Troubleshooting Scenario Questions

A network engineer is troubleshooting slow connectivity between two sites connected via a WAN link. The engineer suspects packet loss due to collisions. Which interface counter should be examined to confirm this?

A
Runts
Why wrong: Runts are frames smaller than 64 bytes, not collision-specific.
B
CRC errors
CRC errors indicate frame checksum failures often caused by collisions.
C
Output errors
Why wrong: Output errors are a general category, not specific to collisions.
D
Giants
Why wrong: Giants are frames larger than maximum size, not collision-specific.

Question 2mediumdrag order

Drag and drop the steps to troubleshoot a network connectivity issue using the OSI model from bottom to top.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 3hardmultiple choice

A network engineer is troubleshooting a Kubernetes deployment where pods are failing to start with the error 'CrashLoopBackOff'. The pod log shows 'bind: address already in use'. The deployment runs multiple replicas of a container that listens on port 8080. What is the most likely cause?

A
The container is attempting to bind to a privileged port without the necessary capabilities.
Why wrong: Port 8080 is not privileged (privileged ports are below 1024).
B
The deployment has hostPort: 8080 specified, causing port conflict when multiple replicas are scheduled on the same node.
hostPort reserves the port on the host node, so only one pod per node can use it. With multiple replicas, subsequent pods fail with address in use.
C
The service is using NodePort and the node port is already in use.
Why wrong: NodePort is a service type; the error occurs at the container level, not the service level.
D
Multiple containers in the same pod are trying to bind to the same port.
Why wrong: Containers in a pod share the same network namespace; they cannot bind to the same port, but the error would occur at pod creation, not as CrashLoopBackOff after start.

Question 4mediummulti select

A network engineer is troubleshooting an issue where hosts in VLAN 100 cannot reach a server at 10.1.1.100. The switch interfaces are configured as access ports in VLAN 100, and the default gateway is 10.1.1.1. The engineer checks the switch and finds that the ARP table does not contain the server's MAC address. Which two actions should the engineer take to resolve the issue? (Choose two.)

A
Ping the server's IP address from the switch management interface.
Why wrong: The switch management interface may be in a different VLAN, so this does not test the specific VLAN 100 path.
B
Ping the default gateway from a host in VLAN 100.
Why wrong: This checks Layer 3 connectivity but does not directly address the missing ARP entry for the server.
C
Check the ARP table on the default gateway router.
The hosts need to resolve the server's MAC, not the gateway's. The issue is on the switch or host side.
D
Check the MAC address table on the switch for the server's MAC.
Why wrong: The MAC address table shows Layer 2 paths, but the issue is ARP resolution which is Layer 3.
E
Verify that the switch port connected to the server is in VLAN 100.
If the server is on an access port in a different VLAN, the hosts in VLAN 100 cannot reach it.

Open the full BGP breakdown →

Question 5hardmultiple choice

A network administrator is troubleshooting BGP path selection for a route received from two different ISPs. The routes have the same local preference and AS-path length, but one route has a shorter MED value. Which route will be preferred?

A
The route with the most specific prefix length
Why wrong: Prefix length is considered later, but for same prefix, other attributes first.
B
The route from the ISP with the higher bandwidth
Why wrong: Bandwidth is not a BGP attribute.
C
The route with the lower MED
Lower MED is preferred.
D
The route with the higher local preference
Why wrong: Local preference is equal, so not decisive.

Question 6hardmulti select

A network automation script using NX-API on a Nexus switch fails intermittently with HTTP 500 errors. Which two troubleshooting steps are most effective in diagnosing the issue? (Choose two.)

A
Check the length of the JSON payload sent to the API.
Why wrong: Payload size limits cause 413 errors, not 500.
B
Ensure the switch is running NX-OS version 9.3(1) or later.
Why wrong: Version is less likely to cause intermittent 500 errors.
C
Enable NX-API debugging on the switch to capture detailed logs.
Debug logs help identify the exact failure point.
D
Verify that the NX-API sandbox feature is enabled and running.
If NX-API is not fully enabled, it can lead to intermittent errors.
E
Use HTTP instead of HTTPS for the API requests.
Why wrong: Using HTTP does not fix the issue and introduces security risks.

Read the full REST/YANG explanation →

Question 7mediummultiple choice

Refer to the exhibit. A developer from subnet 10.10.10.0/24 cannot reach the RESTCONF API on the IOS-XE device. What is the most likely cause?

Exhibit

configure terminal
 ip http server
 ip http secure-server
 ip http authentication local
 ip http access-class 23
!
access-list 23 permit 192.168.1.0 0.0.0.255

A
HTTPS is not enabled on the device.
Why wrong: The 'ip http secure-server' command enables HTTPS.
B
The HTTP server is not enabled.
Why wrong: The configuration includes 'ip http server', so HTTP is enabled.
C
Authentication is not configured as local.
Why wrong: Authentication is set to local with 'ip http authentication local'.
D
The 10.10.10.0/24 subnet is not permitted by the access-class.
Access-list 23 permits only 192.168.1.0/24, blocking all other subnets.

Question 8easymultiple choice

A network engineer is troubleshooting a connectivity issue between two hosts in different VLANs on the same switch. The hosts are in VLAN 10 and VLAN 20, respectively. The switch has an SVI for each VLAN and IP routing is enabled. Which command should be used to verify that the switch is forwarding traffic between the VLANs?

A
show interfaces trunk
Why wrong: Shows trunking status, not routing.
B
show vlan
Why wrong: Shows VLAN membership, not routing table.
C
show ip route
Displays the routing table, confirming inter-VLAN routing.
D
show mac address-table
Why wrong: Shows MAC address table, not routing.

Question 9mediummultiple choice

During a network outage, a technician notices that hosts in VLAN 10 cannot reach the default gateway at 192.168.10.1, but hosts in VLAN 20 can. The switch interfaces are up, and the router is configured with subinterfaces. What is the most likely cause?

A
The trunk link is administratively down.
Why wrong: If the trunk were down, all VLANs would be affected.
B
The switchport trunk native VLAN is mismatched.
Why wrong: A native VLAN mismatch would likely cause issues for all VLANs or at least the native VLAN, not just VLAN 10.
C
The router subinterface for VLAN 10 is down or misconfigured.
A down or misconfigured subinterface prevents routing for that VLAN.
D
The router does not have an IP address configured.
Why wrong: The router must have IP on the subinterface; lack of IP would affect all VLANs.

Question 10easymultiple choice

A network administrator is troubleshooting a connectivity issue. A PC with IP address 192.168.1.10/24 cannot ping a server at 192.168.1.20/24. Both are on the same VLAN and connected to the same switch. What is the most likely cause of the issue?

A
The ARP cache on the PC needs to be cleared.
Why wrong: ARP cache can be cleared, but it is not the most likely cause of persistent failure.
B
The subnet mask on the PC is incorrect.
Why wrong: The /24 mask is correct for the given IP range.
C
The switch port is in the wrong VLAN.
Why wrong: Both are on the same VLAN as stated, so this is not the issue.
D
The server has a firewall blocking ICMP echo requests.
A firewall can block ping, which is a common troubleshooting scenario.
E
The default gateway is misconfigured on the PC.
Why wrong: Default gateway is not required for communication within the same subnet.

Question 11mediummultiple choice

You are deploying a new data center network using Cisco Nexus switches. The design uses Virtual Port Channel (vPC) to provide redundancy and increased bandwidth to servers with dual-homed NICs. The two vPC peer switches are NX1 and NX2, and they are connected via a peer-link. The servers are configured with active/standby NIC teaming. After the deployment, you notice that some ARP requests from servers are not being responded to, leading to connectivity issues. Analysis shows that when a server sends an ARP request for its default gateway (which is a virtual IP on the vPC), only one of the peer switches responds, but the response does not reach the server intermittently. The vPC is correctly configured, and the peer-gateway feature is enabled. What is the most likely cause?

A
The virtual gateway IP is misconfigured with HSRP, causing split-brain.
Why wrong: vPC uses a single IP on both peers; HSRP is not needed.
B
STP is blocking the vPC peer-link, preventing ARP responses.
Why wrong: vPC peer-link is always forwarding; STP is not used on vPC links.
C
The server's MAC address is not pinned to the correct vPC member port.
Why wrong: MAC pinning is for bounce learning; not relevant to ARP responses.
D
The server's NIC teaming is sending ARP requests to the standby switch, which forwards them over the peer-link, and the peer-gateway feature does not respond to ARP requests received over the peer-link.
Peer-gateway only responds to ARP on vPC member ports, not on peer-link.

Review the full subnetting walkthrough →

Question 12hardmultiple choice

An engineer is troubleshooting packet loss between two hosts on different subnets. The traceroute shows that packets reach the first hop router but then stop. The router's ARP table shows an incomplete entry for the next-hop IP address. What is the most likely cause?

A
The MTU is misconfigured on the outgoing interface.
Why wrong: MTU issues cause packet drops but not ARP incompleteness.
B
The routing protocol has not converged yet.
Why wrong: Routing convergence affects the route table, not ARP.
C
The next-hop device is powered off or has a Layer 1 issue.
If the next-hop device is offline, the router cannot complete ARP.
D
An ACL is blocking traffic on the outgoing interface.
Why wrong: ACLs drop packets after routing, they don't prevent ARP resolution.

Study the full Python automation breakdown →

Question 13hardmultiple choice

A developer is troubleshooting a CI/CD pipeline that automatically deploys configuration changes to network devices. The pipeline includes a stage that runs Python unit tests. Which of the following would be a valid test to include in that stage to validate the configuration before deployment?

A
Test that the configuration can be applied to the device by sending it via NETCONF
Why wrong: This is an integration test, not a unit test.
B
Test that the configuration file is valid JSON
A unit test can verify syntax without needing network access.
C
Test that the configuration changes do not break connectivity by pinging the device after deployment
Why wrong: This is a deployment test, not suitable for a unit test stage.
D
Test that the configuration adheres to company naming conventions using a regular expression
Why wrong: While possible, this is more of a linting step than a unit test; however, it could be valid. But option A is more direct.

Study the full Python automation breakdown →

Question 14hardmultiple choice

A Python script using the Cisco ACI Toolkit (aciToolkit) fails with 'LoginError: unable to login to APIC'. The APIC is reachable via HTTPS. What is the most likely cause?

A
The APIC has reached its maximum session limit.
Why wrong: Session limit would produce a different error (e.g., 'max sessions reached'), and is less common than configuration errors.
B
The script uses HTTP instead of HTTPS.
Why wrong: The aciToolkit defaults to HTTPS and will raise a different error if HTTP is forced.
C
The script uses an incorrect APIC domain (e.g., 'apic' instead of the FQDN).
The aciToolkit's login() requires the correct APIC domain; an incorrect domain prevents proper authentication.
D
The APIC is running an unsupported firmware version.
Why wrong: Firmware version is not a direct cause of login failure; the toolkit supports a range of versions.

Read the full REST/YANG explanation →

Question 15hardmultiple choice

An engineer needs to troubleshoot a RESTCONF request that returns a 409 Conflict error when trying to modify a YANG data node. What is the most likely cause?

A
The data node is read-only
Why wrong: Read-only would return a 405 Method Not Allowed or 403.
B
Authentication failure
Why wrong: Authentication failure returns 401 Unauthorized.
C
The resource was modified by another client during the operation
409 Conflict indicates a conflict with the current state.
D
The YANG model version mismatch
Why wrong: Model mismatch would typically yield a 400 Bad Request.