Cisco Certified Support Technician (CCST) NetworkingNetwork AccessMedium
A network administrator is troubleshooting an issue where a user's computer is experiencing intermittent connectivity and very slow network speeds. The computer is connected to a switch port. After checking the cable and verifying the port configuration, the administrator suspects a duplex mismatch. Which command on a Cisco switch would best confirm if a duplex mismatch exists on the connected port?
- Ashow interfaces GigabitEthernet0/1
- Bshow ip interface brief
- Cshow mac address-table interface GigabitEthernet0/1
- Dshow interfaces GigabitEthernet0/1 status
Show answer & explanationAnswer & explanation
Correct answer: A. show interfaces GigabitEthernet0/1
The 'show interfaces GigabitEthernet0/1' command provides detailed information about a specific interface, including its speed and duplex settings, as well as error counters like input/output errors and collisions, all of which are critical for diagnosing a duplex mismatch.
Why the other options are wrong
- B. This command provides a summary of IP addresses and interface status (up/down), but not duplex settings.
- C. This command shows MAC addresses learned on the interface, not speed or duplex settings.
- D. This command shows a brief status including speed and duplex, but 'show interfaces' provides more comprehensive details necessary for diagnosing mismatches and related errors.
Duplex Mismatch
A condition where two connected network devices have different duplex settings (one full-duplex, one half-duplex), leading to severe performance degradation, high collision rates, and intermittent connectivity.
- One device full, other half-duplex
- Causes high collision rates and errors
- Leads to slow speeds and intermittent connectivity
- Best resolved by setting both to auto-negotiate or matching static settings
Memory trick: Duplex mismatch means half-speed, full-collisions.