Be able to pick the right Cisco IOS or Windows command for a given symptom: show interfaces for duplex and errors, show spanning-tree for loops, ping and tracert for reachability and path. The key skill is matching the observed symptom to the command that confirms it.
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Domain overview
This domain covers the Cisco 100-150 troubleshooting workflow: verifying physical/link status, isolating Layer 2 switching loops, checking duplex and speed mismatches, and tracing reachability with ping, traceroute, and show commands on Cisco switches and routers. Questions present a symptom and ask which command or output confirms the fault.
Exam objectives
Using show interfaces to read duplex, speed, and error counters on a Cisco switch port
Using show spanning-tree to confirm STP has blocked a redundant port during a loop
Using ping and tracert from Windows to test reachability and the path to a destination
Recognizing duplex mismatch symptoms: late collisions, CRC errors, and slow or stalling transfers
Confusing ping (reachability) with tracert (path), and choosing one when the question asks about the route to a host
Assuming a link is healthy because it is up/up, while ignoring late collisions and CRC errors that reveal a duplex mismatch
Forgetting that show spanning-tree, not show mac address-table, is what proves a port is blocking due to a loop
Click any question to see the full explanation and answer options, or start a focused practice session above.
A network administrator observes that a workstation cannot ping its default gateway. The physical link light is active, and the local IP configuration appears correct. Which diagnostic step should be performed first to isolate the layer 2 connectivity issue?
2A user reports intermittent connectivity to the internal server. Which TWO commands are most useful to identify if the issue is caused by physical layer flapping or interface errors?
3A user cannot reach a web server. You perform a ping and it fails, but a traceroute shows the packets reaching the last hop before the server. What does this indicate?
4Which tool is best suited for identifying a slow network segment caused by excessive broadcast traffic?
5Refer to the exhibit. What is the most likely cause of poor performance on this link?
6When a network administrator uses the 'ping' command to test connectivity, what is the primary purpose of the ICMP 'Echo Request' and 'Echo Reply' process?
7A network is experiencing high latency. The administrator finds that the switch has high CPU utilization. Which diagnostic step is most appropriate to identify the cause?
8A network technician is troubleshooting a PC that cannot access internal network resources. Which TWO steps are recommended to verify if the PC is receiving a valid IP address?
9Refer to the exhibit. Why is the router unable to reach the internet?
10What is the primary function of a loopback interface in troubleshooting network devices?
11A technician suspects a cable issue on a copper link. Which command should they use to check for electrical issues like shorts or opens?
12A help desk technician is troubleshooting a user who can access internal network shares using an IP address but cannot reach the same shares using the server's hostname. Which network service should the technician investigate first?
13A technician notices a laptop has an IP address of 169.254.11.45. The laptop cannot access the internet or local servers. What is the most likely cause of this issue?
14While troubleshooting a connectivity issue, a technician discovers a switch port is in the 'err-disabled' state. What is the standard first step to attempt to bring the port back online after identifying and fixing the root cause?
15A network administrator is using the 'ping' command to troubleshoot connectivity. Which TWO pieces of information can be determined specifically from the ICMP Echo Reply messages? (Choose two.)
16Which THREE conditions are common causes of 'Input Errors' appearing on a Cisco switch interface? (Choose three.)
17Refer to the exhibit. A technician is investigating why a device connected to FastEthernet0/1 cannot communicate. Based on the output, what is the most likely issue?
18Users in an office report that the wireless network is extremely slow during the middle of the day. A technician discovers a microwave oven and several 2.4GHz cordless phones in the breakroom near the Access Point. What is the cause of this performance issue?
19A technician is troubleshooting a PC that can communicate with other hosts on the same subnet but cannot reach any hosts on different subnets. Which configuration on the PC is most likely incorrect?
20A network engineer is troubleshooting a potential DHCP issue. Which THREE components are provided to a client during a successful DHCP 'Acknowledgment' (ACK) message? (Choose three.)
21Refer to the exhibit. A host connected to port FastEthernet0/2 is unable to communicate with other devices in VLAN 10. Based on the output, what can be concluded about port Fa0/2?
22A technician is troubleshooting a router that can ping its own interface but cannot ping a directly connected router's interface. The technician verifies that both interfaces are 'up/up'. What is the most likely cause?
23A user reports they can access the Internet but cannot connect to a specific internal accounting server. Other users in the same department can access the server without issue. What should the technician check first?
24While monitoring a network, an administrator sees a sudden spike in CPU usage on all switches and very high levels of broadcast traffic. What is the most likely cause of this behavior?
25A technician can successfully ping local servers on the same 192.168.10.0/24 subnet but cannot reach any resources on a different VLAN or the Internet. The technician verifies the local IP address and subnet mask are correct. Which component is the most likely source of the connectivity failure?
26A user reports they cannot access a web server at 192.168.50.10. Which TWO commands would provide the most useful initial diagnostic information regarding the path and reachability to this destination from a Windows workstation? (Choose two).
27A user on VLAN 20 reports that they cannot reach a server on VLAN 30, but they can reach other devices on VLAN 20 and the Internet. The network uses a Layer 3 switch for inter-VLAN routing. The technician verifies that the user's PC has the correct IP address, subnet mask, and default gateway. Which command should the technician run on the Layer 3 switch to verify that inter-VLAN routing is enabled and functioning?
28A help desk technician is troubleshooting a Windows workstation that cannot reach any resources on the local subnet. The technician runs ipconfig /all and notices the workstation has an IP address of 192.168.1.50 with a subnet mask of 255.255.255.0, but the default gateway field is blank. The workstation can ping other hosts on the same subnet. What is the most likely cause of the inability to reach remote networks?
29A technician is troubleshooting a user's workstation that cannot reach any resources on a remote subnet, though local subnet communication works fine. The technician suspects a routing or default gateway issue. Which command should be used on the workstation to verify the configured default gateway address?
30A technician is troubleshooting a workstation that cannot reach any network resources. The workstation's IP configuration shows an address of 169.254.10.22 and a subnet mask of 255.255.0.0. Which condition does this indicate?
31A user calls the help desk and reports that a laptop cannot reach any websites or internal servers. The technician runs ipconfig and sees that the laptop has an IPv4 address of 169.254.88.12 with a subnet mask of 255.255.0.0 and no default gateway. Which action should the technician take FIRST to resolve the problem?
32A network technician is investigating why a user cannot access a file server at 10.1.1.100. The user's workstation can ping the server successfully, but when the user tries to open a shared folder, the connection times out. The technician verifies that other users can access the same share. Which tool should the technician use to determine if a firewall is blocking the specific file-sharing protocol?
33A user reports that they cannot access any websites by name, but they can reach them by typing the IP address directly into the browser. The technician confirms that the workstation has a valid IP address, subnet mask, and default gateway. Which command should the technician use to test whether the DNS server is responding to queries?
34A network administrator is troubleshooting a switch port that connects to a user's PC. The port shows a status of 'err-disabled' and the reason is 'psecure-violation.' Which action should the administrator take first to resolve this?
35A network administrator is troubleshooting a switch that is experiencing high CPU utilization. The administrator suspects a switching loop. Which command should be used to verify whether Spanning Tree Protocol has blocked any ports to prevent a loop?
36A technician is investigating why a user cannot access a web server at 10.1.1.50. The technician runs 'ping 10.1.1.50' and receives a reply, but when the user tries to access the web server via its hostname 'intranet.corp.local', it fails. The user's workstation has a DNS server configured as 10.1.1.10. Which command should the technician use to verify DNS resolution?
37A network technician is troubleshooting a workstation that cannot reach any resources on a remote subnet. The workstation can ping its default gateway and other hosts on the local subnet. The technician runs 'tracert' from the workstation to a remote server and sees the first hop (the default gateway) respond, but all subsequent hops time out. Which is the most likely cause?
38A network technician is troubleshooting a connectivity issue between two switches. The link between them is up, but users on one switch cannot reach devices on the other. The technician suspects a VLAN mismatch. Which command should be used on a Cisco switch to verify the VLAN assignments on a specific interface?
39A technician is troubleshooting a workstation that can reach servers on the local subnet but cannot reach any host on a remote subnet. The workstation's IP address, subnet mask, and DNS server are correct, and pinging the default gateway succeeds. Which command should the technician use to verify the workstation's default gateway and interface configuration?
40A network technician is troubleshooting intermittent connectivity to a server. The technician suspects a duplex mismatch on a switch port connected to the server. Which command should be used to check the duplex setting and error statistics on the switch port?
41A network administrator is troubleshooting a Cisco Catalyst switch where a host connected to port Gi1/0/10 is experiencing intermittent connectivity. The administrator suspects a physical layer issue. Which TWO commands would provide the most direct evidence of physical layer problems on that interface? (Choose two.)
42A technician is troubleshooting a workstation that cannot connect to the network. The workstation has a link light, but ipconfig shows an IP address of 169.254.10.20. The technician suspects a DHCP-related issue. Which two commands should the technician use to attempt to obtain a new IP address from the DHCP server? (Choose two.)
43Users on a floor of an office building report that file transfers to a server are slow and sometimes stall. The technician suspects a duplex mismatch on the switch port connecting the server. Which TWO symptoms or outputs would confirm a duplex mismatch on that link? (Choose two.)
44A network administrator is troubleshooting a workstation that cannot access network resources. The administrator runs the command arp -a and sees an incomplete entry for the default gateway. Which two actions should the administrator take to resolve the issue? (Choose two.)
45A network administrator is troubleshooting a connectivity issue between two devices on the same VLAN. The administrator suspects a duplex mismatch on a switch port. Which command should be used on the Cisco switch to verify the duplex settings and error statistics on the interface?
46A user reports that they cannot access any websites by name, but they can access websites by typing their IP addresses directly into the browser. The user's computer has a valid IP address, subnet mask, and default gateway, and can ping the default gateway successfully. Which is the most likely cause of the problem?
47A technician is troubleshooting a wireless client that associates successfully with an access point but cannot obtain an IP address from the DHCP server on the wired network. The access point is configured with a management IP on the correct VLAN, and other wired clients on that VLAN obtain leases normally. Which is the MOST likely cause?
48A technician is troubleshooting a workstation that cannot connect to the network. The workstation has a valid IP address, subnet mask, and default gateway. The technician can ping the default gateway but cannot ping a server on a remote subnet. Which two commands should the technician use to further isolate the problem? (Choose two.)
49A network engineer is investigating why a switch port Gi1/0/5 is not forwarding traffic, even though the connected device is powered on and the cable is known to be good. The engineer runs 'show interfaces Gi1/0/5 switchport' and sees that the administrative mode is dynamic auto, and the operational mode is access. The port status is 'notconnect'. Which is the most likely reason the port is not forwarding?
50A network technician is investigating why a user cannot reach a public website by its hostname, even though the user can ping the website's IP address successfully. The workstation's default gateway and IP configuration are correct. Which command should the technician run to verify whether the workstation's configured DNS servers are responding?
51A network administrator is troubleshooting a workstation that cannot communicate with any other device on the network. The administrator runs 'ipconfig' and sees that the workstation has an IP address of 169.254.10.20 with a subnet mask of 255.255.0.0. The workstation is connected to a switch port that is up and forwarding. Which is the most likely explanation for the workstation's inability to communicate?
Be able to pick the right Cisco IOS or Windows command for a given symptom: show interfaces for duplex and errors, show spanning-tree for loops, ping and tracert for reachability and path. The key skill is matching the observed symptom to the command that confirms it.
The Courseiva 100-150 question bank contains 51 questions in the Diagnosing Problems domain. Click any question to see the full explanation and answer breakdown.
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