Cannot Connect to Wireless Router

Category: Vista , Windows-7 , Wireless

I ran into a very odd problem with a public WiFi hotspot recently. I learned from it something I didn't know about Windows Vista and Windows 7: their default configuration settings don't work with older wireless networking equipment. Fortunately, there is a fix. Here are the symptoms I encountered and the solutions I found...

Can't connect to wifi with WIndows 7

Vista Or Windows 7 Won't Connect To Wifi

So I'm in a coffee shop, and Windows 7 tried to connect to the WiFi router but failed. I got the message, "unable to connect". But I never even got the dialogue box asking me to enter the encryption key.

Several other WiFi routers were within range so I tried some of those. The "enter password" window appeared. Of course, I didn't know their keys so I could not log in and get on the Internet that way. I had to make "my" router, whose key I knew, work.

My first reaction was to blame the router, of course. It had to be misconfigured. But I noticed that other people in the venue were connected just fine. Perhaps my Windows IP configuration settings were corrupted. So I deleted my WiFi adapter in Device Manager, re-installed it, and tried again. No joy. OK, so maybe there's a problem specific to the combination of this particular router with Vista and Windows 7. I tried changing my operating system. I rebooted into Windows XP Service Pack 2.

Ah-ha! I got the password dialogue window, entered the key, and I was connected to the Internet. There had to be some difference between IP configuration settings in Windows XP versus later versions. A bit of Googling proved my theory correct. It seems certain older routers do not support the DHCP BROADCAST flag. They ignore requests to connect received from client devices which have this flag set.

The Solution: A Bit Geeky Fiddling

Windows XP had its DHCP BROADCAST flag set to "off" by default. Windows 7 and Vista have it set to "on" by default. You have to disable the BROADCAST flag in order to connect to routers which reject the flag. Here is how to disable the BROADCAST flag:

  • Click Start, Run, and enter regedit.exe to start the registry editor.
  • Navigate to the following registry location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\
  • Each of the registry subkeys in {}'s corresponds to one of your hardware network adapters. You don't need to figure out which is which, just disable the BROADCAST flag on all of them, one at a time.
  • Right-click on one of the subkeys to open the Edit menu.
  • If the key DhcpConnForceBroadcastFlag does not exist, use the Edit menu, point to New, and then click DWORD (32-bit) Value. In the New Value #1 box, type DhcpConnForceBroadcastFlag, and then press ENTER. If the key exists, skip this step.
  • Right-click DhcpConnDisableBcastFlagToggle, and then click Modify.
  • In the Value data box, type 0, and then click OK.
  • Close Registry Editor.

Now you should be able to connect to the router. If it's secured with an encryption key, the key entry dialogue box will appear. If it's an unsecured network you will get connected without entering any key. As far as I can tell, there is no downside to turning the DHCP BROADCAST flag off.

I know that sounds rather geeky, but if you have this particular problem, just follow the instructions carefully and it should solve the problem. Got a comment or question? Post it below...

 
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Most recent comments on "Cannot Connect to Wireless Router"

Posted by:

Er. Sajad Ahmed
04 Sep 2010

I had the same problem with Win 7, but instead of setting the DHCP Broadcast Off through registry editing, i tried the other way of connecting and succeeded.
Just simply go to your Adapter Settings and change the default setting of the (TCP/IPv4) properties, which allows the system to Automatically obtain an IP Address.
Choose, Use the following IP Address and then manually input the IP Address, Subnet Mask, Default Gateway and DNS Settings.
Save the settings and you are ready to fire.
In case you want to connect other Systems to the same Router, just change the last 3 digits of the IP Address. All other settings viz Subnet Mask, Default Gateway and DNS Settings remain the same.
So, this way you don't have to go for hectic REG Editing.
Thank You.
Er. Sajad Ahmed.
Srinagar.
Kashmir.


Posted by:

Ken Ormson
04 Sep 2010

Hello Bob,

According to the Microsoft article http://support.microsoft.com/kb/928233, this issue does not apply to Windows 7. Their fix sets the DhcpConnDisableBcastFlagToggle to 1. This means that windows tries to connect with broadcast on and then, if that fails, it tries again with the flag off.
They claim that W7 is always configured with Toggle set to 1.
Thanks for a very useful newsletter.


Posted by:

Ken Ormson
04 Sep 2010

Hello again Bob,
Here is a link to another good explanation of the differences in the way Vista and W7 handle the Broadcast flag:
http://blogs.technet.com/b/teamdhcp/archive/2009/02/12/dhcp-broadcast-flag-handling-in-windows-7.aspx.

It seems that the client always broadcasts its request and acceptance to the DHCP server, but the Broadcast flag indicates whether the client expects a broadcast or unicast response from the server. If the client and server are expecting different things, they will ignore each others communications.
I hope that this helps,
Ken Ormson


Posted by:

Cfrancis31
09 Feb 2011

I had the same problem trying to use a Netgear router. I spent hours on phone with tech support and no joy.
I went back to the store, and the tech I know told me that the easiest router to use is the Cisco "Valet" model M10 router.
Even though $20.00 more than the Netgear, I was suprised, from hookup to connection on both my desktop and laptom less than 30 minutes. and only had to push a few buttons or keys, the usb installation software did it all for me. Check it out, I seldom endorse any company, but this one is really great.


Posted by:

maddrmark
31 Jan 2012

Thanks for this column. You provided clear instructions and this solved a problem that had been bugging me for weeks.


Posted by:

donald
08 Jun 2012

i have a le pan 2 tablet i have a linskey router at work that i have been using and now,i can't hook up my wifi works,on all others. the router at work is an older router g router. I don't know what happen?


Posted by:

Lucian
06 Apr 2014

Hello. I'm running win 7- and my neighbor is sharing wifi to me. When I enter his Password, it will not connect. There are 9 digits( upper & lower case, # sign and two numbers ) What I don't understand is my other neighbor(farther away) also gave my his pass. and they are all letters & I links right up.
Does win7 not recognize # and numbers mixed?

My Ipad however has no problem linking up with my neighbor. I am very confused. Any help would be greatly appreciated!

EDITOR'S NOTE: I don't know of any restrictions on special characters in wifi passwords. Sorry if this sounds insulting, but is the CAPS LOCK key engaged?


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