Trunk

 #en

#conf t

#int fa or gig (fa 0/1 or gig 0/1)

if you need to config more than 1 port at the same time you can :

#int range fa 0/1, fa 1/2

#switchport trunk encapsulation dot1q

#switchport mode trunk

#exit

1. Check Trunk Status and Allowed VLANs

show interfaces trunk

• Displays:
  • Interfaces operating as trunks.
  • Allowed VLANs.
  • VLANs in the active state on the trunk.
  • Native VLAN.

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2. View Detailed Information for a Specific Interface

show interfaces [interface-id] switchport

• Replace [interface-id] with the specific trunk interface, e.g., GigabitEthernet0/1.
• Displays:
  • Administrative mode (e.g., trunk).
  • Operational mode (actual status, e.g., trunk or access).
  • Allowed VLANs and native VLAN.

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3. Verify Running Configuration for the Interface

show running-config interface [interface-id]

• Replace [interface-id] with the specific trunk interface.
• Confirms the configured mode (switchport mode trunk) and other related settings.

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4. Check VLANs Active on the Trunk

show vlan brief

• Ensures VLANs intended for trunking are present and active.

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5. Verify Dynamic Trunking Protocol (DTP)

show dtp interface [interface-id]

• Replace [interface-id] with the trunk interface.
• Provides details on DTP status and negotiation parameters.