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Difficulty: HardVLAN Configuration and Access Port Setup

A network administrator is setting up a Cisco Catalyst switch. Interface GigabitEthernet0/3 is connected to an end-user host that must belong to VLAN 45. VLAN 45 has not been previously created in the switch VLAN database. The administrator enters global configuration mode and executes the following commands:

Switch# configure terminal
Switch(config)# interface gigabitethernet0/3
Switch(config-if)# switchport access vlan 45

Which statement correctly describes the operational state of VLAN 45 and interface GigabitEthernet0/3 after these commands are executed?

  1. VLAN 45 is automatically created in the VLAN database, but the interface will still negotiate Dynamic Trunking Protocol (DTP) unless 'switchport mode access' is explicitly configured.Answer
  2. B
    The command is rejected with a CLI syntax error because VLAN 45 must be explicitly created in global configuration mode using the 'vlan 45' command before interface assignment.
  3. C
    VLAN 45 is automatically created in the VLAN database, and the interface administrative mode is automatically changed to static access mode without requiring further configuration.
  4. D
    Interface GigabitEthernet0/3 drops all incoming host frames until VLAN 45 is explicitly set as the native VLAN using the 'switchport trunk native vlan 45' command.

Answer

VLAN 45 is automatically created in the VLAN database, but the interface will still negotiate Dynamic Trunking Protocol (DTP) unless 'switchport mode access' is explicitly configured.
When the 'switchport access vlan 45' command is entered for a VLAN that does not yet exist, Cisco IOS automatically creates VLAN 45 in the VLAN database (assigning a default name like VLAN0045). However, setting the access VLAN does not change the port's administrative trunking mode. On Cisco Catalyst switches with default DTP settings (dynamic auto or dynamic desirable), the interface will continue to attempt trunk negotiation unless 'switchport mode access' is explicitly configured to force static Layer 2 access mode.

Step-by-Step Solution

1
Analyze the behavior of 'switchport access vlan <vlan-id>' when the target VLAN does not exist.
Cisco IOS automatically creates the non-existent VLAN in the VLAN database (e.g., % Access VLAN does not exist. Creating vlan 45).
IOS features automatic VLAN creation when assigning an access VLAN to an interface.
2
Evaluate the switchport mode state of the interface.
The command 'switchport access vlan 45' configures the access VLAN parameter, but does not explicitly change the interface mode to static access.
By default, Catalyst switch ports operate in dynamic mode (dynamic auto or dynamic desirable), meaning DTP frames are still sent/processed unless 'switchport mode access' is explicitly applied.
3
Determine the necessary complete configuration for a dedicated access port.
Both 'switchport mode access' (to statically force access mode and disable trunk negotiation) and 'switchport access vlan 45' are required.
Best practice requires explicit configuration of both switchport mode access and switchport access vlan.

Key Concept

Cisco IOS Automatic VLAN Creation and Access Port Command Requirements
Estimated Time:2m 0s
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Topics

VLAN Configuration and Access Port Setup

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