CompTIA Network+ Network+ Ethernet Switching and VLANs 3 — Questions and Answers
Question 1: What is the default VLAN on most Cisco switches, and which VLAN should NOT be used for user data as a security best practice?
- VLAN 100; avoid VLAN 100
- VLAN 1; avoid VLAN 1 (Correct answer)
- VLAN 1002; avoid VLAN 1002
- VLAN 4094; avoid VLAN 4094
Correct answer: VLAN 1; avoid VLAN 1
VLAN 1 is the default VLAN on Cisco switches; best practice dictates moving user data off VLAN 1 to reduce attack surface since many management protocols use it by default.
Question 2: Which STP variant significantly reduces convergence time by introducing Rapid Spanning Tree Protocol?
- IEEE 802.1D
- IEEE 802.1Q
- IEEE 802.1W (Correct answer)
- IEEE 802.1S
Correct answer: IEEE 802.1W
IEEE 802.1W defines Rapid Spanning Tree Protocol (RSTP), which reduces convergence time from 30-50 seconds (classic STP) to a few seconds.
Question 3: A switch port connected to a workstation should have which STP feature enabled to prevent it from ever becoming a root port?
- Root guard
- PortFast (Correct answer)
- BPDU guard
- Loop guard
Correct answer: PortFast
PortFast immediately transitions an access port to the forwarding state, bypassing listening and learning states — appropriate only for ports connected to end devices, not other switches.
Question 4: What mechanism prevents a PortFast-enabled port from causing switching loops if a rogue switch is connected?
- Root guard
- Loop guard
- BPDU guard (Correct answer)
- Storm control
Correct answer: BPDU guard
BPDU guard disables a PortFast port if it receives a BPDU, preventing a rogue switch from disrupting the STP topology.
Question 5: Which inter-VLAN routing method uses a single physical link between the router and switch, with multiple logical sub-interfaces?
- Router on a stick (Correct answer)
- Layer 3 switching
- Proxy ARP routing
- Bridged routing
Correct answer: Router on a stick
Router on a stick uses one physical trunk link with sub-interfaces on the router — each sub-interface handles routing for a different VLAN.
Question 6: What is the purpose of the native VLAN on an 802.1Q trunk link?
- It carries management traffic only
- It carries untagged frames across the trunk (Correct answer)
- It is used exclusively for voice traffic
- It provides redundancy for VLAN 1
Correct answer: It carries untagged frames across the trunk
The native VLAN carries untagged frames across an 802.1Q trunk; both ends of the trunk must agree on the same native VLAN to avoid mismatches.
Question 7: A network administrator wants to allow multiple switch ports to share the same VLAN database automatically. Which protocol facilitates this?
- STP
- VTP (Correct answer)
- LACP
- CDP
Correct answer: VTP
VLAN Trunking Protocol (VTP) propagates VLAN configuration from a VTP server to client switches, keeping the VLAN database synchronized.
CompTIA Network+ Network+ Ethernet Switching and VLANs 3
What is the default VLAN on most Cisco switches, and which VLAN should NOT be used for user data as a security best practice?