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Network+ Exam

Interface Port Issues

October 29, 2025

  • #network+

Interface Port Issues

increasing interface counters for CFC

port status issues.

1 CRC error - any error when the check of a data block’s intregrity upon recpton does not match the checksum during transmittion.

the data has been corruptied during the transmision.

increasing numbe of CRc there is a oise or other physical issues impacting network connectifvity

electrical interferance

cable damage

hardware fault

2 increased errors with Runts - frams that are smaller that the minimum frame size.. may be from collisions.

runts can be from nic malfunciton, cable issue, but they are small by natuer.

3 increasing counter with giants thosre are frames that exceed the maximum frame size. can cause conjestion.

many will drop giant frames, if so the number of jiants.

monitor nextork traffic to address root cause.

drops - buffer is full and cannont accomidate incoming frames or packets. if beyond netowrk capabalities, will reduce dataflow and efficency.

5 issues associated with error-disabled - uesed to indicate that a port has experienced an isud.

issues with admin down port status- network has been intiontially disabled by a network administrator. may have shut it down to upgrade or modify it. it will show as admiistrativily down . issue a specefic command within the devand .

no shutdown

ensure that the port is ready to be reactivated to prevent any issues.

issues assocuated with susspended port stause. -viiolation of policy or protocol within the network, if a port may cause an error or loop, it will be suspended.

to solve resolve the underlying isse to make sure it is correctly configured.

🔌 Interface & Port Issues (Network+)

1. CRC Errors

  • Definition: Data fails checksum integrity check on receipt.
  • Causes:
    • Electrical interference (EMI/RFI)
    • Damaged cable
    • Faulty NIC/switch port
  • Exam Tip: A growing CRC counter = physical layer problem.

2. Runts

  • Definition: Frames smaller than the minimum Ethernet frame size (64 bytes).
  • Causes:
    • Collisions
    • NIC malfunction
    • Cable issues
  • Impact: Dropped by switches; indicates a physical or NIC issue.

3. Giants

  • Definition: Frames larger than the maximum Ethernet frame size (1518 bytes without VLAN tagging).
  • Causes:
    • Misconfiguration (e.g., mismatched MTU)
    • Congestion
    • Faulty NICs generating oversized frames
  • Impact: Often dropped; monitor traffic to find root cause.

4. Drops

  • Definition: Frames/packets discarded when a buffer is full.
  • Causes:
    • Congestion beyond capacity
    • Overloaded switch/port
  • Impact: Reduced efficiency, higher latency.

5. Error-Disabled Ports

  • Definition: Port automatically shut down by the switch due to an error (e.g., security violation, loop).
  • Fix: Investigate cause, then re-enable port.

6. Administratively Down

  • Definition: Port manually disabled by a network admin.
  • Fix: Use the no shutdown command (Cisco IOS) after confirming readiness.

7. Suspended Port Status

  • Definition: Port disabled by system policy/protocol violation (e.g., spanning tree loop prevention).
  • Fix: Resolve misconfiguration or violation, then re-enable.

⚡ Must Know for Exam:

  • CRC errors = Layer 1 (Physical) issues.
  • Runts & Giants = frame size anomalies.
  • “Administratively down” ≠ hardware failure → it’s intentional by admin.
  • Cisco loves no shutdown as a PBQ answer.