CCNA Switching and Network Access Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Enter interface configuration mode for the desired switch port.

  Why this is correct

  This is the prerequisite for any port-level configuration, as it selects the exact physical interface (e.g., GigabitEthernet0/1) that will host the IP phone and downstream PC. Without this mode, the subsequent commands would either be invalid globally or unintentionally apply to all interfaces. Interface configuration mode creates the context in which the access VLAN, voice VLAN, and PortFast settings can be consistently applied to the intended single port.

• ✓

  Configure the port as an access port using the switchport mode access command.

  Why this is correct

  Setting the port to static access mode ensures it does not engage in Dynamic Trunking Protocol (DTP) negotiations with the IP phone, which could otherwise turn the link into a trunk and disrupt VLAN assignment. In an access port, the switch strips any VLAN information from untagged frames from the PC and assigns them to the configured access VLAN, while voice frames from the phone remain tagged and are matched to the voice VLAN. This command provides a predictable, deterministic forwarding behavior essential for a mixed-mode voice/data connection.

• ✓

  Assign the data VLAN to the access port with the switchport access vlan command.

  Why this is correct

  This command defines the VLAN that will carry untagged traffic sent by the PC connected to the IP phone's integrated switch, thereby separating data traffic from the voice VLAN. Without a specific data VLAN assignment, the switch would leave the port in its default VLAN (usually VLAN 1), which may conflict with the organization's addressing and security design. Properly assigning the access VLAN ensures that all broadcast frames and user traffic are confined to the correct Layer 2 segment.

• ✓

  Assign the voice VLAN to the port using the switchport voice vlan command.

  Why this is correct

  The `switchport voice vlan` command performs two critical functions: it sets the VLAN that will carry IP phone traffic, and it triggers the switch to send CDP packets with the VLAN ID to the phone, instructing the phone to tag its voice frames with that VLAN. As a result, voice packets are separated from data packets even though both traverse the same physical access port. This separation enables the application of QoS policies that give strict priority to voice traffic over best-effort data.

• ✓

  Enable PortFast on the port with the spanning-tree portfast command.

  Why this is correct

  PortFast bypasses the Spanning Tree Protocol (STP) listening and learning states, moving the interface directly to forwarding state, which is critical for devices like IP phones that need immediate connectivity during boot. Without PortFast, the port could remain in a blocking state for 15 to 30 seconds, causing the phone's call manager to mark it unavailable or delaying DHCP for the PC. It is safe to enable PortFast only on ports that connect to end hosts, never on ports facing other switches, where it could introduce bridging loops.