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What happens if two computers have the same IP address?

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Summary: Two computers should never have the same IP address if they're on the same network. If they do, results are unpredictable.

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.

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.

Related:

Article C2262 - January 18, 2005

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Recent Comments
45 Comments

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?

Posted by: gabi at December 13, 2008 1:51 PM

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

Posted by: Claude Piccini at January 6, 2009 1:44 AM

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 :'(

Posted by: JBourne at January 7, 2009 6:45 PM

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

Posted by: louise at January 27, 2009 2:57 PM

if two systems have same IP address than congestion can occur on the network,slows down the data rate nd speed.

Posted by: aman at March 10, 2009 9:21 AM

How to find that two pc's using the same ip address.

Posted by: ATTAR at April 2, 2009 10:14 PM

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

Posted by: nikamma at May 17, 2009 3:14 AM

"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

Posted by: Jack at July 7, 2009 8:58 AM

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.

Posted by: Scott at August 4, 2009 9:23 PM

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 :)

Posted by: Kris Bolbat at October 2, 2009 10:13 AM

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