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Troubleshoot Network Issues

# Cisco Support Network
Medium

1.5.1 Network Devices as Sources of Information

Cisco IOS Privilege Levels

  • User EXEC mode (>)
    • Privilege level 1.
    • Limited access for basic verification commands.
  • Privileged EXEC mode (#)
    • Privilege level 15.
    • Full access to configuration and diagnostic commands.

Common Cisco IOS Commands

CommandDescription
show versionDisplays uptime, software version, hardware, and licensing information.
show ip interface [brief]Displays interface status and addressing information.
show interfacesDisplays detailed output for each interface.
show cdp neighbors detailDisplays detailed information about neighboring Cisco devices.
show running-configDisplays the active device configuration.
show mac-address tableDisplays the switch MAC address table.
Tip: Use the question mark (?) for context-sensitive help.
shell snippet
1Router# show ?
The command displays a list of the options available in the current context.

1.5.2 Packet Capture and Protocol Analysis

  • Wireshark is a widely used protocol analyzer.
  • Its main capabilities include:
    • Protocol decoding.
    • Traffic filtering.
    • Layer-by-layer analysis.
Protocol analyzers such as Wireshark can help identify connectivity failures and network performance problems.

1.5.3 Lab — Install Wireshark

1.5.4 Lab — Network Tools

1.5.5 Measuring Throughput

Important Concepts

  • Bandwidth: the theoretical transmission capacity of a link.
  • Throughput: the amount of data that is actually transmitted.
  • Latency: the delay introduced during transmission.

Measurement Tools

  1. Internet speed test services.
  2. iPerf.
shell snippet
1C:\tools\iperf> iperf3 -c speedtest.masnet.ec
2 Connecting to host speedtest.masnet.ec, port 5201
3 [  7] local 10.0.0.129 port 58350 connected to 170.83.216.19 port 5201
4 [ ID] Interval           Transfer     Bitrate
5 [  7]   0.00-1.00   sec  576 KBytes   4.72 Mbits/sec
6 [  7]   1.00-2.00   sec  393 KBytes   3.22 Mbits/sec
7 [  7]   2.00-3.00   sec  775 KBytes   6.35 Mbits/sec
8 [  7]   3.00-4.00   sec  713 KBytes   5.83 Mbits/sec
9 [  7]   4.00-5.00   sec  677 KBytes   5.55 Mbits/sec
10 [  7]   5.00-6.00   sec  701 KBytes   5.75 Mbits/sec
11 [  7]   6.00-7.00   sec  718 KBytes   5.89 Mbits/sec
12 [  7]   7.00-8.00   sec  621 KBytes   5.08 Mbits/sec
13 [  7]   8.00-9.00   sec  749 KBytes   6.13 Mbits/sec
14 [  7]   9.00-10.00  sec  738 KBytes   6.05 Mbits/sec
15 - - - - - - - - - - - - - - - - - - - - - - - - -
16 [ ID] Interval           Transfer     Bitrate
17 [  7]   0.00-10.00  sec  6.50 MBytes  5.46 Mbits/sec    sender
18 [  7]   0.00-10.18  sec  6.38 MBytes  5.26 Mbits/sec    receiver
19

20 iperf Done.
21 C:\tools\iperf>
The results include:
  • Interval: the measured time range.
  • Transfer: the amount of data transferred.
  • Bitrate: the measured transfer rate.

1.5.6 Packet Tracer — Troubleshooting Challenge

Objectives:
  • Use documentation to resolve problems.
  • Identify connectivity issues.
  • Implement solutions.
  • Verify network operation.

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