CCNA Network Infrastructure and Connectivity Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  show interface transceiver: Outputs Digital Optical Monitoring (DOM) data such as temperature, voltage, and Tx/Rx power for installed transceivers.

  Why this is correct

  The Cisco IOS command 'show interface transceiver' (including variants like 'show interface transceiver detail') reads the SFF-8472 Digital Optical Monitoring (DOM) registers directly from SFP, SFP+, QSFP, and other optical modules over the I2C management bus. It reports real-time temperature, supply voltage, laser bias current, and optical transmit/receive power in dBm, which are critical for predicting fiber-optic link degradation before packets are actually dropped. For copper interfaces such as 1000BASE-T, this command typically shows only basic identifier data, not the full DOM telemetry, because those PHYs do not implement optical monitoring.

• ✓

  SFP-10G-SR: Multimode fiber transceiver supporting 10 Gigabit Ethernet at 850nm over distances up to 300 meters.

  Why this is correct

  The SFP-10G-SR is a Cisco pluggable optical transceiver that implements the 10GBASE-SR IEEE 802.3ae standard, using an 850 nm vertical-cavity surface-emitting laser (VCSEL) and multimode fiber. Over OM3 fiber it supports a reach of 300 meters, and over the higher-grade OM4 fiber the reach extends to 400 meters. It uses duplex LC connectors and is a low-power, hot-swappable option for short-reach data center and enterprise access links running 10 Gbps.

• ✓

  LC connectors: Small form-factor duplex fiber connectors commonly used with SFP and SFP+ optical modules.

  Why this is correct

  LC (Lucent Connector) fiber connectors feature a 1.25 mm ceramic ferrule, exactly half the diameter of the older SC connector, and a push-pull latch mechanism for secure insertion. They are almost always deployed in duplex pairs—one fiber for transmit and one for receive—which matches the physical port layout of SFP/SFP+ transceivers. The small form factor allows higher port density on switches, panel-to-panel patch panels, and structured cabling, making LC the de-facto standard for high-speed Ethernet optical interfaces.

• ✗

  show interface transceiver: Displays physical layer diagnostics including cable length estimates, MDI/MDI-X status, pair swaps, and link quality counters.

  Why it's wrong here

  The diagnostic data described—cable length estimates, MDI/MDI-X status, pair swaps, and link quality counters—are copper-PHY parameters, typically relevant to 1000BASE-T/10GBASE-T twisted-pair links. Such information is not gathered from the optical transceiver's DDM/DOM interface; instead, Cisco Catalyst switches expose it through the 'show controllers ethernet-controller phy' command after the hardware interrogates the Ethernet copper PHY's registers. Therefore, applying this physical-layer diagnostic definition to 'show interface transceiver' is a category error: the correct command for copper PHY diagnostics is a different one entirely.

• ✗

  Cat6a: Multimode fiber transceiver supporting 10 Gigabit Ethernet at 850nm over distances up to 300 meters.

  Why it's wrong here

  Cat6a is an ANSI/TIA-568 cabling standard for balanced twisted-pair copper using RJ45 connectors, designed to support 10GBASE-T at distances up to 100 meters (and 10GBASE-T at 55m on older Cat6). It is fundamentally different from an optical transceiver: it has no lasers, no 850 nm wavelength, and no fiber propagation. The description of a 10 GbE, 850 nm, 300 m multimode fiber optic device applies to the SFP-10G-SR transceiver, not to any Category-rated copper cable.

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