Cisco IOS (Internetwork Operating System) is the operating system used by Cisco networking devices, including routers, switches, and firewalls. It provides the foundation for network connectivity, routing, security, and management of Cisco devices. Cisco IOS is a modular operating system that supports a wide range of features and protocols, making it highly customizable and flexible for different network environments. Just about all Cisco products make use of Cisco IOS to operate and Cisco CLI to be managed. The fundamental CLI commands for those of them are actually the same, which simplifies Cisco unit control. Here are the command Cisco cheat sheet which identifies the fundamental instructions for configuring, troubleshooting, and securing Cisco network equipment.
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Key Features of Cisco IOS
- Modularity
- Routing Protocols
- Security
- Quality of Service (QoS)
- Network Management
- IPv6 Support
- High Availability
Table of Contents
Fundamental Configuration Commands
Command |
Purpose |
| enable | Logs you within enable mode, and that is likewise recognized as user exec mode as well as a privileged mode |
| configure terminal | Logs you into configuration mode |
| interface fastethernet/number | Enters interface configuration mode for the specified swiftly ethernet interface |
| reload | An exec mode command which reboots a Cisco switch or even router |
| hostname name | Sets a hostname to the current Cisco network device |
| copy from-location to-location | An enable mode command that copies files from one file location to another |
| copy running-config startup-config | An enable mode command that saves the active config, replacing the startup config when a Cisco network device initializes |
| copy startup-config running-config | An enable mode command that merges the startup config with the currently active config in RAM |
| write erase
erase startup-config |
An enable method command which deletes the startup config |
| ip address ip-address mask | Assigns an IP address and a subnet mask |
| shutdown
no shutdown |
Used in interface configuration mode. “Shutdown” shuts down the interface, while “no shutdown” brings up the interface. |
| ip default-gateway ip_address | Sets up the default gateway on a Cisco device |
| show running-config | An enable mode command that displays the current configuration |
| description name-string | A config interface command to describe or name an user interface |
| show running-config interface slot/number | An enable mode command to display the running configuration for a specific interface |
| show ip interface [type number] | Displays the usability condition of interfaces that are set up for IP |
| ip name-server serverip-1 serverip-2 | A configure method command which sets the IP addresses of DNS servers |
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Troubleshooting Commands |
|
| ping {hostname | system-address} [source source-address] | Used in enable mode to diagnose simple network connectivity |
| speed {10 | 100 | 1000 | auto} | A user interface mode command which physically sets the pace to the specified worth or even negotiates it automatically |
| duplex {auto | full | half} | A user interface mode command which physically sets duplex to half, full, or even auto |
| cdp run
no cdp run |
A configuration mode command which allows or maybe disables Cisco Discovery Protocol (CDP) for the device |
| show mac address-table | Displays the MAC address table |
| show cdp | This shows whether CDP is actually enabled globally |
| show cdp neighbors[detail] | Lists summary info about each neighbor hooked up to this particular device; the “detail” alternative lists detailed info about each neighbor |
| show interfaces | Displays detailed information about interface status, settings and counters |
| show interface status | Displays detailed info about interface status, counters & adjustments |
| show interfaces switchport | Displays the interface line condition show interfaces switchport Displays a big range of configuration options and present operational status, such as VLAN trunking information. |
| show interfaces trunk | Lists information about the currently operational trunks and the VLANs supported by those trunks |
| show vlan
show vlan brief |
Lists each VLAN as well as just interfaces assigned to that VLAN but doesn’t include trunks |
| show vtp status | Lists the present VTP status, like the present mode |
Routing and VLAN Commands |
|
| ip routenetwork-number network-mask {ip-address | interface} | Sets a static route in the IP routing table |
| router rip | Enables a Routing Information Protocol (RIP) routing procedure, which places you in router configuration mode |
| network ip-address | In router configuration mode, associates a network with a RIP routing process |
| version 2 | In router configuration mode, configures the software program to receive as well as send just RIP edition two packets |
| no auto-summary | In router configuration mode, disables automatic summarization |
| default-information originate | In router configuration mode, generates a default route into RIP |
| passive-interface interface | In router configuration mode, sets only that interface to passive RIP mode. In passive RIP mode, RIP routing updates are accepted by, but not sent out of, the specified interface. |
| show ip rip database | Displays the contents of the RIP routing database |
| ip nat [inside | outside] | An interface configuration mode command to designate that traffic originating from or destined for the interface is subject to NAT |
| ip nat inside source {list{access-list-number | access-list-name}} interface type number[overload] | A configuration mode command to establish dynamic source translation. Use of the “list” keyword enables you to use an ACL to identify the traffic that will be subject to NAT. The “overload” option enables the router to use one global address for many local addresses. |
| ip nat inside source static local-ip global-ip | A configuration mode command to establish a static translation between an inside local address and an inside global address |
| vlan | Creates a VLAN and enters VLAN configuration mode for further definitions |
| switchport access vlan | Sets the VLAN that the interface belongs to. |
| switchport trunk encapsulation dot1q | Specifies 802.1Q encapsulation on the trunk link. |
| switchport access | Assigns this port to a VLAN |
| vlan vlan-id [name vlan-name] | Configures a specific VLAN name (1 to 32 characters) |
| switchport mode { access | trunk } | Configures the VLAN membership mode of a port. The access port is set to access unconditionally and operates as a non-trunking, single VLAN interface that sends and receives non-encapsulated (non-tagged) frames. An access port can be assigned to only one VLAN. The trunk port sends and receives encapsulated (tagged) frames that identify the VLAN of origination. A trunk is a point-to-point link between two switches or between a switch and a router. |
| switchport trunk {encapsulation { dot1q } | Sets the trunk characteristics when the interface is in trunking mode. In this mode, the switch supports simultaneous tagged and untagged traffic on a port. |
| encapsulation dot1q vlan-id | A configuration mode command that defines the matching criteria to map 802.1Q frames ingress on an interface to the appropriate service instance |
DHCP Commands |
|
| ip address dhcp | A configuration mode command to acquire an IP address on an interface via DHCP |
| ip dhcp pool name | A configuration mode command to configure a DHCP address pool on a DHCP server and enter DHCP pool configuration mode |
| domain-name domain | Used in DHCP pool configuration mode to specify the domain name for a DHCP client |
| network network-number [mask] | Used in DHCP pool configuration mode to configure the network number and mask for a DHCP address pool primary or secondary subnet on a Cisco IOS DHCP server |
| ip dhcp excluded-address ip-address [last-ip-address] | A configuration mode command to specify IP addresses that a DHCP server should not assign to DHCP clients |
| ip helper-address address | An interface configuration mode command to enable forwarding of UDP broadcasts, including BOOTP, received on an interface |
| default-router address[address2 … address8] | Used in DHCP pool configuration mode to specify the default router list for a DHCP client |
Security Commands |
|
| password pass-value | Lists the password that is required if the login command (with no other parameters) is configured |
| username name password pass-value | A global command that defines one of the possibly multiple user names and associated passwords used for user authentication. It is used when the login local line configuration command has been used. |
| enable password pass-value | A configuration mode command that defines the password required when using the enable command |
| enable secret pass-value | A configuration mode command that sets this Cisco device password that is required for any user to enter enable mode |
| service password-encryption | A configuration mode command that directs the Cisco IOS software to encrypt the passwords, CHAP secrets, and similar data saved in its configuration file |
| IP domain-name name | Configures a DNS domain name |
| crypto key generate rsa | A configuration mode command that creates and stores (in a hidden location in flash memory) the keys that are required by SSH |
| transport input {telnet | ssh} | Used in vty line configuration mode, defines whether Telnet or SSH access is allowed into this switch. Both values can be specified in a single command to allow both Telnet and SSH access (default settings). |
| access-list access-list-number {deny | permit} source [source-wildcard] [log] | A configuration mode command that defines a standard IP access list |
| access-class | Restricts incoming and outgoing connections between a particular vty (into a basic Cisco device) and the addresses in an access list |
| ip access-list {standard | extended} {access-list-name | access-list-number} | A configuration mode command that defines an IP access list by name or number |
| permit source [source-wildcard] | Used in ACL configuration mode to set conditions to allow a packet to pass a named IP ACL. To remove a permit condition from an ACL, use the “no” form of this command. |
| deny source [source-wildcard] | Used in ACL configuration mode to set conditions in a named IP ACL that will deny packets. To remove a deny condition from an ACL, use the “no” form of this command. |
| ntp peer <ip-address> | Used in global configuration mode to configure the software clock to synchronize a peer or to be synchronized by a peer |
| switchport port-security | Used in interface configuration mode to enable port security on the interface |
Monitoring and Logging |
Commands |
| logging ip address | Configures the IP address of the host that will receive the system logging (Syslog) messages |
| logging trap level | Used in configuration mode to limit messages that are logged to the Syslog servers based on severity. Specify the number or name of the desired severity level at which messages should be logged. |
| show logging | Enable mode command that displays the state of system logging (Syslog) and the contents of the standard system logging buffer. |
| terminal monitor | An enable mode command that tells Cisco IOS to send a copy of all Syslog messages, including debug messages, to the Telnet or SSH user who issues this command |
CISCO IOS Commands for Troubleshooting, Debugging, And Configuring Network
Troubleshooting Commands
Show IP Interface Brief: Displays a summary of the status and configuration of all interfaces on the device.
Ping: Sends ICMP echo requests to a destination IP address to test connectivity.
Traceroute: Traces the route that packets take from the source device to a destination device, showing the IP addresses of intermediate hops.
Show IP Route: Displays the routing table, showing the network destinations and the next-hop IP addresses.
Show Running-Config: Displays the current configuration of the device.
Show Interfaces: Provides detailed information about the status and statistics of all interfaces.
Debug: Enables debugging messages for various processes. Use with caution as it can generate a lot of output and affect device performance.
Show Log: Displays the system log messages.
Debugging Commands:
Debug IP Packet: Displays detailed information about IP packets as they are processed by the device.
Debug Spanning-Tree: Shows spanning-tree-related information, such as topology changes and port states.
Debug BGP: Enables BGP (Border Gateway Protocol) debugging messages.
Debug DHCP: Displays DHCP (Dynamic Host Configuration Protocol) messages exchanged between the device and DHCP servers.
Debug AAA: Enables debugging messages for AAA (Authentication, Authorization, and Accounting) processes.
Undebug: Disables debugging for a specific debug command.
Configuration Commands:
Configure Terminal: Enters global configuration mode to make changes to the device’s configuration.
Interface: Enters interface configuration mode to configure settings specific to a particular interface.
IP Address: Allocate a specific IP address to the interface.
Hostname: Sets the device’s hostname.
Banner MOTD: Configures a message of the day (MOTD) banner that is displayed when someone logs in to the device.
IP Route: Configures static IP routes.
Access-List: Creates an access control list (ACL) to filter network traffic.
SNMP-Server: Configures SNMP (Simple Network Management Protocol) parameters.
NTP Server: Configures NTP (Network Time Protocol) server settings.
CISCO IOS Fundamental Commands
These are some of the fundamental configuration commands used in Cisco IOS. The specific commands and options available may vary depending on the device platform and software version
Enable: Enters privileged EXEC mode, providing access to advanced configuration and management commands.
Configure Terminal: Enters global configuration mode, allowing you to configure various settings on the device.
Hostname [Name]: Sets the hostname of the device to the specified name.
Interface [Interface-Name]: Enters interface configuration mode for the specified interface, allowing you to configure settings such as IP address, subnet mask, and speed.
IP Address [IP-Address] [Subnet-Mask]: Assigns an IP address and subnet mask to an interface.
No Shutdown: Enables an interface, allowing it to send and receive network traffic.
Clock Rate [Value]: Sets the clock rate for a serial interface. This command is used when the interface is acting as a DCE (Data Communications Equipment) and is connected to a DTE (Data Terminal Equipment).
Description [Description-Text]: Adds a description to an interface for documentation purposes.
Exit: Exits the current configuration mode and returns to the previous mode.
Tracert Or Traceroute: Traces the route that packets take from the source device to a destination device, showing the IP addresses of intermediate hops.
Show Interfaces: Provides detailed information about the interfaces on the device, including their status, IP addresses, and traffic statistics.
Show IP Route: Displays the routing table of the device, showing the routes the device knows about and how it will forward packets.
Copy Running-Config Startup-Config: Saves the current running configuration to the startup configuration, which will be loaded on the device boot.
Write: Saves the current configuration to the startup configuration.
Ping [Destination-Address]: Sends an ICMP echo request to the specified destination address to test connectivity.
Operational and configuration commands to display information on Cisco routers and switches
These commands can help you gather crucial operational and configuration information for troubleshooting, monitoring, and managing Cisco routers and switches.
Show Version: Displays information about the hardware, software version, uptime, and configuration register.
Show Interfaces: Provides detailed information about the status and statistics of all interfaces on the device.
show IP interface brief: Displays a summary of the status and configuration of all interfaces, including IP addresses and interface types.
Show Running-Config: It shows the current configuration of a particular device.
Show Startup-Config: Displays the saved configuration stored in NVRAM (Non-Volatile RAM).
Show Protocols: Shows the routing protocol information, including enabled protocols and their status.
Show Ip Route: Displays the routing table, showing the network destinations and their next-hop IP addresses.
Show Arp: Shows the Address Resolution Protocol (ARP) table, which maps IP addresses to MAC addresses.
Show Mac Address Table: Displays the MAC address table entries, which list MAC addresses learned by the switch.
Show VLAN: Provides information about VLANs configured on the switch.
Show Spanning-Tree: This shows information about the spanning tree protocol, including the spanning tree topology and port states.
Show CDP Neighbors: Displays information about directly connected Cisco devices discovered via the Cisco Discovery Protocol (CDP).
Show Processes CPU: Shows CPU utilization and statistics for various processes running on the device.
Show Logging: Displays the logging configuration and recent log messages.
show access lists: Shows the configured access control lists (ACLs) and their parameters.
show clock: Displays the device’s current date and time settings.
show inventory: Provides information about the hardware inventory of the device.
show environment: It displays environmental information e.g. temperature and power supply.
Security Commands
Username: Creates a local user account with a password for authentication.
Copy code
line VTY: Configures the virtual terminal (Telnet/SSH) lines for remote management.
Login: Enables login authentication for the configured line.
Transport Input: Restricts the allowed protocols for remote access (Telnet/SSH)
Conclusion
The Cisco IOS CLI is actually the primary user interface for configuring, maintaining, and troubleshooting most Cisco products. By this particular user interface, you are able to immediately perform each Cisco IOS command, and it does not matter the way you achieve the Cisco IOS platform; you are able to enter some CLI command from a remote, console, or maybe a terminal screen.
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