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Zorluk: OrtaInterface and Cable Troubleshooting Issues

Two legacy FastEthernet switches are connected directly to each other using an Ethernet cable. The interface configuration on both ends explicitly has `no mdix auto` applied. Upon connecting the devices, execution of `show interfaces fastEthernet 0/12` reports that `FastEthernet0/12 is down, line protocol is down`. What physical cabling condition is the root cause of this interface status?

  1. A standard Category 5e straight-through cable is connected between the two like switch devices.Cevap
  2. B
    A native VLAN ID mismatch exists on the trunk interface connecting the two switches.
  3. C
    The neighbor device is suppressing interface link pulses due to a CDP TLV misinterpretation.
  4. D
    A crossover cable is deployed between the two switch interfaces with mismatched pinouts.

Cevap

A standard Category 5e straight-through cable is connected between the two like switch devices.
When connecting two switches directly without Auto-MDIX enabled, a crossover cable must be used to cross the transmit pairs of one switch to the receive pairs of the other. Connecting them with a straight-through cable connects transmit pins to transmit pins and receive pins to receive pins, which prevents physical link negotiation and causes the interface status and line protocol to remain down.

Adım Adım Çözüm

1
Analyze the interface status and line protocol state.
Both interface status and line protocol report 'down', indicating a Layer 1 (Physical layer) connectivity failure.
When an interface reports down/down, the device is not receiving physical signals or link pulses from the connected endpoint.
2
Evaluate the configuration context and device roles.
Two like devices (switch to switch) are connected, and automatic medium-dependent interface crossover (`no mdix auto`) is disabled.
Like devices transmit and receive on the exact same pin pairs (pins 1,2 for Tx and pins 3,6 for Rx on 10/100 Ethernet).
3
Determine the required cabling type.
A crossover cable must be used so that Transmit (Tx) pins on one switch connect to Receive (Rx) pins on the opposite switch.
If a straight-through cable is used without Auto-MDIX enabled, Tx connects to Tx and Rx connects to Rx, preventing physical link establishment.

Anahtar Kavram

Ethernet Cable Pinouts and Auto-MDIX Requirements
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Konular

Interface and Cable Troubleshooting Issues

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