Question

Difficulty: MediumInterswitch Connectivity and Trunking (802.1Q)

A network administrator needs to manually configure an 802.1Q trunk link on a switch port supporting multi-encapsulation according to security best practices. Place the Cisco IOS configuration commands in the correct execution sequence from initial interface selection to traffic pruning.

  1. 1Enter interface configuration mode (e.g., interface GigabitEthernet0/1)
  2. 2Set trunk encapsulation to 802.1Q (switchport trunk encapsulation dot1q)
  3. 3Configure the interface mode to trunk (switchport mode trunk)
  4. 4Reassign the native VLAN away from default VLAN 1 (switchport trunk native vlan 99)
  5. 5Specify the list of permitted VLANs (switchport trunk allowed vlan 10,20,99)

Answer

The correct configuration sequence is: 1) Enter interface context, 2) Define 802.1Q encapsulation, 3) Set switchport mode to trunk, 4) Reassign the native VLAN ID, and 5) Define allowed VLANs for traffic pruning.
The correct operational sequence begins with entering the interface configuration context. Next, on switches supporting multiple encapsulation protocols, 802.1Q encapsulation must be explicitly configured prior to setting the interface mode to trunk. Once the trunk state is active, security hardening steps follow: reassigning the untagged native VLAN away from VLAN 1, and finally filtering trunk traffic by restricting allowed VLANs.

Step-by-Step Solution

1
Select the target interswitch physical interface context.
Enters interface configuration prompt context.
CLI commands must target the specific interface designated for trunking.
2
Execute switchport trunk encapsulation dot1q.
Defines IEEE 802.1Q frame tagging for the port.
On legacy or multi-layer Catalyst switches, attempting switchport mode trunk before selecting encapsulation results in a CLI error.
3
Execute switchport mode trunk.
Forces interface into permanent trunking state.
Establishes trunk operation and stops unconditional access behavior.
4
Execute switchport trunk native vlan 99.
Changes untagged frame handling to VLAN 99.
Enhances security by avoiding the default native VLAN 1.
5
Execute switchport trunk allowed vlan 10,20,99.
Restricts broadcast/multicast forwarding to specified VLANs.
Implements traffic filtering and pruning across interswitch links.

Key Concept

Manual 802.1Q Trunk CLI Configuration Order
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