A network technician connects SwitchA and SwitchB using interface GigabitEthernet1/0/1 on both devices. Auto-MDIX has been manually disabled on both switch ports. The technician executes `show interfaces gigabitethernet 1/0/1` on SwitchA and observes the following CLI output:
SwitchA# show interfaces gigabitethernet 1/0/1
GigabitEthernet1/0/1 is down, line protocol is down
Hardware is Gigabit Ethernet, address is 0007.7d0e.a101 (bia 0007.7d0e.a101)
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Auto-duplex, Auto-speed
Which underlying physical layer issue is causing the interface status and line protocol to both remain in the down state?
- A straight-through Ethernet cable is connected between similar switch interfaces while Auto-MDIX is disabled.Answer
- BA native VLAN mismatch exists between SwitchA and SwitchB, preventing physical layer link negotiation.
- CCDP neighbor TLV parsing errors on the remote port are keeping the local interface in a down state.
- DPortFast is enabled on the interconnect trunk port, suppressing link pulse detection between the switches.
Answer
A straight-through Ethernet cable is connected between similar switch interfaces while Auto-MDIX is disabled.
When connecting two switches directly (like devices operating MDI-X to MDI-X), a crossover cable is required to connect transmit pins to receive pins. When Auto-MDIX is disabled, using a straight-through cable prevents the interfaces from detecting physical signals, keeping the status and line protocol down.
Step-by-Step Solution
Key Concept
Physical interface troubleshooting and Auto-MDIX dependency on crossover vs straight-through cabling.
Estimated Time:1m 30s