Network Troubleshooting

A network engineer is analyzing a packet capture (pcap) collected from a client workstation that is unable to authenticate with a RADIUS server. The trace shows the workstation sending UDP datagrams to port 1812 on the server IP address, followed immediately by ICMP Type 3, Code 3 (Destination Unreachable - Port Unreachable) response messages from the server. Which of the following conclusions is best supported by the packet analyzer output?

A network administrator has just completed testing a theory and confirmed that an incorrect Maximum Transmission Unit (MTU) setting on an edge router interface is causing packet fragmentation and dropping encrypted site-to-site IPsec VPN traffic. Following the CompTIA troubleshooting methodology, the administrator is now preparing to transition to the phase of establishing a plan of action and implementing the solution. Which of the following specific tasks should be performed during this phase? (Select TWO.)

A network administrator provisions a new VLAN at a remote office site, routing inter-VLAN traffic through a local Layer 3 switch. Clients connected to the new VLAN are unable to access network resources and receive self-assigned IP addresses starting with $169.254.x.x$. The centralized DHCP server located at the main headquarters has a valid, non-exhausted scope created for the new subnet. Which of the following is the most likely cause of this issue?

An infrastructure engineer is investigating an incident where telemetry data feeds from an edge gateway fail to reach a central monitoring cluster. After analyzing packet captures, the engineer successfully confirms that an MTU mismatch along the GRE tunnel path is causing fragmented packets to be dropped. Which action represents the next step the engineer should take according to the CompTIA troubleshooting methodology?

A network technician terminates a new Category 6A horizontal cable run between a patch panel and a modular wall jack using T568B standards. When testing the link, a basic wiremapper confirms that all eight conductors have proper 1-to-1 pin continuity. However, when connected to a multi-gigabit switch, the link fails to negotiate a 10Gbps connection and experiences high frame error rates. A cable certifier reveals severe Near-End Crosstalk (NEXT). Which TWO of the following physical installation faults are the most likely causes of this issue? (Select TWO.)

A network administrator is troubleshooting an issue where hosts on the $10.10.10.0/24$ management subnet cannot establish secure web connections to a server at $10.20.30.50$. Upon reviewing the inbound interface settings on the router, the administrator inspects the following Access Control List (ACL):

text 10 permit tcp 10.10.10.0 0.0.0.255 host 10.20.30.50 eq 80 20 deny ip any any

When attempting to access the server's web control portal via `https://10.20.30.50`, connection attempts time out. Which of the following identifies the root cause of this failure?

A workstation connected to an enterprise network fails to reach internal network resources. A network technician is assigned to troubleshoot the host's IP addressing and DHCP service connectivity. Arrange the diagnostic and troubleshooting steps in the correct order according to standard bottom-up network troubleshooting methodology.

A client workstation requests the IP address for an external hostname (app.sub.example.com) that is not in any local DNS cache. Arrange the steps of the recursive DNS lookup process in the correct order from initial query to final response.

A network technician is deploying IP VoIP phones on VLAN 30 ($172.16.30.0/24$). The centralized DHCP server is located on VLAN 10 ($172.16.10.5$). While devices assigned static IP addresses on VLAN 30 communicate across subnets normally, all phones set to acquire addresses automatically receive IPs in the $169.254.x.x$ subnet and fail to register. Inspecting the Layer 3 switch shows that inter-VLAN routing is active and operational. Which of the following is the most likely cause of this problem?

A network administrator is investigating user reports of severe performance degradation and file transfer timeouts when accessing a local backup server connected to Switch-A. The administrator reviews the interface statistics on switch port GigabitEthernet0/1 and observes a rapidly increasing counter for late collisions, FCS errors, and runts, despite the physical link showing up/up at 100 Mbps. Which of the following is the primary cause of this connectivity issue?

A network administrator is troubleshooting an unbundled Category 6 copper cable run passing through a ceiling plenum that suddenly lost connectivity. The administrator suspects the cable was damaged or cut at an unknown point along its 85-meter length. Which diagnostic instrument should be utilized to measure the exact distance to the cable fault?

A network technician is troubleshooting an issue where client machines on the local network cannot access an internal secure web application hosted at `https://app.corp.local`. The technician executes `nslookup app.corp.local` on a client machine, which successfully resolves `app.corp.local` to IP address `10.10.20.15`. The technician then connects remotely to the server at `10.10.20.15` and runs the `netstat -ano` command, obtaining the following output snippet:

Proto Local Address Foreign Address State PID
TCP 10.10.20.15:80 0.0.0.0:0 LISTENING 2044
TCP 10.10.20.15:8080 0.0.0.0:0 LISTENING 3112
UDP 10.10.20.15:53 *:* 1088

Based on the command output and scenario details, which of the following is the primary cause of the connection failure?

A network administrator is investigating connectivity complaints from users on a newly deployed subnet ($10.20.50.0/24$). An affected workstation displays an IP address of $169.254.112.45$ and a subnet mask of $255.255.0.0$. The organization's central DHCP server is located on a separate administrative segment ($10.20.10.10$). Which of the following issues could cause the client to receive this address? (Select TWO.)

A network technician is troubleshooting connectivity issues for several newly provisioned workstations on the finance VLAN (10.15.30.0/24). While the workstations can communicate with each other on the local switch, none of them can access corporate servers on external subnets or reach the internet. An inspection of `ipconfig /all` on one of the affected clients yields the following output:

IPv4 Address. . . . . . . . . . . : 10.15.30.45
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.15.40.1
DHCP Server . . . . . . . . . . . : 10.15.10.10

Which of the following is the most likely cause of the routing failure?

Match each network diagnostic requirement or scenario to the most appropriate hardware testing tool or protocol analyzer function.

A network administrator is troubleshooting an issue where servers on VLAN 40 (subnet 172.20.40.0/24) can successfully synchronize time with an internal NTP server (192.168.1.50), but fail to retrieve software updates from an HTTP repository located on the same server (192.168.1.50:80).

Inspection of the router's inbound ACL on the VLAN 40 interface reveals the following configuration:

ip access-list extended VLAN40_IN
10 permit tcp 172.20.40.0 0.0.0.255 host 192.168.1.50 eq 443
20 permit udp 172.20.40.0 0.0.0.255 host 192.168.1.50 eq 123

Which of the following TWO statements correctly identify the root cause of the failure and the necessary corrective action? (Select TWO.)

A network administrator is diagnosing two distinct layer 2 issues on Switch-A. First, syslog logs display repeated `%CDP-4-NATIVE_VLAN_MISMATCH` messages for trunk link interface GigabitEthernet0/1 connected to Switch-B. Second, interface statistics for GigabitEthernet0/2 connected to a local database server show a high number of late collisions and alignment errors during heavy transfer periods. Which of the following actions should the administrator take to resolve these issues? (Select TWO.)

A network technician is investigating performance degradation on a desktop host connected to switch port FastEthernet 0/12. The switch port speed and duplex settings were manually configured to 100 Mbps and Full Duplex, while the desktop network adapter was left on auto-negotiation. Running the `show interface fastEthernet 0/12` command reveals a rapidly incrementing counter for late collisions and Frame Check Sequence (FCS) errors.

Which of the following is the root cause of this connectivity issue?

A network administrator is configuring a workstation in a newly provisioned subnet with the IPv4 address $172.16.45.50/25$. The host can successfully ping other devices on the $172.16.45.0/25$ local network, but cannot reach any external subnets or the internet. Executing `ipconfig` reveals the default gateway is configured as $172.16.45.130$. Which of the following is the root cause of the connectivity failure?

A network administrator is troubleshooting an unexpected link outage on a 2 km single-mode fiber optic backbone connecting two enterprise distribution switches. While both optical transceivers are functioning properly, no signal reaches the remote end. The administrator needs to pinpoint the exact location of a suspected physical break along the cable run within an underground conduit. Which diagnostic tool should the administrator use?