EWAN v4 Chapter 8 Check Your Understanding: Network Troubleshooting

1. Match each item with its appropriate diagram type:

Cable type
IP address and subnet
Connection type
Device ID
Operating system version
Device type and model
Routing protocols
Connector type

A. Physical diagram
B. Logical diagram

Cable type Physical diagram
IP address and subnet Logical diagram
Connection type Logical diagram
Device ID Logical diagram
Operating system version Physical diagram
Device type and model Physical diagram
Routing protocols Logical diagram
Connector type Physical diagram

2. What is one symptom of a physical layer problem?

  • High CPU utilization
  • Excessive broadcasts
  • Slow STP convergence
  • Routing loops

Explanation: Common symptoms of physical layer problems include performance less than the baseline; loss of connectivity; high collision counts; network bottlenecks or congestion; high CPU utilization rates on routers, switches, and servers; and console error messages.

3. A network administrator receives the output “Serial0 is up, line protocol is down” from the show interface s0 command. At what layer is this problem most likely being caused?

  • Physical layer
  • Data link layer
  • Network layer
  • Transport layer

Explanation: The first part, “Serial0 is up,” indicates that the physical layer is operational. The second part, “line protocol is down,” indicates a Layer 2 problem.

4. Which statement is true about network models?

  • Although it’s similar to the OSI model in construction, the TCP/IP model has more layers.
  • The network access layer in the OSI model incorporates both physical and data link layers in the TCP/IP model.
  • Both users and application layer processes interact with software applications that contain a communications component in the OSI model.
  • TCP/IP communications relate to only the TCP/IP model.

5. Which protocols can be involved in network layer problems? (Choose three.)

  • DNS
  • IP
  • RIP
  • TCP
  • UDP

Explanation: Only EIGRP, IP, and RIP operate at Layer 3. TCP and UDP operate at Layer 4. DNS operates at Layer 7.

6. Match the application layer protocol with the port number it is commonly associated with:


A. 20 and 21
B. 23
C. 25
D. 80
E. 110
F. 161

FTP 20 and 21
POP3 110
SNMP 161
Telnet 23

7. A technician has been asked to troubleshoot a simple network problem that seems to be caused by software. Which troubleshooting approach would you suggest?

  • Bottom-up
  • Top-down
  • Divide-and-conquer
  • Middle-out

Explanation: Software interacts with Layer 7. Therefore, the top-down approach is the most logical place to start.

8. Which questions are appropriate to ask when gathering information from a user? (Choose three.)

  • What does work?
  • Who did you call after the problem appeared?
  • When did you first notice the problem?
  • When does the problem occur?
  • What is your password?
  • What did you do after the problem occurred?

Explanation: These are logical questions that will help you narrow down the specific problem. Questions B, E, and F do not add any value and are not pertinent.

9. Which network troubleshooting tool can you use to test the physical medium for defects, such as near-end crosstalk?

  • Cable analyzer
  • Cable tester
  • Digital multimeter
  • Baselining tool

Explanation: The only tool listed that detects near-end crosstalk is a cable analyzer. Cable testers, digital multimeters, and baselining tools do not detect NEXT.

10. Which documents are needed to efficiently diagnose and correct network problems? (Choose three.)

  • Network management command reference
  • Network configuration tables
  • Network device installation guide
  • Network topology diagrams
  • End-system configuration tables
  • Service provider documentation

Explanation: Although the documents listed in answers A, C, and F could be of help, documents B, D, and E are required.

11. What are the steps for establishing a network baseline? (Choose three.)

  • Determine the type of network management traffic to be collected and evaluated.
  • Determine the types of data to be collected and evaluated.
  • Identify devices and ports to be monitored.
  • Identify the virtual interfaces, VLANs, and virtual routing tables to be monitored.
  • Determine the number of baseline tests to establish a typical picture of the network.
  • Determine the duration for baseline testing to establish a typical picture of the network.

Explanation: Option A would be trivial to collect. Option D does not make sense. Option E is incorrect because you should conduct the baseline over a period of time and not have multiple baseline tests.

12. What is associated with the first step of correcting application layer problems?

  • Analyzing existing symptoms
  • Making a backup of configurations
  • Making the initial hardware or software changes
  • Pinging the default gateway to verify Layer 1 to Layer 3 functionality

Explanation: Before proceeding, ensure that a valid configuration has been saved for any device on which the configuration may be modified. This provides for recovery to a known initial state.

13. Explain the function and contents of network documentation, including router, switch, and end-user documentation, as well as network topology diagrams.

Router documentation:

  • The router documentation should include the router names, model designation, location in the enterprise (building, floor, room, rack, panel), configured interfaces, data link layer addresses, network layer addresses, routing protocols configured, and any additional important information about the device.

Switch documentation:

  • The switch documentation should include the switch names, model designation, location in the enterprise (building, floor, room, rack, panel), management IP address, port names and status, speed, duplex, STP state, PortFast setting, trunk status, Layer 2 or Layer 3 EtherChannel, VLAN IDs, and any additional important information about the device.

End-user documentation:

  • The end-user documentation should include the server names and functions, operating system version, IP address, gateways, DNS server, network application, and any additional important information about the device.

Topology diagrams should be available in a physical and logical variation.

Physical network topology diagram:

  • A graphical representation that identifies the physical location of the networking device.
  • Also details the types of cabling between them and the cable identification numbers.

Logical network topology diagram:

  • A graphical representation that uses symbols to identify each network device and how it is interconnected.
  • Also details the logical architecture, including interface types and numbers, IP addresses, subnet masks, routing protocols, autonomous system domains, and any additional important information, such as DLCI numbers and Layer 2 protocol.

14. Explain the recommended steps for planning the first network baseline.

Step 1: Determine what types of data to collect:

  • Start simply, by selecting a few variables that represent the defined policies, and finetune along the way.
  • Generally, some good starting measures are interface utilization and CPU utilization.

Step 2: Identify devices and ports of interest:

  • Devices and ports of interest must be identified, such as network device ports that connect to other network devices, servers, key users, and anything else considered critical to the operation.

Step 3: Determine the baseline duration:

  • This period should be at least seven days to capture daily or weekly trends and should last two to four weeks.
  • Do not perform a baseline measurement during times of unique traffic patterns.
  • Should be conducted on a regular basis, such as an annual analysis of the entire network or a baseline of different sections of the network on a rotating basis.

15. Explain the three stages of the general troubleshooting process.

Stage 1: Gather symptoms:

  • Symptoms may appear in many different forms, including alerts from the network management system, console messages, and user complaints.
  • Gather and document symptoms from the network, end systems, and users.
  • In addition, determine which network components have been affected and how the network’s functionality has changed compared to the baseline.

Stage 2: Isolate the problem:

  • The problem is not truly isolated until a single problem, or a set of related problems, is identified.
  • Examine the characteristics of problems at the logical layers of the network so that the most likely cause can be selected.
  • Depending on the problem characteristics identified, gather and document more symptoms.

Stage 3: Correct the problem:

  • Work to correct the problem by implementing, testing, and documenting a solution.

16. Explain the three main troubleshooting methods.

Bottom-up troubleshooting method:

  • Start with the network’s physical components, and work up through the layers of the OSI model until you identify the cause of the problem.
  • This is a good approach to use when you suspect that the problem is physical.

Top-down troubleshooting method:

  • Examine the end-user application first.
  • The analysis continues downward from the upper layers of the OSI model until the cause of the problem is identified.

Divide-and-conquer troubleshooting method:

  • Select a layer, and test in both directions from the starting layer.
  • If you can verify that a layer is functioning properly, typically it is safe to assume that the layers below it are functioning.
  • If a layer is not functioning properly, gather symptoms of the problem at that layer, and work your way down.

17. Explain the six steps of designing or modifying a WAN.

Step 1: Locate LANs:

  • Establish the source and destination endpoints that will connect via the WAN.

Step 2: Analyze traffic:

  • Find out what data traffic must be carried, its origin, its destination, bandwidth requirements, latency, and jitter tolerance.

Step 3: Plan the topology:

  • Identify the various endpoints, geographic considerations, and requirement for availability.

Step 4: Estimate the required bandwidth:

  • After considering the endpoints and the links chosen, you can estimate the necessary bandwidth.

Step 5: Choose the WAN technology:

  • After you determine the bandwidth availability, you select suitable link technologies.

Step 6: Evaluate costs:

  • Determine installation and operational costs for the WAN, and compare them with the business needs driving the WAN implementation.

18. List at least three things to check when troubleshooting Layer 1 problems.

Check for bad cables or connections:

  • Use a cable tester to verify that the cable from the source interface is properly connected and is in good condition.
  • When you doubt a cable’s integrity, swap the suspect cable with a known working cable.

Make sure that the correct cabling standard is adhered to throughout the network:

  • Verify that the proper cable is being used for the connection.

Check that devices are cabled correctly:

  • Verify that all cables are connected to their correct ports or interfaces.

Verify proper interface configurations:

  • Check that all switch ports are set in the correct VLAN and that spanning-tree, speed, and duplex settings are correctly configured.
  • Confirm that any active ports or interfaces are not shut down.

Check operations statistics and data error rates:

  • Use Cisco show commands to check for statistics such as collisions, input, and output errors.
  • The characteristics of these statistics vary depending on the protocols used on the network.

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