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1.0 Network Infrastructure and Connectivity

Interface & Cable Diagnostics Practice Questions

Updated for CCNA v2.0

Collisions, errors, duplex and speed mismatches, copper and fibre limits, pinouts, and optical signal levels.

CCNA v2.0 objective 1.1 · objective map

Author-reviewed by LabFabric · 25 September 2026 · Report a content issue

One solved question, so you can see how these are marked

A switch interface shows a growing count of late collisions. Which cause is most likely?

A duplex mismatch, with the counting side operating at half duplex

Late collisions occur when a half-duplex port sees a collision after the first 64 bytes, which is typical of a duplex mismatch or an over-length cable segment. Full-duplex links do not have collisions.

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All 11 Interface & Cable Diagnostics questions in this set

Answers and explanations appear when you work through the set above.

  1. One end of a link is hard-coded to 100 Mb/s full duplex and the other end is set to auto. What outcome is typical on a Cisco switch?

    • The auto side detects the speed but falls back to half duplex, causing a duplex mismatch
    • Both sides negotiate 1 Gb/s
    • The link stays down permanently
    • The auto side also becomes full duplex

  2. In a duplex mismatch, which side typically reports late collisions and which reports CRC and runt errors?

    • The half-duplex side reports late collisions and the full-duplex side reports CRC and runt errors
    • Both sides report only late collisions
    • The full-duplex side reports late collisions and the half-duplex side reports CRC errors
    • Neither side reports errors

  3. Which maximum length applies to a Cat 5e or Cat 6 copper Ethernet link for 1000BASE-T?

    • 100 meters
    • 10 meters
    • 550 meters
    • 1 kilometer

  4. A fiber link between two switches will not come up. The technician suspects transmit and receive fibers are reversed. What is the usual fix?

    • Swap the transmit and receive fibers at one end
    • Replace the switch with a router
    • Change the port to trunk mode
    • Enable PortFast on both ports

  5. Which fiber type is designed for long distances, such as 10 km or more, using a very small core?

    • Single-mode fiber
    • Multimode OM1 fiber
    • Cat 6a copper
    • Coaxial cable

  6. A single-mode optic is connected to a multimode fiber patch cord with a matching connector. What is the likely result?

    • High loss or an unreliable link, because the fiber type does not match the optic
    • The link works normally at full distance
    • The link works, but only in half duplex
    • The switch automatically converts the light wavelength

  7. An engineer needs to check the received optical power on an SFP. Which type of output would show it, if the module supports digital diagnostics?

    • Transceiver output such as show interfaces transceiver, with Rx power in dBm
    • show ip interface brief
    • show vlan brief
    • show running-config

  8. A fiber link comes up but has many CRC errors, and the Rx power is far lower than the optic's specification. Which action is most appropriate first?

    • Clean the fiber connectors and inspect the patch cord and splice quality
    • Change the VLAN of the port
    • Enable a spanning tree portfast edge trunk
    • Reduce the MTU of the interface

  9. Which cable type is needed to connect two switches by copper if neither switch supports Auto-MDIX?

    • Crossover
    • Straight-through
    • Rollover
    • Coaxial

  10. In a T568B straight-through Ethernet cable, which two pairs carry data on a 10/100 Mb/s link?

    • Pins 1, 2, 3 and 6
    • Pins 4, 5, 7 and 8
    • Pins 1, 4, 5 and 8
    • Only pins 3 and 4

  11. Which show command lists interface error counters such as CRC, runts and collisions in a compact per-port table on a Catalyst switch?

    • show interfaces counters errors
    • show ip route
    • show cdp neighbors
    • show spanning-tree summary