July 31, 2003

By Karen Kenworthy


Hi! Have a seat. The weather's so nice, I'm spending the day out here on the porch. Sure, take your pick. That rocking chair's free, and so's the porch swing. Sit anywhere. You can even put your feet up on the table if you like. :)

And here, let me pour you a glass of lemonade. It was squeezed fresh this morning. And help yourself to the sugar cookies! Don't they smell great? They just came out of the oven.

Test Them All!

Ah... It feels good to sit down and relax. I've been working a lot lately, making changes to several programs.

Remember my 'Net Monitor program? That's right, it monitors the health of remote computers. The original version tested web sites, making sure they respond, and deliver the correct information.

Later, the program learned to monitor e-mail servers too. Periodically, it connects to a server, pretending to send a message. It doesn't actually finish sending the message. But it talks to the computer long enough to make sure its behaving the way a good e-mail server should. :)

Well, recently several readers asked me to teach the 'Net Monitor a new trick. They want the program to test connections to any remote computer, even it it's not running web or e-mail server software.

It's a great idea. So good, in fact, that I added this feature!

I can see this new feature being used to monitor computers storing databases, or other important files. It can also check on computers that process logins, or perform other important jobs. It can even keep an eye on routers!

If the new test succeeds, you'll know the remote computer or other device is up and running. The connection between your computer, and the gizmo being tested, must be good too.

But if the test fails, you may have lost your connection to the Internet or local network. Or the remote computer may be having problems of its own. A descriptive error message helps you diagnose the exact problem.

And because the 'Net Monitor records the results of every test in a permanent log file, you can document the performance of your Internet connection. If it's not up to par, you'll know exactly when it failed, how often, and for how long. That should impress your ISP or system administrator!


How does the new test work? I'm glad you asked. Have another cookie and I'll tell you the story...

Have you ever seen a movie about submarines? There's usually one sailor who spends his time wearing headphones, intently listening, and turning dials. He's the "sonar operator".

A sonar device sends short bursts of sound, called "pings", from a small speaker. Nearby objects -- another submarine, a whale, or an undersea mountain -- reflect that sound, creating an echo.

A microphone on the outside of the sub detects the returning sound, feeding it to the sonar operator's headphones. A skilled operator, today with the help of a sophisticated computer, can determine the type of object lurking in the murky deep, and also its distance.

Well, as we've seen before, computer folks love to steal good ideas. Inspired by the submariner's sonar, a brilliant programmer named Mike Muuss devised something called the "Internet Control Message Protocol," or ICMP.

This standard defines a special "packet" -- a group of bits that can be sent over the Internet. Computers that receive ICMP packets are required to immediately echo them, sending a copy back to the original computer.

In effect, these packets bounce off the remote computer, reflecting back to the sender the way a sonar ping returns to a submarine. In fact, the similarity is so strong that programmers and other tech-types call these ICMP packets "pings".

And that's the secret! The new 'Net Monitor can ping computers, routers, some network printers, and other hardware that supports the ICMP standard. If a ping never returns, the monitor records that failure in its log. It can also send an e-mail message alerting you to the problem.

The program records successful pings too, noting the time they take completing their round-trip journeys. Typically, a ping travels across a local area network (LAN) in a few thousandths of a second. Pings visiting more distant devices, or which travel over slow connections, might take a full second or more. Wherever your pings go, however long they take, anything trip that's out of the ordinary might indicate a budding problem.

Ping Problem

There's no doubt about it. Pings are a cool tool. But they do have some shortcomings. For example, among all the data traveling across the Internet, ping packets are considered among the least important.

That makes sense when you think about it. Other packets may contain credit card information, vital company data, or pictures of your vacation. If a mere ping gets lost, while traveling through a particularly busy part of the 'net, it's no big deal. We can just re-send the ping, and see if it succeeds on its second, third, or fourth attempt.

Because pings are unreliable, the new 'Net Monitor lets you decide how many pings should be sent during a test. You can select as few as one ping, or as many as ten. You also choose how many pings must complete their trip before the 'Net Monitor decides a problem exists.

For example, you can ask the monitor to send 10 pings to a particularly remote or hard-to-reach computer. You can then tell the program that if three of them make the trip unscathed, all is well.

But when testing a nearby computer, or one whose connection is usually very reliable, you might only request only one or two pings per test. But if even one of them fails, the 'Net Monitor should raise the alarm.

Gosh, you're a good listener! I've been talking your ear off. And yes, the new 'Net Monitor is free (for personal use). To download a copy, drop by the program's home page at:


As always, the programs' free Visual Basic source code too!

Or if you prefer, get the latest version of every Power Tool, including the new 'Net Monitor, on CD. The disc also includes three bonus Power Tools, not available anywhere else. You'll find every back issue of my newsletter, and a few articles, in the CD's library. The CD even includes a special license that lets you use your Power Tools at work.

Best of all, buying a CD is the easiest way to support the web site and this newsletter. To find out more about the CD, visit:


Well, I hate to see you go. But it's getting late and there's a new moon out tonight. You'll have to leave now to get home before dark.

Take a handful of cookies with you. And come back soon. Until we meet again, if you see me on the porch or on the 'net, be sure to wave and say "Hi!"

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