Getting started with the Cisco CLI

First lab on the Cisco CLI: one switch (SW2), one router (R1), and my notes from the session, written down so I can find this stuff again later.

Command modes

Logged into SW2 and landed at Switch>. That’s user EXEC.

Typed enable and the prompt changed to Switch#, which is privileged EXEC. From there configure terminal got me to Switch(config)#, and interface Eth0/0 dropped me into Switch(config-if)#.

• User EXEC, Switch>: where login drops you. exit leaves.
• Privileged EXEC, Switch#: enable to get in, disable to drop back.
• Global config, Switch(config)#: configure terminal to get in; end, exit, or Ctrl-Z to get out.
• Interface config, Switch(config-if)#: interface <id> to get in; exit goes up one level, end jumps straight back to privileged EXEC.

Two things I noticed while bouncing between modes. exit only backs out one level, while end and Ctrl-Z jump all the way back to privileged EXEC from any config sub-mode. And ? in user EXEC shows way fewer commands than in privileged EXEC: the command set changes with the mode.

Getting help

Spent some time just poking at ? to see how it behaves:

• ? lists every command available in the current mode
• s? lists commands starting with “s” (no space before the ?)
• show ? lists the arguments valid after show (space before the ?)
• show r? narrows those to arguments starting with “r”
• Tab completes a unique abbreviation

The space matters. s? filters command names, but s ? asks what arguments follow a command called s.

Tab completion needs enough characters to be unambiguous. sh plus Tab completed to show, but con plus Tab did nothing. Typed con? and saw why: configure and connect both match.

Paging through output

At the --More-- prompt, Space goes to the next page and Enter goes to the next line. Ctrl-C, Q, or another key quits the output (which key varies by device and IOS version).

Editing and terminal history

Up and Down arrows recall previous commands. Two things I learned here.

Each mode keeps its own history buffer. In config mode I couldn’t recall the EXEC commands I typed earlier, and vice versa.

And history stores every command I entered, including the mistyped ones that never ran. That’s what makes it useful for fixing typos.

The cursor shortcuts:

• Ctrl-A jumps to the beginning of the line, Ctrl-E to the end
• Left and Right arrows move one character; Backspace deletes to the left
• Ctrl-Z exits config mode

My typo-fix routine ended up being: Up Arrow to recall, Ctrl-A, arrow right to the bad character, Backspace, type the fix, Enter.

Same trick handles repetitive config. After setting up Serial 1/0 on R1, configuring Serial 1/1 was three Up-Arrow recalls with one character changed each time.

Configuration files

There are exactly two files to care about. running-config lives in RAM: it’s the live config, changes take effect immediately, and it’s lost on reload. startup-config lives in NVRAM and gets loaded at boot.

The commands that move between them:

• show running-config / show startup-config display each one
• copy running-config startup-config saves changes so they survive a reload
• erase startup-config wipes the saved config, and it’s the one command here that cannot be abbreviated
• reload reboots the device

I proved the volatility to myself on SW2: changed the hostname, ran reload, answered No to the save prompt, and the device came back with the old name. Changes live in RAM until you copy them to NVRAM. Saying yes at that prompt overwrites startup-config, so No is how you throw changes away on purpose.

I also ran erase startup-config and reloaded, which took the switch back to factory defaults, including the default hostname Switch.

What I entered on R1:

hostname Temp
interface Serial 1/0
 description Link to SP1
 no shutdown

no shutdown was needed because router interfaces default to administratively down.

Output filtering

Append a pipe | after a show command, then a filter keyword and an expression:

• include shows only lines containing the expression
• exclude shows only lines not containing it
• begin shows everything from the first match onward
• section shows the matching line plus its indented sub-lines

What I ran:

show running-config | include hostname
show startup-config | include hostname
show running-config | begin interface
show running-config | section interface
show running-config | exclude !

section is the one I’ll actually use for config review. It pulls the whole interface block, not just the header line. exclude ! strips the comment lines that pad out show running-config.

For the exam

• Know which prompt corresponds to which mode, and the command to move between each.
• enable and disable move between user and privileged EXEC; configure terminal enters global config.
• erase startup-config cannot be shortened.
• Changes live in RAM until copied to NVRAM.
• include, exclude, begin, section: know what each one returns.