Layer 1 and Layer 2 Troubleshooting Flashcards by vadim craevschi

What is the first step in troubleshooting a network connectivity issue at Layer 1?
A) Check the routing table
B) Verify the IP configuration
C) Inspect physical cable connections
D) Test the DNS server
Answer: C) Inspect physical cable connections

Answer: C) Inspect physical cable connections

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Which of the following is NOT a common symptom of a Layer 1 issue?
A) Interface status showing “down/down”
B) High latency in packet transmission
C) Incorrect subnet mask configuration
D) No link light on the network interface

Answer: C) Incorrect subnet mask configuration

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What could cause an Ethernet port to show “down/down” status?
A) Incorrect VLAN assignment
B) Unplugged cable or faulty port
C) Misconfigured IP address
D) Duplex mismatch

Answer: B) Unplugged cable or faulty port

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Which tool can be used to verify proper wiring in a twisted-pair Ethernet cable?
A) Protocol analyzer
B) Cable tester
C) Ping utility
D) SNMP monitor

Answer: B) Cable tester

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What is a possible cause of intermittent connectivity at Layer 1?
A) Incorrect default gateway
B) Loose or damaged cable
C) Wrong DNS settings
D) ACL blocking traffic

Answer: B) Loose or damaged cable

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Which of the following is a symptom of EMI (Electromagnetic Interference) on a network cable?
A) Consistent high-speed data transfer
B) Frequent CRC errors on the interface
C) Perfect signal strength
D) No impact on performance

Answer: B) Frequent CRC errors on the interface

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What happens if an Ethernet cable exceeds its maximum allowed length?
A) Increased bandwidth
B) Signal attenuation and errors
C) Faster data transmission
D) No noticeable effect

Answer: B) Signal attenuation and errors

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Which type of cable is most susceptible to EMI?
A) Fiber optic
B) Coaxial
C) Shielded twisted pair (STP)
D) Unshielded twisted pair (UTP)

Answer: D) Unshielded twisted pair (UTP)

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What does a blinking green LED on a switch port typically indicate?
A) No link detected
B) Port is administratively shut down
C) Active data transmission
D) Duplex mismatch

Answer: C) Active data transmission

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What is the purpose of a loopback test?
A) To test routing protocols
B) To verify physical port functionality
C) To check DNS resolution
D) To measure wireless signal strength

Answer: B) To verify physical port functionality

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What is a common symptom of a Layer 2 issue?
A) Incorrect default gateway
B) High CPU utilization on a router
C) Excessive ARP broadcasts
D) DNS resolution failure

Answer: C) Excessive ARP broadcasts

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What could cause a switch port to be in a “err-disabled” state?
A) Port security violation
B) Incorrect IP address
C) Duplex mismatch
D) Slow network speed

Answer: A) Port security violation

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Which command displays the MAC address table on a Cisco switch?
A) show ip route
B) show mac address-table
C) show arp
D) show interface

Answer: B) show mac address-table

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What is a possible cause of excessive collisions on an Ethernet network?
A) Full-duplex mode enabled
B) Half-duplex mode with high traffic
C) Fiber optic cabling
D) Properly terminated cables

Answer: B) Half-duplex mode with high traffic

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What happens when two switches are connected with mismatched duplex settings?
A) Increased bandwidth
B) No connectivity issues
C) Late collisions and performance degradation
D) Automatic negotiation fixes the issue

Answer: C) Late collisions and performance degradation

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Which protocol helps prevent loops in a Layer 2 network?
A) ARP
B) STP (Spanning Tree Protocol)
C) OSPF
D) EIGRP

Answer: B) STP (Spanning Tree Protocol)

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What is a symptom of a broadcast storm?
A) High unicast traffic
B) Low CPU utilization on switches
C) Network slowdown and high switch CPU
D) No impact on performance

Answer: C) Network slowdown and high switch CPU

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What does a high number of CRC errors indicate?
A) Properly functioning network
B) Physical layer issues (cable/interface problems)
C) Correctly configured VLANs
D) Optimal switch performance

Answer: B) Physical layer issues (cable/interface problems)

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How does a switch handle an unknown unicast frame?
A) Drops the frame
B) Floods it to all ports in the VLAN
C) Sends it to the default gateway
D) Forwards it only to the correct port

Answer: B) Floods it to all ports in the VLAN

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What is the purpose of VLANs in Layer 2 switching?
A) To increase broadcast domains
B) To decrease security
C) To merge all devices into one collision domain
D) To segment broadcast domains

Answer: D) To segment broadcast domains

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What is a common symptom of a faulty fiber optic cable?
A) Increased signal strength
B) Complete loss of light transmission
C) Faster data transfer speeds
D) No impact on connectivity

Answer: B) Complete loss of light transmission

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Which cable type should be used to connect two switches directly without a crossover feature?
A) Straight-through cable
B) Rollover cable
C) Crossover cable
D) Serial cable

Answer: C) Crossover cable

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What happens if an Ethernet cable has incorrect pinouts?
A) No connectivity issues
B) Increased bandwidth
C) Intermittent or no connection
D) Automatic correction by the switch

Answer: C) Intermittent or no connection

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Which command checks the physical status of an interface on a Cisco switch?
A) show ip interface brief
B) show running-config
C) show interface status
D) show vlan brief

Answer: C) show interface status

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What could cause a "no link light" issue on a switch port? A) Correct VLAN assignment B) Properly configured IP address C) Damaged cable or disabled port D) Functional DNS settings

Answer: C) Damaged cable or disabled port

Which tool helps detect breaks in a copper Ethernet cable? A) Multimeter B) Protocol analyzer C) TDR (Time Domain Reflectometer) D) SNMP monitor

Answer: C) TDR (Time Domain Reflectometer)

What is the maximum recommended length for a Cat6 UTP cable? A) 50 meters B) 100 meters C) 150 meters D) 200 meters

Answer: B) 100 meters

What is the effect of using a straight-through cable instead of a crossover between two switches? A) No connectivity B) Faster speeds C) Automatic negotiation fixes it D) No difference

Answer: A) No connectivity

Which LED color typically indicates a 1 Gbps connection on a switch? A) Green B) Amber C) Red D) Blue

Answer: A) Green

What does a steady amber LED on a switch port indicate? A) Active data transmission B) Port is blocked by STP C) No link detected D) Port is disabled

Answer: B) Port is blocked by STP

What is the most likely cause of a switch port in "err-disabled" state? A) Incorrect VLAN assignment B) Port security violation C) Duplex mismatch D) Slow network speed

Answer: B) Port security violation

Which command enables a disabled switch port? A) no shutdown B) enable port C) restart interface D) reload

Answer: A) no shutdown

What happens if two switches have different STP priorities? A) Both become root bridges B) The lower priority switch becomes root C) STP fails to converge D) No effect on the network

Answer: B) The lower priority switch becomes root

What is a symptom of a switching loop? A) Increased unicast traffic B) High CPU usage on switches C) No ARP requests D) Stable MAC address table

Answer: B) High CPU usage on switches

Which command shows STP status on a switch? A) show stp B) show spanning-tree C) show stp status D) show stp details

Answer: B) show spanning-tree

What is the effect of a missing VLAN on a trunk port? A) No impact B) Traffic for that VLAN is dropped C) All VLANs stop working D) Increased bandwidth

Answer: B) Traffic for that VLAN is dropped

What causes MAC address flapping? A) Duplicate IP addresses B) A loop in the network C) Incorrect subnet mask D) Slow DNS resolution

Answer: B) A loop in the network

Which command displays ARP cache on a Cisco switch? A) show arp B) show mac address-table C) show ip arp D) show arp cache

Answer: A) show arp

What happens if two devices have the same MAC address? A) No issues occur B) The switch drops all frames from both C) Intermittent connectivity for both devices D) Increased network speed

Answer: C) Intermittent connectivity for both devices

What is the purpose of BPDU Guard? A) Prevents rogue switches from causing loops B) Increases STP convergence time C) Disables VLANs D) Blocks all BPDUs

Answer: A) Prevents rogue switches from causing loops

What is a common symptom of a damaged fiber optic cable? A) Increased bandwidth B) Complete loss of light signal C) Higher signal strength D) No effect on connectivity

Answer: B) Complete loss of light signal

Which type of cable is required to connect a switch directly to a router’s Ethernet port? A) Crossover cable B) Rollover cable C) Straight-through cable D) Serial cable

Answer: C) Straight-through cable

What happens if an RJ-45 connector is improperly crimped? A) The cable works at reduced speed B) No connectivity or intermittent failures C) The switch automatically corrects errors D) The port LED turns blue

Answer: B) No connectivity or intermittent failures

Which command shows the physical and data link status of an interface on a Cisco switch? A) show ip interface brief B) show interface fa0/1 C) show cdp neighbors D) show vlan

Answer: B) show interface fa0/1

What could cause a switch port to remain in a "down/down" state? A) Incorrect VLAN assignment B) The cable is unplugged C) Duplex mismatch D) STP blocking the port

Answer: B) The cable is unplugged

Which tool is used to measure signal loss in a fiber optic cable? A) Multimeter B) OTDR (Optical Time Domain Reflectometer) C) Cable tester D) Loopback plug

Answer: B) OTDR (Optical Time Domain Reflectometer)

What is the maximum allowable length for a Cat5e UTP cable in Ethernet networks? A) 50 meters B) 100 meters C) 150 meters D) 200 meters

Answer: B) 100 meters

What happens if you connect two switches using a straight-through cable instead of a crossover? A) The link works at half-duplex B) No link is established C) The switches auto-negotiate the connection D) Only VLAN 1 traffic passes

Answer: B) No link is established

What does a solid green LED on a switch port typically indicate? A) The port is administratively shut down B) The port is operating at 100 Mbps C) The port has an active link but no traffic D) The port is in error-disabled state

Answer: B) The port is operating at 100 Mbps

What could cause intermittent connectivity on a wired network? A) Correctly configured VLANs B) A loose or damaged Ethernet cable C) Properly configured STP D) A functioning DNS server

Answer: B) A loose or damaged Ethernet cable

What causes CRC errors on a switch interface? A) Correctly terminated cables B) Electromagnetic interference (EMI) or cable damage C) Properly configured VLANs D) Optimal signal strength

Answer: B) Electromagnetic interference (EMI) or cable damage

How does a switch handle "runt" frames? A) Forwards them normally B) Drops them and increments the runts counter C) Fragments them into smaller packets D) Buffers them for later transmission

Answer: B) Drops them and increments the runts counter

What is the most likely cause of "late collisions"? A) Full-duplex mismatch B) Cable length exceeding 100 meters C) Properly configured STP D) Optimal switch performance

Answer: B) Cable length exceeding 100 meters

What is a common cause of "giants" in an Ethernet network? A. Duplex mismatch B. Incorrect MTU settings C. CRC errors D. Switch congestion

Answer: B

Late collisions are typically caused by which of the following? A. Cable is too short B. Duplex mismatch or excessive cable length C. Port security D. MTU mismatch

Answer: B

Which Ethernet error indicates frame corruption most often caused by interference or damaged cables? A. Late collision B. CRC error C. Giant D. Runt

Answer: B

Which Layer 1 issue can contribute to frequent CRC errors on copper Ethernet? A. VLAN mismatch B. EMI from fluorescent lights C. Routing loops D. IP addressing issues

Answer: B

What tool can be used to help identify cabling issues causing CRC errors? A. Ping B. TDR (Time Domain Reflectometer) C. NetFlow D. SNMP

Answer: B

What is the minimum Ethernet frame size to avoid a "runt" classification? A. 46 bytes B. 64 bytes C. 100 bytes D. 128 bytes

Answer: B

What is a likely symptom of a half-duplex link connected to a full-duplex port? A. Late collisions B. Port flapping C. Frame tagging errors D. CRC mismatch

Answer: A

What is a possible result of mismatched MTU settings on two connected interfaces? A. CRC errors B. Giants C. MAC address flooding D. VLAN mismatch

Answer: B

Which layer does a CRC error occur at? A. Layer 1 B. Layer 2 C. Layer 3 D. Layer 4

Answer: B

Which command on a Cisco switch helps detect Ethernet errors? A. show ip interface brief B. show vlan C. show interfaces counters errors D. show spanning-tree

Answer: C

If a switchport reports a large number of input errors and CRCs, what should you check first? A. STP configuration B. Port VLAN ID C. Cable condition and EMI D. PortFast status

Answer: C

What does a large number of "runts" typically suggest about a switch port in a half-duplex environment? A. Normal operation B. MTU is too small C. Frequent collisions D. Routing issues

Answer: C

What does a "late collision" indicate in Ethernet? A. Collision occurred within the first 64 bytes B. Frame exceeded MTU C. Collision detected after 64 bytes due to duplex mismatch D. Port security triggered

Answer: C

In what mode is a switch port more likely to experience late collisions? A. Full-duplex B. Half-duplex C. Trunk mode D. Monitor mode

Answer: B

Which error type is commonly associated with shielded twisted pair (STP) cabling in noisy environments? A. Runt B. CRC C. Giant D. MTU mismatch

Answer: B

If you're seeing a mix of CRC and late collisions on a port, what’s the most likely cause? A. Port security B. VLAN mismatch C. Duplex mismatch D. MTU mismatch

Answer: C

Which tool helps to detect excessive late collisions in real time? A. Wireshark B. SNMP C. show interfaces D. show version

Answer: C

Which issue can occur if two switches run different VTP versions and try to share VLAN information? A. VLAN pruning B. VLAN deletion C. VTP version mismatch D. STP loop

Answer: C

Which protocol is responsible for negotiating trunk links on a Cisco switch? A. VTP B. CDP C. DTP D. STP

Answer: C

What happens if a trunk port’s native VLAN doesn't match on both ends? A. Trunk negotiation fails B. Native VLAN traffic may be misrouted C. STP will block the port D. VLAN pruning will occur

Answer: B

What is the result of a missing VLAN on a trunk port? A. All VLAN traffic is dropped B. Only native VLAN traffic is passed C. Traffic from that VLAN is not forwarded across the trunk D. STP will block the trunk

Answer: C

Which command helps verify VTP status on a Cisco switch? A. show vlan B. show vtp status C. show interfaces trunk D. show cdp neighbors

Answer: B

If trunk negotiation fails between two switches, what should be checked first? A. VLAN names B. PortFast settings C. DTP settings or trunk mode D. STP priority

Answer: C

Which trunking mode does not initiate DTP negotiation? A. Trunk B. Desirable C. Dynamic auto D. Nonegotiate

Answer: D

A switchport is configured as switchport mode dynamic auto on both ends. What is the resulting port mode? A. Access B. Trunk C. EtherChannel D. Blocking

Answer: A

What command shows which VLANs are allowed across a trunk? A. show vlan B. show spanning-tree C. show interfaces trunk D. show vtp status

Answer: C

What is a sign that VLANs are not properly propagating across switches using VTP? A. All interfaces are down B. VLANs are missing from the show vlan output C. Switch reboots repeatedly D. STP convergence fails

Answer: B

Which mode must at least one side of a trunk link be set to for DTP to successfully negotiate a trunk? A. Access B. Nonegotiate C. Desirable D. Monitor

Answer: C

What does VTP pruning do? A. Prevents VLAN updates from propagating B. Limits broadcast traffic to switches that need it C. Blocks unused trunk links D. Converts trunk ports to access

Answer: B

Which mismatch can cause native VLAN traffic to be dropped or misinterpreted? A. MTU B. Trunking protocol C. Native VLAN D. Interface speed

Answer: C

Which configuration prevents dynamic trunking protocol from operating? A. switchport mode trunk B. switchport mode access C. switchport mode dynamic desirable D. switchport nonegotiate

Answer: D

Which of the following is required for a VLAN to pass over a trunk link? A. VLAN must exist on both switches B. VLAN must be the native VLAN C. VLAN must be manually routed D. VLAN must be set to transparent mode

Answer: A

A switch is set to VTP client mode. What happens if a new VLAN is configured locally? A. The VLAN is saved and propagated B. The VLAN is ignored C. The VLAN is deleted on reboot D. Configuration is not allowed

Answer: D

Inconsistent native VLANs on trunk links can result in which issue? A. BPDU loops B. VLAN deletion C. Spanning-tree root bridge flapping D. VLAN 1 flooding or traffic being misrouted

Answer: D

Which VTP mode allows a switch to add new VLANs and propagate them? A. Server B. Client C. Transparent D. Passive

Answer: A

What is one of the dangers of VTP in server mode on a new switch? A. It blocks trunk ports B. It can overwrite VLAN database of the entire domain C. It disables STP D. It changes all ports to access

Answer: B

What happens if a trunk port does not allow a specific VLAN? A. It will be assigned to VLAN 1 B. That VLAN's traffic will be dropped C. STP disables the port D. It becomes native VLAN

Answer: B

What determines which switch becomes the STP root bridge? A. Switch with the highest MAC address B. Switch with the lowest bridge ID C. Switch with the highest port priority D. First switch to send a BPDU

Answer: B

Which component is part of the STP bridge ID? A. IP address and port ID B. MAC address and VLAN ID C. Bridge priority and MAC address D. Switch hostname and MAC

Answer: C

What is the default STP priority value on Cisco switches? A. 1024 B. 4096 C. 32768 D. 65535

Answer: C

Which condition could cause a switch that shouldn't be the root bridge to become one? A. PortFast misconfiguration B. BPDU Guard disabled C. Lower bridge priority on that switch D. Trunking issue

Answer: C

What is the purpose of PortFast? A. Prevents loops on trunks B. Speeds up STP convergence on access ports C. Disables BPDUs D. Forces ports into forwarding state on all VLANs

Answer: B

What danger does enabling PortFast on a trunk port create? A. VLAN mismatch B. STP loop C. CRC errors D. VTP pruning

Answer: B

Which feature shuts down a port when it receives a BPDU and PortFast is enabled? A. BPDU Filter B. Root Guard C. Loop Guard D. BPDU Guard

Answer: D

You’ve enabled BPDU Guard on an access port, and it immediately goes into err-disabled state. What caused this? A. MTU mismatch B. BPDU received on the port C. CRC error D. Trunk port misconfiguration

Answer: B

Which STP version supports rapid convergence? A. PVST B. MST C. RSTP D. IEEE 802.1D

Answer: C

What is a key difference between RSTP and PVST+? A. PVST+ is vendor-neutral B. RSTP provides per-VLAN STP C. RSTP converges faster D. PVST+ does not support BPDUs

Answer: C

What happens to a non-root port in STP that has the best path to the root bridge? A. Goes into blocking B. Becomes a root port C. Becomes a designated port D. Goes to listening state only

Answer: B

Which STP state is used for learning MAC addresses but not forwarding traffic? A. Blocking B. Forwarding C. Listening D. Learning

Answer: D

Which Cisco STP mode allows one instance per VLAN? A. RSTP B. PVST+ C. MST D. Rapid PVST

Answer: B

Which feature prevents a port from becoming a root port even if it receives superior BPDUs? A. Loop Guard B. Root Guard C. BPDU Guard D. PortFast

Answer: B

What does Loop Guard protect against? A. MAC address table overflow B. VLAN pruning C. Unidirectional link failures causing loops D. MTU mismatches

Answer: C

You suspect a switching loop. What STP-related symptom might confirm it? A. High CPU usage and MAC flapping B. BPDU Guard errors C. VLAN mismatch D. CRC errors

Answer: A

Which command checks the STP role of each port on a Cisco switch? A. show vlan brief B. show spanning-tree C. show interfaces status D. show cdp neighbors

Answer: B

What type of port does RSTP consider edge ports? A. Ports in trunk mode B. Ports connected to end devices C. Blocked ports D. Root ports

Answer: B

What is the purpose of enabling UplinkFast? A. Improves convergence on edge ports B. Speeds STP convergence for access layer uplinks C. Allows multiple root bridges D. Enables VLAN pruning

Answer: B

Which of the following is true about STP convergence? A. Takes milliseconds in all STP versions B. Is instant if PortFast is used C. Takes 30–50 seconds in traditional 802.1D STP D. Happens only on trunk ports

Answer: C

Which two protocols are used for EtherChannel negotiation? A. DTP and STP B. PAgP and LACP C. VTP and DTP D. PAgP and CDP

Answer: B

Which EtherChannel protocol is Cisco proprietary? A. LACP B. PAgP C. DTP D. STP

Answer: B

What must match across all ports for EtherChannel to form? A. Interface numbers B. Duplex and speed settings C. STP cost D. VTP domain

Answer: B

Which configuration will prevent LACP from forming an EtherChannel? A. Speed mismatch B. Using active on both sides C. Same native VLAN D. Using on mode on both sides

Answer: A

What is a common cause of EtherChannel load-balancing inefficiency? A. Asymmetric trunking B. Using only MAC-based load balancing C. Mismatched IP addresses D. Excessive VLANs

Answer: B

What command shows EtherChannel summary on a Cisco switch? A. show etherchannel summary B. show interfaces etherchannel C. show channel-group D. show port-channel

Answer: A

Which EtherChannel mode combination prevents negotiation but forms a channel if settings match? A. On – On B. Auto – Desirable C. Passive – Active D. Desirable – Desirable

Answer: A

What happens when port security detects a violation in “shutdown” mode? A. The switch logs a warning B. The port goes into err-disabled C. The switch removes the violating MAC D. The port remains in forwarding state

Answer: B

In sticky MAC address mode, what happens if a new MAC is learned after the max limit is reached? A. It replaces the oldest one B. It is dropped C. Port security violation is triggered D. MAC address table is cleared

Answer: C

Which command enables sticky MAC address learning on a port? A. switchport port-security sticky B. switchport mac-address sticky C. mac-address sticky enable D. switchport security enable sticky

Answer: A

Layer 1 and Layer 2 Troubleshooting Flashcards

(120 cards)