FREE CCNA LAB

In these Cisco Packet Tracer activities you will be required to correct the configuration errors for each trouble tickets. For these labs, do not use login or password protection on any console lines to prevent accidental lockout. Use ciscoccna for all passwords in this scenario.

Learning Objectives:
Upon completion of this lab, you will be able to

• Cable a network according to the topology diagram in Figure 8-2.
• Erase the startup configuration and reload a router to the default state.
• Load the routers and switches with supplied scripts.
• Find and correct all network errors.
• Document the corrected network.

Troubleshooting Methodologies:
A good troubleshooting methodology will save an organization time and money. Before a Technician can troubleshoot a network, proper documentation should exist, which will assist with finding the problem quickly. A layered approach can be used when troubleshooting a logical network model such as the OSI reference model. The upper layers (5–7) deal with software application issues, and the lower layers (1–4) deal with data transport issues. In Layers 1 and 2, data is placed on the physical medium. Layers 3 and 4 are implemented within software configuration. A general troubleshooting procedure requires you to gather information from symptoms, isolate the problem, and then correct the problem. Troubleshooting methods include the following:

• The bottom-up troubleshooting method: Requires you to start at the physical layer and work your way up. This approach works well because most network problems, such as bad cabling and connections, reside on the bottom layers.
• The top-down troubleshooting method: Starts with end-user applications at Layer 7 and works its way down.
• The divide-and-conquer troubleshooting method: Requires you to collect user experience on the problem, document it, and predict which layer might have the problem. If that layer is functioning properly, work your way up the layers. If the layer is not functioning properly, work your way down.

Gathering symptoms allows a network administrator to analyze network functionality, which will allow him to properly diagnose network failures/abnormalities. Tools that enable you to troubleshoot and analyze symptoms on a network include baseline tools, protocol analyzers, network management tools such as What’s Up Gold NMS software, and online knowledge-based websites such as Google.

Network Troubleshooting:
A network diagram along with documentation is the only way to properly troubleshoot and diagnose issues within your network. A physical diagram of the network should include device type, make and model, and operating system, just to name a few. A logical diagram of the network should include interface identifiers, connection types, routing protocols, and connection speeds.

When troubleshooting Layer 1 (physical layer), symptoms may include loss of connectivity, high collision rates, and performance lower than the baseline. Possible physical layer problems can be related to hardware, cabling

Symptoms of Layer 2 (data link layer) problems include no connectivity at the network layer or above, network performance operating below the baseline, and excessive broadcast and console error messages. Causes of data link layer problems include encapsulation, address mapping, and framing errors and STP failures or loops.

When troubleshooting Layer 3 (network layer), symptoms may include network failure and performance below the baseline. Troubleshooting Layer 3 problems includes checking for topology changes and routing issues, which may include network relationships and topology database issues.

Layer 4 (transport layer) errors and symptoms may include intermittent network problems, security, and address translation problems. Translation issues could be related to improper Dynamic Host Control Protocol (DHCP) configurations and errors with encryption and tunneling protocols.

Layer 7 (application layer) is the layer closest to the user and includes protocols such as Telnet, HTTP, FTP, and TFTP. Problems with the application layer include complaints about slow application performance and application and console error messages. When troubleshooting the application layer, verify connectivity to the default gateway and verify Network Address Translation (NAT) and access control list (ACL) operation.

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