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HELP DESK: Unix traceroute utility discovers network problems . . . catches spammers

HELP DESK: Unix traceroute utility discovers network problems . . . catches spammers

Q I have heard there's a command in Windows 95 or Windows NT that, when you enter it at a DOS prompt, will show the hops that a message takes across the Internet. Sounds pretty cool, but does it really exist?

A The command you have in mind is called TRACERT. It's Microsoft's implementation of a Unix networking utility called "traceroute". Any manager responsible for maintaining a TCP/IP network should know about it.

A TCP/IP network often is composed of many smaller networks connected by routers called gateways. (The Internet consists of tens of thousands of such networks.) Because the Internet, like a robust corporate WAN, is multiply connected, there may be many possible routes from point A to point B. It can be tough for a network troubleshooter to determine where a bottleneck, outage or broken router might be. The traceroute program, developed by Van Jacobson in response to a suggestion by Steve Deering, is one of the most powerful tools for this job.

The traceroute utility exploits a feature of the TCP/IP protocol called the TTL ("time to live") field. This field, present in every IP packet, holds an integer that decreases each time the packet passes through a gateway. When the integer reaches zero, the packet is discarded - preventing it from wandering around the Net forever. The router that discards the packet usually returns a polite notification, called a TIME_EXCEEDED message, to the sender.

The traceroute utility works by sending a series of packets towards the destination, setting the TTL field to 1 and gradually increasing it. It notes the addresses of the routers that discard the packets along the way, and compiles from them a list of the stops packets will make en route to their destination. It also records the time it took to get a response from each router, making it easy to identify bottlenecks. Though routing on the Net is dynamic, and successive packets may take different routes to the same destination - in practice the route seldom changes while traceroute is running. Microsoft's implementation doesn't have all of the features and options of the latest Unix traceroute, so you may find that a Unix machine provides more detailed diagnostic information.

Heavy, widespread use of traceroute can cause network congestion and is not recommended. But when used in moderation, traceroute is an excellent diagnostic tool.

In particular, it's been a key tool in the ongoing war against spam.

By tracing the route back to a spammer's lair, you can discover the identity of the spammer's ISP and ask that he or she be disconnected.

Manage large files without clogging your hard diskQ Our employees frequently send and receive copies of large files as attachments to e-mail, mainly because it's easier than using FTP. What is the best way to handle these?

AThe disadvantage of using e-mail to deliver large files as attachments is that the file usually is replicated in each user's inbox, taking up large amounts of space on your server.

If the server's across a WAN, the pipe will get congested. Here are some ways to make distribution of large files more convenient and efficient. First, if the recipients are running an e-mail client such as Eudora or Netscape, you can put a single copy of the file on an FTP or Web server and then embed the URL of the file in the message. Clicking on the URL (which will be highlighted when the user reads the message) will automatically start the user's Web browser and begin the transfer. This is easier than manual FTP and does not require the user to understand the vagaries of FTP file transfers (which can be tricky).

A second approach is to use Qualcomm's free QPopper Post Office Protocol (POP) server (see ftp.qualcomm.com/quest/servers/unix/popper/) for Unix. This server lets you create a single message called a "POP bulletin"; every user gets it the next time he or she downloads e-mail. Both approaches let you keep a single copy of the file instead of cramming your server's hard disk with many identical messages.

Saving Windows Explorer settings

Q Do you know of any way to save the Windows Explorer settings (for example, window location and size) for each folder?

AI have been asked this many times and have searched high and low for a satisfying answer. Unfortunately, the consensus seems to be that Windows Explorer - unlike the Macintosh - does not maintain this information.

If anyone knows of a utility that adds this feature, I would love to report on it in this column.

Demonic graphics cards

Q I frequently experience serial port "overrun" errors when I run Windows 95's Dial-up Networking. I discovered this when I used the Modem Properties property sheet to enable the creation of a log file. I never connect at a speed greater than 26Kbit/sec due to poor line quality. When I turn down the graphics acceleration setting on my graphics card, the error goes away. What's wrong?

AIf the problem goes away when you turn off graphics acceleration, your video card is probably disabling interrupts as it redraws the screen.

Graphics card manufacturers sometimes do this to increase performance in magazines' benchmark tests.

But it's an unfortunate and sometimes dangerous practice; it can cause errors in other peripherals. Your best bet is to leave the accelerator at the less aggressive setting or to get a serial port with a large buffer.

When away from the office

Q I need to connect from home to my office and access e-mail, the Web, and files on the company's server. The facilities to do this exist at my office, but the Dial-up Networking icon in my system's My Computer folder is not there. What do I do?

AAbout 95 per cent of all Windows 95 systems ship with Dial-Up Networking pre-installed. But if yours did not, you must load it from diskette or from CD-ROM. Open Control Panel, select Add/Remove Programs, and click on the Windows Setup tab. Select Communications and press the button marked Details. Check the box Dial-up Networking to install it. After the installation, upgrade immediately to Dial-Up Networking, Version 1.2. It fixes many bugs in the original.

Brett Glass has been working with PCs and networks and fixing their bugs for 15 years. To submit a Help Desk query, send an e-mail to brett_glass@infoworld.com


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