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Difficulty: HardVLAN Configuration and Access Port Setup

A network administrator is inspecting a port configuration on a Cisco Catalyst switch after connecting an end-host workstation. The output of the command `show interfaces fastethernet 0/15 switchport` displays the following information:

text
Name: Fa0/15
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: On
Access Mode VLAN: 20 (VLAN0020)
Trunking Native Mode VLAN: 1 (default)

Which statement correctly explains why the operational mode of interface FastEthernet 0/15 is reported as `static access`?

  1. The connected end-host does not send Dynamic Trunking Protocol (DTP) negotiation frames, so the port defaults to operating as an access port in VLAN 20.Answer
  2. B
    The interface was explicitly configured with the `switchport mode access` command in interface configuration mode.
  3. C
    A native VLAN mismatch occurred between the switch port and the end-host, forcing the switch to downgrade the link to an access port.
  4. D
    The interface is operating in static access mode because VLAN 20 is configured as the 802.1Q native VLAN on the switch.

Answer

The connected end-host does not send Dynamic Trunking Protocol (DTP) negotiation frames, so the port defaults to operating as an access port in VLAN 20.
The Administrative Mode of FastEthernet 0/15 is `dynamic auto`, meaning the interface is capable of becoming a trunk if the neighboring device actively requests it (such as a port in `dynamic desirable` or `trunk` mode). Because an end-host workstation does not run Dynamic Trunking Protocol (DTP), no DTP frames are received. Consequently, the interface defaults to functioning as a single-VLAN access port assigned to Access Mode VLAN 20.

Step-by-Step Solution

1
Analyze the Administrative Mode and Operational Mode from the CLI output.
Administrative Mode is `dynamic auto` and Operational Mode is `static access`.
Administrative Mode indicates how the port is configured to negotiate, while Operational Mode shows its actual behavior.
2
Evaluate DTP behavior in `dynamic auto` mode.
Ports set to `dynamic auto` respond to DTP negotiation (desirable or trunk) but will not initiate DTP packets to form a trunk.
Since the end device is a host workstation, no DTP packets are received by the switch port.
3
Determine the operational state and active VLAN.
Failing to form a trunk link causes the switch port to fall back to access mode, assigning untagged host traffic to Access Mode VLAN 20.
An un-negotiated dynamic switchport defaults to an access port carrying traffic for its configured access VLAN.

Key Concept

DTP Negotiation Mechanics and Access Port Operational States
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Topics

VLAN Configuration and Access Port Setup

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