A technician connects two legacy switch ports directly to each other using a standard straight-through Ethernet cable. Neither port supports Automatic Medium-Dependent Interface Crossover (Auto-MDIX). Running a status check on the local switch port yields the following CLI output:
text
FastEthernet0/1 is down, line protocol is down
Hardware is FastEthernet, address is 000d.bd2c.4a01 (bia 000d.bd2c.4a01)
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Which physical cabling issue is the direct cause of the interface remaining in a down/down state?
- A straight-through Ethernet cable was used instead of a crossover Ethernet cable to connect two like switch devices.Answer
- BA native VLAN mismatch exists between the two connected switch interfaces.
- CThe local interface is misinterpreting the remote interface identifier from CDP neighbor TLV data.
- DA rollover cable was used instead of a straight-through cable to connect the switch to a patch panel.
Answer
Using a straight-through Ethernet cable instead of a crossover cable to connect two switch ports (like devices) without Auto-MDIX support prevents physical link establishment, resulting in a down/down interface state.
Switches are MDI-X devices that transmit on pins 3 and 6 and receive on pins 1 and 2. When connecting two switches together directly without Auto-MDIX functionality, a crossover cable must be used to map transmit pins on one switch to receive pins on the other switch. Using a straight-through cable connects transmit pins to transmit pins, resulting in no electrical link and keeping the interface state down/down.
Step-by-Step Solution
Key Concept
Ethernet cable pinouts and physical interface troubleshooting (straight-through vs crossover cable selection)