How do I troubleshoot my Wi-Fi connection when an exclamation mark appears?

Question

Sometimes, when I am in a public Wi-Fi an exclamation mark appears in the greyed out Wi-Fi icon.

I can connect to the Wi-Fi (I get assigned an IP address), but I cannot establish an internet connection - while other Mac users can. Every network where this has happened, I have been connected to before.

I've tried tried the following without success:

• run the troubleshoot assistant
• disconnect and reconnect from Wi-Fi
• disable and reenable Wi-Fi
• remove the network from the list of known networks
• restart the computer

Because none of my attempts to solve this problem yielded any positive results, I always end up not using the internet at all.

Now my sister has been calling me two times already, telling me that the same problem occurred to her. As I could not provide a fix, I need your help :)

My sister is running 10.7.3 on a Macbook 4.1. I am running 10.7.3 on a MBP 8.2.

Answer 1

You need to get more information, so please do some troubleshooting and report back.

Troubleshooting steps:

• Hold down the Option key while clicking on the Wi-Fi icon in the menu bar and let us know what you see. Lion: New Wi-Fi Diagnostics tool
• When you first see the exclamation point appear, open System Preferences > Network. If you get a window like this one

with the Self-Assigned IP beside a yellow button, then you were not able to get a local address from the Wi-Fi router's DHCP server. This can happen because the base station is using MAC address restrictions rather than real passwords. This can also happen because the base station has exhausted its available set of local IP address leases.

When you connect to a network using DHCP, a network router (e.g. the Wi-Fi access point) gives you an IP address to use and promises you can use it for some period of time, which is called a "lease". (This is so there is no confusion about when someone else can start using the IP address that you are using. You either renew the lease or know you have to stop using that address and get a new one.) Once the server leases you the IP address, it cannot give it to anyone else until your lease expires. A typical home router might be set up with only 250 addresses to give out and a lease period of 24 hours. That's fine at home, but in a heavily trafficked coffee shop, they might get more than 250 Wi-Fi using customers in a day, at which point they would be out of addresses. Worse, lease times can be much longer (I've seen 14 days on some routers) and DHCP servers can have arbitrarily small numbers of addresses to hand out. So this really happens sometimes, and it is probably what is happening to you.

In any case, it's probably a configuration error on the router that the router owner has to fix.

Answer 2

If you have admin privileges on your Mac you can use the following:

In the Terminal.app (/Applications/Utilites/Terminal.app) type...

sudo ifconfig en1 down
sudo ifconfig en1 up

Which is surprising, because I thought that this is just the same as turning the Airport off and back on - which I've tried before, but did not succeed.

However, maybe that's not entirely true. According to the manpage, the down command will attempt to reset the interface (whatever that means in detail...).

From the manpage of ifconfig:

 down    Mark an interface ``down''.  When an interface is marked
         ``down'', the system will not attempt to transmit messages
         through that interface.  If possible, the interface will be reset
         to disable reception as well.

Answer 3

In system preferences make sure your Network preferences are set to the Apple default (should be 'Automatic') and for the WiFi device confirm under the 'Advanced...' settings that under 'TCP/IP' your 'Configure IPv4' is 'Using DHCP'

Answer 4

I got it fixed today from www.leshdigital.com The thing is: Sometimes your Mac is a self-assigned IP address that is different from your local IP address(Mine is 192.168.1.1 and the self-assigned IP address is different from that) So what we should do is:

We go to network preferences and ADVANCED-->TCP/IP-->configure IPv4(manually) IPv4 Address: 192.168.1.19(My local IP is 192.168.1.1 so I changed 1 to 19) Subnet Mask is a default value: 255.255.0.0 and this is important:ROUTER->your local IP, mine is: 192.168.1.1 Hit Ok and then you're done. Enjoy your wifi which is successfully set up.

Answer 5

In my case, the problem is solved by changing the mac address. As Change MAC address in OS X Yosemite just run three commands

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport --disassociate
sudo ifconfig en0 ether $(openssl rand -hex 6 | sed 's/\(..\)/\1:/g; s/./0/2; s/.$//')
networksetup -detectnewhardware

Answer 6

Though I doubt this will help many, I was experiencing these symptoms after entering my password incorrectly. Somehow I was not notified that the password was incorrect, so I was able to connect to the router, but it wouldn't issue and IP address.

Answer 7

I just successfully solved the problem by connecting to another Wi-Fi (mobile hotspot) which worked as expected and then re-connecting to the Wi-Fi that caused trouble.

Answer 8

When you are in such a situation, open

System Preferences... > Network

and select on the left table the Wi-Fi or AirPort interface.

If you see you get a "Self-Assigned IP" like here: then this means that didn't received a valid IP address from your router and in place your Mac decided to use a default IP address which is called an APIPA ( automatic private IP addressing ). In this screen capture, 169.254.169.243 is such an APIPA. This address doesn't permit to access your router, and of course not the Internet which is beyond your router.

In such a case, the only thing to do is to open the Advanced… down-right sub-menu, select the TCP/IP options, and there ask to renew your DHCP obtained address:

A few seconds later ( typically 6 s ), you will get either a new DHCP valid IP address ( in this case 10.0.2.29 ) from your router and everything will be OK from there, or again an APIPA ( starting with 169.254 ).

In this last failure case, you will know for sure that your router failed to attribute you a valid IP address. It is up to the administrator of this router to tune correctly the DHCP parameters. You can't do anything here to improve the situation from your Mac side. No need to change anything or reboot your Mac, this will be a total waste of time.

The Apple Wireless Diagnostics… can't diagnose this correctly since it can't access the router DHCP configuration.

Answer 9

I guess it's a corrupt plist. I cannot reproduce the error, so I'm not sure it will help you out.

Try to delete /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist and restart your computer. Deleting this file and restarting is supposed to allow your system to "re-install" the correct drivers for your hardware.

Also, I can recommend you to reinstall the combo update.