Cisco IOS user interface is divided into different modes. Use ? to check list of commands available in that mode.
When we first login into the switch or router, we are in user mode also known as EXEC mode. This mode is identified with “>” symbol. It has limited commands. Only show or clear commands are available. We can use clear command to reset the interface counters. The second mode is the Privileged mode and it is identified with “#” symbol.
csr1000v-1#? Exec commands: <1-99> Session number to resume access-profile Apply user-profile to interface access-session Access-session options for eEdge alps ALPS exec commands app-hosting Application hosting appnav IOS Wide Area Application Services archive manage archive files attach Connect to a module's console audio-prompt load ivr prompt authentication Authentication options for eEdge auto Exec level Automation beep Blocks Extensible Exchange Protocol commands bfe For manual emergency modes setting bulkstat Bulkstat exec commands call Voice call call-home Call-Home commands cd Change current directory clear Reset functions clock Manage the system clock cns CNS agents configure Enter configuration mode connect Open a terminal connection controller-mode controller-mode service copy Copy from one file to another credential load the credential info from file system crypto Encryption related commands. cts Cisco Trusted Security Exec Commands debug Debugging functions (see also 'undebug') delete Delete a file diagnostic Diagnostic commands dir List files on a filesystem disable Turn off privileged commands disconnect Disconnect an existing network connection dns DNS Protocol commands do-exec Mode-independent "do-exec" prefix support dot1x IEEE 802.1X Exec Commands eap EAP Exec Commands emadmin Extension Mobility Commands enable Turn on privileged commands erase Erase a filesystem ethernet Ethernet parameters
To make changes to a device, we must go into global configuration mode. Use configuration terminal to move into global configuration mode. From global configuration mode, we can make changes to the running configuration, add an IP address to the interface, configure SSH or telnet.
csr1000v-1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. csr1000v-1(config)#
Interface configuration mode
csr1000v-1(config)#interface GigabitEthernet1 csr1000v-1(config-if)#
Line configuration mode
csr1000v-1(config)#line vty 0 4 csr1000v-1(config-line)#