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Zorluk: OrtaTroubleshooting VLAN, Trunking, and Switching Issues

A network administrator is troubleshooting severe performance degradation on an enterprise network segment. Users report extreme file transfer delays when communicating with a local server connected to interface GigabitEthernet 0/5 on Switch-SW1. Interface metrics on Switch-SW1 reveal a rising count of late collisions, frame check sequence (FCS) errors, and alignment errors, despite low overall bandwidth utilization. Further inspection shows the server's network adapter is manually configured for 1000 Mbps Full-Duplex, whereas the connected switch port is set to auto-negotiation. Which of the following accounts for the root cause of this issue?

  1. A
    Physical cable damage or electromagnetic interference along the run is causing signal attenuation and frame corruption.
  2. The switch port auto-negotiation failed to detect full-duplex mode, defaulting to half-duplex and creating a duplex mismatch.Cevap
  3. C
    The switch interface and server interface are configured with mismatched native VLANs, causing untagged frame drops.
  4. D
    Spanning Tree Protocol has assigned a high numerical priority to Switch-SW1, placing interface GigabitEthernet 0/5 into an STP blocking state.

Cevap

The switch port auto-negotiation failed to detect full-duplex mode, defaulting to half-duplex and creating a duplex mismatch.
When an Ethernet port configured for auto-negotiation is connected to a port with manually hardcoded speed and duplex, IEEE 802.3 standards specify that the auto-negotiating port can detect speed through parallel detection but cannot negotiate duplex. Consequently, the auto-negotiating switch port defaults to half-duplex mode. Because the connected server operates in full-duplex mode, it transmits data without checking for carrier sense. The switch port, operating in half-duplex, perceives these simultaneous transmissions as collisions. When collisions occur after the collision window (64 bytes), they are logged as late collisions and cause FCS/CRC errors, resulting in extreme performance degradation.

Adım Adım Çözüm

1
Analyze the reported interface statistics and symptoms.
Identified late collisions, FCS errors, and alignment errors alongside slow transfer rates.
Late collisions occur when a device operating in half-duplex detects a collision after transmitting the first 64 bytes of a frame.
2
Evaluate the interface speed and duplex configuration settings on both connected ends.
Determined that the server adapter is hardcoded to full-duplex while the switch port is set to auto-negotiation.
Ethernet auto-negotiation standards dictate that if link partner parameters cannot be negotiated, speed can be detected via parallel detection, but duplex defaults to half-duplex.
3
Synthesize the configuration mismatch with the observed symptoms.
The server transmits continuously in full-duplex mode, while the switch port expects half-duplex CSMA/CD operation, causing the switch to detect collisions during server transmission.
This operational mismatch directly generates late collisions, FCS errors, and severe packet retransmissions.

Anahtar Kavram

Duplex auto-negotiation behavior and symptom identification in Ethernet switching
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Konular

Troubleshooting VLAN, Trunking, and Switching Issues

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