EtherChannel: LACP Mode Mismatch
EtherChannel gives a campus both bandwidth and redundancy, but its member links form a bundle only when both ends agree on the negotiation method. This lab teaches the small set of commands that separates a physical-link issue from an LACP configuration mismatch.
The problem
SW1 and SW2 are connected by two healthy trunk links. The intended LACP port channel never forms, leaving both links as separate interfaces and causing STP to block one of them.
What you'll practice
- Read EtherChannel summary flags
- Compare LACP mode and channel-group settings on both switches
- Recognize active/passive negotiation requirements
- Repair a port-channel configuration without creating a loop
- Verify both links are bundled
The topology
Two access switches connect over two parallel 802.1Q trunk links carrying user VLANs. The topology is intentionally minimal so the port-channel state is the evidence, not a hidden routing dependency.
Commands to run yourself
The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.
show etherchannel summaryshow lacp neighborshow interfaces trunkTopology diagram
Frequently asked
Must both LACP sides use active mode?
No. At least one side must be active; active/passive forms an LACP bundle, while passive/passive does not initiate negotiation.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.