Lab Objective
Bundle two physical links between two switches into a single EtherChannel using static mode, then reconfigure the same bundle using PAgP, then LACP, verifying successful formation each time, and finally observe what happens when the two sides use mismatched modes.
Lab Purpose
EtherChannel combines multiple physical links into one logical interface, providing both aggregated bandwidth and Spanning Tree-transparent failover. Knowing all three formation methods — and recognizing a mode mismatch quickly — is essential, since the wrong combination silently prevents a bundle from forming.
Lab Topology
Switch1 ---- Gi1/0/1, Gi1/0/2 ---- Switch2
Two physical links to be bundled into
Port-channel 1Task 1: Configure a Static EtherChannel
Bundle Gi1/0/1 and Gi1/0/2 into Port-channel 1 using static (unconditional) mode on both switches.
Task 2: Verify the Static Bundle
Confirm both member ports show as bundled (P) in the channel group.
Task 3: Reconfigure Using PAgP
Remove the static configuration and reconfigure using PAgP with desirable mode on both switches.
Task 4: Reconfigure Using LACP
Remove the PAgP configuration and reconfigure using LACP with active mode on both switches.
Task 5: Introduce a Mode Mismatch
Set Switch1 to LACP active while leaving Switch2 on PAgP desirable, and observe the resulting failure.
Solution and Verification
Switch1(config)# interface range gigabitethernet1/0/1-2
Switch1(config-if-range)# channel-group 1 mode on
Switch2(config)# interface range gigabitethernet1/0/1-2
Switch2(config-if-range)# channel-group 1 mode onSwitch1# show etherchannel summary
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------
1 Po1(SU) - Gi1/0/1(P) Gi1/0/2(P)
-- "-" for protocol confirms static mode
-- (no negotiation protocol used), and (P)
-- confirms both ports are bundled and activeSwitch1(config)# interface range gigabitethernet1/0/1-2
Switch1(config-if-range)# no channel-group 1 mode on
Switch1(config-if-range)# channel-group 1 mode desirable
Switch2(config)# interface range gigabitethernet1/0/1-2
Switch2(config-if-range)# no channel-group 1 mode on
Switch2(config-if-range)# channel-group 1 mode desirable
Switch1# show etherchannel summary
Group Port-channel Protocol Ports
1 Po1(SU) PAgP Gi1/0/1(P) Gi1/0/2(P)Switch1(config)# interface range gigabitethernet1/0/1-2
Switch1(config-if-range)# no channel-group 1 mode desirable
Switch1(config-if-range)# channel-group 1 mode active
Switch2(config)# interface range gigabitethernet1/0/1-2
Switch2(config-if-range)# no channel-group 1 mode desirable
Switch2(config-if-range)# channel-group 1 mode active
Switch1# show etherchannel summary
Group Port-channel Protocol Ports
1 Po1(SU) LACP Gi1/0/1(P) Gi1/0/2(P)Switch2(config)# interface range gigabitethernet1/0/1-2
Switch2(config-if-range)# no channel-group 1 mode active
Switch2(config-if-range)# channel-group 1 mode desirable
Switch1# show etherchannel summary
Group Port-channel Protocol Ports
1 Po1(SD) LACP Gi1/0/1(I) Gi1/0/2(I)
-- (I) means "individual" -- the ports failed
-- to bundle, since LACP active and PAgP
-- desirable are incompatible negotiation
-- protocols that cannot form a channel togetherKey Takeaway
The show etherchannel summary output's port flag is the fastest diagnostic check: (P) confirms a port successfully bundled, while (I) confirms it remains individual — almost always caused by a mode or protocol mismatch between the two switches, exactly as demonstrated when mixing LACP and PAgP.