ICND1 LAN Switching Technologies 3 — Questions and Answers
Question 1: Which EtherChannel negotiation protocol is Cisco proprietary?
- LACP
- PAgP (Correct answer)
- RSTP
- DTP
Correct answer: PAgP
Port Aggregation Protocol (PAgP) is Cisco proprietary, while LACP is the IEEE 802.3ad standard.
Question 2: What happens when a port configured as a PortFast port receives a BPDU?
- It ignores the BPDU
- It transitions normally through STP states
- BPDU Guard shuts the port if enabled (Correct answer)
- It becomes the root port
Correct answer: BPDU Guard shuts the port if enabled
If BPDU Guard is enabled, receiving a BPDU on a PortFast port immediately puts the port in err-disabled state.
Question 3: How many bits make up a VLAN ID in an 802.1Q tag?
- 8
- 10
- 12 (Correct answer)
- 16
Correct answer: 12
The VLAN ID field in an 802.1Q tag is 12 bits, supporting VLAN IDs 0–4095.
Question 4: Which type of switch attack exploits the limited size of the MAC address table to force flooding?
- VLAN hopping
- MAC flooding attack (Correct answer)
- STP manipulation
- ARP spoofing
Correct answer: MAC flooding attack
A MAC flooding attack fills the CAM table so the switch floods all frames, allowing an attacker to capture traffic.
Question 5: What is the purpose of a native VLAN on an 802.1Q trunk?
- It carries management traffic only
- It is used for untagged frames traversing the trunk (Correct answer)
- It is the VLAN with highest priority
- It encrypts frames between switches
Correct answer: It is used for untagged frames traversing the trunk
The native VLAN carries untagged Ethernet frames across an 802.1Q trunk link.
Question 6: Which command displays the VLANs that are allowed and active on a trunk interface?
- show vlan brief
- show interfaces trunk (Correct answer)
- show vtp status
- show spanning-tree
Correct answer: show interfaces trunk
'show interfaces trunk' lists trunk ports with their native VLAN, encapsulation, and allowed VLANs.
Question 7: In STP, which switch becomes the root bridge?
- The switch with the highest MAC address
- The switch with the lowest bridge ID (Correct answer)
- The switch with the most ports
- The switch with the highest priority only
Correct answer: The switch with the lowest bridge ID
The root bridge is elected as the switch with the lowest Bridge ID, which combines priority and MAC address.
ICND1 LAN Switching Technologies 3
Which EtherChannel negotiation protocol is Cisco proprietary?