EtherChannel Troubleshooting Capstone (L2 LACP)

Bundle lab

Advanced EtherChannel capstone, run as a fault hunt. The uplink bundle between two access switches is not passing traffic and the hosts either side cannot reach each other. Some members are up, the bundle is not, and nothing was recorded. You get symptoms and the required end state — no fault list. Both ends of a bundle have to agree about several things at once, and only one end was touched during the change — so comparing them is the exercise.

Learning objectives

• Diagnose an EtherChannel that will not form, from operational state alone
• Compare both ends of a bundle rather than assuming the local switch owns the fault
• Recognise a negotiation-mode mismatch (static on against LACP) as distinct from a member that is simply down
• Know that member ports and the port-channel must agree about switchport mode and VLAN
• Restore the bundle without resorting to configuring every port statically

Troubleshooting focus

• If a Port-channel remains down or members show suspended/individual, compare the channel-group number per member on the SAME device to ensure they join the same aggregator.
• Confirm both ends are using compatible EtherChannel modes: on/on (static), active/active or active/passive (LACP), desirable/desirable or desirable/auto (PAgP).
• Validate that each member’s switchport parameters are identical on its local device (mode access or trunk, VLAN or allowed list, speed/duplex) so the bundle can form.
• Check that the logical Port-channel interface has the intended Layer-2 settings and that the members inherit the same parameters.
• Use show etherchannel summary and show etherchannel 100 detail to correlate state flags, partner information, and reasons a member is not bundled.