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Difficulty: MediumInterswitch Connectivity and Trunking (802.1Q)

A network administrator is configuring a secure interswitch 802.1Q trunk link on Cisco switch interface GigabitEthernet0/1. The task requires statically enabling trunking, stopping DTP frame negotiation, reassigning the native VLAN to VLAN 99, and removing VLAN 1 from the trunk's allowed list. Place the CLI commands and actions in the correct logical configuration order.

  1. 1Access the target interface configuration mode (interface GigabitEthernet0/1).
  2. 2Statically configure the interface into trunk mode (switchport mode trunk).
  3. 3Disable Dynamic Trunking Protocol negotiation (switchport nonegotiate).
  4. 4Reassign the untagged native VLAN to VLAN 99 (switchport trunk native vlan 99).
  5. 5Prune VLAN 1 from passing traffic over the link (switchport trunk allowed vlan remove 1).

Answer

The correct sequence begins by entering interface mode, enforcing static trunking, disabling DTP negotiation, setting native VLAN 99, and finally removing VLAN 1 from the allowed VLAN list.
Configuring a static 802.1Q trunk on a Cisco Catalyst switch requires stepping into interface configuration mode first. Setting switchport mode trunk must precede switchport nonegotiate because DTP disabling is rejected by Cisco IOS on dynamic interfaces. Configuring native VLAN 99 and pruning VLAN 1 completes the trunk hardening workflow.

Step-by-Step Solution

1
Execute interface GigabitEthernet0/1 in global configuration mode.
Enters interface configuration context.
Port configuration parameters must be applied within the specific interface context.
2
Execute switchport mode trunk.
Sets administrative state to unconditional trunking.
Cisco IOS requires an explicit static mode (trunk or access) prior to issuing switchport nonegotiate.
3
Execute switchport nonegotiate.
Stops transmission of DTP frames.
Prevents unauthorized trunk negotiation while ensuring the link remains statically operational.
4
Execute switchport trunk native vlan 99.
Configures VLAN 99 as the native untagged VLAN.
Overrides default VLAN 1 untagged frame behavior to prevent security issues such as VLAN hopping.
5
Execute switchport trunk allowed vlan remove 1.
Removes VLAN 1 from the trunk forwarding topology.
Ensures default management VLAN traffic does not traverse the interswitch link.

Key Concept

802.1Q Trunk CLI Configuration Order and DTP Prerequisites
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Topics

Interswitch Connectivity and Trunking (802.1Q)

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