Upstream Provider Woes? Point the Ping of Blame - page 2

Network Admin's Best Tool

You know the drill -- is everything plugged in? Are there blinky lights? Did you pay your electric and ISP bills?

Then, start by taking your trusty laptop, or whatever machine you have available, and plug directly into your connection source. Bypass your firewall, router, proxy, content scanners, everything that stands between your LAN and the big bad Internet, so you can quickly find out if the problem is local, or outside of your LAN. You probably don't want to take your entire LAN offline, so you'll need to fix up a DMZ (define) segment to plug into.

Next, fire up mtr (My Traceroute), which if you don't have it already is a free download. mtr combines traceroute and ping in a single handy-dandy utility. First try it on a large, well-supported site like Yahoo, Google, CNN.com, or some such, just to test it out:

$ mtr yahoo.com

A window will pop up and show you the live progress, like in Figure 1.

Figure 1. (Click for a larger image)

This example shows a problem highlighted in red. Packet losses under 5% are not important; this is typical of the Internet on a busy day. But 29% is definitely a problem. Should you contact the admins at Level3.net? You might, as a courtesy. In this case, it's safe to assume there are many routes to Yahoo, so it's probably not all that important to you. (Don't forget to turn mtr off after you've run 100-200 packets!)

The interesting hop in this example is the very first one, router.ortelco.net. That is my ISP, the very first stop on the path from my computer to yahoo.com. Since the example shows 1% packet loss, that means that the ISP is not the bottleneck. (Please don't run tests on ortelco.net; use your own ISP. It's a small-town ISP--be kind.)