220-1101 Question 317
Single answerEthernetA technician is troubleshooting a desktop that was recently moved to a different office cubicle. The user reports that the PC can access network resources, but file transfers to the server are much slower than expected. The switch port shows a link light, and the technician notices the NIC status on the PC indicates 100 Mbps instead of the expected 1 Gbps. The patch cable in use is an older cable with no visible category label. Which of the following is the MOST likely cause of the reduced Ethernet speed?
- A
The connection is using a cable that does not meet the requirements for Gigabit Ethernet
- B
The PC must be connected with a rollover cable to negotiate 1 Gbps
- C
The switch port is using PoE, which limits data speeds to 100 Mbps
- D
The NIC is operating at 100 Mbps because Ethernet cannot auto-negotiate speed on modern switches
Show answer and explanation
Correct answer: A
Explanation
This scenario tests practical Ethernet troubleshooting. When a desktop links at 100 Mbps instead of 1 Gbps after being moved, one of the first things to check is the cable. Gigabit Ethernet over copper, defined as 1000BASE-T by IEEE 802.3, requires appropriate twisted-pair cabling and all four pairs to be properly connected. In contrast, 10/100 Ethernet can operate with only two pairs, so damaged, low-category, or poorly terminated cables often still produce link but only at 100 Mbps. Best practice is to verify the switch port configuration, confirm the NIC supports 1 Gbps, and replace the patch cable with a known-good Cat 5e or better cable before escalating further. This aligns with common CompTIA A+ troubleshooting expectations and standard Ethernet implementation guidance.
- A. Correct.
Correct. 1000BASE-T Gigabit Ethernet commonly requires cabling that meets at least Cat 5e standards and uses all four wire pairs. If the technician finds an older or improperly terminated cable, the link may fall back to 100 Mbps instead of 1 Gbps. This is a very common real-world cause when a system is moved and connected with an unknown patch cable.
- B. Incorrect.
Incorrect. A rollover cable is used for console connections to network devices, not for normal Ethernet connections between a PC and a switch. Using a rollover cable for a workstation network connection would not be the proper method for achieving Gigabit Ethernet.
- C. Incorrect.
Incorrect. Power over Ethernet provides electrical power over Ethernet cabling to supported devices such as IP phones, cameras, and access points. PoE itself does not inherently limit a switch port to 100 Mbps. Many PoE ports support Gigabit speeds.
- D. Incorrect.
Incorrect. Ethernet auto-negotiation is a standard and is widely used on modern NICs and switches to determine the best supported speed and duplex settings. If a link settles at 100 Mbps, a cabling issue, hardware limitation, or manual configuration problem is more likely than the idea that Ethernet cannot auto-negotiate.