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Zorluk: ZorInterface and Cable Troubleshooting Issues

A network engineer is troubleshooting various network interface issues on Cisco switches and routers. Match each interface status or error counter symptom on the left with its most likely physical or data-link layer root cause on the right.

  • Interface status is down, line protocol is downPhysical layer fault, such as an unplugged cable, faulty transceiver, or unpowered remote peer
  • Interface status is up, line protocol is downData link layer framing failure, such as encapsulation mismatch, missing clock rate, or keepalive loss
  • Interface status is up, line protocol is up, with rapidly incrementing late collisionsDuplex mismatch configuration where the local port is operating in half-duplex while the peer is set to full-duplex
  • Interface status is up, line protocol is up, with rapidly incrementing giants and jabber errorsConnected device transmitting frames exceeding the maximum transmission unit (MTU) size or a malfunctioning NIC

Cevap

The interface symptoms match as follows: 'down/down' corresponds to a Layer 1 physical fault; 'up/down' corresponds to a Layer 2 framing or keepalive failure; incrementing late collisions corresponds to a half-duplex/full-duplex mismatch; and incrementing giants/jabbers corresponds to oversized frames or a defective NIC.
Each status pattern and counter maps directly to standard Cisco IOS interface troubleshooting logic: Layer 1 physical link failures cause 'down/down'; Layer 2 framing/keepalive failures cause 'up/down'; half-duplex operating against full-duplex causes late collisions; and frames exceeding 1518 bytes with invalid FCS register as giants/jabber errors.

Adım Adım Çözüm

1
Analyze interface states by differentiating Layer 1 (Line Status) from Layer 2 (Line Protocol).
Line status indicates physical carrier detection, whereas line protocol indicates data link layer framing and keepalive state.
A physical failure results in 'down/down', whereas a framing or encapsulation mismatch maintains physical link ('up') but drops data link signaling ('down').
2
Diagnose the cause of late collision error counters on Ethernet interfaces.
Late collisions indicate that collision detection occurred after transmitting 512 bits (64 bytes).
Because half-duplex expects collisions only during the slot time (first 64 bytes), late collisions uniquely signal that the remote peer is operating in full-duplex mode and ignoring CSMA/CD rules.
3
Evaluate framing error statistics such as giants and jabbers.
Giants represent frames larger than the standard Ethernet MTU (1518 bytes) with bad CRC, while jabbers represent invalid continuous signals.
These symptoms point directly to MTU misconfigurations or damaged Network Interface Cards (NICs) transmitting invalid frame sizes.

Anahtar Kavram

Interface Line Status Combinations and Error Counter Root Causes
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Konular

Interface and Cable Troubleshooting Issues

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