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Switch Implementation PBQs and Common Misconfigurations

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CompTIA Network+ N10-009

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1 Introduction & Exam Overview

Current Exam Facts and Applied Networking Judgment Official Domain Weights and an 8-12 Week Study Plan How to Use Labs, Practice, and PBQ Workflow Missed-Question Notebook and Final Readiness Metrics

2 Domain 1: Networking Concepts (23%)

OSI and TCP/IP Models with Device and Protocol Mapping Networking Appliances and Where They Operate Ports and Protocol Decision Table Traffic Types and Encapsulation Flow

3 Domain 1: Media, Connectors, Transceivers, and Network Architectures

Copper, Fiber, Coax, and DAC Media Connector and Transceiver Selection Network Topologies and Design Patterns Cloud and Virtual Networking Concepts

4 Domain 1: IP Addressing and Subnetting Mastery

IPv4 Classes, Private/Public, APIPA, and Loopback CIDR, VLSM, and Subnet Math IPv6 Address Types and Notation Routing Basics and Longest Prefix Match

5 Domain 2: Network Implementation - Routing

Static vs Dynamic Routing and Route Selection OSPF, EIGRP, and BGP Basics at Network+ Depth NAT/PAT, VIP/FHRP, and Subinterfaces Routing PBQs and Troubleshooting Route Table Clues

6 Domain 2: Network Implementation - Switching

VLANs, Access Ports, Trunks, and Native VLAN STP/RSTP Loop Prevention and Bridge Roles Port Aggregation/LACP, MTU, Jumbo Frames, and Interface Settings Switch Implementation PBQs and Common Misconfigurations

7 Domain 2: Network Implementation - Wireless and Physical Implementation

Wi-Fi Standards, Bands, and Channels SSID Security, Guest Networks, and Authentication Antennas, Coverage, Roaming, Interference, and Site Surveys Physical Installation Implications

8 Domain 2: Network Implementation - Services Implementation

DNS Record Types and Troubleshooting Cues DHCP, DHCPv6, SLAAC, Scopes, Leases, and Relay NTP, PTP, NTS, and Time-Sensitive Networking Service Implementation PBQs: DNS, DHCP, VLANs, and Firewall Direction

9 Domain 3 Part A: Network Operations Documentation and Governance

Physical, Logical, Rack, Cable, Wireless Diagrams, and IPAM Asset Inventory, Baselines, SLAs, SOPs, and Runbooks Change Management and Request Tracking Lifecycle, EOL, EOS, Decommissioning, and Configuration Management

10 Domain 3 Part B: Monitoring, Remote Access, and Resilience

SNMP, Flow, Syslog, Packet Capture, Log Aggregation, APIs, and Port Mirroring Baselines and Performance Metrics Remote Access, Management Paths, and Secure Admin Habits DR and HA Concepts: RPO, RTO, MTTR, MTBF, Sites, Failover, and Testing

11 Domain 4: Logical Security and Secure Access (14%)

Encryption in Transit, Encryption at Rest, PKI, and Certificates IAM, MFA, SSO, Directory Services, and AAA Authorization, Least Privilege, RBAC, Geofencing, and Time-Based Access VPNs and Secure Management Design

12 Domain 4: Segmentation, Risk, and Network Attacks (14%)

Segmentation for Guest, BYOD, IoT, IIoT, SCADA, ICS, and OT Risk, Compliance, Audit, Data Locality, PCI, and GDPR Network Attacks and Scenario Cues Attack-to-Mitigation PBQ Tables

13 Domain 4: Security Controls and Hardening (14%)

Firewalls, IDS, IPS, Security Zones, and Screened Subnets ACLs, Filtering, NAC, Hardening, and Key Management Deception Technologies and Physical Security Zero Trust, SASE, and Trusted or Untrusted Zone Decisions

14 Domain 5: Troubleshooting Methodology and Tools (24%)

Official Troubleshooting Methodology and Evidence Handling Command-Line Tools: ping, traceroute, nslookup, dig, ipconfig, ifconfig, ip, arp, netstat, ss, and route Packet, Protocol, and Wi-Fi Analyzers Choosing the Right Tool by Symptom PBQs

15 Domain 5: Physical, Interface, and Wireless Troubleshooting (24%)

Cable Issues: Type, Attenuation, Crosstalk, Termination, and TX/RX Interface Issues: Errors, Discards, Duplex, Speed, Port Status, and PoE Transceiver, Fiber, and Signal Strength Troubleshooting Wireless Troubleshooting: Interference, Channels, Roaming, RSSI/SNR, Security, and Captive Portals

16 Domain 5: Network Services, Switching, Routing, and Performance Troubleshooting (24%)

DHCP, DNS, NTP, and IP Addressing Issues VLAN, STP, Trunk, Native VLAN, and ACL Issues Routing, Default Gateway, Route Table, and NAT Issues Congestion, Latency, Jitter, Packet Loss, and Application Performance Clues

17 Performance-Based Question Labs

Subnetting and VLSM Design Lab VLAN, Trunk, Router-on-a-Stick, and Firewall Rule Lab Wireless Deployment and Troubleshooting Lab Monitoring, Log Triage, and Route or Service Troubleshooting Lab

18 High-Yield Reference and Final Study Plan

High-Yield Ports and Protocols Table Wi-Fi, Cabling, Connectors, and Transceivers Quick Table Acronyms and Command-Line Tool Quick Table Final 7-Day Review Plan and Readiness Checklist

19 Final Synthesis: Strategy, Remediation, and Readiness

Mixed-Set Decision Strategy for Qualifiers and Close Answers Missed-Question Remediation Notebook by Error Type Exam-Day Time Management and PBQ Order 100-Question Readiness Simulation Blueprint Mapped to N10-009 Weights

Switch Implementation PBQs and Common Misconfigurations

Key Takeaways Explain This Topic AI

Switch PBQs usually ask you to repair a few mismatched settings, not redesign the network.

Use a working port or VLAN as your reference template and compare the broken one line by line.

Troubleshoot bottom-up: physical, access VLAN, trunk, STP, aggregation, Layer 3 gateway, then policy.

One endpoint problem points to a port/cable/NIC/DHCP issue; a whole VLAN problem points to trunk/STP/gateway.

Interface counters, MAC tables, STP state, and VLAN tables separate switching faults from routing faults.

Last updated: June 2026

How Switching PBQs Are Scored

Performance-based questions on the N10-009 give partial credit and almost always present a mostly working topology with one or two broken pieces. The fastest path to points is comparison: find the working port, VLAN, trunk, or bundle and treat it as your template, then change only what differs on the broken one. Avoid the temptation to rebuild the design - the smallest correct change is the intended answer.

Bottom-Up Troubleshooting Pattern

  • Layer / feature What to check Evidence to read
  • Physical Link state, cable, optic, speed/duplex up/down, CRC, runts, giants
  • Access VLAN Correct endpoint VLAN VLAN table, MAC table, DHCP scope
  • Trunk Mode, allowed VLANs, native VLAN trunk status and VLAN list
  • STP/RSTP Port role and root bridge blocking/discarding state
  • Aggregation LACP state, member consistency port-channel summary
  • Layer 3 gateway SVI, router subinterface, firewall gateway ping, route table
  • Policy ACL, port security, 802.1X denied counters, logs
  • The Misconfiguration Catalog
  • Misconfiguration Symptom Repair
  • Wrong access VLAN Host gets wrong subnet Assign correct VLAN
  • VLAN not created Port assigned but VLAN inactive Create the VLAN, allow it where needed
  • VLAN missing from trunk One VLAN fails on uplink Add to allowed list
  • Native VLAN mismatch Untagged traffic misbehaves Match native VLAN both ends
  • Trunk to an endpoint Unstable endpoint connectivity Set port to access mode
  • STP root on access switch Inefficient paths, odd blocking Lower priority on the core
  • Port-channel mismatch Member suspended Match speed/duplex/VLAN/MTU/LACP
  • MTU mismatch Large transfers fail Align MTU end to end
  • Port-security violation Device blocked after MAC change Clear/adjust the policy

PBQ Example: New Office Floor

Requirements:

  • Device Required network
  • User PCs VLAN 110
  • IP phones Voice VLAN 120
  • Wireless APs (multi-SSID) Trunk: VLANs 130 and 140
  • Uplink to distribution Trunk: 110, 120, 130, 140

Correct actions:

Set user PC ports to access VLAN 110 .

Set phone ports to data VLAN 110 + voice VLAN 120 .

Set AP ports to trunk (they carry multiple VLANs/SSIDs).

Set the uplink to trunk and allow 110, 120, 130, 140 .

Verify a Layer 3 gateway (SVI or subinterface) exists for each VLAN.

Confirm the native VLAN matches the distribution switch.

PBQ Example: One VLAN Down

  • Evidence Interpretation
  • VLAN 20 works on access switch A VLAN exists; local ports fine
  • VLAN 20 fails across uplink to B Trunk or STP issue likely
  • Trunk allowed list = 10, 30, 40 VLAN 20 is missing
  • Other VLANs cross the same uplink Physical link is healthy

The smallest correct fix is to allow VLAN 20 on the trunk . Replacing the switch, re-IPing, or disabling STP all contradict the evidence that everything else works.

Reading Evidence

  • Output clue Meaning
  • MAC learned on wrong VLAN Access VLAN or tagging issue
  • Interface admin down Disabled in configuration
  • Err-disabled port BPDU guard, security, or link-flap protection fired
  • STP blocking Likely intentional loop prevention
  • Rising CRC errors Physical layer - cable or optic
  • Rising giants counter Oversize frames / MTU mismatch
  • No MAC from endpoint Cable, NIC, port state, VLAN, or security

Scope Before You Touch Shared Infrastructure

The single biggest PBQ discipline is blast-radius awareness . Before changing a trunk, an SVI, or the root bridge, ask how many users are affected by the symptom. If exactly one host is broken, the fault is on that one access port, cable, NIC, or DHCP reservation - changing a shared uplink would be wrong and could break working VLANs.

  • Trap Better reasoning
  • Change routing when a host is in the wrong VLAN Fix Layer 2 membership first
  • Disable STP so every link forwards Keep loop prevention; fix root/path design
  • Add all VLANs to every trunk Carry only required VLANs to limit scope
  • Treat one bad endpoint as a core outage Scope the impact before touching uplinks
  • Ignore the switch management gateway Remote management from another subnet needs a gateway
  • The Line-by-Line Comparison Tactic

When a PBQ shows a working port and a broken port side by side, walk these attributes in order and stop at the first difference:

  • switchport mode (access vs trunk)
  • access VLAN and voice VLAN
  • trunk allowed VLANs
  • native VLAN
  • STP state and edge/PortFast/BPDU guard
  • port security settings
  • speed , duplex , and MTU

The answer is almost always the single attribute that differs from the working reference. This method beats guessing, gives partial credit on multi-step PBQs, and mirrors how real switch troubleshooting is done. Document the change you make so the simulator's verification step credits the corrected setting rather than an unrelated edit.