initiation to CLI/IOS command line

5 min readMay 23, 2021


first you must download the cisco packet tracer and create an account to be able to follow these tutorials. Don’t be afraid it’s free.

CLI (interface line command): we will use this different modes// according to the configurations that we want to effect on our.

The different Modes in CLI

1-User EXEC Mode

this is the first mode you have access to, when you connect to a command line device. here you will be able to carry out commands only as a user, to check that we are in user mode we look at the sign after the name of the device for example:

2-Privileged Exec Mode

to switch from user mode to privileged mode, write the “enable” command. It can be written in three ways
* enable + enter
* en + Tab +enter
or by searching for the word en +?.
here we can see more commands than the user mode.

3-Configuration Mode

In privileged mode you can observe several commands using the show command but cannot modify the configurations.
to make changes you must go to configuration mode using the following commands:
* configuration terminal + enter
* conf t + Tab + enter

*conf ?
to exit this mode I just have to type exit

  • Global configuration

it allows you to make configurations that will affect all the equipment

Example: change the name
“hostname R1”

this mode allows us to perform configurations at the interfaces.
already to know the different interfaces of a device we can do:
* show ip interface when in mode
privileged simple
: <R1> # show ip interface brief
* do show ip interface in configure terminal mode
: <R1> (config) #do show ip interface brief

  • interface configuration mode

being in configure terminal mode.
I write the command interface + the name of the interface + enter;
Example: I will add an ip address to an interface
<R1>(config) #interface Gigabitethernet0 / 0 + enter

<R1>(config-if)#ip address

  • Subinterface configuration mode

this configuration is the same like the interface mode

4-Rommon mode

who comes from Read
only memory is the mode that allows you to modify the configurations of your equipment before it is started. Iwill do a specific write on it.

5- now you will do some practice to work on what we have learned

set a host name
configure an interface

connect 2 routers network, host 1 and 2 after verify the connection using a ping

  • we choose the 2 routers.

-we connect them together with a cable.

-we give the address
to the first route(router0)

-we give the address
to the second router(router1)

-to put small notes(yellow), we use this and to return to normal mode I press here(red).

-also to look at all the configurations running on my router
I type:
"show running-config + enter"
"show run + Tab”

“do show run + Tab if you are in configure terminal mode”


“do show running-config

here we can see the different configurations on our interface.

  • to browse the run config page, press the space button

here we can see that we are assigning the ip address:
to this interface.
also the interface presents a shutdown signal this means that it remains closed even after configuration.
to activate the interface we must enter the interface configuration and type the command no shuttdown

if we type the command "do show ip int brief" to look at all the configurations of all the interfaces of our equipment

you can see that the protocol of our interface GigabitEthernet0/0/0 is set down,it means that our interface is not connect to another device. so you must connect the second device(router1).

we finish the configuration of the routeur1(we put the hostname,the ip address and type the command “no shut” to set up the protocol )so that it can connect to the other router.

Now you can observ that the cable is green means that the two routeurs are connected each other.

Before ping the two routeurs, we will talk about the ARP protocol, this protocol help any device to storage in his Mac Table all the correspondence between an interface and his ip address. SO if a device don’t have in his Mac Table the correspondence between ip address and interface of the other device the can’t respond to this device.

The first arp this device only nows about his own interface, the second arp it nows about his own interface and all the interfaces that he tried to talk with them.

The first ping that the device send from anoter, we will use to learn the ARP Table/Mac Table we called the “arp request”, so the acheive from the second ping.

Exanple: in the image below we read “success rate is 80 percent (4/5) …”, means that the first of this five pings failed.