May 19, 2009

How can one computer kick another computer off the WiFi?

Maybe someone can help me with this. I have several computers, but I like using my MacBook Air around this house. It works fine with the WiFi here when I'm the only one on, but if the other person uses his MacBook (the original MacBook), it breaks my connection. Using the Network Diagnostics application, I can restore my connection, but it will break again, perhaps the every time the other user clicks from one website to another. If I get on one of my older laptops, I don't have the problem. My own old MacBook (original MacBook) interferes with my Air exactly the same way. When we're at our other house, I don't have this problem. I also have this problem at some caf├ęs but not others.

How can this happen, and what could fix it?


rhhardin said...

I don't know.

But there's a time that your assigned address is reserved for, that can be set in the house's wifi device.

I'm thinking maybe that is short, and perhaps most computers send out keep-alive messages often enough to keep it reserved, and yours does not.

But I only have experimental knowledge where I've actually had a problem that needed fixing, and this isn't one.

EDH said...

Woops. Bad link above.

Can't this happen if the computers have the same IP address?

Jack said...

Possibly your Macbook air is asking for a specific IP address while your router is assigning them randomly. Call your Apple Genius. Isn't that why you pay extra for Macs?

al said...

EDH is probably correct. Your router is likely issuing the same IP address to two computers at the same time. That shouldn't happen with DHCP but its possible someone configured fixed IPs to be issued by DHCP in the router. Or maybe set the range of addresses that can be issued to be smaller than the number of computers that are in the house.

Either way - the problem is likely at the router rather than the computer. Factory reset and reconfigure might solve the problem.

m00se said...

I'd help out but as a PC owner I am clearly not worthy to offer advice to superior Mac owners...

Quayle said...

MC Air wireless has been widely condemned as crap.

Lots of stuff on the web. You might try this hereor this here (there are lots of tips in the comments, so read them too.)

Good luck.

goesh said...

- you may as well ask me to argue a case in front of the SC for all I know about such things - good luck - despite my happiness, health and money, I do little magic rituals every day to sustain my good fortune being computer dumb as I am..

OldGrouchy said...

Ah, the revenge of the Robots,and their Computers! Where's Sarah Connor when we need her kind?

Ain't technology grand?

madawaskan said...

Give Meade a jelly donut...

MadisonMan said...

This happens at my house too, if I'm out my Macbook downstairs, and either Son is on the iMac -- next to the modem -- or daughter is internetting (is that a word?) on her iPod touch.

I solve the problem by telling them to get off the internet. Works every time.

Sofa King said...

Boy, things sure have gone to crap since Steve Jobs left.

KLDAVIS said...

Yeah, my guess is DHCP conflict. From the description it sounds like one of the machines is configured to use a static IP, which the router is then assigning to the second computer. I don't work on Macs, so can't give a step-by-step, but you should be able to tell both machines to get their IP via DHCP from the router, and that should solve it after a reboot of all machines and the router. If you still have conflicts, a reasonably advanced router should have an IP mapping table where you can tell it what IP to assign to each machine that connects to it.

rhhardin said...

I don't think it's a static address thing, or it wouldn't connect lots of places.

I prefer the address timeout idea.

BJM said...

I too think it's a DCHP issue and don't do no Macs so can't provide a specific fix.

An easy work around is use the adapter's MAC address (Media Access Control) to assign access to the router. I only use MAC addressing on networks as it's more secure.

Here's an explanation of MAC addressing and wireless routers. There should be how-to support on the router manufacturer's site.

You should be able to setup different access profiles on your laptops (home, roam, guest, etc.) so you can access via IP when you wish. My PC notebook is set up for three access profiles; wired, IP roaming and MAC.

Korla said...

Also check to make sure each machine has a unique DHCP Client ID (in System Prefs-->Network). But yeah, it sounds like the router is programmed to give out short subscriptions, and may be set to only give a limited number of connections (maybe only 1).

It could also be something else, like interference. Is the other Mac accidentally set up to share its Internet connection, which then sends out DHCP addresses from its Airport antenna?

Glen said...

It just works.

Joe said...

This is a known issue, though it's rather unclear whether Apple admits it or is doing anything about it. It is a problem with OSX itself (dual boot Macs have no problems with getting kicked off WiFi when running Windows) though why is a mystery.

Lem said...

I sent an email to my brother..

Try un-checking the option to “Ask to Join New Networks” option from the Network System Preferences. If that doesn’t work try applying the 10.5.1 or the 10.5.2.

Good luck.

Lance said...

I don't think it's a static address thing, or it wouldn't connect lots of places.OS X is smart enough to use different configurations for each network. Thus when I'm on my home network, I have IP addr X. When I'm at work, I have IP addr Y (and IP addrs Z, A, and B on other networks).

I agree with EDH and others, it's probably router's DHCP settings. Might be a conflicting static address, or two "fixed" entries for the same address, or an insufficiently small address pool.

Lance said...

This business with the missing line feeds is getting annoying.

RobertL said...

Your router may only allow 1 computer at a time, or you have the IP address fixed so that it conflicts with another device.

Either way, the answer lies inside your router someplace.

Bruce Hayden said...

Yeah, my guess is DHCP conflict.'

Or, more likely the IP address is sticky, either in your system, or some else's. This problem is really bad with Windows Vista. Not so much that you get kicked off, but rather that it just won't connect, or if it does connect, it won't run well. Why? Because Vista thinks that it is smarter than DHCP.

DHCP's primary goal in life is to assign dynamic IP addresses upon request. It does other things too, such as provide you with DNS, Wins (inapplicable for Apple), and gateway addresses, as well as some parameters such as subnet masks. Vista tries to remember the IP address you used the last time you were on a network, and then use that. And, it is often wrong.

This is what I mean though about sticky IP addresses - the computer trying to reuse an IP address from a previous session, when it really should be going to DHCP to get a new one.

Bruce Hayden said...

Let me add that at least in the PC world, it isn't an issue with static and dynamic IP addresses. With static addresses, you assign (hard code) all the relevant addresses, masks, etc. yourself. With dynamic addresses, you are supposed to get them from DHCP. But, as noted, Vista tries to cheat here, and fails, for dynamic addresses, and this may be part of what is going on with your Mac.

commenter said...

since apple went green, maybe it is not green to have so many laptops in your house.

One laptop per professor qualified with per home

Joe said...

BTW, MacBooks can also get in a state where the OS "believes" it has a connection, yet no connection exists and nothing you do will convince OSX otherwise.

This bug has nothing really to do with DHCP, but with a very, very crappy IP stack implementation by Apple.

F15C said...

I agree this seems to be DHCP related. I assume either Mac will work fine as long as the other one is not connected.

Simple things first. If you haven't power cycled the router, do so. Same with the Macs.

If you still have the problem, ensure both Macs are set to use DHCP:

Mac OS X
1. From the Apple menu, select System Preferences.
2. Click the Network icon.
3. From the Location drop-down list, select Automatic.
4. From the Show drop-down list, select Built-in Ethernet.
5. Select the TCP/IP tab.
6. Configure TCP/IP to use DHCP.
• In Mac OS X v10.3: From the Configure IPv4 drop-down list, select Using
• In Mac OS X v10.2: From the Configure drop-down list, select Using DHCP.
7. Click the Apply Now button.
8. Restart your computer.

Mac OS 8/9
1. From the Apple menu, select Control Panels
2. Select TCP/IP.
3. If a window opens with the message "TCP/IP is currently inactive", click the Yes button.
4. From the Connect Via drop-down list, select Ethernet.
5. From the Configure drop-down list, select Using DHCP Server.
6. Close the TCP/IP(LAN) window.
7. Click the Save button.
8. Restart your computer.

If you still have the problem, then most likely the router is either mis-configured or damaged.

Lem said...

So what happened?

Did any of these fixes work?

Joe said...

Yes, it does sound like an IP address conflict, and as noted above, just using DHCP at the client level does not guarantee that you'll avoid that.

I grew so fed up with OS X (and why in heaven's name didn't they just call it "OSX", for easier Googling?) that I installed Vista on my iMac. Now I only boot to OS X to research some OS-specific question.

Ann Althouse said...

I still have the problem.

The IP addresses were different.

I re-set up the router (an Apple Airport).

I did that DHCP thing in the network preferences of both computers.

Sofa King said...

Vista tries to remember the IP address you used the last time you were on a network, and then use that. And, it is often wrong. It has every right to do so, if the lease time has not elapsed and it has not sent a RELEASE request to the DHCP server. If the DHCP server is re-allocating addresses it leased out and not released before the lease has elapsed, it is the server that is wrong.

Sofa King said...

Have you checked to make sure the Airport's firmware is up to date? It might need patching.

Ann Althouse said...

Firmware updated yesterday.

Joe said...

I begin to suspect the hardware and/or drivers associated with your Macbook WiFi adapter. I've seen various complaints that indicate the MacBook Air may have troubles there.

If I were you, I'd try an external USB WiFi adapter on that MadBook to see if the problem goes away. It likely will. May not help and may not mean much, but at least it would tend to exculpate the router and possibly other suspects...though not with absolute certainty.

In any case, you might look for an updated driver for the machine's internal adapter. That's not necessarily easy to do, but Apple may publish one. My iMac uses Broadcom WiFi hardware, and I had to take a machete to the Internet to find a newer driver...and as I commented above, I decided in the end to go with Vista anyway. Unlike OS X, Windows both works and does the things a modern workstation OS must do.

Florian said...

Hallo I am using a Mac and had a similar problem. Though switching off AirPort (WiFi) and restaring always did the job I considered it not very elegant. My Solution: The problem is that Mac OS X -- at least in my configuration -- though set to get the IP Adress by DHCP is assuming to always get the same adress from the router. What I did was setting up Mac OS X to get connected by DHCP with fixed IP Adress. I configured this crappy router to assign my computer (you need the network name and it's AirPort-MAC-Numer) a fixed IP-Adress that I told Mac OS X to use.

Steven said...

Just so you all know, this issue is not Mac specific, My Mom's Acer with D-Link wireless adapter is having the same issue.

Amar pawar said...

You can do this if you own a rooted android device. There is an app called wofokill that do the job for you. Due to its potential risks,this app is no longer available on the Playstore but you can find it by googling. After installing the app you need to connect your mobile device to Wifi network .After connecting you can see all the devices connected to the network and kick any device off the wifi network(by knowing their IP).
When your phone is connected to the Wireless network, this app sends spoofing packets to all other devices and make then think that your phone is access point (or router). As a result, all the packets start flowing through your phone and then you can kick off them. This app will not disconnect them but only disable their Internet access and make them think that they are connected to a very slow Internet connection.

Source Wifikill