Another device on the network is using your IP address - but its not my IP address

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Level 1

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Another device on the network is using your IP address - but its not my IP address

The last few days, a macbook air and an iMac have both give the error "Another device on the network is using your IP address". They are both using the latest OSX and are both set to use DHCP assigned by my Virgin cable router. I've searched and seen other responses to this question - however what is strange here, is that the address reported in the popup window is NOT the address that either computer was assigned at the time (the first time, I thought it was odd, and I had an ipad handy and used fing to search my network to see what device had just used that address and I didn't see anything). This time - I was on my iMac and happed to have a terminal open, so I did a quick ifconfig - and my ip address was not the one indicated in the message (it was saying 192.168.0.8) and my address was 192.168.0.12. In fact I think that the other day it was complaining about the same .0.8 address.

This seems very odd to me? Is there something I can check?

I do have 2 devices that have a hard coded ip-address (but they are right at the beginning of the range, and in fact I have instructed the router to skip those addresses and just dish out ip's from .0.3 onwards). All other devices use DHCP.

My wifi network isn't open - so I'm a bit at a loss as to what might be causing this? Is it possible someone is trying an attack? Or is there some OSX bug?

Tim

iMac, OS X Mavericks (10.9.4)

Posted on Sep 8, 2014 9:29 AM

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Answer 1

macta Author

Level 1

24 points

Sep 8, 2014 9:34 AM in response to macta

Just to show this - I took a screenshot and put the device network settings underneath the error (ifconfig showed the same .0.12 address). I could also access the internet without any problems - so it wasn't like another device had knocked me off the network.

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Answer 2

Eric Root

Level 10

684,027 points

Sep 8, 2014 12:29 PM in response to macta

Try going to System Preferences/Network/Wi-Fi - click the Advanced tab, go to TCP/IP, and select Renew DCHP Lease.

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Answer 3

macta Author

Level 1

24 points

Sep 9, 2014 2:57 AM in response to Eric Root

I can see how that will attempt to assign me a new ip address (right?) - but I'm trying to understand why I would get that message when it's not my actual IP address?

In fact I did nothing, and happily worked for a few more hours with no problems. So something is weird, that I would like to understand (if I can).

Would renewing my lease actually correct something that has gone wrong - or is there something else suspicious going on?

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Answer 4

Sep 9, 2014 3:17 AM in response to macta

macta wrote:

I do have 2 devices that have a hard coded ip-address (but they are right at the beginning of the range, and in fact I have instructed the router to skip those addresses and just dish out ip's from .0.3 onwards). All other devices use DHCP.

Tim

Tim, I see that you have two devices that have a static IP address. Which are located at the beginning of the IP pool. You also instructed the router to skip those addresses as ones to "give out" to DHCP devices.

I too have my router skip IP addresses, however it's in the 1.20 range. So all of the reserved IP addresses are from 1.01 to 1.20. My friend set it up like that for me. I could get away with only 10 as being reserved. Basically what I am saying is to increase your reserved patch of IP addresses. Say to 10, so that the first 10 IP addresses are reserved. Thus all of the DHCP devices will start at 1.10(11) for IP addresses.

Just a thought.

By the way, the two devices that have a reserved IP are my two Macs. At first I had them as static IP at the Mac themselves. But if I were to take them anywhere else, I would have to reconfig them so that they would work. So I ended up putting the "static" IP on the router itself. I did so via the MAC address, so the router will give a certain IP to this Mac's MAC.

KOT

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Answer 5

macta Author

Level 1

24 points

Sep 9, 2014 7:08 AM in response to macta

A friend asked me if I had rebooted my router recently, and that is something that I had done earlier in the day (when I had a cable outage). The first occurrence of the above error was about 6 hours after that reboot (on the macbook & the iMac was asleep at that point). The iMac complained about a 1.5days later (and the macbook was asleep at that point).

I suppose its possible that if the iMac was asleep, it could have had 0.8 assigned to it before it was asleep, and then the macbook somehow got assigned 0.8 after the reboot. Thinking about it, I may have rebooted the router a second time - and then the macbook would have got another address. Is it possible there might be something left running on the macbook that had inherited that old address? It seems odd to me though - but I guess it might be possible (it really depends how its all implemented under the hood).

Someone in the office did mention that I should try dmsg in the console and see if that shows anything?

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Answer 6

macta Author

Level 1

24 points

Sep 9, 2014 7:13 AM in response to Kingoftypos

Just to clarify on my setup - the initial two devices are given fixed static ip addresses (they are actually configured to boot that way and don't use DHCP- which is why I've told the router to skip that range). I'm pretty sure they aren't causing any problem (and certainly haven't for several years now). As they are devices that stay in the house - I don't have the same requirements as you.

I'm now thinking that maybe it is something to do with my recent reboot of the router - but it still seems odd to me to get an error about an IP that the machine isn't currently using (but maybe I need to check a log to confirm that).

Tim

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Answer 7

Sep 9, 2014 9:58 AM in response to macta

Oh that would make sense. I've ran into that too with Sleeping Macs. It would seem when they wake up, they assume that they have the same address. Especially after a router reboot.

Since you've rebooted the router, you have nothing to worry about as for security breach.

You could do what I did, and make each Mac's MAC reserved at the router. So when they wake up, they'll have the same IP Address each time. Or since you said that they don't leave the house. Make the static IP Address at the Mac themselves.

KOT

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Answer 8

macta Author

Level 1

24 points

Sep 9, 2014 10:10 AM in response to Kingoftypos

Where you write "they assume that they have the same address" - do we think that is a bug? It can't be that hard to check before reporting the error (or at least clarifying the error a bit if this case is detected).

Tim

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