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How to Diagnose your Flaky Internet Connection July 12, 2009
I have Verizon Avenue DSL, the worst ISP I've ever had, so I've gotten to learn a few tricks on how to troubleshoot my internet problems. Here are the steps:

Can you ping the outside world?

Try pinging a well-known IP address like 4.2.2.2 You should see successful results (0% packet loss) like that below:
If you get messages like "no route to host", or get 100% packet loss, you've got much bigger problems. (If so, try doing "ping 192.168.0.1" - if that doesn't even work, then you probably aren't even connected to your router.)

Does resetting just the router help things?

Try unplugging (waiting 20 seconds) and re-plugging the power to your router. Does that help things? If so, you might have a crappy/old/broken router. I've had 3 different Netgear/DLink routers where resetting helped things. (In fairness, 1 of those was my fault: I plugged a 12v power supply into a router that wanted 7.5v -- the plug fit, the router got really hot, and periodically reset it self.)

Does resetting the modem and router help?

Try unplugging (waiting 30 seconds) and re-plugging the power to your dsl/cable modem, and also to your wireless router. Occasionally, your modem can get stuck with a bad IP address, and this will force it to get a new one. This really shouldn't happen if you have a good ISP, but it can. But this is only something that might happen every few months or so, not every day. If doing this helps all the time, you probably have a different problem.

Is it your DNS?

If you are getting a lot of "host/server not found" errors in your browser, and/or the "looking up domain.com ..." message in the status-bar at the bottom takes a long time, the problem might be a bad DNS server.

Background on DNS:

When you plug your wireless router into your cable/dsl modem, the router is given an IP address, as well as the IP address of where to do DNS lookups. (These DNS servers are hosted by your ISP, and are often flaky/overloaded.) When you plug your computer into the router (or connect over wireless), the router tells your computer to use 192.168.0.1 (the IP address of the router) as the DNS server. Your computer thinks that your router is the DNS server, but really, your router just turns around and does the DNS lookup for you.

How to fix your DNS:

One thing you can easily try is to tell your computer to use a different DNS server. Go to opendns.org -- they have instructions on how to do this for your particular computer. Their DNS Server IP addresses are 208.67.222.222 and 208.67.220.220
(Or you can use Verizon's public DNS servers of 4.2.2.2 and 4.2.2.3, or (new) Google's DNS servers of 8.8.8.8)
Alternately, you can change the settings on your router to use these IP addresses. (It's hard to explain how to do this - you have to visit http://192.168.0.1 from a computer that is plugged directly into your router's special port.) This way, all the computers in your home will benefit from having these new DNS servers.

If using these DNS servers fixes your internet woes, then you've found your problem (and your solution).

Is your wireless connection flaky?

Try pinging 192.168.0.1 from your laptop that's connected wirelessly, and see what the packet loss is. (You really need to do 50 or 100 pings to get a fair estimate.) Ideally, the packet loss should be 0% -- if you do a ping from a computer that is plugged directly into the router that is what you'll get.
In my house, I would get packet losses of at least 3%, sometimes as high as 8% or even higher. The symptom is that the internet seemed very flaky. Sometimes web pages don't load, or take extremely long to load. Sometimes my ssh connections would lock up. If your wireless is the true cause, then all of these should be symptoms that you don't have when plugged directly into your router (all ethernet, no wireless).

How to fix your wireless connection:

I don't have a great solution here, since the problem might be that your house is just a "dead zone" as far as wireless goes. Or there might be too many other routers/microwaves/cordless phones/other interference right around you.

But here are some ideas to try: Update: I bought the Apple MB763LL/A AirPort Extreme Dual-band Base Station and so far everything is great - 0% packet loss, great range. It's a bit pricey, but I've decided I'm not going to skimp on productivity tools that I use every day.
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