Which load-balancing method is most commonly used by Cisco EtherChannel to distribute traffic across the bundled links?
Correct Answer: B
Detailed Explanation: EtherChannel is a technology that allows multiple physical Ethernet links to be bundled together to form a single logical link. This aggregation increases the available bandwidth between devices and provides redundancy. An essential component of EtherChannel is its ability to distribute traffic across all member links effectively—a process known as load balancing. Cisco switches implement load balancing using various algorithms that hash certain header fields of the packets to determine which physical link should carry the traffic. Although multiple methods exist, the most common load-balancing mechanism on modern Cisco switches is based on a hash of the source and destination IP addresses. How IP Address Hashing Works: Extraction of Fields: The switch extracts the source and destination IP addresses from each packet. Hash Calculation: These addresses are combined and run through a hash function. The result is then used to select one of the member links in the EtherChannel group. Even Distribution: This method ensures that traffic flows for different conversations (or sessions) are distributed across the available links. Because the hash is based on IP addresses, the algorithm generally results in a balanced distribution when many flows are present. Why IP Address Hashing is Preferred: Efficiency: IP address hashing is computationally efficient and works well in high-throughput environments. Deterministic: It produces consistent results for a given flow. This consistency is important for ensuring that packets belonging to the same conversation follow the same physical path, which is essential for proper reassembly and performance. Adaptability: Many Cisco switches allow administrators to adjust the load-balancing method based on the network environment, but the default method of using source and destination IP addresses is widely adopted due to its effectiveness in most scenarios. Other Options: Round Robin (Option A): Although round-robin is a simple method, it is not typically used for EtherChannel because it does not ensure that packets of the same flow follow the same path, potentially causing out-of-order delivery. Source MAC Address Hashing (Option C): This method might be used in some cases, but it is less common because it does not account for the destination of traffic. Random Distribution (Option D): A random approach would not provide the consistency needed for proper traffic distribution and could lead to unbalanced load on the member links. Practical Implications: Network administrators can view the load-balancing method on Cisco switches by checking documentation or using diagnostic commands. In environments with many concurrent flows, IP address hashing tends to result in a more even distribution of traffic, maximizing the throughput and reliability of the EtherChannel. Conclusion: The most commonly used load-balancing method for Cisco EtherChannel is based on source and destination IP address hashing (Option B). This method provides a reliable, deterministic, and efficient way to distribute traffic across bundled links, ensuring both increased bandwidth and redundancy in modern network designs.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.