IP address conflict

[Evilization]

Hey guys
im using windows 7 and i just got a message that there is an IP address conflict with another system on the network. Im in a house where all PCs are connected to 1 router.

Anyway, im still able to connect to the internet and all. What problems does this cause anyway? Can i just ignore it?

[Qicmee]

Maybe could ignore it... Sometimes this problem goes away on it's own because the IP gets reassigned in due course. Other times, the PC with duplicate IP address cannot connect to the network.

Here's some good info and 4 basic fixes to try if needed:
How to fix an IP address conflict

That source includes a link to this info:
Change IP address and DNS servers using the command prompt

Good luck!

[Evilization]

thanks qicmee
let me get this straight though, as long as I can connect to the internet, that means the problem has gone away right?
if the problem is still here, I wouldnt be able to connect to the internet, right?

also, when ppl say "connecting to the network", is it the same as "connecting to the internet"?

[Qicmee]

If the error message goes away and never comes back, it fixed itself. Life is good. Move on.

If the error message comes back, then it's worth trying to find the cause.

"Network" refers to your side of the firewall (inside the house). "Internet" refers to the other side of the firewall. This hardware boundary is usually your router that connects to the cable or DSL line. Networks & the Internet use similar IP address formats, but our house network addresses aren't used on the Internet.

[mapes]

A quick note here. You prolly have a router with a DHCP server enabled. Is it possible that you rebooted your router? You see when hosts are configed for DHCP when they boot they send out a packet on the local lan. The DHCP server listens for these packets. When the router gets such a request it will look up in a table what IP's are free to hand out to a system. So it's most likely possible that system A booted up and got assigned an IP. Then you rebooted the router wiping it's state info on what computer has what IP. Then you booted system B. Which booted up and requested an IP. The router not knowing better dishes out the same IP as system A.

Usually the DHCP servers are smart and try to mitigate this by pinging the IP before handing it out. But not all do this.

You can get rid of the error by issuing this command on every system on the network

ipconfig /release
ipconfig /renew


You will be able to talk out the network and eventual system A that has the dup IP will try to renew the IP (systems configed for DHCP hold an IP for an amount of time and then try to renenw it). When it tries to renew the DHCP server in the router will give it a diff IP.

The only problem that may happen is when both of the machines try to talk at the same time. The switch in the router will send packets to which ever machine talked last. For example System B starts a file download. All is good and packets are going from the internet to system B. suddenly system A goes to a webpage. Now the web page data and the file download data will be sent to system A

[Evilization]

Hey Mapes
I see an IPv4 address and an IPv6 address
the ipv4 has only numbers and dots, the ipv6 has all sorts of characters
it seems that if i do the commands, both ipv4 and ipv6 stay the same as before
which one should i be looking at anyway?

[mapes]

Hey Mapes
I see an IPv4 address and an IPv6 address
the ipv4 has only numbers and dots, the ipv6 has all sorts of characters
it seems that if i do the two commands, the ipv4 always stays the same, but the ipv6 keeps changing
which one should i be looking at anyway?

Thats fine. The two ip addresses can coexist on the same network interface. Basically you network card has an ipv4 address and an ipv6 address. If you want you could go to the network interface properties and uncheck the ipv6 box and it will go away. IPv6 has crazy characters because its a different numbering scheme. Much larger amount of ip address available. Basically in a nutshell IPv4 has four octets (things seperated by dots)that range from 0-255 (called octal BTW). In IPv6 also has four seperate areas but instead of using decimal (you know 0-9)it uses hex numbering(0-F yes its 0123456789ABCDEF).

[Evilization]

i just noticed though, that ipv4 and ipv6 actually stay the same after ipconfig/release and ipconfig/renew

I mean, isnt the IP address conflict supposed to be solved when I get a new IPv4? at least that was the impression i was getting from your posts

[Sir Psycho Sexy]

also ive noticed from my own experience that people using windows vista combined with windows 7 on the same router if any computer goes into sleep mode it messes with the ip's as well if that helps, in order to fix it where im at is just power cycle the router and everything is good again. You can also set up all attached devices on your router to use the same address as it had before. Kinda like reserving a slot, i do that for all my port forward/port triggers so i dont have to keep editing them

[mapes]

i just noticed though, that ipv4 and ipv6 actually stay the same after ipconfig/release and ipconfig/renew

I mean, isnt the IP address conflict supposed to be solved when I get a new IPv4? at least that was the impression i was getting from your posts

Ok so here is how DHCP works. Each machines network adapter has a unique hardware address called a MAC. That is set by the H/W vendor. This address is how computers talk to each other on the local net. So the comp boots. It then sends a broadcast message out. So every machine on the net will receive a copy of this packet. The packet says hey if there is a DHCP server out there I need an IP. The DHCP server will see this packet and because the packet has the requesters H/W MAC it can respond. So what the DHCP server does is look at it's config for a free IP and sends it...Since it knows the MAC of the requester it can send directly to it.

Now when a machine gets an IP it has it for a certain amount of time. This is called a lease. As soon as DHCP requester gets it's IP it starts a timer. When the timer reaches a certain point the requester will try to request the same IP from the DHCP server.

So at this point here is what you got. A the requestor has an IP and at a certain time will try to renew the lease for the same IP. B. The router has a configuration of available IP's and and table in memory of what IP's it has dished out to each machine tracked by the the requesters MAC.

So lets look at problems now.

1. You reboot the router. The router has no idea what machine has what IP and could dish out an IP that is already in use

2. As Psycho said a machine goes to sleep. After a certain amount of time it's lease will expire. The router ages that lease back into the unused IP pool and dishes it out. Although the machine will try to renew it and the DHCP server should say no use this one. This should not be a problem but, I suppose it could be on computers that have bad implementation of the DHCP client.

3. Somewhere out on the network a computer has been setup for a static IP. In this case the IP of that machine is also in the available pool of IP's that will be dished out by the DHCP server.

So check and make sure each and every network device (computers, printers, espresso machines whatever is on your net) is configured for DHCP.

Also if you have a conflict it will tell you what machine is conflicting. When a conflict occurs your machine will list the offending machines MAC address. Usually something like this 00-22-69-86-20-79

Go around to each and every machine and type ipconfig /all This will show the MAC address and you can find the culprit.

Good luck

[mapes]

Did you figure this out or did it go away?

[DougBob]

I'm curious too.

[Evilization]

We needed to move the router and modem to a different place for a different reason, and once everything was plugged back in, I think i got a different IP address and havent had any problem since

note: i only have access to my PC, other PCs are owned by other family members and they are all very private about their belongings. I personally dont care about their stuff. So, as long as the problem is not on my PC, I am happy