Here's a few great online tools to help troubleshoot a slow or laggy Internet connection. Most reputable ISPs recognize the results of these tools as valid, so if you use one and it's reporting you have a problem, chances are good if you call your ISP and say that one of these tools says you have a problem, they will take your seriously and work with you.
SpeedTest.net is a flash-based tool that tests your Internet ping and upload and download speeds. SpeedTest.net is a great tool to see if your ISP is really giving you the speed that they claim. This is also something that ISPs will direct you to if you are claiming that your Internet connection seems slow. If SpeedTest.net shows your speed is what is expected, but you're still having slow connections, it's likely some routing point between you and the resource you are accessing.
PingTest.net is a tool that tests both ping and packet loss. Ping is a measure of the time it takes for an internet packet to travel point-to-point and is measured in milliseconds (ms). A millisecond is 1/1000th of a second. Typical point-to-point ping is under 150ms. If you're testing with this tool and seeing high ping measurements (300ms or more) or any measurable packet loss, contact your ISP. If your PingTest measurements are fine, then it's likely some routing point between you and the resource you are accessing.
Another valuable tool for linux users is iftop. iftop measures the bandwidth of the top network connections on your computer, both to Internet and LAN IP addresses, and sorts them by rate. Ubuntu users can install iftop using the following command:
sudo apt-get install iftop
iftop is run using the following syntax:
sudo iftop [-i interface]
If iftop is run without the interface parameter, it defaults to eth0. Users with wireless networks will typically use wlan0
Do you have a favorite tools that you use to troubleshoot network connections?