EtherChannel: Two Passive Ends and a Bundle That Never Forms
A bundle with matching channel-group numbers and up links that never forms, because both ends are passive. Diagnose it and fix it yourself, live, right below.
Symptom
Two switches have matching channel-group numbers and physical links that are up, yet the EtherChannel stays down. Both ends are passive, so neither one starts LACP negotiation.
Your mission
Prove the cause, then fix it
Format
Guided CLI investigation
Investigate before you configure.
Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.
Observe the symptom and link state.
Diagnose by comparing the protocol evidence.
Verify the expected device state and confirm the original symptom is resolved.
Console access: SW1 · SW2
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Lab debrief
Turn the session into a repeatable troubleshooting pattern.
Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.
The problem
SW1 and SW2 are connected by Gi0/1 and Gi0/2. Both links are physically up, both sides use channel-group 1, and the intended Po1 is Layer 2 with LACP. The bundle is not forwarding because every member interface is configured with channel-group 1 mode passive.
What you'll practice
- Read the full EtherChannel summary and distinguish Po1(SD) from healthy Po1(SU)
- Use port-channel, LACP neighbor, trunk, and member configuration output to isolate the fault
- Explain why two passive LACP ends exchange no useful packets
- Make both members on one side active and verify both links bundle
1. Physical up is not bundled
show interfaces GigabitEthernet0/1 would report the member as up, line protocol is up. That proves the cable and link state, not EtherChannel membership. The summary output is where the D and P member flags tell you whether the links actually joined Po1.
2. Passive needs an active peer
LACP passive listens for LACP packets but does not initiate them. With passive on both ends of each member link, there are no partner rows in show lacp neighbor and Po1 remains Ag-Not-In-Use. One active end is enough for the pair to negotiate.
3. A bundle needs every intended member
Changing only Gi0/1 creates a partial bundle while Gi0/2 remains passive. The simulator calls out the remaining passive member, so you can see why the final fix must be applied to both members on the active side.
The topology
SW1 and SW2 are linked by two parallel Layer 2 members: Gi0/1 and Gi0/2. Each member uses channel-group 1, the logical bundle is Port-channel1, the protocol is LACP, and the intended trunk allows VLANs 1-4094.
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
Why are the links up if the EtherChannel is down?
Physical link state and EtherChannel membership are different things. The adapter reports both member interfaces as up, line protocol is up, but show etherchannel summary reports Po1(SD) with Gi0/1(D) and Gi0/2(D). The D flags show that neither link is bundled into the port-channel.
Why does passive plus passive never form an LACP bundle?
Passive waits for LACP packets from the peer. Since both ends wait, no LACP packets are exchanged, show lacp neighbor prints no useful partner rows, and the port-channel remains Ag-Not-In-Use. Active plus passive and active plus active both provide an initiator and can form the bundle.
Why not use channel-group 1 mode on to force it?
mode on creates a static EtherChannel and does not send LACP packets. The simulator keeps the bundle down when one side is static and the other side is passive LACP, so use channel-group 1 mode active on both members of one side instead.
Ready to run this lab yourself?
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