Recommended EtherChannel Load-Balancing Mode for Cisco WLCs?
What is the recommended switch load-balancing mode for Cisco WLCs?
Community Insight
The question tests which EtherChannel load-balancing hash the switch should use on WLC-facing ports, and the trap is assuming Layer 2 devices must hash only MAC addresses instead of recognizing that modern switches routinely hash Layer 3 fields.
When a Cisco Wireless LAN Controller connects to a switch through an EtherChannel/LAG, the switch must choose a hash mode to spread frames across the bundled links. Cisco's WLC configuration best-practices guidance identifies source-destination IP address as the typically recommended load-balancing option, making A the correct choice.
Option D (source-destination MAC address) is the most common wrong pick, because learners reason that a switch 'only works at Layer 2' and therefore cannot inspect IP headers — but Catalyst switches do support and commonly recommend src-dst-ip hashing on controller links.
Community Discussion (10 comments)
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Expert Analysis
Why the Answer Is Correct
Cisco's Wireless LAN Controller Configuration Best Practices note lists "source-destination IP" as the typically recommended option for switch-side EtherChannel load balancing toward WLCs. Hashing on both source and destination IP spreads the many distinct client-to-controller flows across all bundle members, because each client typically has its own IP while the controller keeps a stable IP, producing a well-distributed hash. This keeps all frames of a given flow on one link, preserving order for tunneled controller traffic while still balancing aggregate load. Options such as source-destination IP are supported precisely because Catalyst switches can parse Layer 3 headers in hardware, so the premise that a switch cannot read IP addresses is incorrect.Why the Other Options Are Wrong
Option D (source-destination MAC address) hashes on client and controller MAC addresses; since a WLC is typically reached through one or a small number of MAC identities, the resulting hash distribution is far less even than IP-based hashing across many clients, which is why it is not the recommended default. Option B (destination IP only) and option C (destination MAC only) each look at a single field, so all traffic headed to the controller's one address funnels into a subset of links, defeating the purpose of the bundle. Neither single-field mode accounts for the many client-side sources, so utilization stays uneven. Option C also ignores Layer 3 diversity entirely.Community Comment Notes
Commenters were split, but the strongest evidence points to A: dropspablo quoted the official best-practices text naming "source-destination IP" as "the typically recommended option," and Tompoo concurred that "Cisco recommends source-destination IP (src-dst-ip)" because the switch makes the hashing decision. shaney67 and JulesAZ argued for D or a situational answer, and matass_md admitted getting "them mixed" before switching positions, illustrating the classic Layer 2 hashing misconception. mageknight's top-voted comment also confirms source-destination IP, noting it keeps all traffic for a specific client-WLC pair on the same physical link.Official Reference
Exam Strategy
On CCNA EtherChannel questions, remember that Catalyst switches offer src-dst-ip, src-ip, dst-ip, src-dst-mac and similar modes, and that Cisco recommends src-dst-ip for WLC and server-facing bundles. If an option offers both source and destination of a richer header field, it usually beats a single-field or MAC-only mode.
Frequently Asked Questions
Why isn't source-destination MAC the right choice if switches work at Layer 2?
Catalyst switches can hash Layer 3 fields in hardware, and Cisco's WLC best-practices note recommends source-destination IP for more even distribution across many clients.
Does load-balancing mode affect traffic order on a WLC EtherChannel?
Hashing on source-destination IP keeps each client-to-controller flow on one link, preserving frame order while balancing aggregate traffic across the bundle.
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