Back in the old days we as engineers used to live and die by the CLI (Command Line Interface). I can remember days when fighting a fire on the network meant having 20 different telnet windows open and alt-tabbing between them as I displayed my technical wizadry with Cisco's CLI - whipping back routing loops, spanning tree problems, and broadcast storms like a circus trainer controls a pack of hungry lions. All the while putting the technical neophytes standing around me watching into a state of awe comparable to the way that Luke Skywalker was awed when Yoda lifted the x-wing tie fighter from the swamp and placed it safely on dry ground using the Force... Yeah, I said it - shock and awe level CLI skills. Jedi level CLI skills. Eat your heart out Napoleon Dynamite... Wow, those were the days!!!
Nowadays you can do a lot of your work without having to drop to a CLI. In many cases, web GUIs have replaced telnet and SSH and the days of using Cisco's CLI to edit your router config or using the command-line to change the configuration of your Linux server's configuration are somewhat behind us. A lot of today's "experts" will tell you that the CLI is to be avoided and that with today's technology it's an unnecessary skill.
I'm here to tell you - don't believe it for a second. Learn the CLI. Start out with either Cisco's CLI or the command-prompt on a Linux machine (whichever you have easier access to) and go from there. The key here is to get comfortable working in this mode. Everybody's CLI is a little different so don't worry so much about syntax. Most of today's network gear has a CLI that is based on Cisco's. Many hardware vendors even advertise a "Cisco-like CLI", so starting there is a great choice.
There's quite a bit of free help available online and some of the free CCNA study guides and labs are a great way to get some exposure; but, bottom line - dive in and get your hands dirty... The best way to learn this stuff is by doing it.
Trust me, there will be times when you need to be able to work from just an IP address and an SSH client and go from there. Download a copy of puTTY for free and keep a copy on every system that you work from. Someday you'll thank me...
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