Something using my computer’s IP address?

jblass · 01-29-2013, 12:12 AM

Occasionally (not really very often) when I come back to my home computer and wake it up I get this message:

"Another device on the network is using your computer’s IP address. [the IP address is listed here]. Try connecting again later. If you continue to have problems, change the IP address of this computer or the IP address of of the other device."

What would this be? My computer is an iMac running OS 10.8.2. I have a small home network using a D-Link router. Other items on the network are another iMac, an iPad, Apple TV, a wireless printer, and my TiVo. I can't imagine why any of those would be using my computer's IP address.

I can't see that this is causing me any problem. As soon as I try to go online, everything works normally and I seem to be connected to the network. Is this something I should be concerned about?

hayne · 01-29-2013, 01:41 AM

1) Make sure that all of your devices are up to date with software/firmware updates.
(There have apparently been bugs in the past where devices (e.g. iPads) tried to retain an IP address that they shouldn't have.)

2) Make sure that all of your devices are configured to get an IP address dynamically using "DHCP". This is usually the default. What you don't want is static addresses - unless you configure your router to have a range of static IP addresses that it doesn't use for DHCP.

3) Maybe try running the following command in a Terminal window the next time you have a problem:

Code:

arp -a

This should show you all the known devices on the network with their IP addresses and MAC addresses. If you see an IP address conflict, the MAC address should allow you to figure out which device is causing the problem.

trevor · 01-29-2013, 10:31 AM

The most common reason that I've seen an IP address conflict is that there are two (or more, I guess but usually two) DHCP servers on the network. Because the two DHCP servers don't know about each other, they hand out the same IP addresses, and you get IP address conflicts.

Another, almost-as-common reason for an IP address conflict is that one machine is manually set with an IP address in the same range as the DHCP server is giving out IP addresses. If you need to have an IP address manually set on one machine, then make sure it is inside your subnet, but outside of the range given out by the DHCP server. For example, if your subnet goes from 192.168.1.0 to 192.168.1.255, then set your DHCP server to give out 192.168.1.2 to 192.168.1.100, and manually set IP addresses from 192.168.1.101 to 192.168.1.254.

Trevor

jblass · 01-29-2013, 12:00 PM

Thanks! This morning when I came to the computer it was showing the error message, but as usual, when I went to an application, that message went away and everything worked normally. I did arp -a in the terminal, and got a list of 4 devices, all using different IP addresses. I then checked each of the devices listed in my original post (except for the printer—I don't know how to access it's system). I got the IP addresses that they list, and there are no duplications. They are configured to use DHCP that there was an update available for my Apple TV, and it is being installed now.

I am inclined to ignore this message, since I can't see that I'm really having any problem with the computer. I am not, however, very "computer savvy" so I wonder if something is happening that I need to be concerned about.

Thanks for your help!

bookshop · 02-06-2013, 05:13 AM

Quote:

Originally Posted by jblass


	Occasionally (not really very often) when I come back to my home computer and wake it up I get this message: "Another device on the network is using your computer’s IP address. [the IP address is listed here]. Try connecting again later. If you continue to have problems, change the IP address of this computer or the IP address of of the other device." What would this be? My computer is an iMac running OS 10.8.2. I have a small home network using a D-Link router. Other items on the network are another iMac, an iPad, Apple TV, a wireless printer, and my TiVo. I can't imagine why any of those would be using my computer's IP address. I can't see that this is causing me any problem. As soon as I try to go online, everything works normally and I seem to be connected to the network. Is this something I should be concerned about?

I see this a lot in the office where I work, which uses nothing more than a Wi-Fi router. It's probably down to equipment going into sleep mode then assuming they can continue on the same DHCP lease.

If you have access to your router's configuration panel then you might be able to use "Address Reservation" to ensure each device sticks with the IP address it's been assigned.

Alternatively, setup a static IP on your Mac but just choose one in the DHCP range the router hands-out and make it high -- if the router hands out addresses from 192.168.0.1-255, choose something like 192.168.0.190. Then you should never get a clash -- unless you have end-up with more than 190 devices on your network...

mclbruce · 02-06-2013, 10:08 PM

Quote:

Originally Posted by jblass


	I can't imagine why any of those would be using my computer's IP address.

All of your devices get an IP address from your router.

Quote:

Originally Posted by jblass


	As soon as I try to go online, everything works normally and I seem to be connected to the network. Is this something I should be concerned about?

I'd say no.

What usually causes this one device going to sleep. When that happens, some routers will decide that the sleeping device doesn't need it's IP address anymore. The router will assign that address to some other device. When the sleeping device wakes up, it remembers it's old IP address. It tries to talk to the router with the old IP address, the router gets mad, and that causes the error message. Fortunately both the router and the Mac are smart enough to negotiate a new IP address and move on.

jblass · 02-06-2013, 11:43 PM

Thanks for the the replies. Here's one more thing which may only be a coincidence. A few days ago I discovered that a series of spam emails had been sent out from me to people whose addresses were in my list of previous recipients. Deciding that I had been hacked in some way, I downloaded ClamX and ran it. It found four items that it called worms or Trojans. I located those items and removed them. Since then I have not had a single repetition of that error message about some other device trying to use my computer's address. Is it possible that those two things are related?

01-29-2013, 12:12 AM	#1
jblass Triple-A Player Join Date: Jun 2007 Posts: 53	Something using my computer’s IP address? Occasionally (not really very often) when I come back to my home computer and wake it up I get this message: "Another device on the network is using your computer’s IP address. [the IP address is listed here]. Try connecting again later. If you continue to have problems, change the IP address of this computer or the IP address of of the other device." What would this be? My computer is an iMac running OS 10.8.2. I have a small home network using a D-Link router. Other items on the network are another iMac, an iPad, Apple TV, a wireless printer, and my TiVo. I can't imagine why any of those would be using my computer's IP address. I can't see that this is causing me any problem. As soon as I try to go online, everything works normally and I seem to be connected to the network. Is this something I should be concerned about? Last edited by jblass; 01-29-2013 at 12:13 AM. Reason: correction

01-29-2013, 01:41 AM	#2
hayne Site Admin Join Date: Jan 2002 Location: Montreal Posts: 31,941	1) Make sure that all of your devices are up to date with software/firmware updates. (There have apparently been bugs in the past where devices (e.g. iPads) tried to retain an IP address that they shouldn't have.) 2) Make sure that all of your devices are configured to get an IP address dynamically using "DHCP". This is usually the default. What you don't want is static addresses - unless you configure your router to have a range of static IP addresses that it doesn't use for DHCP. 3) Maybe try running the following command in a Terminal window the next time you have a problem: Code: arp -a This should show you all the known devices on the network with their IP addresses and MAC addresses. If you see an IP address conflict, the MAC address should allow you to figure out which device is causing the problem. __________________ hayne.net/macosx.html

01-29-2013, 10:31 AM	#3
trevor Moderator Join Date: Jun 2003 Location: Boulder, CO USA Posts: 19,550	The most common reason that I've seen an IP address conflict is that there are two (or more, I guess but usually two) DHCP servers on the network. Because the two DHCP servers don't know about each other, they hand out the same IP addresses, and you get IP address conflicts. Another, almost-as-common reason for an IP address conflict is that one machine is manually set with an IP address in the same range as the DHCP server is giving out IP addresses. If you need to have an IP address manually set on one machine, then make sure it is inside your subnet, but outside of the range given out by the DHCP server. For example, if your subnet goes from 192.168.1.0 to 192.168.1.255, then set your DHCP server to give out 192.168.1.2 to 192.168.1.100, and manually set IP addresses from 192.168.1.101 to 192.168.1.254. Trevor __________________ How to ask questions the smart way

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01-29-2013, 12:00 PM	#4
jblass Triple-A Player Join Date: Jun 2007 Posts: 53	Thanks! This morning when I came to the computer it was showing the error message, but as usual, when I went to an application, that message went away and everything worked normally. I did arp -a in the terminal, and got a list of 4 devices, all using different IP addresses. I then checked each of the devices listed in my original post (except for the printer—I don't know how to access it's system). I got the IP addresses that they list, and there are no duplications. They are configured to use DHCP that there was an update available for my Apple TV, and it is being installed now. I am inclined to ignore this message, since I can't see that I'm really having any problem with the computer. I am not, however, very "computer savvy" so I wonder if something is happening that I need to be concerned about. Thanks for your help!

02-06-2013, 11:43 PM	#7
jblass Triple-A Player Join Date: Jun 2007 Posts: 53	Thanks for the the replies. Here's one more thing which may only be a coincidence. A few days ago I discovered that a series of spam emails had been sent out from me to people whose addresses were in my list of previous recipients. Deciding that I had been hacked in some way, I downloaded ClamX and ran it. It found four items that it called worms or Trojans. I located those items and removed them. Since then I have not had a single repetition of that error message about some other device trying to use my computer's address. Is it possible that those two things are related?