It implies much more than just your address.
It all depends on how they got your IP address and whether it’s really yours at all.
At least one scenario represents a serious security risk, but there are also situations in which it’s not really an issue under your control.
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My neighbor and my IP address
- The only way your neighbor can truly be using your IP address is if they have access to your local network.
- The most common scenario is that they’ve connected to your open wireless hotspot. Secure the hotspot by adding a wireless password.
- It’s also possible that your IP address has changed, and was once theirs.
- It’s very easy to misread IP address information, depending on your source.
- Malicious software on your machine could also be sending email appearing to be from your neighbor.
It implies they’re on your network
If your neighbor is truly using your IP address, it implies they are connected to your network.
That’s a bad thing, unless you trust them and have explicitly allowed them to do so. I’m guessing from your question that’s not the case.
The most common reason is that you have an open wireless hotspot.
- You have a wireless router or access point.
- The wireless connection is not password protected.
- Your neighbor is in range and is using it.
Your neighbor could be completely unaware. It can happen accidentally if they’re not paying attention to what they’re connecting to. I would not assume malicious intent unless you have information that says otherwise.
The fix is very simple: password-protect the wireless connection. Configure the wireless access point to use WPA2 or 3, which requires a password to connect.
No one except those you’ve authorized will be able to connect to your network.
As a bonus, your connections will be encrypted and no one will be able to “sniff” them (as is possible at most free wireless hotspots).
Other explanations
There are a few other reasons your neighbor might appear to have sent email “from” your IP address.
You could have misread the email headers. Your IP address, as the destination when you download your email, may appear within it, in addition to the IP and email address the mail was sent from.
You and your neighbor could have IP addresses assigned by the same ISP. This has two interesting ramifications:
- Your IP address could be very similar to that of your neighbor. Even a single-digit difference means it’s a different IP address. Read the IP addresses carefully.
- IP addresses can change; your IP address today could easily have been your neighbor’s IP address yesterday, when they were sending email.
The email might not be from your neighbor at all. Your machine could be infected with a spam-sending virus or bot, and it could be spoofing the “From” address so as to appear that it was sent by your neighbor.
Changing your IP address
Can you change your IP address? Well, it depends.
First, if you’ve been assigned a static (unchanging) IP address, you’ll need to contact your ISP and coordinate changing it with them.
If you have a more common dynamic IP address (if you don’t know, then it likely is), you can try to change the address by unplugging your internet-connected modem and/or router, waiting awhile, and plugging it back in again. This causes it to “ask” for a new IP address.
The problem here is that there’s no way to force the newly assigned address to be different than whatever you had before. Many ISPs try to give you the same IP address for “a while”, even when you’re not connected for a time, as it can be slightly more efficient for them.
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“…important to note that your neighbor could be completely unaware…”.
Excellent point, Leo. You truly stand out in the advice sector. That little comment probably has 50% of your readers relaxing. Put down the AK47s and tomahawks, folks, most things done by newbies are unintentional.
Amazing how many folks immediately think the worse. I run into this most of the time. It is never their “fault” for not following protocol or just simple tried and proven good computing steps.
Goos advice, Leo. Kudos.
Awwwww, how did you know I was going to suggest putting a hatchet in the neighbor’s computer? :-D
A question that came to me in the first place was “how did the guy know his neighbor had used his IP address?” It’s not exactly displayed by default in any email program (local or webmail) I’ve heard of. And since I have DHCP, I generally don’t know what my IP address is at any given time; I usually go to http://www.whatismyipaddress.com if I even need to know. (Hey, Leo! Another tip! “How to find out what your IP address is!”)
20-Jul-2009
Weeble – it’s been done: http://ask-leo.com/whats_my_ip_address.html
It’s not so good that in the US, routers are often configured with unsecured wireless access and it’s up to the user to create an access key. My Fritzbox router in Germany is preconfigured with a unique key printed on the router. The number can be read by anyone who has access to the router, but until I know someone has compromised this key (detached the router and copied the number) I’ll stick with it as my kids are often changing computers and in spite of the small risk, the convenience is worth it at the moment.
It still amazes me (though to a lesser degree) how many people simply plug in a wireless router and go. At the moment, my laptop sees three SSIDs of “linksys”, all unsecured. Out of curiosity, I have on occasion, connected to one of them, brought 192.168.1.1 up in my browser, and logged into the administrator control panel using the out-of-the-box login and password. Good thing my morals prevent me from doing anything malicious.
Another Point to Remember – Make sure you keep your Network Security password ID written down in a safe place in the even you forget it. Also, when setting up your encryption – make sure you do your homework first- as some older wireless cards may not be compitable with some of the newer encryption. If you like online games – check this out: [link removed]
If the neighbor is in fact sharing a wireless connection, and that connection is like my Linksys Wireless Router, the local router will get an IP address from the ISP and then assign a DHCP address to each unit on the local network. Commonly this is in the default range of 192.168.1.xxx. The 192.168.1.xxx range of IP addresses is “not routable” and will not be passed across the router to the outside world.
To the outside world (on the other side of the router from the local network) there is a single IP address assigned by the ISP to the router port directly connected to it. The router determines which local IP address is involved in the transaction and passes the traffic through to the appropriate hidden and non-routable local address. That is part of what routers do.
So from the outside world perspective, every unit served by the local router appears to be the same IP address that was provided by the ISP.
The result of all this is that anyone who sends an e-mail from the local network will appear to have sent from the same ISP assigned IP address that is assigned to the port on “world” side of the router and to be using the ISP assigned address. The 192.168.1.xxx IP addresses are not disclosed across the router to the outside world.
This is a probable answer as to why the addresses are the same.
The other comments about the neighbor’s use of the same wireless network by design or ignorance are germane. Appropriate wireless connection security is the answer.
Another good tip to stop a neighbor using your IP address, is to set up an access list on your router, that is of course assuming that your router supports this.
An access list will allow you to limit the devices that can access your network by specifying their MAC addresses.
22-Jul-2009
I agree with Gary, I found the easiest way was to specifiy the MAC addresses in the router set-up. Most modern (last 5 years) routers seem to support this.
You still did not answer the question-how he knew his neighbor was using his IP address. I am curious to know that.
23-Jul-2009
All of the comments are great and true.
Another way to secure your wireless is to Disable your SSID broadcast.
….Robert
23-Jul-2009
You may be surprised to know that in my country many ISP (They call them ISP) provide IP address to customer directly from there switch/hub with more then /29 subnet! Also many customer in same subnet and there is no protection at all! yes this is true. If asker is in this scenario, I would suggest him/her to change that ‘unsecured’ ISP. I worked for my Government’s Cyber Security Department for while and found it is very common practice among ISP’s in my country.
Bauani’s Tech Blog
I filled a form with my phone number and house address.when connecting wireless.now anyone can look up my e-mail address and get my name,phone number and physical address.Is there anyway for me to erase,hide or change the information ?
25-Jul-2009
if you know how many computers will connect to your network, can you restrict this number? Would such a restriction only be applicable, though, assuming all of your computers(full capacity of allowed connections) were filled and active at all times the network is active?
Also, a question about networks. I am connecting to the Internet using a wireless router which is connected to a cable modem. I have disabled file-sharing on my computers. Is this strictly a Wireless Internet Access point then? How can I tell if the computers which use this wireless access to the Internet are exposed or able to be explored by any other computers using this connection?
My neighbour has an open system, when I (out of interest of course)I had a look at her router settings, I found my computer name under LAN clients, does that mean she would be able to access my computer?
Bob.