ubuysa
The BSOD Doctor
This is apropos of nothing really it's just something I came across whilst troubleshooting someone else's laptop and it was something I'd not come across before, so I'd thought I'd share it here.
We have all seen the annoying "Limited" wifi connection now and then. The user who brought their laptop to me to fix complained that even though the connection usually showed as Limited they could often still connect. They wanted to know why and get it fixed so it didn't show as Limited any more.
The connection shows as Limited because Windows has established that a connection to the wireless router has been made but that no Internet connectivity exists. This led me to the question; how does it know?
That led me into the new (for me ) world of the Network Connectivity Status Indicator (NCSI - yes, Gibbs gets everywhere!) which you can read all about at http://technet.microsoft.com/en-us/library/cc766017%28WS.10%29.aspx.
Basically it seems that Windows uses one of two methods to determine Internet access when you connect to a hotspot:
1. A DNS request is sent for the name dns.msftncsi.com and any reply is checked for the correct mapping 131.107.255.255.
2. An http request is issued for http://www.msftncsi.com/ncsi.txt and the response is checked for a single line of text that says "Microsoft NCSI."
If either (or both) of these tests pass then the connection is marked as active, if both fail the connection is marked as Limited.
The above website also describes a registry key that controls whether the connectivity test should be done at all. The registry key is at
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NlaSvc\Parameters\Internet\EnableActiveProbing
a value of 0 means do not check for connectivity, a value of 1 means do check for connectivity (ie. do the above tests) and this is (or should be) the default.
In my users case this registry key was set to 0, so Windows never did the connectivity tests and all connections showed up as Limited. I've no idea how it got set to 0, I can only assume it's been that way since installation, this user doesn't even know what the registry is so I'm certain they haven't been messing with it. I did wonder whether the third-party Internet connectivity software they had been using might have changed it?
Apologies if this is well-known, it was all new to me - though in the past I have often wondered how Windows knew it had an Internet connection. Anyway, I offer it here in the hope it might help someone one day....
We have all seen the annoying "Limited" wifi connection now and then. The user who brought their laptop to me to fix complained that even though the connection usually showed as Limited they could often still connect. They wanted to know why and get it fixed so it didn't show as Limited any more.
The connection shows as Limited because Windows has established that a connection to the wireless router has been made but that no Internet connectivity exists. This led me to the question; how does it know?
That led me into the new (for me ) world of the Network Connectivity Status Indicator (NCSI - yes, Gibbs gets everywhere!) which you can read all about at http://technet.microsoft.com/en-us/library/cc766017%28WS.10%29.aspx.
Basically it seems that Windows uses one of two methods to determine Internet access when you connect to a hotspot:
1. A DNS request is sent for the name dns.msftncsi.com and any reply is checked for the correct mapping 131.107.255.255.
2. An http request is issued for http://www.msftncsi.com/ncsi.txt and the response is checked for a single line of text that says "Microsoft NCSI."
If either (or both) of these tests pass then the connection is marked as active, if both fail the connection is marked as Limited.
The above website also describes a registry key that controls whether the connectivity test should be done at all. The registry key is at
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NlaSvc\Parameters\Internet\EnableActiveProbing
a value of 0 means do not check for connectivity, a value of 1 means do check for connectivity (ie. do the above tests) and this is (or should be) the default.
In my users case this registry key was set to 0, so Windows never did the connectivity tests and all connections showed up as Limited. I've no idea how it got set to 0, I can only assume it's been that way since installation, this user doesn't even know what the registry is so I'm certain they haven't been messing with it. I did wonder whether the third-party Internet connectivity software they had been using might have changed it?
Apologies if this is well-known, it was all new to me - though in the past I have often wondered how Windows knew it had an Internet connection. Anyway, I offer it here in the hope it might help someone one day....
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