You can remotely access a Sisco IOS (Internetworking Operating System) in what is knows as an EXEC session to control a router using its CLI (Command Line Interface).

EXEC sessions are separated into a basic user EXEC level and a privileged EXEC level to run configuration and other critical commands.

Critical Cisco Router configuration commands
‘————’ is used to prefix comments in this small tutorial

Router>enable ———— enable is used to change into privileged level
Password: —————— if passwords is enabled
Router# ———————- # means we are in privileged level
Router#disable ———– switch to user EXEC level
Router>

Router>ping xxx.xxx.xxx.xxx ———— ping is supported

The show command is used to troubleshoot your Cisco router

Router#show ?—————————— display arguments
Router#show interfaces
Router#show ip protocols
Router#show ipv6 protocols
Router#show ip route
Router#show ipv6 route
Router#show ip arp
Router#show ipv6 neighbors
Router#show running-config———— display running-configuration
Router#show startup-config———— display startup-configuration stored in NVRAM

P.S. typing ‘?’ after a word directly (no space in between) such as ‘co?’ shows all command wards starting with co

The configuration mode

Router#config———————————————————– start config
Router(config)#——————————————————— inside config mode
Router(config)#hostname MyRouter—————————- change router name to MyRouter
MyRouter(config)#
MyRouter(config)#enable secret [password]—————– set password for privileged level
MyRouter(config)# no enable secret—————————- remove password

Within config mode there are three levels. These are: interface, router and line.

Interface level example

MyRouter(config)#interface FastEthernet0/1
MyRouter(config-if)#ip address 192.168.0.1 255.255.255.0
MyRouter(config-if)#ipv6 address fe80::230:1bff:fe80:b8ea/64
MyRouter(config-if)#ipv6 enable
MyRouter(config-if)#no shutdown—————— to activate interface
MyRouter(config-if)#ctrl-z—————————– ctrl-z is used to save&exit

Routing engine level example

MyRouter(config)# router rip —————– to configure RIP (Routing Information Protocol) routing engine
MyRouter(config-router)# network 192.168.4.0———— adds network 192.168.4.0 to RIP engine
MyRouter(config-router)# network 192.168.5.0———— adds network 192.168.5.0 to RIP engine
MyRouter(config-router)# exit————————————- exits back to global configuration level

MyRouter(config)#ip name-server xxx.xxx.xxx.xxx———– To specify the address of one or more name servers
MyRouter(config)# ip route 0.0.0.0 0.0.0.0 20.2.2.3———— configures a static IP route (global)

Line level (CTY, VTY, AUX, TTY/ASYNC) example

‘Lines’ on Cisco routers are physical or visual serial ports. For instance, the console (CTY) port is used to connect your computer to the router using a cable through a serial interface. This port require protection as such we should set a password for future connection attempts.

MyRouter(config)#line con 0
MyRouter(config-line)#password [password]————- set a PW for the console line
MyRouter(config-line)#login————————————– activate login/password requirement
MyRouter(config-line)#exit

VTY ports are visual ports. As such, they are used for remote access using Telnet or SSH.
The following examples demonstrate how to configure VTY ports in a Sisco router

MyRouter(config)#line vty 0 4———————————— typically there are 5 ports
MyRouter(config-line)#password [password]————- set a PW for the Virtual Terminal Line
MyRouter(config-line)#login————————————– activate login/password requirement
MyRouter(config-line)#exit

note, you may add ‘?’ to learn last line number as in the following example

MyRouter(config)#line vty 0 ?
<1-4> Last Line Number
MyRouter(config)#

An AUX port acts as a secondary console port.
TTY/ASYNC exist only if the router has an ASYNC card.

Finally, make sure your new configurations will be perminant with the following command

MyRouter# copy running-config startup-config ———— or ‘write memory’ for old IOS prior to 11.x

References:

[1] Configure lines and VTYs on Cisco routers.

http://www.techrepublic.com/blog/networking/configure-lines-and-vtys-on-cisco-routers/409

[2] Cisco IOS Command Line Interface Tutorial. http://www.cisco.com/warp/cpropub/45/tutorial.htm