireless. but now i cant, my laptop says limted or no connectivity and the home computer says 2 have the same ip address whats happened?
    Thaanks.

    Reply
  31. I am trying to run a server for a game on my computer but the problem is that everyone in my neighborhood has the same IP because of how the network is set up, is there any way to get around this without having to use programs like Log Me In – Hamachi

    Reply
  32. LEO, my computer keeps saying that it has the same ip address as something else, i have an xbox up stairs and i use the ip address of the computer downstairs, i also have a labtop up stairs and i get internet from my neighbor. so do you think that my xbox is ruining it or my labtop, or something else? i need help

    Reply
  33. am i to understand that if i two seperate emails come from two seperate people in two seperate towns yet both emails have the same ip addresses, that i am actually being fooled by one single person? i had my suspicions due to the wording being far to similar, so i checked the ip addresses and turns out they are the same. what if the mails are being sent via a mobile phone isp?

    Reply
  34. Hi Leo

    My Home network and my work network computers, have the same IP addresses.I want to remote to my work network with my laptop that is networked at home.

    Do I have to manually change the IP addresses at home? If I do, do I also change the router stetting?

    thank you
    Claude

    Reply
  35. Call me crazy, but i got this warning message after being away from home all day and I only left one computer turned on that was connected to my router. Have you ever heard of this warning coming up falsely in XP Pro? My only other explanation is that someone plugged in a computer to my router while I was gone :'(

    Reply
  36. I got a laptop and sharing wirless with someone else in the house, it was working fine until yestersday when it was telling me that i have the same ip address as another computer and now my internet wont work .. why is this

    Reply
  37. hi leo can u help me i am using modem dailup someone use same my computer ip and blackmaling peoples how that happen and how i trace him ? can u help me

    Reply
  38. “What happens if two computers have the same IP address?”: I read this article- something similar has happened to me. There are 2 computers on my network, mine and my neighbours’. Is it possible for my neighbour to access my internet history/passwords and files that I have stored on the internet? Thanks, Jack.

    If you don’t have proper security set up, such as a firewall and keeping your machine up to date, of course. But it has nothing to do with IP addressing, duplicates or otherwise.

    – Leo
    08-Jul-2009

    Reply
  39. Leo:

    I need to create multiple IP addresses. Do I need separate computers, separate connections to the internet, or just unique e-mail addresses from separate e-mail servers??? Help me out! Thanks.

    Reply
  40. Hi Leo, I’ve had a linksys wireless router for 3 years, running 3 wireless pcs & a wireless printer. About 3 weeks ago, my internet stopped. I contacted Comcast & did all their checks. Finally, I connected a cable from the model to one PC & got the Internet. I was referred to Linksys & paid for 6 troublecalls. They ran me through configuring the router & it worked. A week later, it stopped. I again called Linksys & they said to get a newer one. I paid $200 for the latest N. Same exact problem kept happening, called Linksys & went through the reconfiguring again. It worked for a day and then same thing happened so I returned it, hooked up the old one and it worked again. Next day it stopped so I cabled all but the MAC, as it is near the sofa. Today, cabled, no Internet. Checked modem & reset it, then cabled it to my laptop and can now get out to write this. However, before I cabled it, it had that message about 2 having the same IP address which doesn’t make sense as the router gives each a different end number (.2.3 etc). Any ideas? Thank you 🙂

    Reply
  41. I have the same problem but mine is odd, i have a laptop with vista and a desktop with XP their internal IP is diff by 2 digits and the IP Adress is the same, i re-installed the OS on my laptop and its still the same IP, What gives??

    Reply
  42. on each computer the ip ad is the same but on mcafee network map they are different, i do not understand? can you help please

    Reply
  43. I got a problem recently. I was reconfiguring my office network and discovered that at least 2 of the computers on my lan network have the same IP address. I need to change it so that I dont have this problem. Any suggestions?

    Reply
  44. I just moved back home and my ip address is now the same as the home computers. How do I change this, or do I even need too??

    Reply
  45. one of my friends been tracking an account n the user has same ip address as me how is tht possilble n he swares tht account is mine

    Reply
  46. I go on pokerunderground and when i try to do two profiles, its says,must have unique ip,can i have more than one ip from one moderm i have a router, what do i do to have two different ips

    Reply
  47. Hi.

    I recently moved in to a new apartment. Used my laptop the first days and internet worked fine. Static ip controlled by the landlord. Now when I have bought a second computer, the second computer only have restricted access, and no internet. My laptop still does. Don’t have a router. What to do? Please help.

    Reply
  48. Ok this is the question that I have. If I have two of my computers cabled together correctly and they both have the same IP address, will they beable to communicate with each other? They are both run VISTA OS. The reason for this question is my brother is taking IT training and I am in courses in OJC in LaJunta Colorado, are argueing this point and nothing is getting done with our network that we are setting up. He wants to do it that way and I said that it will not work with both useing the same IP addresses.

    Reply
  49. Hi,
    I was found my pc and another pc of my network the same ip 188.XX.XX.XXX. now what i should do to cahnge this? pls reply me as soon. Tnx

    Reply
  50. hi,

    l got a network error, it says there is another pc with the same IP address as mine. My internet connection is wifi but i am not using a router we have our own modem. what should i do?

    Reply
  51. Can two computers that share the same IP Address also download and share the same software without having to pay for the subscription twice? If so, how do we do that?

    Reply
  52. I am new to this and I think I have found the IP address, can 4 people have the same IP address?…what if the use the same pc?…1 email is from rocketmail and another from yahoo but the Ip #’s are the same….what does that mean?

    The same IP address can appear if a) they were all using the same computer, b) they were all using computers behind the same router, or c) it’s a dynamic IP address that happened to be assigned to each at different times.

    Leo
    29-Nov-2010

    Reply
  53. If someone on my network has my IP address on their machine, will they intercept my internet traffic? Will they be able to access and control my computer? How can I prevent this from happening?

    Reply
  54. If it says that a family member’s computer and my laptop share the same ip address and it is restricting my family members action on there pc how do we fix this?

    Reply
  55. @Paris
    Sounds like it might be a problem with your router which is giving the same internal IP to 2 computers. You might want to try resetting or unplugging your router and see if this solves the problem.

    Reply
  56. I had an error message come up earlier that said another device on the network had the same IP address, and that I should contact the network administrator. Is this just because, being a home network, there are 3 computers on the network, or is it something I should be worried about?

    Reply
  57. both of my computers on the same network have the same ip address. i have an airport extreme, a macbook pro and a dell w/xp.

    How do I get them to have separate ip addresses so i can utilize remote desktop?

    Reply
  58. can 2 computers have the same ip address, i m having a problem where sumone is using ma IP address and trying to play tricks with me……..need urgent help……

    I’d recommend re-reading the article you just commented on. It addresses your question.

    Leo
    01-Nov-2011

    Reply
  59. We have our router and modem connected to my desktop which I only use a hour or so a day if then. The rest of the time I use my laptop. My daughter and son in law all have laptops also. We haven’t had any problem until recently when my daughter bought a new lap top and gave her old one to my grandson (here in the same house). At the same time she bought him a Xboc Kennect. Now if I am using my desktop everyone else has a problem getting internet on their computers. We have to reset the modem and router, turn off my desk top and then reboot our laptops computers. The notice that comes up says it can’t find the iP address. Is there a way to fix this so we can all use the laptops and I can still sign on to my desktop if I need to without making everyone else go offline?

    Reply
  60. @Tom – I remember in my university days we were alloted download quotas and to bypass once we reached out quotas we scanned for MAC addresses cloned them on our pc and used up the other person’s quota. using this method the DHCP would think we are the same device and say “did’nt i give you 192.168.x.x ip” and our machines would say “*shrug* I guess so we must’ve forgotten cani use it now?”DHCP”Sure” a few minutes later “IP conflict exists on this network please fix the problem”. Now i am not saying that there might be someone cloning your MAC but for some types of wireless and wired networks it is possible to compromise them by this method. Also this method is used by some malware, though it is pretty rare to find.

    @WM ensure your device is set to allow a whole range of devices it might be that your device has a range of only two ip addresses which it is trying to share between itself and two devices.

    @Nancy your problem might also be the number of devices that can be assigned an address and time of expiry. so what i can see happening is that your router has 10 addresses to share and you desktop being wired gets one for sure. the other devices get their ip’s expired and try to renew but the DHCP is unable to resolve this problem. you reboot the router the previous cache is cleared and the problem is temporarily resolved. Please ensure your router has enough addresses to assign usually under web management DHCP options you will find a range that is allowable for your router.

    Reply
  61. yes we have two same IPAddress on two computer only if both computer is not connected through any router or connected within the local area network.
    it so, they are in connected through router then
    how client will came to know that what is the
    remote end point and from where the data comes from and we get unpedictable output.

    Reply
  62. what is the difference between a workgroup and a domain?
    And also the difference between a peer to peer network and a domain network?

    Reply

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