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Zorluk: OrtaInterface and Cable Troubleshooting Issues

An administrator is connecting switch SwitchA to switch SwitchB via interface GigabitEthernet1/0/15. Auto-MDIX has been manually disabled on interface GigabitEthernet1/0/15 using the `no mdix auto` command, and a standard Category 6 straight-through Ethernet cable is used between the two switches. The output of the `show interfaces GigabitEthernet1/0/15` command displays the following:

text
GigabitEthernet1/0/15 is down, line protocol is down
Hardware is Gigabit Ethernet, address is 0007.7d00.4a15
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255

Which condition is the primary cause of the interface remaining in a down/down state?

  1. An incorrect cable pinout is used for connecting two like network switches when auto-MDIX is disabled.Cevap
  2. B
    A native VLAN mismatch exists between the 802.1Q trunking configurations on SwitchA and SwitchB.
  3. C
    The neighbor discovery protocol TLV exchanges are failing to complete Layer 2 protocol negotiation.
  4. D
    Incompatible EtherChannel negotiation modes prevent the line protocol from reaching an operational state.

Cevap

The primary cause is an incorrect cable pinout used for connecting two like network switches when auto-MDIX is disabled.
Connecting two switches (like-to-like devices) requires a crossover cable so that the transmit pins on one end connect to the receive pins on the other end. While Auto-MDIX dynamically detects and corrects cable pinout mismatches, disabling Auto-MDIX with the `no mdix auto` command forces the switch interface to rely strictly on correct physical cable wiring. Using a straight-through cable between two switches with Auto-MDIX disabled prevents physical link detection, causing the interface status and line protocol to remain in a down/down state.

Adım Adım Çözüm

1
Analyze the CLI output for interface status and line protocol state.
The output shows 'GigabitEthernet1/0/15 is down, line protocol is down', indicating a physical Layer 1 connectivity failure.
When both the interface and line protocol are down, the device cannot establish a physical electrical link with the remote peer.
2
Evaluate physical cable pinout requirements for like devices.
Switch-to-switch connections (like devices) transmit on pins 1,2 and receive on pins 3,6 (for 10/100/1000BASE-T). Connecting two like devices with a straight-through cable connects transmit pins to transmit pins and receive pins to receive pins.
Without Auto-MDIX automatically swapping transmit and receive pin pairs, a crossover cable is strictly required to establish physical link alignment.
3
Determine the impact of disabling Auto-MDIX.
Disabling Auto-MDIX (`no mdix auto`) forces the interface to rely entirely on correct physical cable pinouts, keeping the interface in a down/down state when connected via a straight-through cable.
Correcting the cable type to a crossover cable or re-enabling Auto-MDIX resolves the physical layer signaling failure.

Anahtar Kavram

Auto-MDIX and Cable Pinout Compatibility in Layer 1 Troubleshooting
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Konular

Interface and Cable Troubleshooting Issues

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