220-1101 Question 127
Single answerManagedA small business replaces its consumer-grade wireless router with a managed switch and separate wireless access points. Users report that devices connected to the switch are limited to 100 Mbps even though the PCs, switch ports, and patch cables are all rated for 1 Gbps. During inspection, a technician notices that several switch ports connected to office PCs have been manually configured instead of left at their defaults. Which configuration change is MOST likely to restore gigabit connectivity?
- A
Set the affected switch ports to auto-negotiate speed and duplex
- B
Enable port mirroring on the affected switch ports
- C
Assign the affected switch ports to a different VLAN
- D
Disable Spanning Tree Protocol on the affected switch ports
Show answer and explanation
Correct answer: A
Explanation
This question focuses on applying managed-switch knowledge to a real support scenario. When a gigabit-capable device links at only 100 Mbps, common causes include bad cabling, only two wire pairs being connected, or incorrect port settings. Because the scenario explicitly states that the PCs, switch ports, and patch cables are rated for 1 Gbps and also notes that the ports were manually configured, the most likely issue is improper speed/duplex configuration. In practice, best practice on modern managed switches is usually to leave access ports at auto-negotiate unless there is a documented reason to hard-code settings. IEEE 802.3 Gigabit Ethernet standards and vendor documentation from major switch manufacturers commonly note that 1000BASE-T depends on auto-negotiation for proper operation. Managed switches provide features such as VLANs, STP, and port mirroring, but those features address segmentation, loop prevention, and traffic analysis rather than restoring a down-negotiated Ethernet link.
- A. Correct.
Correct. On managed switches, manually forcing an incorrect speed or duplex can prevent links from negotiating at their highest supported rate. Gigabit Ethernet over copper typically relies on proper auto-negotiation to establish 1000 Mbps operation and full duplex. Returning the ports to auto-negotiate is the most likely fix when otherwise capable hardware is linking at only 100 Mbps.
- B. Incorrect.
Incorrect. Port mirroring copies traffic from one port to another for analysis with a packet sniffer. It is useful for troubleshooting but does not increase link speed or correct a speed/duplex mismatch. A candidate might choose this because it is a common managed-switch feature associated with diagnostics.
- C. Incorrect.
Incorrect. VLAN assignment controls logical network segmentation, not the physical link speed between the switch port and the connected device. Changing VLANs might affect network access or broadcast domains, but it would not normally cause or resolve a 100 Mbps link on gigabit-capable hardware.
- D. Incorrect.
Incorrect. Spanning Tree Protocol helps prevent Layer 2 switching loops. Disabling STP does not solve a port speed issue and can create serious network instability if redundant paths exist. Someone might select this if they confuse link-state problems with topology-control features.