Podcast
Questions and Answers
Which command can be used to test Layer 3 connectivity?
Which command can be used to test Layer 3 connectivity?
What type of errors can be identified at Layer 1?
What type of errors can be identified at Layer 1?
Which troubleshooting tool is best suited for identifying the path a packet takes from source to destination?
Which troubleshooting tool is best suited for identifying the path a packet takes from source to destination?
Which command would be used to monitor router activity in real-time?
Which command would be used to monitor router activity in real-time?
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In the context of software verification, which tool indicates proper functioning of upper-layer applications and lower layer services?
In the context of software verification, which tool indicates proper functioning of upper-layer applications and lower layer services?
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What command can be used to gather detailed information about the routes installed on a router?
What command can be used to gather detailed information about the routes installed on a router?
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Which command is appropriate to confirm Layer 1 and Layer 2 problems?
Which command is appropriate to confirm Layer 1 and Layer 2 problems?
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To identify the path packets take between networks, which command is most suitable?
To identify the path packets take between networks, which command is most suitable?
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Which command is used to monitor router activity?
Which command is used to monitor router activity?
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For verifying the application layer software between source and destination stations, which command should be used?
For verifying the application layer software between source and destination stations, which command should be used?
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What does it indicate if the interface is up and the protocol is down according to the provided text?
What does it indicate if the interface is up and the protocol is down according to the provided text?
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What should be done first when a cabling problem is suspected according to the text?
What should be done first when a cabling problem is suspected according to the text?
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What does the appearance of an asterisk (*) during a traceroute indicate?
What does the appearance of an asterisk (*) during a traceroute indicate?
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Which command is useful for debugging connectivity issues according to the text?
Which command is useful for debugging connectivity issues according to the text?
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If Telnet failure is not related to connectivity, what could be a likely cause according to the text?
If Telnet failure is not related to connectivity, what could be a likely cause according to the text?
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Study Notes
Network Troubleshooting
- IGRP uses load balancing between two links after the variance command is executed
Troubleshooting by OSI Layers
- Layer 1 errors can include:
- Broken, disconnected, or intermittent cables
- Cables connected to the wrong ports
- Rollover, crossover, or straight-through cables used incorrectly
- Transceiver problems
- DCE or DTE cable problems
- Devices turned off
- Layer 2 errors can include:
- Improperly configured serial or Ethernet interfaces
- Improper encapsulation set
- Improper clockrate settings on serial interfaces
- Network interface card (NIC) problems
- Layer 3 errors can include:
- Routing protocol not enabled or wrong routing protocol enabled
- Incorrect IP addresses or subnet masks
Layer 3 Troubleshooting using Ping
- Used for troubleshooting Layer 3 issues
Layer 7 Troubleshooting using Telnet
- A successful Telnet connection indicates that the upper-layer application and the services of lower layers are functioning properly
- If Telnet connection fails, verify lower layer connectivity
Troubleshooting Router Issues
- Use the
show interfacescommand to troubleshoot Layer 1 issues - The "line" parameter refers to the physical layer, while the "protocol" parameter refers to the Layer 2 protocol
- If the interface is down, a hardware problem exists or it is administratively down
- If the interface is up and the protocol is down, a Layer 2 problem exists
Troubleshooting using Show CDP
- Use the
show cdp neighbors detailcommand to troubleshoot connectivity issues - CDP can be a potential security hole, so it should be configured only on links between Cisco devices and disabled on user ports or links that are not locally managed
Troubleshooting using Traceroute
- An asterisk (*) appears if the packet fails
- The round trip time (RTT) is the time required to send an echo packet and get a response
- The default maximum TTL for traceroute is 30
Router Commands
-
show ip route: To gather detailed information about the routes installed on the router -
ping: To perform basic network connectivity tests -
telnet: To verify the application layer software between source and destination stations -
show interfaces: To confirm Layer 1 and Layer 2 problems -
show ip routeandshow ip protocol: To identify routing issues -
show cdp: To verify Layer 2 connectivity -
traceroute: To identify the path packets take between networks -
show controllers serial: To ensure the proper cable is attached -
debug: To monitor router activity
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Description
Learn about IGRP load balancing after executing the variance command and troubleshooting network issues at different OSI layers. Identify common Layer 1 and Layer 2 errors that can affect network connectivity.
