Examkin

Network Troubleshooting

486 soru

Tüm türler486Çoktan seçmeli248Çoklu seçim111Eşleştirme61Sıralama66
Soru 181Soru →

A network technician is troubleshooting a workstation that cannot communicate with servers on remote subnets. The technician executes `ipconfig` on the workstation and observes the following network settings:

text
IPv4 Address. . . . . . . . . . . : 192.168.1.50
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.2.1

The workstation can ping local host 192.168.1.10192.168.1.10, but all outbound traffic to external networks fails. Which of the following is the root cause of the connectivity failure?

Cevabı ve açıklamayı göster

Cevap: The default gateway is configured on a different IP subnet than the host.

Cevap

The default gateway is configured on a different IP subnet than the host.
For a host device to send traffic outside its local network, its configured default gateway must be an IP address located on the same IP subnet. The host is configured with 192.168.1.50/24192.168.1.50/24, but the gateway is set to 192.168.2.1/24192.168.2.1/24. Because they reside on different subnets, the host cannot ARP for the gateway's MAC address, preventing all traffic destined for remote networks.

Adım Adım Çözüm

1
Analyze host IP address and subnet mask.
IP address 192.168.1.50192.168.1.50 with subnet mask 255.255.255.0255.255.255.0 (/24) places the host in the local network range 192.168.1.1192.168.1.1 through 192.168.1.254192.168.1.254.
Determines the valid local subnet boundary.
2
Compare the default gateway address to the host's subnet range.
The configured default gateway 192.168.2.1192.168.2.1 falls into the 192.168.2.0/24192.168.2.0/24 subnet.
Identifies whether the gateway is directly reachable via local Layer 2 broadcast domain.
3
Determine why outbound communication fails.
Because the default gateway is not on the same IP subnet, the host cannot perform ARP resolution to forward off-subnet traffic to its gateway router.
Confirms the root cause of failure for remote destination traffic.

Anahtar Kavram

Default Gateway Subnet Matching
Soru 182Soru →

A network administrator is troubleshooting an issue where a client workstation fails to connect to an internal database server named `db01.prod.lan`. The technician executes two commands on the workstation and observes the following output:

C:\Users\Admin> ipconfig /displaydns

Record Name . . . . . : db01.prod.lan
Record Type . . . . . : 1
Time To Live . . . . : 86400
Data Length . . . . . : 4
Section . . . . . . . : Answer
A (Host) Record . . . : 10.20.4.150

C:\Users\Admin> nslookup db01.prod.lan 192.168.1.10
Server: dns01.corp.lan
Address: 192.168.1.10

Name: db01.prod.lan
Address: 10.20.4.200

Which TWO of the following statements correctly identify the cause of the connection failure and the required step to resolve it?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The client system is attempting to connect using a stale IP address stored in its local DNS resolver cache.; Running `ipconfig /flushdns` on the workstation will clear the outdated entry and allow applications to obtain the updated IP address from the DNS server.

Cevap

The workstation is attempting to connect to the server using a stale IP address stored in its local DNS resolver cache. Running `ipconfig /flushdns` on the client clears this cached entry so the system queries the authoritative DNS server for the correct address.
The output demonstrates that the client's local DNS resolver cache holds an outdated A record (`10.20.4.150`), which the OS uses when applications initiate network traffic. Because `nslookup` bypasses local client caching and queries the DNS server directly, it returns the current IP address (`10.20.4.200`). Flushing the local resolver cache with `ipconfig /flushdns` purges the stale entry and restores proper connectivity.

Adım Adım Çözüm

1
Analyze the output of `ipconfig /displaydns`.
The local DNS cache holds an entry for `db01.prod.lan` pointing to `10.20.4.150` with a TTL of 86,400 seconds.
When standard applications request name resolution, the OS checks its local resolver cache before sending a query across the network.
2
Analyze the output of `nslookup db01.prod.lan 192.168.1.10`.
The DNS server `192.168.1.10` resolves `db01.prod.lan` to `10.20.4.200`.
The `nslookup` utility bypasses local OS cache mechanisms and queries the specified DNS server directly, revealing that the DNS server has the updated record.
3
Determine the necessary remediation.
Clearing the cache via `ipconfig /flushdns` removes the stale entry, forcing subsequent application lookup requests to query the DNS server.
Removing the cached record ensures the client receives the active IP address (`10.20.4.200`).

Anahtar Kavram

Operating System DNS Resolver Cache vs. Direct Command-Line DNS Queries
Soru 183Soru →

Match each switching troubleshooting symptom or log message on the left with its underlying root cause on the right.

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Öğeler

Switch log continuously displays '%CDP-4-NATIVE_VLAN_MISMATCH' on trunk link interface Gig0/1.
Workstation connected to a switch port experiences degraded performance with high counts of late collisions.
Traffic for VLAN 20 fails to pass across an active 802.1Q trunk, while VLAN 10 traffic passes successfully.
An unexpected switch becomes the root bridge after a topology change, causing suboptimal traffic routing.

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

1. CDP native VLAN mismatch logs match with mismatched native VLAN IDs on opposing trunk ends. 2. High late collision counters match with a duplex mismatch configuration. 3. Selective VLAN failure across an operational trunk matches with VLAN exclusion in the allowed VLAN list. 4. Suboptimal root bridge election matches with default or unconfigured STP bridge priority settings.
Each symptom matches its specific Layer 2 switching failure mode: CDP native VLAN mismatch logs indicate mismatched native VLAN settings; late collisions indicate a duplex mismatch; selective VLAN traffic drops point to missing VLAN entries in the trunk allowed list; and unexpected root bridge selection stems from unconfigured STP bridge priority values.

Adım Adım Çözüm

1
Analyze the CDP warning log symptom.
Identify that CDP detects mismatched native VLAN settings across an 802.1Q trunk connection.
802.1Q trunks send untagged frames for the native VLAN; if both ends differ, frames are received on the wrong VLAN.
2
Analyze interface statistics showing late collisions.
Identify duplex mismatch as the root cause of late collisions.
Half-duplex interfaces listen for collisions throughout transmission; full-duplex interfaces send continuously without listening, triggering late collisions on the half-duplex peer.
3
Analyze single-VLAN failure on a trunk link.
Identify allowed VLAN list configuration errors.
Trunk interfaces prune traffic for VLANs not explicitly permitted in their allowed VLAN list.
4
Analyze unexpected STP root bridge placement.
Identify unconfigured STP bridge priority.
STP root bridge selection defaults to lowest priority; if priorities are equal, the lowest MAC address becomes root unless priority is explicitly lowered.

Anahtar Kavram

Troubleshooting VLAN, Trunking, and Switching Issues
Soru 184Soru →

A network engineer observes that hosts on VLAN 10 connected to Switch-Alpha are unexpectedly able to communicate with hosts on VLAN 20 connected to Switch-Beta across an 802.1Q trunk link without traversing a Layer 3 router. Console logs on Switch-Alpha report a CDP native VLAN mismatch warning indicating GigabitEthernet0/1 is in native VLAN 10, while Switch-Beta reports native VLAN 20 on its connecting port. Which of the following technical explanations accounts for this cross-VLAN communication behavior?

Cevabı ve açıklamayı göster

Cevap: Switch-Alpha transmits frames originating from VLAN 10 without an 802.1Q header across the trunk, and Switch-Beta accepts these untagged frames and assigns them directly to its local native VLAN 20.

Cevap

Switch-Alpha transmits frames originating from VLAN 10 without an 802.1Q header across the trunk, and Switch-Beta accepts these untagged frames and assigns them directly to its local native VLAN 20.
Under the IEEE 802.1Q standard, traffic associated with a trunk port's native VLAN is sent across the link without an Ethernet VLAN tag. When Switch-Alpha (native VLAN 10) transmits untagged frames for VLAN 10, Switch-Beta (native VLAN 20) receives these untagged frames and assigns them to its own native VLAN 20. This causes Layer 2 traffic from VLAN 10 on Switch-Alpha to leak directly into VLAN 20 on Switch-Beta without passing through a Layer 3 device.

Adım Adım Çözüm

1
Analyze the trunk configuration and behavior for 802.1Q native VLANs.
802.1Q trunks transmit traffic belonging to the native VLAN untagged (without an 802.1Q VLAN header tag).
Understanding how native VLAN encapsulation works is key to tracing untagged frame delivery.
2
Trace frame egress from Switch-Alpha.
Frames from hosts on VLAN 10 leave Switch-Alpha over GigabitEthernet0/1 untagged because native VLAN on Switch-Alpha is VLAN 10.
Switch-Alpha strips VLAN 10 tags (or does not append them) prior to sending them on its native trunk port.
3
Trace frame ingress on Switch-Beta.
Switch-Beta receives untagged frames on GigabitEthernet0/1 and places them into its local native VLAN, which is configured as VLAN 20.
Ingress untagged frames are automatically assigned to the receiving switchport's configured native VLAN, leaking traffic between VLAN 10 and VLAN 20.

Anahtar Kavram

802.1Q Native VLAN Mismatch Traffic Leakage
Tahmini Süre:2m 0s
Soru 185Soru →

Mobile laptop users in an enterprise environment report dropped VoIP calls and high latency when moving between offices. Wireless diagnostic logs show that client devices remain attached to a distant access point (AP) at −83 dBm-83\text{ dBm} RSSI, despite being positioned directly underneath a nearby AP. An RF audit reveals that both 2.4 GHz and 5 GHz radios on all APs are operating at maximum transmit power (+23 dBm+23\text{ dBm}). Which of the following administrator actions will best remediate this sticky client roaming issue? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Reduce the transmit power of the 2.4 GHz radios on all access points relative to the 5 GHz radios.; Configure minimum RSSI disassociation thresholds and band steering on the wireless controller.

Cevap

Reducing the 2.4 GHz transmit power to align coverage cells with 5 GHz radios, alongside configuring minimum RSSI disassociation thresholds and band steering, effectively forces sticky clients to disconnect from weak distant access points and roam to nearby access points.
Reducing 2.4 GHz radio transmit power shrinks the large 2.4 GHz coverage cell so that it matches the smaller 5 GHz cell size, preventing client devices from remaining connected to distant APs. Additionally, configuring minimum RSSI thresholds and band steering on the controller actively disassociates clients when signal quality degrades below a specific threshold, forcing them to roam to a closer access point.

Adım Adım Çözüm

1
Analyze the reported symptom and RF environment metrics.
Identified 'sticky client' behavior where client devices hold onto distant AP signals (−83 dBm-83\text{ dBm} RSSI) because maximum power (+23 dBm+23\text{ dBm}) on 2.4 GHz causes AP signal to reach clients even though client uplink power is insufficient.
2.4 GHz signals propagate further and penetrate obstacles better than 5 GHz, creating an asymmetric power link when radios run at maximum power.
2
Balance cell coverage sizes across frequency bands.
Lower 2.4 GHz transmit power so 2.4 GHz coverage matches 5 GHz coverage.
Equalizing effective coverage areas prevents clients from seeing 2.4 GHz as usable when far away from the AP.
3
Enforce controller-based roaming management.
Enable minimum RSSI disassociation limits and band steering.
When a client signal drops below the configured RSSI threshold, the AP sends a disassociation frame, compelling the client device to scan and associate with the local, high-signal AP.

Anahtar Kavram

Sticky Client Roaming Remediation & Transmit Power Cell Balancing
Soru 186Soru →

A network administrator is investigating a sudden connectivity disruption in a fulfillment center where mobile handheld scanners are receiving APIPA (169.254.x.x169.254.x.x) addresses and failing to communicate with the warehouse management system. Place the following troubleshooting steps in the correct sequential order according to the CompTIA troubleshooting methodology, from the initial step to the final step.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequential order following the CompTIA troubleshooting methodology is: 1. Gather information to identify the problem, 2. Formulate a hypothesis for the probable cause, 3. Perform a packet capture to test the theory, 4. Develop a plan of action and evaluate effects, 5. Execute commands to verify system functionality, and 6. Record details in the ticketing system for documentation.
The compulsory CompTIA troubleshooting workflow follows a strict chronological progression: Identify the problem -> Establish a theory of probable cause -> Test the theory to determine cause -> Establish a plan of action to resolve the problem and identify potential effects -> Implement the solution or verify full system functionality -> Document findings, actions, and outcomes. Gathering information identifies the problem, forming a hypothesis creates the theory, capturing packets tests the theory, drafting the port shutdown plan forms the plan of action, renewing IP leases verifies functionality, and logging the ticket completes the final documentation step.

Adım Adım Çözüm

1
Identify the Problem
Scope of affected devices and initial symptoms (APIPA addressing) are established.
CompTIA methodology dictates gathering user input and identifying symptoms as the first step.
2
Establish a Theory of Probable Cause
A plausible cause (rogue DHCP server) is hypothesized.
After identifying the problem, the technician must question the obvious and form a hypothesis.
3
Test the Theory to Determine Cause
Diagnostic packet capture confirms or refutes the presence of rogue DHCP OFFER messages.
The technician must confirm the hypothesis using diagnostic techniques before making changes.
4
Establish a Plan of Action and Identify Potential Effects
A plan to shut down the rogue port and implement DHCP Snooping is created.
Before making configuration changes, a structured plan considering network impact is required.
5
Verify Full System Functionality
Endpoints successfully obtain valid IP leases and regain network communication.
After implementing changes, system functionality must be verified to ensure complete resolution.
6
Document Findings, Actions, and Outcomes
Resolution history and preventative configurations are permanently logged.
Documentation is the mandatory final step of the CompTIA troubleshooting methodology.

Anahtar Kavram

CompTIA 6-Step Network Troubleshooting Methodology
Soru 187Soru →

A workstation on a local network is configured to obtain an IP address dynamically. Arrange the four messages of the DHCP lease acquisition process (DORA) in the correct chronological sequence from start to finish.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct chronological sequence for the DHCP lease acquisition process is: 1. DHCPDISCOVER broadcast by client, 2. DHCPOFFER sent by server, 3. DHCPREQUEST broadcast by client, 4. DHCPACK confirmation sent by server.
The DHCP DORA process follows the mnemonic DORA: Discover (client broadcast searching for server), Offer (server response offering IP configuration), Request (client broadcast requesting offered IP), and Acknowledge (server confirmation finalizing the lease). Placing the items in the order DHCPDISCOVER -> DHCPOFFER -> DHCPREQUEST -> DHCPACK represents the standard four-way handshake for dynamic IP allocation.

Adım Adım Çözüm

1
Identify the initial communication step taken by a client without an IP address.
The host broadcasts a DHCPDISCOVER packet to locate any listening DHCP server on the local broadcast domain.
Since the client does not yet have an IP configuration, it must broadcast to find DHCP servers.
2
Identify the server's immediate response to the discovery broadcast.
The server sends a DHCPOFFER message offering an available IPv4 address, default gateway, and subnet mask.
The server reserves an unassigned address from its active scope and offers it to the client.
3
Identify the client's selection response to the offered parameters.
The host broadcasts a DHCPREQUEST message accepting the offer.
Broadcasting the request notifies the offering server that its proposal was accepted while informing other DHCP servers to release any offered addresses.
4
Identify the final acknowledgment step from the DHCP server.
The server responds with a DHCPACK message finalizing the lease contract.
The ACK message binds the IP configuration to the client's MAC address and permits the client to use the assigned parameters.

Anahtar Kavram

DHCP DORA Process (Discover, Offer, Request, Acknowledge)
Soru 188Soru →

Match each physical layer cabling issue or measurement requirement on the left with the most appropriate diagnostic tool or technique on the right.

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Öğeler

Measuring high Alien Crosstalk (ANEXT) and Near-End Crosstalk (NEXT) noise across frequency spectrums on a newly installed Category 6A UTP drop to verify standard compliance.
Locating the exact physical distance to a microbend attenuation point midway along a 600-meter single-mode fiber optic trunk.
Quantifying total end-to-end optical power loss (in dB) across a multi-splice fiber link to confirm it operates within the engineered loss budget.
Detecting a split pair condition on a Category 6 cable where pin-to-pin electrical continuity tests pass but twisted-pair pairing integrity is compromised.

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

1. Measuring ANEXT/NEXT spectrum noise on Cat 6A matches with Cable Certifier.
2. Locating distance to a microbend along a fiber trunk matches with Optical Time-Domain Reflectometer (OTDR).
3. Quantifying total optical power loss (dB) across fiber link matches with Optical Power Meter (OPM) paired with an Optical Light Source (OLS).
4. Detecting a split pair where continuity tests pass matches with Time-Domain Reflectometer (TDR) / Advanced Wiremap Analyzer.
Each diagnostic instrument serves distinct physical layer troubleshooting functions: Cable certifiers measure high-frequency signal metrics (NEXT, ANEXT) against TIA standards; OTDRs analyze reflected light to determine the precise distance to optical fiber defects; Optical Power Meters with light sources measure overall insertion loss across fiber runs; and TDRs or advanced wiremap analyzers detect subtle pair imbalances like split pairs that bypass basic continuity checks.

Adım Adım Çözüm

1
Analyze high-frequency parameter validation requirements for Category 6A copper cabling.
Identify that evaluating parameters such as Alien Crosstalk (ANEXT) and Near-End Crosstalk (NEXT) across operating frequencies requires a specialized Cable Certifier.
Standard continuity or wiremap testers cannot sweep frequencies or verify compliance against TIA/EIA Category 6A transmission standards.
2
Determine the tool required to locate distance to localized optical anomalies.
Select the Optical Time-Domain Reflectometer (OTDR) because it measures Rayleigh backscatter and Fresnel reflections against time to calculate exact distance along the strand.
OTDR technology maps signal attenuation as a function of fiber distance.
3
Determine the equipment combination required for end-to-end optical insertion loss testing.
Select an Optical Power Meter paired with an Optical Light Source, which injects a reference optical power level at one end and measures received power at the opposite end.
Measuring absolute dB power loss across a complete link requires a calibrated optical signal source and power reader.
4
Analyze the physical mechanics of a split pair cabling fault.
Identify that split pairs preserve point-to-point pin alignment but break the physical twisting pattern of wire pairs, requiring a TDR or advanced analyzer to detect impedance mismatches and capacitive cross-coupling.
Basic wiremap continuity testers only check simple DC electrical continuity and will incorrectly pass a split pair link.

Anahtar Kavram

Selecting specialized physical layer diagnostic tools based on media type (copper vs. fiber) and specific fault characteristics.
Soru 189Soru →

A network technician is troubleshooting name resolution issues on a Linux client system. The client can successfully reach internal resources by IP address, but system applications fail to resolve the hostname `app.lab.internal`.

The technician executes a targeted query using `dig` and receives the following output:

$ dig @172.16.0.10 app.lab.internal A

; <<>> DiG 9.16.1-Ubuntu <<>> @172.16.0.10 app.lab.internal A
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41258
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; QUESTION SECTION:
;app.lab.internal. IN A

;; ANSWER SECTION:
app.lab.internal. 3600 IN A 172.16.50.25

Despite the direct query returning a valid record from `172.16.0.10`, standard system tools and web browsers on the workstation still fail to resolve `app.lab.internal`. Which of the following potential root causes could explain this behavior? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The local system resolver configuration file (`/etc/resolv.conf`) is pointing to a different DNS server instead of `172.16.0.10`.; An incorrect static entry for `app.lab.internal` exists in the client's local `/etc/hosts` file.

Cevap

The two valid causes are that the workstation's `/etc/resolv.conf` file specifies a different DNS server than `172.16.0.10`, and that an erroneous static entry exists in the local `/etc/hosts` file.
The `dig` tool with the `@server` parameter directly queries the targeted DNS server (`172.16.0.10`) while ignoring local OS resolution mechanisms. Because the `dig` command succeeded with `NOERROR` and returned an A record, `172.16.0.10` is reachable and functional. System applications fail either because `/etc/resolv.conf` is pointing the system to a different, failing DNS server, or because an entry in `/etc/hosts` takes precedence over DNS queries and contains a bad mapping.

Adım Adım Çözüm

1
Analyze the output of the `dig @172.16.0.10 app.lab.internal A` command.
The response status is `NOERROR` with an answer section providing IP `172.16.50.25`. This confirms the DNS server at `172.16.0.10` has a valid record and is reachable over port 53 UDP.
Direct DNS server queries test the server's record availability and network reachability independently of the host's operating system resolver settings.
2
Identify how operating system name resolution differs from direct utility queries like `dig`.
Standard system calls check the local host configuration (e.g., `/etc/hosts`) first, followed by the default DNS servers listed in `/etc/resolv.conf`.
Utilities such as `dig` bypass local OS resolution order and `/etc/hosts` files to query target IP addresses directly.
3
Deduce potential local misconfigurations causing system-wide resolution failure.
If `/etc/resolv.conf` does not list `172.16.0.10` or if `/etc/hosts` contains a conflicting/stale mapping, system applications will fail while `dig @172.16.0.10` succeeds.
Discrepancies between host-level configuration files and explicit server queries pinpoint client-side configuration issues.

Anahtar Kavram

Discrepancies between direct DNS queries (dig/nslookup specifying a server) and operating system name resolution mechanisms (resolver configuration and host files).
Soru 190Soru →

A network administrator is troubleshooting an issue where a workstation configured with IP address 10.200.48.5010.200.48.50 and subnet mask 255.255.240.0255.255.240.0 (/20) can communicate with other hosts on its local network but cannot access external destinations. Running `traceroute 198.51.100.25` fails immediately on the first hop. Reviewing the workstation's network settings reveals that the default gateway is configured as 10.200.64.110.200.64.1. Which of the following is the root cause of the connectivity issue?

Cevabı ve açıklamayı göster

Cevap: The default gateway address resides on a different subnet than the host IP address.

Cevap

The default gateway address resides on a different subnet than the host IP address.
Subnet mask 255.255.240.0255.255.240.0 (/20) dictates that subnets increment by 16 in the third octet (256−240=16256 - 240 = 16). The host network is 10.200.48.0/2010.200.48.0/20, spanning addresses 10.200.48.010.200.48.0 through 10.200.63.25510.200.63.255. The configured gateway address 10.200.64.110.200.64.1 belongs to the 10.200.64.0/2010.200.64.0/20 network block. Because a host must send Layer 2 ARP requests to discover its default gateway, the gateway must reside on the same IP subnet as the host interface.

Adım Adım Çözüm

1
Calculate the network range for IP 10.200.48.50 with subnet mask 255.255.240.0 (/20).
A /20 subnet mask yields a block size of 16 in the third octet (256−240=16256 - 240 = 16). Network address: 10.200.48.0. Usable range: 10.200.48.1 to 10.200.63.254. Broadcast address: 10.200.63.255.
Defining the subnet boundaries determines which destinations the host considers local.
2
Evaluate the configured default gateway IP address relative to the local subnet.
The configured gateway IP address 10.200.64.1 falls into the next subnet block (10.200.64.0/20).
A host can only ARP directly for a default gateway that shares its local IP subnet.
3
Determine the root cause of the destination unreachability.
Because 10.200.64.1 is off-subnet, the host cannot ARP for its default gateway to forward off-subnet traffic.
Reconfiguring the workstation's default gateway to a valid IP within 10.200.48.0/20 (such as 10.200.48.1) restores external connectivity.

Anahtar Kavram

Default Gateway Subnet Alignment
Soru 191Soru →

A systems administrator is configuring a newly deployed Linux server assigned the IPv4 address 172.31.88.45/22172.31.88.45/22 (subnet mask 255.255.252.0255.255.252.0). The server can successfully ping other local hosts within its local network segment, but fails to reach any external subnets or remote application servers. The administrator inspects the host network interface and routing table using standard command-line tools:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.31.88.45 netmask 255.255.252.0 broadcast 172.31.91.255

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.31.92.1 0.0.0.0 UG 100 0 0 eth0
172.31.88.0 0.0.0.0 255.255.252.0 U 0 0 0 eth0

Which of the following identifies the root cause of the remote connectivity failure?

Cevabı ve açıklamayı göster

Cevap: The configured default gateway IP address (172.31.92.1) resides outside the server's local IPv4 subnet range.

Cevap

The configured default gateway IP address (172.31.92.1) resides outside the server's local IPv4 subnet range.
For a host to communicate with remote networks, its default gateway must be on the same local IP subnet. The host is configured with 172.31.88.45/22172.31.88.45/22 (255.255.252.0255.255.252.0), which defines the local subnet range as 172.31.88.0172.31.88.0 to 172.31.91.255172.31.91.255. The configured default gateway of 172.31.92.1172.31.92.1 is part of the 172.31.92.0/22172.31.92.0/22 network. Because it resides outside the local subnet boundary, the server cannot send Layer 2 ARP requests directly to reach the gateway's MAC address, preventing all traffic destination routes outside the local subnet from establishing.

Adım Adım Çözüm

1
Calculate the subnet boundary for the host IP address 172.31.88.45 with a /22 prefix (netmask 255.255.252.0).
The block size is 256 - 252 = 4 in the 3rd octet. Subnet base is 172.31.88.0/22.
Determining the subnet boundary reveals the range of valid IP addresses on the local broadcast domain.
2
Identify the usable IP address range and broadcast address for the 172.31.88.0/22 network.
Network ID: 172.31.88.0, Usable Hosts: 172.31.88.1 through 172.31.91.254, Broadcast ID: 172.31.91.255.
A default gateway must reside within the host's local usable IP range to answer Address Resolution Protocol (ARP) requests.
3
Compare the configured default gateway IP (172.31.92.1) against the local subnet boundaries.
172.31.92.1 is in the next subnet (172.31.92.0/22).
Because 172.31.92.1 is on a different IP subnet, the host cannot perform ARP resolution for its default gateway, failing all off-subnet traffic forwarding.

Anahtar Kavram

Default Gateway Subnet Mismatch
Soru 192Soru →

Match each physical cabling or connector defect with its primary root cause or characteristic physical symptom.

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Öğeler

Dirty Fiber Ferrule
Exceeded Cable Bend Radius
T568A to T568B Mismatch
Deformed RJ45 Port Pin

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Dirty Fiber Ferrule corresponds to contamination on the optical end-face; Exceeded Cable Bend Radius corresponds to light leakage from sharp curving; T568A to T568B Mismatch corresponds to an accidental crossover pinout configuration; Deformed RJ45 Port Pin corresponds to physical damage inside a modular jack preventing electrical contact.
Each cabling defect is accurately mapped to its underlying physical cause: Dirty Fiber Ferrule causes optical contamination loss; Exceeded Cable Bend Radius induces micro-fractures or macrobending loss; T568A to T568B Mismatch creates an inadvertent crossover cabling configuration; and a Deformed RJ45 Port Pin physically disrupts electrical conduction in modular copper jacks.

Adım Adım Çözüm

1
Analyze optical connector issues
Identify that foreign particles on fiber connector end-faces cause high optical loss and back-reflection, which matches the dirty ferrule defect.
Cleanliness is critical for fiber end-faces to allow unobstructed light transmission.
2
Examine physical stress on optical media
Identify that exceeding the allowed curvature limit of a fiber cable leads to macrobending loss and light escaping through the cladding.
Optical fiber relies on total internal reflection, which fails when bend radius thresholds are violated.
3
Evaluate twisted-pair pinout wiring standards
Match T568A on one end and T568B on the other end to an accidental crossover cable.
T568A and T568B swap the green and orange wire pairs.
4
Inspect modular copper receptacle hardware
Associate bent metallic contact pins in an RJ45 jack with electrical open circuits or intermittent physical link faults.
Modular connectors require mechanical spring contact against patch cable pins to complete the circuit.

Anahtar Kavram

Physical layer cabling defects and diagnostic characteristics
Soru 193Soru →

A network administrator is troubleshooting connectivity between a corporate client workstation (172.16.40.25/24172.16.40.25/24) and an off-site secure web server (192.168.200.10/24192.168.200.10/24). The client can successfully ping its default gateway (172.16.40.1172.16.40.1), but connection requests to the web server over HTTPS time out.

The administrator reviews the inbound Access Control List (ACL) applied to the client's router interface:

text
Extended IP access list 101_INBOUND
10 permit tcp 172.16.40.0 0.0.0.255 host 192.168.200.10 eq 80
20 deny ip 172.16.40.0 0.0.0.255 any
30 permit tcp 172.16.40.0 0.0.0.255 host 192.168.200.10 eq 443

Which of the following identifies the root cause of this connection failure?

Cevabı ve açıklamayı göster

Cevap: Rule 20 shadows Rule 30, causing all HTTPS traffic from the subnet to be dropped before reaching the permit rule for port 443.

Cevap

Rule 20 shadows Rule 30, causing HTTPS traffic to be denied by Rule 20 before reaching the permit rule for port 443.
Router Access Control Lists use top-down evaluation logic and terminate processing upon finding the first matching rule. In this configuration, Rule 20 (`deny ip 172.16.40.0 0.0.0.255 any`) matches all IP traffic originating from the client's subnet. Consequently, HTTPS packets matching port 443 are denied at Rule 20 and never reach Rule 30. This phenomenon is known as ACL rule shadowing.

Adım Adım Çözüm

1
Analyze the sequential evaluation of the Access Control List entries.
Network ACLs execute line-by-line in top-down numerical order, stopping evaluation at the first matching rule.
Top-down execution dictates that broader match rules placed above more specific rules will intercept matching packets first.
2
Trace an outbound packet destined for 192.168.200.10 on TCP port 443 through the ACL.
The packet source (172.16.40.25) does not match Rule 10 (port 80). It then matches Rule 20 (`deny ip 172.16.40.0 0.0.0.255 any`) and is dropped immediately.
Because Rule 20 matches all IP traffic from the 172.16.40.0/24 network, Rule 30 is shadowed and will never process any packets.
3
Determine the necessary remediation.
Move Rule 30 above Rule 20 (e.g., to sequence line 15) so specific HTTPS traffic is permitted before general IP traffic from the subnet is denied.
ACL design best practices require placing specific permit rules prior to general deny statements.

Anahtar Kavram

ACL Rule Shadowing and Top-Down Execution Sequence
Tahmini Süre:2m 0s
Soru 194Soru →

A technician is troubleshooting a newly installed twisted-pair Ethernet cable run that fails to establish a link. A basic wire mapper indicates that pin 1 on one end is wired to pin 3 on the other end, and pin 2 is wired to pin 6. Which TWO of the following actions or tools should the technician use to resolve and verify this specific cabling issue?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Re-terminate the cable connectors according to a single TIA/EIA 568B wiring standard on both ends.; Use a continuity wire mapper after re-termination to confirm correct pin-to-pin mapping.

Cevap

The technician should re-terminate the cable connectors according to a consistent TIA/EIA 568B wiring scheme on both ends and use a continuity wire mapper to verify correct conductor alignment.
Re-terminating both ends of the cable according to the TIA/EIA 568B standard ensures proper pin alignment for a straight-through patch cable. Using a wire mapper after re-termination is the standard procedure to verify that all eight conductors map correctly pin-to-pin.

Adım Adım Çözüm

1
Identify the cause of the failure based on the wire mapper reading.
Pins 1 and 2 mapped to pins 3 and 6 indicate an unintentional crossover or miswire condition.
Straight-through copper Ethernet runs require identical pin configurations (e.g., T568B to T568B) on both ends.
2
Correct the physical cabling termination.
Cut and re-strip the cable ends, then crimp modular RJ-45 connectors using standard T568B pinouts at both ends.
Proper pin alignment resolves the physical layer crossover fault.
3
Verify pin mapping with an appropriate cable testing tool.
Perform a test using a continuity wire mapper to confirm pin 1 connects to pin 1, pin 2 to pin 2, etc.
A wire mapper confirms pin-to-pin continuity and correct pair arrangement.

Anahtar Kavram

Pinout Standards and Wire Mapping Verification
Tahmini Süre:1m 0s
Soru 195Soru →

Match each wireless connectivity symptom observed in an enterprise network environment to its underlying RF phenomenon or configuration cause.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Wireless clients in a breakroom experience packet loss and latency spikes during lunch hours without AP log errors.
Signal strength drops drastically when moving from the main office floor into a newly constructed elevator vestibule.
Mobile laptops maintain connections to a weak Access Point far away rather than switching to a closer Access Point with stronger signal.
Access points deployed on channels 1, 2, and 3 report excessive frame collisions and diminished throughput.

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

The correct pairings match each wireless issue to its RF root cause: lunch-hour breakroom drops correspond to non-802.11 RF interference; sudden signal loss behind elevator vestibules corresponds to physical attenuation/absorption; clients failing to switch APs corresponds to sticky client behavior; and frame collisions across channels 1, 2, and 3 correspond to adjacent channel interference.
Each wireless symptom directly correlates to a fundamental RF behavior: non-802.11 equipment like microwaves causes temporary localized outages; dense building materials absorb RF energy leading to attenuation; unoptimized client roaming decisions lead to sticky clients; and non-standard channel selections (channels 1, 2, and 3) cause adjacent channel interference.

Adım Adım Çözüm

1
Analyze environmental patterns for Non-802.11 interference
Identify that breakroom microwave ovens emit 2.4 GHz interference during lunch hours.
Microwave ovens operate on unlicensed 2.4 GHz frequencies and interfere with Wi-Fi without generating 802.11 protocol errors.
2
Evaluate building materials causing signal degradation
Identify elevator shafts and reinforced concrete as sources of physical attenuation.
Dense metal and concrete structures absorb and block RF energy rapidly.
3
Examine client roaming thresholds
Identify client reluctance to dissociate from distant APs as sticky client behavior.
Client driver roaming aggressive settings or AP transmit power mismatches prevent timely roaming.
4
Assess channel allocation plan in the 2.4 GHz band
Identify channels 1, 2, and 3 assignment as adjacent channel interference.
In 2.4 GHz Wi-Fi deployments, non-overlapping channels are 1, 6, and 11. Partial channel overlaps create uncoordinated cross-talk.

Anahtar Kavram

Wireless RF Troubleshooting (Interference, Attenuation, Roaming, Channel Overlap)
Soru 196Soru →

A network administrator is troubleshooting an issue where hosts on a newly provisioned user subnet (VLAN 50, 10.50.10.0/2410.50.10.0/24) are receiving APIPA IPv4 addresses (169.254.x.x169.254.x.x) instead of valid leases from the central DHCP server located on VLAN 10 (10.10.10.210.10.10.2). Place the diagnostic and remediation steps in the correct logical sequence from initial verification to final resolution confirmation.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct logical order begins with host configuration verification (`ipconfig /all`), followed by checking the gateway's DHCP relay (`ip helper-address`) configuration, applying the missing relay/ACL configuration, and concluding with host lease renewal (`ipconfig /renew`) to verify full functionality.
Following standard network troubleshooting methodology, an engineer first identifies the problem at the client host by checking `ipconfig /all`. Because the host has an APIPA address (169.254.x.x169.254.x.x) and resides on a separate subnet from the DHCP server, the engineer must next inspect the gateway router for a missing `ip helper-address`. Once identified, configuring the helper address and verifying UDP 67/68 traffic flow remediates the relay failure. Finally, forcing a lease renewal with `ipconfig /renew` on the client confirms full operational recovery.

Adım Adım Çözüm

1
Verify client network state
Confirmed client is configured for DHCP but assigned an APIPA address (169.254.x.x169.254.x.x).
Establishes the problem scope at the host before investigating network infrastructure.
2
Check Layer 3 gateway relay configuration
Identified that `ip helper-address` is missing on the SVI/interface for VLAN 50.
DHCP broadcasts cannot cross Layer 3 boundaries without a configured relay agent.
3
Implement solution and check ACLs
`ip helper-address 10.10.10.2` is configured and UDP ports 67/68 are allowed across the router.
Remediates the root cause by converting client broadcast requests into unicast packets routed to the DHCP server.
4
Verify complete resolution
Client successfully obtains a lease within 10.50.10.0/2410.50.10.0/24.
Confirms system functionality as required by standard troubleshooting methodology.

Anahtar Kavram

DHCP Relay and Helper Address Troubleshooting across Layer 3 Subnets
Soru 197Soru →

A network technician is following the standard CompTIA troubleshooting methodology to resolve a remote gateway connectivity failure reported on a client workstation. Place the troubleshooting steps in the correct sequential order from first to last.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct troubleshooting sequence follows the established CompTIA methodology: 1. Gather initial diagnostic information (Identify the problem). 2. Establish a theory of probable cause suggesting a subnet mask mismatch. 3. Test the theory using targeted ICMP ping tests. 4. Establish a plan of action and reconfigure the host's subnet mask. 5. Verify full system functionality and document the resolution.
The standard CompTIA troubleshooting methodology requires executing steps in strict sequence: 1) Identify the problem, 2) Establish a theory of probable cause, 3) Test the theory to determine cause, 4) Establish a plan of action to resolve the problem and implement the solution, 5) Verify full system functionality and implement preventive measures, and 6) Document findings, actions, and outcomes. Gathering diagnostic details represents problem identification. Suggesting a subnet mismatch establishes a theory. Ping testing evaluates the theory. Correcting the subnet mask implements the plan of action. Restoring remote access and logging findings fulfills verification and documentation.

Adım Adım Çözüm

1
Identify the problem
Host IP configuration details are gathered via CLI output.
Systematic troubleshooting requires gathering empirical symptoms before making assumptions.
2
Establish a theory of probable cause
Formulated a targeted hypothesis regarding a default gateway subnet mask mismatch.
Analyzing gathered data leads to a probable cause hypothesis.
3
Test the theory to determine the cause
Targeted ping test fails, confirming local routing context isolation.
Validates the theory without risking unnecessary baseline system changes.
4
Establish a plan of action and implement the solution
The host subnet mask is updated to align with the gateway interface.
Resolves the verified root cause.
5
Verify full system functionality and document findings
Remote connectivity is restored and actions are logged in tickets.
Ensures no secondary issues remain and preserves historical knowledge.

Anahtar Kavram

CompTIA Troubleshooting Methodology for Gateway and Subnet Configuration
Soru 198Soru →

A network technician is troubleshooting a newly installed 2.4 GHz Wi-Fi deployment in a open-plan office. Users report frequent packet drops and inconsistent throughput despite showing strong signal indicators on their devices. A wireless spectrum analyzer reveals heavy adjacent-channel interference between three neighboring access points currently configured to operate on channels 1, 3, and 5 with 20 MHz channel widths. Which of the following actions should the technician take to resolve the wireless interference and optimize performance?

Cevabı ve açıklamayı göster

Cevap: Reconfigure the access points to operate on channels 1, 6, and 11 while maintaining a 20 MHz channel width.

Cevap

Reconfigure the access points to operate on channels 1, 6, and 11 while maintaining a 20 MHz channel width.
In the 2.4 GHz wireless frequency band, 20 MHz channels require a minimum of 25 MHz separation between center frequencies to prevent overlapping. Channels 1, 6, and 11 are the industry-standard non-overlapping channels. Reconfiguring adjacent access points from channels 1, 3, and 5 to channels 1, 6, and 11 eliminates adjacent-channel interference and restores expected wireless throughput.

Adım Adım Çözüm

1
Analyze the current wireless channel assignments and physical band characteristics.
The APs operate on 2.4 GHz using 20 MHz channel widths on channels 1, 3, and 5.
Each 20 MHz channel in the 2.4 GHz spectrum extends 10 MHz above and below its center frequency, creating a 22-25 MHz total spectral mask. Channels 1, 3, and 5 overlap heavily with one another.
2
Identify the standard non-overlapping 2.4 GHz channel scheme.
Channels 1, 6, and 11 provide at least 25 MHz of center-frequency separation.
By assigning neighboring access points to channels 1, 6, and 11, adjacent-channel interference is completely eliminated.

Anahtar Kavram

2.4 GHz Non-Overlapping Channels
Soru 199Soru →

A workstation on an enterprise network is unable to access internal network shares or the Internet. A network technician runs `ipconfig` on the command prompt and receives the following output:

IPv4 Address. . . . . . . . . . . . : 169.254.184.91
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . :

Which of the following is the most likely cause of this issue?

Cevabı ve açıklamayı göster

Cevap: The workstation failed to reach a DHCP server and self-assigned an Automatic Private IP Addressing (APIPA) address.

Cevap

The workstation failed to reach a DHCP server and self-assigned an Automatic Private IP Addressing (APIPA) address.
An IPv4 address in the range 169.254.0.1 through 169.254.255.254 indicates that the operating system assigned an Automatic Private IP Addressing (APIPA) address after failing to contact a DHCP server.

Adım Adım Çözüm

1
Examine the IP address assigned to the host from the command output.
The host IP is 169.254.184.91 with a subnet mask of 255.255.0.0.
IP addresses in the 169.254.0.0/16 block are reserved for Automatic Private IP Addressing (APIPA).
2
Determine why an APIPA address is assigned to a DHCP client.
APIPA is activated when a DHCP client sends a broadcast request but fails to receive a DHCPOFFER response.
The client self-assigns an address to enable local link communication while indicating a failure to contact the DHCP server.

Anahtar Kavram

Automatic Private IP Addressing (APIPA) Identification
Tahmini Süre:45s
Soru 200Soru →

A network technician connects two switches, Switch-A and Switch-B, via an 802.1Q trunk link. Users on VLAN 10 connected to Switch-A cannot communicate with users on VLAN 10 attached to Switch-B. Console output on Switch-A displays `%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on interface GigabitEthernet0/1 (10), with Switch-B GigabitEthernet0/1 (1)`. Which TWO of the following statements correctly explain the network behavior and the required resolution?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: Untagged frames sent by Switch-A on native VLAN 10 are received by Switch-B and assigned to VLAN 1.; Configuring the native VLAN to match on both ends of the trunk interface will resolve the connectivity issue.

Cevap

The two correct statements are that untagged frames sent by Switch-A on native VLAN 10 are received by Switch-B and assigned to VLAN 1, and configuring the native VLAN to match on both ends of the trunk interface will resolve the connectivity issue.
Under the IEEE 802.1Q standard, traffic on the native VLAN travels untagged across trunk links. When Switch-A uses VLAN 10 as native and Switch-B uses VLAN 1, untagged frames sent from Switch-A's VLAN 10 arrive at Switch-B and are incorrectly processed as VLAN 1 frames. Reconfiguring both switch interfaces to share the same native VLAN restores proper frame segregation and trunk connectivity.

Adım Adım Çözüm

1
Analyze the syslog console error message
Identify that Switch-A is using VLAN 10 as its native VLAN on link GigabitEthernet0/1, whereas Switch-B is using VLAN 1.
Cisco Discovery Protocol (CDP) flags discrepancies when native VLAN configurations differ across a trunk.
2
Determine 802.1Q frame encapsulation behavior
Recognize that untagged frames leaving Switch-A on native VLAN 10 enter Switch-B untagged and are placed into Switch-B's configured native VLAN 1.
802.1Q trunking standard specifies that native VLAN traffic is forwarded without an IEEE 802.1Q header tag.
3
Identify the troubleshooting remediation steps
Configure identical native VLAN numbers on both switch interfaces forming the trunk.
Trunk interfaces must have matching native VLAN settings to maintain consistent Layer 2 domain boundaries.

Anahtar Kavram

802.1Q Trunk Native VLAN Mismatch Identification and Resolution
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