220-1101 Question 217
Single answerRJ45A technician is replacing a damaged Ethernet wall jack in a small office. After terminating the cable to the new RJ45 keystone jack, the user reports that the PC links at only 100 Mbps instead of 1 Gbps. The switch port is known to support Gigabit Ethernet, and the cable run tested fine before the jack was replaced. Which action is the MOST likely to resolve the issue?
- A
Re-terminate the jack and verify that all four twisted pairs are punched down according to the same wiring standard, such as T568B
- B
Replace the RJ11 patch cable between the wall jack and the PC with a longer cable to reduce signal reflection
- C
Move the cable from the switch to the uplink port so the connection can negotiate at a higher speed
- D
Disable auto-negotiation on the NIC and manually set the speed to 1 Gbps full duplex
Show answer and explanation
Correct answer: A
Explanation
This question tests practical troubleshooting of RJ45 terminations. In real installations, replacing a keystone jack or connector is a common point where wiring mistakes occur. For 10/100 Mbps Ethernet, only two pairs are used, so a partially working termination may still link at 100 Mbps. However, 1000BASE-T requires all four pairs to be correctly connected and terminated. Best practice is to use a recognized pinout standard, typically T568A or T568B, and keep the same standard on both ends of the run unless intentionally creating a crossover cable. Technicians should also preserve pair twists as close as possible to the termination point to maintain signal integrity. This aligns with Ethernet cabling best practices and TIA/EIA structured cabling standards commonly referenced in networking documentation.
- A. Correct.
Correct. 1000BASE-T requires all four wire pairs in an RJ45 Ethernet connection to be properly terminated. If even one pair is open, miswired, or punched down inconsistently, the link may fall back to 100 Mbps, which uses only two pairs. Verifying that the keystone jack is terminated consistently to a standard such as T568A or T568B on both ends is the most likely fix after a jack replacement.
- B. Incorrect.
Incorrect. RJ11 is a smaller connector used for telephone lines, not standard Ethernet patching to an RJ45 NIC and wall jack. Cable length does not address the core issue here, and 'signal reflection' is not the likely cause in this scenario. The problem began after re-terminating the wall jack, pointing to pair termination or pinout consistency.
- C. Incorrect.
Incorrect. An uplink port does not inherently provide a higher Ethernet speed. Modern switches typically auto-sense port roles, and moving to an uplink port would not fix a miswired or partially terminated RJ45 jack. The symptom specifically suggests a physical layer termination problem.
- D. Incorrect.
Incorrect. Manually forcing 1 Gbps is not an appropriate fix for bad cabling or improper termination. Gigabit Ethernet depends on successful negotiation and proper use of all four pairs. If the cable is not correctly terminated, manually changing the NIC setting will not create a stable 1 Gbps link.