Linux Admin Asked Savvy Scientist For IT Help And The Boffin Blew It

Who, Me? Welcome, gentle reader, to another exciting week at the coalface of tech and therefore the anticipation of five joyous productive days ahead and a fresh edition of Who, Me? – The Register's reader-contributed tales of tech gone awry.

This week's main character we'll Regomize as "Igor" because he used to work in a lab back in the day. The lab was full of networked computers, but none of the boffins – for Igor was a boffin – knew much of how the software side of it all worked.

What Igor did know how to do was put together the custom cables and RJ45 connectors that linked it all up. Thus it came to be that when one of the network admins needed a hand adding some new Linux boxes to the network, Igor was recruited to handle the physical stuff while the admin worked magic at the keyboard.

Mostly this involved removing cases, inserting network cards, restoring cases and then attaching all the appropriate cables into the right ports on the machines. However, this was in the days before network cards automagically configured and diagnosed themselves, so the network guy asked Igor to rig up a loopback cable for that purpose.

Such cables connect to the transmitting and receiving ports on the card and ensure that it can, at least, talk to itself. It's a little more complicated than that but this is Who, Me? – not a networking tutorial.

When Igor's loopback cable was plugged in to a working card the little green activity light would spring to life, providing reassuring warm fuzzies all round. Such a handy thing to have.

Before very long, the new machines were all networked and the lab was screaming along at ten spectacular megabits per second, which was considered quite speedy in those days.

• Compression? What's that? And why is the network congested and the PCs frozen?
• After we fix that, how about we also accidentally break something important?
• Personalized pop-up was funny for about a second, until it felt like stalking
• Did you hear the one about the help desk chap who abused privileges to prank his mate?

The next day Igor returned to the lab and his usual boffinry duties, but found the network not nearly so speedy as he would have liked. Indeed no-one in the lab was able to boffin as quickly as they would have liked, and the network admin's demeanor had turned sour as he muttered strange phrases like "packet loss" and "failed pings" and "collisions".

When Igor went to join them at the hardware cabinet, he was shocked at what he saw: orange and red lights had almost completely replaced the lovely green he saw the previous day.

Just then he had a thought. "Could this have anything to do with my loopback cable," he asked?

"What do you mean?"

"Well," he said, "I found it so handy yesterday that I didn't want to lose it, and I thought one of the unused ports in here would be as good a place as any to keep it …"

With that he reached in and unplugged the cable, at which point all the red and orange lights immediately turned green and joyous sounds were heard throughout the lab.

Well, almost throughout the lab. The admin had some choice words for Igor about not plugging anything into the network cabinet without asking. And Igor learned that what can be a powerful tool when you know what you're doing can be very dangerous when you don't.

Have you ever discovered that you know just enough about something to do some damage? Tell us about it in an email to Who, Me? and we might share your knowledge with other readers and brighten some future Monday. ®