Troubleshooting practice 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?

Trap 1: Runts

Runts are frames smaller than 64 bytes, not collision-specific.

Trap 2: Output errors

Output errors are a general category, not specific to collisions.

Trap 3: Giants

Giants are frames larger than maximum size, not collision-specific.

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?

Trap 1: The container is attempting to bind to a privileged port without…

Port 8080 is not privileged (privileged ports are below 1024).

Trap 2: The service is using NodePort and the node port is already in use.

NodePort is a service type; the error occurs at the container level, not the service level.

Trap 3: Multiple containers in the same pod are trying to bind to the same…

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.

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.

Open the full VLAN trunking answer →

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.)

Trap 1: Ping the server's IP address from the switch management interface.

The switch management interface may be in a different VLAN, so this does not test the specific VLAN 100 path.

Trap 2: Ping the default gateway from a host in VLAN 100.

This checks Layer 3 connectivity but does not directly address the missing ARP entry for the server.

Trap 3: Check the MAC address table on the switch for the server's MAC.

The MAC address table shows Layer 2 paths, but the issue is ARP resolution which is Layer 3.

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?

Trap 1: The route with the most specific prefix length

Prefix length is considered later, but for same prefix, other attributes first.

Trap 2: The route from the ISP with the higher bandwidth

Bandwidth is not a BGP attribute.

Trap 3: The route with the higher local preference

Local preference is equal, so not decisive.

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.)

Trap 1: Check the length of the JSON payload sent to the API.

Payload size limits cause 413 errors, not 500.

Trap 2: Ensure the switch is running NX-OS version 9.3(1) or later.

Version is less likely to cause intermittent 500 errors.

Trap 3: Use HTTP instead of HTTPS for the API requests.

Using HTTP does not fix the issue and introduces security risks.

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.

Open the full VLAN trunking answer →

Question 7easymultiple 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?

Trap 1: show interfaces trunk

Shows trunking status, not routing.

Trap 2: show vlan

Shows VLAN membership, not routing table.

Trap 3: show mac address-table

Shows MAC address table, not routing.

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.

Open the full VLAN trunking answer →

Question 8easymultiple 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?

Trap 1: The ARP cache on the PC needs to be cleared.

ARP cache can be cleared, but it is not the most likely cause of persistent failure.

Trap 2: The subnet mask on the PC is incorrect.

The /24 mask is correct for the given IP range.

Trap 3: The switch port is in the wrong VLAN.

Both are on the same VLAN as stated, so this is not 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.

Review the full subnetting walkthrough →

Question 9hardmultiple 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?

Trap 1: The MTU is misconfigured on the outgoing interface.

MTU issues cause packet drops but not ARP incompleteness.

Trap 2: The routing protocol has not converged yet.

Routing convergence affects the route table, not ARP.

Trap 3: An ACL is blocking traffic on the outgoing interface.

ACLs drop packets after routing, they don't prevent ARP resolution.

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 10hardmultiple 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?

Trap 1: Test that the configuration can be applied to the device by sending…

This is an integration test, not a unit test.

Trap 2: Test that the configuration changes do not break connectivity by…

This is a deployment test, not suitable for a unit test stage.

Trap 3: Test that the configuration adheres to company naming conventions…

While possible, this is more of a linting step than a unit test; however, it could be valid. But option A is more direct.

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.

Read the full REST/YANG explanation →

Question 11mediummulti select

A developer is troubleshooting a Cisco RESTCONF API call that returns a 409 Conflict error. Which two scenarios could cause this? (Choose two.)

Trap 1: Authentication token is missing.

Missing token results in 401 Unauthorized.

Trap 2: The resource does not exist.

A missing resource would give 404, not 409.

Trap 3: The request contains invalid data types.

Invalid data types result in 400 Bad Request.

A
Authentication token is missing.
Why wrong: Missing token results in 401 Unauthorized.
B
The resource's current state conflicts with the requested change (e.g., trying to delete a resource that is in use).
State conflicts, like deleting a resource that is referenced, cause 409.
C
The resource already exists and the request attempts to create a duplicate.
Creating a duplicate resource is a typical cause of 409.
D
The resource does not exist.
Why wrong: A missing resource would give 404, not 409.
E
The request contains invalid data types.
Why wrong: Invalid data types result in 400 Bad Request.

Study the full SD-WAN breakdown →

Question 12hardmultiple choice

A developer is troubleshooting an API call to Cisco SD-WAN vManage. The request fails with HTTP 400 status and the response body: '{"error": "Bad Request", "details": "Invalid JSON: unexpected token at position 42"}'. Which tool or technique should the developer use to quickly identify the syntax error?

Trap 1: Increase the timeout value for the HTTP request.

Timeout does not cause a 400 error; it would cause a timeout error.

Trap 2: Check the API key validity in the header.

An invalid API key would return 401 Unauthorized, not a JSON parsing error.

Trap 3: Review the API documentation for required fields.

Missing required fields would cause a different error; this error is about malformed JSON.

A
Use a JSON validator to check the request body.
A JSON validator can identify syntax errors such as unexpected tokens.
B
Increase the timeout value for the HTTP request.
Why wrong: Timeout does not cause a 400 error; it would cause a timeout error.
C
Check the API key validity in the header.
Why wrong: An invalid API key would return 401 Unauthorized, not a JSON parsing error.
D
Review the API documentation for required fields.
Why wrong: Missing required fields would cause a different error; this error is about malformed JSON.

Question 13mediummultiple choice

An engineer is troubleshooting a Cisco DNA Center API call that returns a 401 error. What is the most likely cause?

Trap 1: The network device is unreachable

Device unreachable results in a different error, not a 401.

Trap 2: The request body is invalid

Invalid body results in 400 Bad Request.

Trap 3: The API endpoint is incorrect

Incorrect endpoint returns 404 Not Found.

A
The authentication token has expired
401 indicates missing or invalid authentication credentials.
B
The network device is unreachable
Why wrong: Device unreachable results in a different error, not a 401.
C
The request body is invalid
Why wrong: Invalid body results in 400 Bad Request.
D
The API endpoint is incorrect
Why wrong: Incorrect endpoint returns 404 Not Found.

Read the full REST/YANG explanation →

Question 14hardmultiple choice

An engineer is troubleshooting a NETCONF session that fails to establish with a Cisco IOS XE device. The SSH connection succeeds, but NETCONF capabilities are not exchanged. What is the most likely cause?

Trap 1: The device requires authentication via SSH keys but password was…

That would cause authentication failure, not capabilities exchange issue.

Trap 2: The firewall is blocking port 830.

SSH connection succeeded, so port 830 is reachable.

Trap 3: The device is running an older IOS version that does not support…

If SSH works, IOS XE generally supports NETCONF if enabled.

A
The device requires authentication via SSH keys but password was used.
Why wrong: That would cause authentication failure, not capabilities exchange issue.
B
The firewall is blocking port 830.
Why wrong: SSH connection succeeded, so port 830 is reachable.
C
The device is running an older IOS version that does not support NETCONF.
Why wrong: If SSH works, IOS XE generally supports NETCONF if enabled.
D
The device's NETCONF server is not enabled.
If netconf-yang feature is not enabled, SSH connects but no NETCONF capabilities.

Review the full subnetting walkthrough →

Question 15easymultiple choice

You are troubleshooting connectivity for a remote branch office. The branch router (BR) connects to the head office router (HQ) via a point-to-point T1 link. The HQ router is also connected to the internet via a separate interface. Users at the branch can access the internet but cannot reach servers at the head office (subnet 10.10.10.0/24). You run 'show ip route' on BR and see a default route pointing to HQ's IP address, but no specific route for 10.10.10.0/24. The HQ router has a connected route for that subnet. On HQ, you see that the interface towards BR is up/up, and you can ping the BR's interface IP. What is the most likely cause of the issue?

Trap 1: An ACL on the HQ router is blocking traffic from the branch subnet.

There is no indication of ACL blocks; the issue is more fundamental.

Trap 2: The default route on BR is not pointing to the correct next-hop.

If internet works, the default route is correct for outgoing traffic.

Trap 3: The T1 link is experiencing errors causing packet loss.

Internet connectivity works, so the link is functional.

A
The HQ router does not have a route for the branch's local subnet.
Without a return route, traffic from branch to HQ can leave but replies are dropped.
B
An ACL on the HQ router is blocking traffic from the branch subnet.
Why wrong: There is no indication of ACL blocks; the issue is more fundamental.
C
The default route on BR is not pointing to the correct next-hop.
Why wrong: If internet works, the default route is correct for outgoing traffic.
D
The T1 link is experiencing errors causing packet loss.
Why wrong: Internet connectivity works, so the link is functional.