Internetwork Operating System
is the OS Cisco
uses on their brand of
es and router
s. It's basically all from from a Command Line
, and requires knowledge of hundreds of commands to configure.
Well, actually it's pretty helpful if you forget some specifics...
at any time typing '?' will get you a list of available commands and
there is plenty of '?' information about each command. It has nice
little things like it's *nix
-like behaviour of completing lines for you
when you hit Tab
, but the massive amount of context sensitive
help is great.
The IOS has a few different modes:
- User Exec Mode This is the first mode you are dumped into
after logging into a router. You can issue a few informational
commands but you can't do any real damage because all the good
commands are disabled. So you type enable (actually just
typing 'en' will suffice)
- Enabled / Privileged Mode Now we're talking, this is where
you can enter real commands, and by that I mean: wreck shit. From
here you can do a lot of show commands and pretty
much get any information you need and there's a lot of other commands
you can use here that are outside the scope of this doc. You
can reach configuration mode by typing 'config t'
- Configuration Mode From here you can edit the configuration
of the router, routing protocols, interfaces and the console.
To back out of a current mode to go back to the last mode you can type 'exit
or hit ctrl + z
. The default prompt consists of the hostname of the device followed by your
location in the system, much like a *nix system works:
The current release at the time of this writing is 12.2. You can read about the various features
assosiated with each release on Cisco's website ( http://www.cisco.com/warp/public/732/releases/ ).
Some fun commands to explore:
- This command is crazyass. I can't count the number of times I've been
warned against this command. It basically logs all these debug messages to
the console for debugging (duh) purposes. Sometimes this can generate a lot
of extra overhead and crash a router.
- delete nvram
- NVRAM stands for Non-Volatile RAM, which is where the config is saved.
- This leads you through setting up some basics on the router to
get it up and running. It will lead you through configuring what protocols
will be running on it as well as setting up any interfaces that are
present. It's good for newbies, but 'router gods' will look down on you.
- 'show ?' will get you a bunch of options. Basically
show is your window into everything that's going on in the router. Some good
options are: show interfaces, show version, show ip route, show running config.
These will get you started, and these are commands you end up using all the time.
- IOS runs telnet clients and servers on all the devices so you can
hop around from router to router using this. It can get a bit confusing
because you can keep hopping from router to router until you're going though
a half dozen devices, and on top of that you can run multiple concurrent
sessions on each router. You gotta keep an eye on your prompt and
remember where you are...
See also: Cisco IOS