mediumMultiple Choice
350-401 Practice Question: Is troubleshooting an EtherChannel between two…
A network engineer is troubleshooting an EtherChannel between two Cisco switches. The show etherchannel 1 port-channel command shows the port-channel is up, but traffic is not load-balanced evenly. The engineer notices that all traffic is using only one link. The physical ports are all configured identically. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the misconception that any load-balancing method will automatically distribute traffic evenly, but the trap here is that the hash algorithm's output depends on the diversity of the hashed fields—if those fields are identical for all traffic, only one link is used regardless of the method.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The load-balancing method is set to src-dst-ip, and all traffic is between the same two IP addresses.
When the load-balancing method is set to src-dst-ip, the hash is computed from the source and destination IP addresses. If all traffic flows between the same two IP addresses, the hash result will always be identical, causing all frames to be forwarded over the same physical link. This explains why the port-channel is up but only one link carries all traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The load-balancing method is set to src-mac, and the traffic is from multiple MAC addresses.
Why it's wrong here
With the src-mac load-balancing algorithm, the EtherChannel hash is computed solely from the source MAC address. If traffic originates from multiple distinct MAC addresses, those frames produce different hash values and are distributed across different member links, not all on one link. Therefore, this scenario cannot explain why all traffic is traversing a single port.
- ✓
The load-balancing method is set to src-dst-ip, and all traffic is between the same two IP addresses.
Why this is correct
The src-dst-ip method hashes both the source and destination IP addresses together to select an egress link. When every packet between two IP endpoints is going between the same pair, the hash output is identical for each packet, so the deterministic hash always maps to the same member port. This is exactly the condition that forces all traffic onto a single link, even if multiple flows exist between those IPs.
- ✗
The physical ports have different speeds.
Why it's wrong here
If member ports operated at different speeds, the EtherChannel would not form correctly; Cisco switches require all ports in a channel to have matching speed and duplex settings. Ports with mismatched speeds would be excluded from the bundle or the channel would fail, rather than the channel staying up and simply sending all traffic on the fastest port. Since the port-channel is operational, speed mismatch is not the underlying cause.
- ✗
The port-channel is configured with 'lacp fast-switchover'.
Why it's wrong here
The 'lacp fast-switchover' feature reduces the time needed to move traffic to a hot-standby port when an active port fails; it does not alter the load-balancing hash or influence how traffic is initially distributed across links. It is a failover optimization for LACP EtherChannels, not a mechanism that changes steady-state forwarding behavior. Hence, it cannot be responsible for single-link congestion.
Go deeper
Related to this question
About these practice questions
One of 1,923 original 350-401 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.