1. Bottom-up approach
2. Top-down approach
3. Divide and conquer approach

To effectively and efficiently troubleshoot problems, you should have a specific methodology to follow. The best approach for any particular problem depends on the characteristics of the problem.

• Bottom-up - You should use this approach when you know or suspect that the problem is in the Network, Data link, or Physical layer of the OSI model. Using this approach the troubleshooter begins troubleshooting at the Physical layer and works his or her way up the OSI model. Most network problems reside at the lower levels; therefore, implementing the bottom-up approach will usually result in problem resolution. The disadvantage to this approach is that it can be difficult to find out which network device is causing the problem. If symptoms of the problem come from the network, the bottom up approach will be more effective.
• Top-down - You should use this approach when you know or suspect that the problem resides in the top-half of the OSI model. Using this approach the troubleshooter begins troubleshooting at the Application layer and works down to the lower levels of the OSI model. This approach works best when the troubleshooter believes that the problem is with an application and not the network or network devices. The disadvantage to this approach is that it can be difficult to find out which application is causing the problem. If problems come from the users, the top-down approach will be more effective.
• Divide and conquer - Using this approach the troubleshooter begins at a middle layer (Transport, Network, or Data link) and begins testing in both directions. Once the troubleshooter has identified the direction of the problem, he or she can work in that direction until the cause of the problem is identified. For example, if you begin troubleshooting at the Network layer and everything seems to be working, it is safe to assume that the Data link and Physical layers are working as well.

2. Answer B is correct. Ethernet duplex settings reside at the Data link layer. Therefore, the most effective approach would be the bottom-up approach.

3. Answer A is correct. The "Be consistent" guideline recommends that you use templates and maintain a library of graphics and icons that can be reused when creating topology diagrams. Using the same graphics and icons to represent common devices ensures that the topology diagrams remain consistent and clear.

There are five network documentation guidelines that you should follow when documenting your network:

• Determine the scope - You should only document those networks and devices that are within your administrative responsibility.
• Know your objective - You should only document information that is relevant to the documentation objectives. Sufficient detail should be included; however, extraneous data should be omitted. Over-documentation makes documented information hard to understand.
• Be consistent - Use consistent symbols and icons to represent like devices in the topology diagrams. If possible, maintain a library of common symbols and icons that can be used for future documentation. Using common symbols and icons creates consistency across topology diagrams and increases usability and comprehension.
• Keep the documents available - Once documentation is complete it should be stored close to where it will be needed for troubleshooting. Additional copies should be stored off site in a secure location.
• Maintain the documentation - Network documentation is a living document. The documentation should change at the same rate as the network. Each network project should conclude with the updating of existing documentation reflecting the changes and additions to the network.

4. Answer D is correct. You should use the 'show cdp neighbors' command during the device discovery stage.

There are five steps in the network documentation process:

• Log In - Log in to a device on the network.
• Interface Discovery - Discover the relevant information about the device using show commands. Relevant information includes all components that have been chosen on the network configuration tables.
• Document - Once the relevant information has been discovered, it must be documented in the network configuration table. If the device is a component on the topology diagram, proceed to step four (Diagram); otherwise, skip to step five.
• Diagram - Transfer information discovered about the device to the network topology diagram. When all information is transferred to the diagram, move to stage five
• Device Discovery - Use the 'show cdp neighbors' command to discover directly attached devices. If new, undocumented devices are discovered, return to step one.

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5. Answer B is correct.

• The 'debug ip icmp' command allows you to determine whether the router is sending or receiving ICMP messages. This helps troubleshoot end-to-end problems.
• The 'debug arp' command checks the flow of information on transactions that resolve IP addresses to MAC addresses (ARP cache entries). This can help you to troubleshoot intermittent connectivity problems.
• The 'debug ip rip' command allows you to view RIP packet information.
• The 'debug ip eigrp' command allows you to analyze the Enhanced IGRP packets that an interface sends and receives.
• The 'debug ip igrp events' command displays IGRP routing information. This tool can be used to troubleshoot network problems in your routing table when the network is very busy.

6. Answer E is correct.

• The 'debug ip packet detail 110' command is used to debug the functions of access list 110. This allows the debug output to focus on a single access list (restricting the amount of information you need to examine) and to test the effectiveness of the access list. Since the access list is an extended IP access list, you know that the type of traffic you need to debug is IP traffic.
• The 'debug ip ospf events' command is used to view OSPF-related events such as the shortest path first calculation, the adjacencies, the flooding information, and the designated router (DR) selection. It is helpful in determining whether two neighboring routers that use the OSPF protocol have the same hello and dead intervals and whether their subnet masks are the same. The 110 parameter in the answer is invalid for this command.
• The 'debug serial interface' command can be used to isolate the cause of a connection failure due to a timing problem. This command can be used to troubleshoot the Frame Relay connection at the Data-Link layer. The 110 parameter in the answer is invalid for this command.
• The 'debug ip packet' command is used to check the flow of IP packets transmitted between local and remote hosts. This command is useful when troubleshooting an end-to-end connection problem. The resulting display of this command shows the packets received, packets generated, and packets forwarded.
• The 'debug ip rip' command allows you to view RIP packet information. In addition, it is useful in debugging Windows 95/NT TCP/IP routing. Its output includes the RIP routing transactions, including updates sent and received.

7. Answers A and B are correct. Application problems could be causing the problems with the timekeeping application. The failure of ping and trace commands could be caused by access lists that are blocking ICMP messages. Both trace and ping utilize the Layer 3 protocol ICMP.

8. Answer C is correct. The "datagram size" field is used to increase or decrease the size of the datagram. The default setting is 100.

The "repeat count" setting is used to specify the number of ping packets to send to the destination address. The default setting is 5.

The "protocol" field is used to specify the protocol to use for the ping command (IP, IPX, and AppleTalk).

The "Set DF bit in IP header field" is used to troubleshoot performance problems on the network caused by a router configured to use a large Maximum-Transmission Unit (MTU). Setting the DF bit will block all routers from fragmenting the packet.

9. Answer B is correct. The 'show ip interface brief' command can be used to view a summary of the router interfaces. As seen below, the resulting output from this command displays the IP address, interface status, and additional information.

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This command can be used when completing the network configuration tables and can be useful when completing the topology diagrams.

10. Answer B is correct .An " * " indicates that the probe timed out waiting for a response from the host or network device. Below is a list of the possible output characters associated with the trace command.

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