Limited connectivity using wireless internet in Vista Home SP1

I've had an issue with "limited connectivity" on my Vista Home SP1 installation. It is a laptop that connects wirelessly (WiFi) to a router. The router is connected to the internet via DSL. The router is working fine and the connection to the internet is ok. However, after using the internet for some time, sometimes half an hour, sometimes minutes, the wireless connection displays a yellow exclamation mark with the message "limited connectivity". It is not the router, since rebooting the laptop fixes the issue... for some time, and then it happens again. After that, trying to open network connections, or any other application related to the network, hangs that application.

I've collected the following possible remedies. I'm not sure which one solved it in the end. Obvious remedies like "put the laptop wifi switch to ON", "put in a correct WEP key" (or any other encryption key) or "check if the router is turned on" are left out:

• (20090618) I put this upfront, because all the tips that follow didn't resolve the issue for me, so I finally bought a new Wifi USB dongle. After buying a new laptop to add to my wireless network I noticed that the WEP encryption I was using didn't work for the new laptop. So in the end I changed protocols from WEP to the stronger WPA. After that, all PC's and even the Wii worked flawlessly. Even after switching back to the original wifi NIC on the laptop that first had the "limited connectivity" message, that laptop hasn't had the problem. So in short: try changing encryption protocols. Start with none (unsecured) to see if the problem is gone and then move on to stronger ones.
• Update drivers. There is a great free tool to update almost all drivers on your system, called DriverMax. Just register and it can be used legitimately for 30 days. I am not sure why it is "freeware" if it states that you can "use it freely for 30 days". It is based around a community of users uploading drivers. It the tool detects a new driver, you can then update it. This is a bit tedious, but always better then scouring the internet manually. The current version of the driver that is going to be updated is uploaded to DriverMax first. It is stored in their driver base for other users.
• Reset TCPIP stack. Execute the following statement at the command prompt:
  NETSH INT IP RESET
• Reset Winsock. Execute the following statement at the command prompt:
  NETSH WINSOCK RESET. Or remove both winsock registry keys, reboot, and reinstall TCP/IP protocol: http://support.microsoft.com/kb/811259
• Disable auto-tuning. Execute the following statement at the command prompt:
  NETSH INTERFACE TCP SHOW GLOBAL. Check if "Receive Window Auto-Tuning Level" is disabled. If not, then disable it:
  NETSH INTERFACE TCP SET GLOBAL AUTOTUNINGLEVEL=DISABLED. Re-enable with "=NORMAL".
• Disable IP6 protocol. Uncheck IPv6 protocol on the network adapters and disable in the registry. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters, add or change DWORD key "DisabledComponents", set to hex "FF".
• Disable other protocols. Additionaly uncheck QoS Packet Scheduler, Link-Layer Topology Discovery Mapper I/O Driver, and Link-Layer Topology Discovery Responder.
• Disable power management on NIC. Right click the wireless network adapter in Device Manager, select properties, tab "Power Management" and uncheck the box "Allow the computer to turn of this device to save power". In my case it was turned back on again at a later point in time, but that could be due to installing a new driver afterwards.
• Change wireless channel. Try different channel numbers for the NIC. Each channel number (mostly between 1 and 13) corresponds to a different frequency. The property can be set on the advanced tab of the driver for the NIC in device manager. Set the adhoc channel accordingly in the wireless router configuration.
• Disable and re-enable network adapter. Apparently, this sometimes fixes issues.
• Reboot in Safe Mode. A solution like the previous one. Reboot the system, press F8, select "safe mode". After it has fully restarted, reboot again. Windows starts normally again.
• Run the System File Checker utility. Execute the following statement at the command prompt:
  SFC /SCANNOW. This is not of much of use to the majority of laptop owners, since they often do not own a copy of their Windows OS installation disk. When SFC finds a component (e.g. DLL) on the system, that is different from the one that was installed during the original installation, then it needs to get that original one from the installation disk.
• Check eventviewer. I have error messages concerning a NTIOMIN service that cannot start, TCPIP.SYS signing issues, and Kerberos related messages (can supposedly be ignored when the laptop is not part of a domain). Still haven't figured out the first two. I'm also getting "informational" events about the NETw5v32 wireless driver. This is related to an incorrect driver.
• Run registry or system cleaners: nice tools to run are HijackThis and CCleaner. The first can be used to remove questionable or corrupt services, browser helper objects, protocols, etc. The latter cleans the registry, removing orphanaged keys.
• Repair wireless. Right click the wireless network icon in the notification area and select "diagnose and repair". Alternative method. Execute the following statement at the command prompt:
  %windir%\system32\rundll32.exe ndfapi,NdfRunDllDiagnoseIncident. Do this before "limited connectivity" message pops up. In my case it displayed a message: "TCP/IP settings not optimized", and it optimized them. Running it again didn't display the message again, so I guess it did something the first time.
• Run Intel PROSet/Wireless diagnostics. If using Intel on-board wireless (I am using 3945ABG), then you can run the diagnostics utility. Execute the following statement at the command prompt:
  %windir%\system32\iPROSet.cpl. Run "diagnose" to check hardware, driver, radio, etc. Run "statistics" to check beacons, transmit errors, and power and power levels.
• Downgrade driver. Sometimes the most recent driver is not the best one for your device. Some drivers available are: NETw3v32, NETw4v32 (11.5.0.34), NETw5v32 (12.2.0.11). In my case, the NETw4v32 driver gave 100% signal quality, while a NETw3v32 driver gave only 60%. The NETw5v32 filled my eventlog with messages (see remark elsewhere).
• Set router to G-Only: put the router in network mode "G-Only". This way, the older B-mode is not supported, but throughput is improved.
• (Run Network Diagnostics tool. Execute the following statement at the command prompt: NETSH DIAG GUI. Check all scanning options and start. This should work in Vista when the command prompt is started with admin rights, but I couldn't get it to work)
• (NIC settings. If supported, try putting the adapter in full-duplex mode, or if it is already, in half-duplex mode. Experiment what works best. I cannot do this myself and wonder if this is even possible for a wireless adapter?)
• (Run netdiag tool. Unfortunately, this tool is only availabe in Windows XP as part of "Microsoft Windows XP Support Tools". So, only for those using Windows XP, execute the following statement at the command prompt:
  NETDIAG /TEST:WINSOCK /V. Use the outcome of the test for further analysis.)

Links: http://ask-leo.com/what_is_limited_connectivity_and_how_do_i_fix_it.html