Who, Me? Rejoice, dear reader, for it is Monday – the day to which everyone looks forward. No? Well, the silver lining to this particular cloud is another instalment of Who, Me? – _The Reg_'s weekly tales of techies who thought they were fixing something, but flamed out.
This week's hero is a network tech whom we will Regomize as "Sherlock." Back in the 1990s he was working as an IT manager for a business that had a number of regional hubs, each linked to HQ over a 128K link. Smaller regional offices were linked to their hubs with 64K connections.
Cisco knows that netadmins are a busy lot, and one feature of the command line for its IOS is an autocomplete that means typing some characters of a command followed by the TAB key offers tells the OS to complete whatever syntax you're typing.
Typing `sh`\-TAB can therefore be a shortcut to the command `show`, thus saving two whole keystrokes and valuable microseconds for greater productivity.
The version Sherlock used back in the day had a similar feature that he discovered could cause problems when driving boxes over a wide area network. So when he typed `net sh ip xxx` to get settings for a remote box, his network connection disappeared. Attempts to re-establish the link were to no avail – no link existed.
A hasty examination of the Cisco manual revealed the issue: over a network connection, the abbreviation `sh` corresponds not to `show` but to `shut`. Sherlock had destroyed his connection because in the 1990s, when IOS was young, no-one had thought to ensure that the same shortcut didn't mean two entirely different commands in different contexts.
Understanding the issue was one thing – fixing it another. Sherlock managed to find a modem with which he could dial back in to the remote office, and successfully established a connection that way. He still had to re-establish the link to head office though.
He tried the command `net open ip xxx`, but to no avail. There was still no connection. And the manual was no help this time either.
In desperation he consulted an engineer friend – let's call him "Watson" – and asked if he knew how to detangle this conundrum.
Watson thought for a moment and asked if he had un-shut the network connection. Sherlock thought he had – isn't that what `open` is for?
No, it seems not. In this ancient edition of IOS, before `open` would make a connection, users had to reverse the `shut` condition. So the appropriate command was `net no sh ip xxx`.
With that done, Sherlock was able to continue his work, with a valuable lesson learned.
Ever had a moment when something you did resulted in something you didn't want to happen, and reading the manual didn't help? Tell us about it in [an email to Who, Me?](mailto:whome@theregister.com) and we may feature your misadventure on some future Monday. ®