Why does my internet connection fail intermittently?

Question

On my laptop, my internet connection fails now and again. I'll go to a web page (Let's say Google) and I'll get page not found. I'll then sit and press F5 to refresh the page until eventually after a minute or so it'll suddenly work. All will be well for a while after that until suddenly it'll happen again.

Now, there are some peculiarities to this problem...

• This only happens on one laptop. My work laptop on the same wifi network always seems to be fine, as does my XBox.
• If I'm downloading a large file, the download continues even while I'm failing to bring up web pages.
• Sometimes I can get some pages, and not others. Sometimes I can get partial pages.

My limited knowledge of such things seems to suggest some kind of DNS lookup problem, albeit one that's confined to one laptop.

Does this sound remotely possible? Is there something I may have missed here?

Oh, and I'm on Windows Vista, in case that matters.

Answer 1

The university of Berkeley has a website that will analyze all sorts of aspects of your Internet connection such as DNS, ports, upload/download speed etc. It will report anomalies to you. It is here:

http://n1.netalyzr.icsi.berkeley.edu/

Answer 2

I was having this issue on Windows 7 with a RealTek wireless card. Reinstalling drivers for the wireless adaptor (and numerous other attempts at a solution) didn't fix the problem.

On a whim, I disabled 802.11N on the wireless adapter properties (reverted to G and B only) and it started working! My intermittent network drops (connected but no internet access) went away.

Answer 3

It sounds a lot like a DNS problem, considering downloads do not drop out and it only affects one laptop on the same wirless network.

I would try different DNS servers.

I had a similar problem once and it turned out to be that my ISP's DNS servers were crappy (but that affected everybody on my network).

Answer 4

Does this happen when you are idle? Are your IP's static or do you do DHCP? Is the power management savings setting on the network cards disabled, or do you have the network card set to shut off to save power?

My guess - you have DHCP and the network card of the laptop powers off to save power. The DHCP server then doesn't see you and drops your IP info. If you keep trying to reconnect, eventually you will assigned a new address once the network card wakes back up and requests one. That in turn will allow you to get out.

As far as a transfer occurring even while you can't browse, I'm not sure, but if you have already established the download and the session already exists, the router/switch should have a memory of your old MAC address in the tables. I'm guessing (any network specialist here?) any incoming packet pointing to your session should still be able to go through since once it comes in to your router, it will go out to your MAC and not depend on IP addressing.

Answer 5

You don't say what browser you're running but I'll guess it's firefox.

Firefox recently changed how it handles DNS - it's got this new "prefetch" logic that can sometimes totally overload things.

https://developer.mozilla.org/en/controlling_dns_prefetching

Here's additional information on things that can go wrong with ff and dns:

http://kb.mozillazine.org/Error_loading_any_website

Answer 6

Have you tried following the openDNS guide here, to make sure it's not a DNS issue? I used to get this all the time, but since switching they've gone away.

Answer 7

It probably is a DNS problem, but your local DNS cache may be broken, you may not have a plug in (for some of the pages) or a problem may exist with your browser.

Answer 8

Don't rule out the possibility it could be hardware related. I had the same problem with my ISP provided router. Till I went out and bought my own... now problem is fixed...

Answer 9

From the command line (assuming the various computers are all versions of Windows 2000 or higher) type this command on each computer:

ipconfig /all

I'm betting that the 'problem' laptop will have different DNS settings than your other computers. To resolve this on Vista follow these instructions:

• Go to the Start Menu.
• Type the word Network, and select Network and Sharing Center.
• On the left, click Manage network connections.
• Right-click on your wired or wireless network connection icon, and choose Properties.
• Highlight the line labeled Internet Protocol Version 4 (TCP/IPv4) and click Properties.
• Change the DNS servers back to Automatic, or manually type in the DNS servers appropriate for your network.

Answer 10

Set the power saving mode of your WLAN adapter to OFF or CAM (constantly awake mode).