no shutdown
Enables an interface that has been administratively disabled, allowing it to forward traffic and participate in network operations.
no shutdownWhen to Use This Command
- After configuring a new interface, use 'no shutdown' to activate it.
- When troubleshooting a down interface that shows 'administratively down', re-enable it with this command.
- After making configuration changes on an interface that was shut down for maintenance, bring it back online.
- When recovering from a security incident where an interface was disabled, re-enable it after verifying the threat is resolved.
Command Examples
Activating a GigabitEthernet interface
interface GigabitEthernet0/1
no shutdownRouter(config-if)#no shutdown Router(config-if)# *Mar 1 00:05:23.123: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to up *Mar 1 00:05:24.124: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up
The first syslog message indicates the interface hardware state changed to up. The second message indicates the line protocol (Layer 2) is up, meaning the interface is fully operational.
Re-enabling a VLAN interface after maintenance
interface Vlan10
no shutdownRouter(config-if)#no shutdown Router(config-if)# *Mar 1 00:10:45.678: %LINK-3-UPDOWN: Interface Vlan10, changed state to up *Mar 1 00:10:46.679: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed state to up
Similar to physical interfaces, VLAN interfaces (SVI) also generate link and line protocol up messages when enabled.
Understanding the Output
The 'no shutdown' command itself produces no direct output on the CLI. Instead, the router generates syslog messages indicating the interface state change. The first message '%LINK-3-UPDOWN' shows the physical interface state transitioning to 'up'. The second message '%LINEPROTO-5-UPDOWN' indicates the line protocol (Layer 2) is up, meaning the interface can pass traffic. If the line protocol does not come up, it suggests a Layer 1 or Layer 2 issue (e.g., cable unplugged, mismatched encapsulation). In a production network, always verify with 'show interfaces' to confirm the interface status is 'up/up'.
CCNA Exam Tips
Remember that 'shutdown' disables an interface and 'no shutdown' enables it; the default state for most interfaces is 'shutdown'.
On CCNA exam, you may be asked to troubleshoot a down interface; check if it's 'administratively down' and apply 'no shutdown'.
The 'no shutdown' command is available in interface configuration mode for physical interfaces, SVIs, and subinterfaces.
After applying 'no shutdown', always verify with 'show interfaces' or 'show ip interface brief' to confirm the interface is up.
Common Mistakes
Forgetting to enter interface configuration mode before issuing 'no shutdown' (will get '% Invalid input detected').
Typing 'no shutdown' in global configuration mode instead of interface mode.
Assuming 'no shutdown' fixes all interface issues; it only removes administrative disablement, not physical or protocol problems.
Related Commands
show interfaces
Displays detailed status and statistics for all interfaces or a specific interface, used to verify interface operational state, errors, and performance.
show ip interface brief
Displays a summary of all IP interfaces on the device, including their IP address, status, and protocol state, used for quick verification of interface configuration and connectivity.
shutdown
Disables an interface, preventing it from sending or receiving traffic, typically used for administrative shutdown or troubleshooting.
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