Someone is using my IP address

Most likely, you're getting a network address from your router. The address assignment ("lease") expires, and has to be renewed, after a certain amount of time, which might be one hour or one day. The lease expired without being renewed because the device was offline at the time. Meanwhile, the address was leased to another device on the network. When the first device comes back online, it still has the address that's now also leased to the second device. Depending on what kind of router you have, the conflict may resolve itself automatically. If not, then from the menu bar, select

 ▹ System Preferences ▹ Network

If the preference pane is locked, click the lock icon in the lower left corner and enter your password to unlock it. Then click the Advanced button and select the TCP/IP tab. Now look at the menu labeled Configure IPv4. If the selection in that menu is Using DHCP, click the button labeled Renew DHCP Lease. Test.

Less likely, you have a network address that you assigned yourself, and another device is assigning itself the same address. In that case, the selection in the Configure IPv4 menu will be either Manually or Using DHCP with manual address. This kind of conflict won't be resolved automatically. You have the following options to resolve it:

1. Change the menu selection to Using DHCP.
2. Change the manually-assigned address to one that isn't being used by another device.
3. Change the address of the other device.

Which of these options you should choose depends on the details of why you're using a static IP address. Any change you make to the network settings must be applied before it takes effect. To do that, click OK and then Apply.

this happens when one of your devices is already using the same ip address your macbook wants to use.

it usually happens to me once in a while. what i usually do is turn all my devices off then restart my router.

then one by one, i turn each device back on and ip conflict is usually resolved.

give it a shot. might work for you too.

Having the same issue too. This actually worked well for the most part. The notice stopped coming up, but when I go to "Users and Groups" it's still saying that there is a guest user. The guest user is offline, but it's still a bit disconcerting. Is it normal for this kind of problem? Or is this another more serious problem and I should be thinking of changing my IP address?

addresses in the three ranges, 192.168.yyy.zzz; 72.16-31.yyy.zzz, and 10.xxx.yyy.zzz are strictly local, cannot be used outright on the Internet, and are a problem ONLY on your local Home network, not anywhere else and you are not being intruded on or hacked.

The most common reason for finding "someone is already using your IP address" is that you have been sloppy about assigning fixed and DHCP (automatic) IP addresses, and there has been a collision.

Guest User is an available MacOS FEATURE, it does not mean anyone has logged onto your Mac behind your Back. No Mac User has access to any other Mac User's files. Guest user also has no access to any other User's files, only to Applications, and when Guest logs off, any files created there are discarded.

MacOS, especially when behind a Router you control, is essentially immune from random attack from the Internet.

But it is not immune from things you download because a web site told you to.

First of all let me make a comment on how exceptionally RUDE you were.

Secondly I don't download anything "because a site told me to". I'm the only one in my family who seems to be cautious of downloads, pop ups, and all that. BOTH my step dad and younger brother have infected the desktop (PC) multiple times because they download stuff they shouldn't have. I for one DO NOT do any of that crap on my MacBook Pro.

And here we get to my third point. My Mac is used. Got it from a family friend. It's also customized to me and how I want to be able to use it. He said he reset and fixed all the settings and that all I needed to do was set up a login. So if the IP address was "set up sloppily" it was him NOT me who did it. Sorry for assuming that a trusted friend and person who has been fixing and refurbishing computers and devices most of his life would know what he was doing. And FYI I wasn't allowed near the computer while it was being built. There were times when he let me look at it to see it's progress, but when I actually got it the settings were already set up. Of course when I got it I tweaked some of the settings I felt needed to be changed to make my computer more secure. Like blocking certain things. Things like that, but yeah it didn't occur to me that my IP address was one of the things that I should have tweaked so I left it what it already was. So really I wasn't there for the whole set up.

So thank you, but I'm not thankful. It's quite hard to feel any gratitude toward you because of how you worded things. Just because someone asks for help, confirmation, or verification doesn't make them a complete idiot. Yeah I didn't know that "Guest User" was an OS feature, but that doesn't make me an idiot. This is my first Mac. I was a PC user until my poor laptop completely died and I had to get a new one (my Mac). So certain things are going to still be new to me until I explore it or need to ask for help when I can't figure out what a feature is or if I need to confirm or verify what one is. So just because a question sounds stupid to you doesn't make the question stupid or the person who asked stupid.

My response above consists of simple declarative sentences. There are no deprecating words or anything even approaching character assassination included in those sentences.

I did use the word "sloppy" when describing the allocation of local IP addresses on your network. In my opinion, unless you have methodically made certain that there is no way to encounter a duplicate local Address on your Home Network, by tuning your manual IP addresses and your DHCP ranges, that description stands.

Any other pejorative tone you read in my response is unintentional. If you read my words at face value (which is the only way you can read a response from a total stranger) you will not find any support for your assertion that I was maligning you in any way. I spent my time composing a response to be helpful, not to put you down. I am sorry for any offense I caused you.

I wrote my response to assure you that you were not being invaded. As I wrote, I included additional items along the same line which are also nothing to worry about. But when I re-read what I had written, I realized my response was so upbeat and glowing that it might imply there was nothing to worry about. That is why I included the sentence that says there ARE things to worry about, and they are specifically the mistaken download of malware disguised as something else (the so-called Trojan Horse malware). Readers post complaints about malware that could only have been downloaded in this way by the handful each and every day here.

Readers here are other users like you. We are not employees of, and get no compensation of any kind from, Apple. We do not speak for Apple, Inc. If you prefer support from Apple employees instead of other Users, please contact Apple directly by telephone, or make an appointment at the genius bar of an Apple-owned store for an evaluation (which is free).

There seems to be confusion about what and where an IP address is and where it comes from. Lets take this scenario: you live in a house, you have an Internet Service Provider (IP) you pay for internet connection and you have a router.

in the majorty of cases your IP address should be assigned to you by a router, in the event you have a router your Internet Service Provider will assign another IP to the router, to get it to be able to let every device connected to it use the internet. (if you did not have a router your ISP will assign the IP from their servers to your computer and you would only have one internet connection in your house)

To simplify this we will stick with IPV4 which uses the xxx.xxx.xxx.xxx format, not IPV6.

Every ISP has a block of IP address avaiable to them to give out, each ISP is given a unique set by an origination that does this. No two ISP's have the same block of IP addresses, they can't or they would be conflicting with one another.

Your router uses an internal network address that are managed entirely inside the router, and at no point do these internal IP's out into the internet. Think of your router as a "waiter" between the "customer" (your computer), and the "kitchen" (the internet)

Now for example your ISP assigned you a IP address to your monthly account of (a random number I'm making up) 218.44.50.11. Your router assigned your computers an internal IP addresses, it could be 192.168.1.102, or 10.1.1.105, or some internal IP address unique to your router. Again, internal IP's do not go out to the internet. So now the user on computer 192.168.1.102 wants to go to Apple.com , They type in "apple.com" to their brower and hit return. The computer on192.168.1.102 sends that info to the router, the router knows who asked (192.168.1.102 asked) then the router on 218.44.50.11 goes out to the DNS server of the ISP or whoever they use, then the DNS severs sends the information for Apple.com back to 218.144.50.11 (the router) and the router sends information from 17.172.224.47 aka "apple.com" directly back to 192.168.1.102; the computer that asked for it. if your iPhone on 192.168.1.118 asked to go there your router would know to go give that information back to 192.168.1.118. Because the router uses addresses like 192.168.1.xxx or 10.1.1.xxx there are likely billions of devices using these IP's to talk to routers, but not getting past the router which has an IP assigned directly by the ISP.

When you get "IP address is in use" What is very likely the problem is that the computer that was using 192.168.1.102 today, was not using it two days ago or a week ago, and it might have been your iPhone using 192.168.1.102 or your apple TV using 192.168.1.1012 or some other device in your house using 192.168.1.102 and your router did not stop the lease on the IP address when it assigned your computer the same IP address. If that is the case you have a problem with the router, reboot it, or if it keeps doing it it may be broken and unable to stop the "lease" on 192.168.1.102

in this event you need to address the problem with the router which is responsible for the internal IP conflict.

Thank you. It solved the issue on my mac. 🙂