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Question 30
A duplex fiber link has compatible optical modules and correct wavelengths at both ends. A cable audit discovers the patch connects Tx at switch A to Tx at switch B, and Rx to Rx. What is the specific physical correction?
- Cross-connect each transceiver Tx to the opposite transceiver Rx
- Change the routed static default route on the switches
- Increase the VLAN trunk allowed list on both ports
- Add an Ethernet collision-detection setting to both full-duplex optical interfaces
Explanation
Correct Answer
A:A standard two-fiber optical link needs each transmitter to feed the receiver at the far end; Tx-to-Tx and Rx-to-Rx cannot provide this path.
Incorrect Answers
B:A Layer 3 route change cannot remedy an optical transmitter patched into another transmitter.
C:Trunk VLAN allowances operate above physical link establishment and do not fix mispatched optical pairs.
D:Modern full-duplex optical Ethernet does not use collision-detection settings to repair crossed optical fiber paths.
Question 31
A carrier provides a dedicated circuit with exactly two network interfaces, one at each office, and no third station sharing the physical medium. Which link topology description matches this service?
- A point-to-point connection between the two endpoint interfaces
- A multiaccess Ethernet collision domain containing several independent endpoints
- A broadcast LAN hub shared with additional stations on the same wire
- A multipoint WAN connection with separate third-party customer endpoints
Explanation
Correct Answer
A:Point-to-point identifies a direct pair of endpoints; that is the precise topological property of a two-ended dedicated circuit.
Incorrect Answers
B:A multiaccess domain has potentially more than two stations sharing a medium, contrary to the exactly two-endpoint constraint.
C:A shared hub segment creates a half-duplex multi-station collision domain rather than a dedicated two-interface link.
D:A multipoint WAN involves multiple attached endpoints, which the stated dedicated two-interface circuit explicitly excludes.
Question 32
A legacy half-duplex Ethernet segment shares one physical collision domain through a repeating device, and two simultaneous transmitters may collide. Which shared-medium model describes that design?
- A full-duplex point-to-point switched Ethernet link with no shared collision domain
- A shared half-duplex Ethernet collision domain
- A set of independent full-duplex switch links, each without collisions
- An IP routed network where collisions are determined by longest-prefix matching
Explanation
Correct Answer
B:A repeater or hub preserves one shared half-duplex medium. Multiple stations can transmit concurrently and trigger Ethernet collisions, which CSMA/CD addresses.
Incorrect Answers
A:Dedicated full-duplex switch links do not share a half-duplex collision domain; they have no CSMA/CD contention between independent transmitters.
C:Full-duplex switched connections have independent paths and do not use the legacy shared-medium collision mechanism identified in the scenario.
D:IP routing selects a Layer 3 destination route; it does not determine whether two stations collide while transmitting on a shared half-duplex Ethernet segment.
Question 33
A 500-meter Ethernet run crosses electrically noisy industrial motors. Both ends have compatible optical transceivers and a supported fiber budget. Which link medium avoids electrical conduction and electromagnetic pickup along this route?
- Use the specified fiber-optic link between the matched optical ports
- Use unshielded Cat5e copper over the entire 500 meters
- Use shielded copper cabling but keep the 500-meter Ethernet copper segment unchanged
- Install copper coax with passive adapters on both optical SFP ports
Explanation
Correct Answer
A:An optical fiber carries light rather than electrical current and is immune to electromagnetic pickup along the dielectric fiber path, assuming the optical budget and optics are compatible.
Incorrect Answers
B:Twisted-pair 1000BASE-T copper over 500 meters exceeds standard copper Ethernet reach and remains susceptible to severe EMI in this environment.
C:Shielding mitigates some electromagnetic interference but does not turn an overlength Ethernet copper link into a standards-compliant 500-meter medium.
D:A passive coax adapter cannot convert an optical transceiver's light signals into electrical coax signaling, nor satisfy the specified installed optical interfaces.
Question 34
A 200-meter data-center duplex fiber run uses legacy OM1 multimode cabling, but both ends already have functional 850-nm Cisco SFP-10G-SR optics. Cisco rates this SR optic for about 33 meters on OM1 but 300 meters on OM3. Which physical remediation can support the required 200-meter 10-Gb/s link without replacing the SR transceivers?
- Keep the 200-meter OM1 cable and change only the connector keying to LC duplex
- Replace the OM1 run with suitable OM3 multimode fiber and keep the matching SR transceivers
- Keep the 200-meter OM1 run and assume a VLAN trunk configuration increases its modal bandwidth
- Swap the SR modules for 1310-nm 10GBASE-LR modules while retaining the OM1 run as if it were single-mode
Explanation
Correct Answer
B:Cisco specifies up to 300 meters for these SR optics on OM3 and only about 33 meters on OM1. Replacing the entire overlong OM1 path with verified OM3 preserves the 850-nm SR hardware and meets the requested optical reach, subject to link budget and installation quality.
Incorrect Answers
A:Connector fit does not increase OM1 fiber modal bandwidth; the specified optical reach remains below 200 meters.
C:An 802.1Q trunk changes Ethernet frame tagging but cannot repair an out-of-spec optical transmission plant.
D:10GBASE-LR optics are designed for compatible single-mode fiber at 1310 nm. Retaining the specified OM1 multimode plant does not satisfy that optical system and also violates the request to retain SR optics.
Question 35
A Cisco switch has an installed duplex-LC SFP-10G-SR optical module, but the technician brought an RJ-45 copper patch lead. The far end uses a matching SR optic and 100-meter OM3 plant. Which physical patching change is correct?
- Insert the RJ-45 lead into the SFP+ LC sockets with an adapter that requires no optical conversion
- Use any single-mode LC fiber because matching connectors guarantee matching optical reach
- Install a suitable duplex-LC OM3 multimode patch pair and connect Tx to the far-end Rx
- Leave the copper lead in place and configure 802.1Q tagging to convert the physical signal
Explanation
Correct Answer
C:The SR transceivers need compatible multimode fiber and the two optical directions must cross transmitter to receiver.
Incorrect Answers
A:An RJ-45 copper lead carries electrical signals; a passive plug adapter cannot convert that medium into 850-nm optical transmission.
B:Connector shape alone does not make single-mode cable interchangeable with the multimode SR link specified in the question.
D:VLAN tagging changes Ethernet framing, not the physical medium or the required LC optical path.
Question 36
A legacy 100-Mb/s Ethernet handoff is hard-set full duplex on one end but half duplex on the other. The observed CRC errors and late collisions began immediately after this configuration change. What corrective action targets the identified cause?
- Raise the IP interface MTU on both devices to avoid late collisions
- Align both link partners on a supported identical duplex configuration or compatible auto-negotiation
- Increase the trunk allowed VLAN list to include all production VLANs
- Change the default gateway so the traffic avoids the mismatched link
Explanation
Correct Answer
B:Matching duplex behavior removes the mismatch that causes the half-duplex side to see collisions while the full-duplex side does not apply CSMA/CD.
Incorrect Answers
A:MTU affects frame sizing and fragmentation behavior, not the inconsistent half/full duplex setting demonstrated here.
C:A trunk VLAN list controls Layer 2 VLAN transport after a usable link exists and does not correct a duplex conflict.
D:Changing routing does not repair the physical Ethernet duplex disagreement on the handoff.
Question 37
Gi0/1 is hard-set to 1 Gb/s while its older link partner supports only 100 Mb/s, and auto-negotiation cannot establish a common speed. Which change addresses the speed incompatibility before IP troubleshooting?
- Force the switch to 1 Gb/s full duplex while leaving the 100-Mb/s-only peer unchanged
- Change only the VLAN allowed list on the trunk
- Configure compatible link speeds or auto-negotiation
- Increase interface MTU from 1500 to 9000 bytes
Explanation
Correct Answer
C:Both interfaces must share a supported Ethernet speed or negotiate a common setting before the physical link can operate. Adjusting duplex or routes without resolving a hard-coded speed incompatibility will not establish the PHY.
Incorrect Answers
A:The peer cannot establish a common 1-Gb/s physical rate, so the link remains incompatible.
B:802.1Q permissions are above the physical-layer speed mismatch and cannot create a compatible PHY link.
D:A frame-size setting cannot negotiate a common Ethernet line rate with 100-Mb/s-only hardware.
Question 38
A cable certifier reports an open pair on a twisted-pair uplink that intermittently drops when the patch lead moves. Which physical repair should the technician perform first?
- Test and replace the faulty cable or termination
- Change the interface subnet mask without touching the open conductor
- Reduce the router’s OSPF interface cost to avoid a link flap
- Increase the autonegotiation retry timer while keeping the broken cable
Explanation
Correct Answer
A:A damaged conductor, termination or patch cable can corrupt electrical symbols, which are detected as CRC/FCS errors in received frames. Cable certification and replacement directly test that physical cause rather than changing routing configuration.
Incorrect Answers
B:IP addressing cannot restore an electrically open copper pair identified by certification.
C:Routing metrics may change path selection but do not fix the damaged physical patch or termination.
D:Repeated negotiation cannot consistently repair a physical open pair.
Question 39
A switch interface remains down and the operator needs to distinguish `administratively down` from a cable-related `down/down` state. Which first read-only interface evidence is necessary?
- Inspect interface administrative and line state
- Run show ip route and infer that any route absence means the port is shutdown
- Change speed and duplex settings before reading the current link state
- Replace the patch cable without checking whether shutdown is configured
Explanation
Correct Answer
A:Interface output distinguishes administrative shutdown from the operational line state: a shutdown interface is administratively down even with working cabling. Physical disconnection produces a different status and should not be treated as a configured shutdown.
Incorrect Answers
B:Routing information alone cannot distinguish a software administrative disable from lack of carrier.
C:Reconfiguration is premature when a read-only status can separate shutdown from physical down/down.
D:A healthy cable cannot bring up an administratively shut interface, and the requested first step is state inspection.
Question 40
An office's 1000BASE-T link uses a 140-meter permanent copper run. It remains up but accumulates input CRC errors; the engineer also suspects inconsistent peer settings. Which two PHY-related conditions should be checked before changing the IP routing?
- Verify the installed copper channel length and the peers' speed/duplex negotiation
- Change the IPv4 gateway to an alternate next hop without inspecting the Ethernet segment
- Add all VLANs to the 802.1Q trunk allowed list to eliminate CRC corruption
- Increase the IPv4 MTU so oversize frames are no longer detected as FCS errors
Explanation
Correct Answer
A:1000BASE-T is designed for a standards-compliant copper channel rather than a 140-meter run; inspect cabling certification and both ends' supported speed/duplex negotiation to isolate physical errors.
Incorrect Answers
B:Changing a route might bypass the link but cannot diagnose or correct an out-of-spec physical channel or inconsistent link partner settings.
C:A VLAN permission list governs logical transport of tagged frames, not electrical signal integrity on overlength copper pairs.
D:IP MTU changes packet sizing and possible fragmentation; they cannot correct corrupted FCS bits caused by cable loss or PHY mismatch.
Cisco Certified Network Associate (CCNA) (200-301) Practice Tests
