RANGER GAMEZ

CompTIA Network+ (N10-009) · chapter 24 of 29

Week 24: Copper and glass

In this chapter Objectives 5.2, 5.5

  1. Cable issues
  2. Hardware tools for Layer 1
  3. Practice questions
  4. Chapter recap

Objective 5.2

Cable issues

Incorrect cable

The wrong cable for the job causes errors or no link:

  • Single-mode vs. multimode: SMF (yellow, long distance, laser) and MMF (orange/aqua, shorter) don't mix with the wrong optics
  • Category 5/6/7/8: Cat5e 1 Gbps; Cat6 10 Gbps to ~55 m; Cat6a 10 Gbps to 100 m; Cat7 10 Gbps, shielded; Cat8 25/40 Gbps to 30 m
  • STP vs. UTP: shielded twisted pair for high-EMI areas; unshielded for normal offices

Exam tip 10 Gbps over a 90 m Cat6 run gives errors; Cat6a is rated for 10 Gbps at 100 m.

Signal degradation

Signals weaken or get corrupted by:

  • Crosstalk: signal bleeds between pairs (NEXT/FEXT), often from untwisted pairs at the connector
  • Interference (EMI): motors, fluorescent lights, power cables
  • Attenuation: signal loss over distance; copper Ethernet is limited to 100 m

Exam tip Copper next to a big motor + CRC errors = interference. Use STP or re-route.

Improper termination and TX/RX transposed

Improper termination: wrong pin order (split or mixed-up pairs, or T568A on one end and T568B on the other of a straight-through run), too much untwisted wire, or a loose crimp. Leads to no link, low speed or errors. TX/RX transposed: the transmit and receive sides are swapped, common with fiber patch cords. Fiber link stays down until you flip the pair. On copper, auto-MDIX usually hides it.

Exam tip New fiber run, no link, light visible at both ends? Try swapping the TX/RX strands.

Objective 5.5

Hardware tools for Layer 1

Cable tester

A cable tester checks copper wiring: continuity, wire map (opens, shorts, split or crossed pairs) and often length. Certifier-grade testers also measure crosstalk and attenuation to prove a run meets its category.

WIRE MAP  Jack WH-D4-01
1 ---- 1   OK
2 ---- 2   OK
3 -X-- 6   CROSSED
6 -X-- 3   CROSSED
4,5,7,8   OK
Length: 71 m

Exam tip Tester shows a split/crossed pair? Re-terminate the end.

Toner (tone generator and probe)

A toner puts a tone on a cable at one end; the probe picks it up so you can find the other end in a bundle or patch panel. Perfect when the cable map is missing or wrong.

Exam tip 'Which of these 48 unlabeled cables goes to dock 4?' → toner and probe.

Visual fault locator and taps

A visual fault locator (VFL) shines bright red laser light into fiber; breaks, tight bends and bad connectors glow where light leaks out. A network tap is a hardware device inserted in a link that copies all traffic to a monitor port, including errors, without the drops a busy mirror port can have.

Exam tip Find a break in short fiber runs → VFL. Copy every frame on a link for analysis → tap.

Check yourself 1A new 10 Gbps run of 85 m is installed with Cat6 and shows CRC errors at 10 Gbps but works at 1 Gbps. What is the most likely cause?

  1. A rogue DHCP server
  2. The switch port is administratively down
  3. TX/RX transposed
  4. Wrong cable category for the length
Show the answer

Answer: D. Wrong cable category for the length

Cat6 supports 10 Gbps only to about 55 m. At 85 m use Cat6a (or better), rated for 10 Gbps at 100 m.

Practice questions

Answer in your head, then open the answer. Ranger's Packet Trail has 483 questions like these for Network+, with mock exams.

Question 1A new 10GBASE-T server NIC is patched to a switch over an existing 70 m run of Cat 5e cable. The link comes up only at 1 Gbps. What is the BEST fix?

  1. Replace the run with Cat 6a cable
  2. Enable jumbo frames on the switch port
  3. Set the switch port to half duplex
  4. Replace the patch cord with Cat 5 cable
Show the answer

Answer: A. Replace the run with Cat 6a cable

Cat 5e is rated for 1000BASE-T; 10GBASE-T needs Cat 6a (or better) for a full 100 m (Cat 6 only to about 55 m). The NIC falls back to 1 Gbps on the wrong cable category.

Question 2Two switches are linked with 10GBASE-LR (1310 nm) optics. A technician patched them with an orange OM2 jumper from the spares bin. The link flaps and shows many errors. What is the MOST likely cause?

  1. The TX and RX strands are transposed
  2. A multimode jumper was used with single-mode optics
  3. The PoE power budget was exceeded
  4. A duplex mismatch exists between the two switch ports
Show the answer

Answer: B. A multimode jumper was used with single-mode optics

LR optics are designed for single-mode fiber; OM2 (orange) is multimode. Mixing the two causes high loss and errors, so a single-mode (OS1/OS2, usually yellow) jumper is needed.

Question 3A plant is adding Ethernet drops along a wall shared with large motors and variable-frequency drives. Which cable choice would BEST prevent future link errors on these runs?

  1. Unshielded twisted pair, Cat 6
  2. Plenum-rated unshielded twisted pair, Cat 6a
  3. Crossover-wired twisted pair
  4. Shielded twisted pair, properly grounded
Show the answer

Answer: D. Shielded twisted pair, properly grounded

Shielded twisted pair (grounded at the proper point) resists the EMI that motors and drives generate. Plenum UTP only changes the jacket's fire rating.

Question 4A copper Ethernet run to a remote shed measures 130 m. The link is unstable, and the cable tester reports the signal is too weak at the far end. Which issue is this?

  1. Crosstalk
  2. Electromagnetic interference
  3. Attenuation
  4. Improper termination
Show the answer

Answer: C. Attenuation

Attenuation is the loss of signal strength over distance; twisted pair Ethernet is limited to 100 m. Crosstalk and EMI add noise rather than weaken the signal with length.

Question 5A cable tester fails a newly installed run on NEXT. The technician finds that the installer untwisted about 3 inches (7.5 cm) of each pair at the jack. What problem did this create?

  1. Attenuation
  2. TX/RX transposed
  3. Electromagnetic interference
  4. Crosstalk
Show the answer

Answer: D. Crosstalk

NEXT is near-end crosstalk. Twisting cancels coupling between pairs, so untwisting too much at the termination lets signals bleed between pairs.

Practice it in Ranger's Packet TrailThe same lessons as a story, with drills, hands-on labs and mock exams. Free, in your browser.
Play free

CompTIA, A+, Network+, Security+ and Linux+ are trademarks of CompTIA, Inc. Ranger Gamez is not affiliated with or endorsed by CompTIA. The practice questions are written to the published exam objectives; they are not real exam questions.