Modifying EtherChannels

October 15, 2025 - Reading time: 4 minutes

In the previous lesson, we focused on the fundamentals of EtherChannel by bundling multiple interfaces using LACP in active mode. In this lesson, we will build on that foundation by adding an additional interface to our existing EtherChannel and converting the LACP configuration to static “on.” These two tasks will help you deepen your understanding of EtherChannel’s flexibility. By following along, you will see how to expand and adapt a port-channel configuration to suit different requirements.

Lab Topology Assumption

• Two Cisco switches: Switch1 and Switch2
• Existing EtherChannel group (Group 1) with two interfaces already bundled (Fa0/1, Fa0/2).
• We will add Fa0/3 to the same group and then convert the LACP configuration to static “on.”

1. Additional Interface to the Existing EtherChannel

Switch1

Switch1> enable
Switch1# configure terminal
Switch1(config)# interface FastEthernet0/3
Switch1(config-if)# switchport mode trunk
Switch1(config-if)# channel-group 1 mode active
Switch1(config-if)# no shutdown
Switch1(config-if)# end

• This adds FastEthernet0/3 to the same EtherChannel group (1), in active LACP mode.

Switch2

Switch2> enable
Switch2# configure terminal
Switch2(config)# interface FastEthernet0/3
Switch2(config-if)# switchport mode trunk
Switch2(config-if)# channel-group 1 mode active
Switch2(config-if)# no shutdown
Switch2(config-if)# end

• Matches the configuration on Switch2, ensuring that the same group number and mode are used.

Expected Outcome:

• Port-channel1 now has three interfaces bundled on each switch (Fa0/1, Fa0/2, Fa0/3).

2. Converting LACP to Static “on” Mode

In some scenarios, you may wish to disable negotiation and force the EtherChannel to form unconditionally. We will remove the current LACP config and set it to on.

Switch1

Switch1# configure terminal
Switch1(config)# interface range FastEthernet0/1 - 3
Switch1(config-if-range)# no channel-group 1
Switch1(config-if-range)# channel-group 1 mode on
Switch1(config-if-range)# end

• First, remove the old channel-group statement to clear LACP references, then reapply it using mode on.

Switch2

Switch2# configure terminal
Switch2(config)# interface range FastEthernet0/1 - 3
Switch2(config-if-range)# no channel-group 1
Switch2(config-if-range)# channel-group 1 mode on
Switch2(config-if-range)# end

• Ensures both sides are using the same static configuration.

Expected Outcome:

• The EtherChannel forms without LACP negotiation, displaying (S) (Layer2) and (U) (in use) in the summary.

Verification Commands

Below are key verification commands with typical explanations and example console outputs:

1. show etherchannel summary

   • Explanation: Displays a summary of your EtherChannel groups, their mode, and member interfaces.
   • Example Output:
     Switch1# show etherchannel summary
     Flags:  D - down        P - in port-channel
             I - stand-alone s - suspended
             R - Layer3      S - Layer2
             U - in use      f - failed to allocate aggregator
     
     Group  Port-channel  Protocol    Ports
     ------+------------+-----------+-----------------------
     1      Po1(SU)        -         Fa0/1(P) Fa0/2(P) Fa0/3(P)
     

     The “Protocol” field is blank/dash (-) when in static on mode.

2. show interfaces port-channel 1

   • Explanation: Verifies the status and member interfaces of the Port-Channel.
   • Example Output:
     Switch1# show interfaces port-channel 1
     Port-channel1 is up, line protocol is up
     Hardware is EtherChannel, address is 0001.6432.ab00 (bia 0001.6432.ab00)
     MTU 1500 bytes, BW 3000000 Kbit/sec, DLY 10 usec
     Full-duplex, 1000Mb/s
     Members in this channel: Fa0/1, Fa0/2, Fa0/3
     

3. show run interface port-channel1

   • Explanation: Confirms the port-channel’s configuration.
   • Example Output:
     Switch1# show run interface port-channel1
     Building configuration...
     
     Current configuration : 46 bytes
     interface Port-channel1
      switchport mode trunk
     end
     

Common Mistakes

1. Not Clearing Old Channel-Group Config Before Changing Mode

   • Symptom: Ports retain the previous mode or fail to join the channel after a mode change.

   • Solution: Remove the existing channel-group statement before reapplying with the new mode.

2. Mode/Protocol Mismatch

   • Symptom: Bundle doesn’t form; ports remain in stand-alone or suspended state.

   • Solution: Match the mode type between switches (mode on↔mode on or matching LACP modes).

3. Interface Parameter Mismatches

   • Symptom: One or more member ports show as suspended in show etherchannel summary.

   • Causes:

     • Speed mismatch

     • Duplex mismatch

     • Switchport mode mismatch (access vs trunk)

     • VLAN mismatch (different access VLANs, or different trunk allowed VLAN lists)

     • Different native VLAN on trunk ports

     • STP setting mismatches (portfast, cost, priority, BPDU guard/filter)

     • Layer type mismatch (one side Layer 2, other Layer 3)

   • Solution: Match all Layer 1 and Layer 2 parameters on both sides of each member port before bundling.

User Challenge

1. Configure a Second EtherChannel Group

   • Task: On the same switches, create a new port-channel (Group 2) for different interfaces, then verify both port-channels operate independently.
     
     

2. Simulate a VLAN Mismatch

   • Task: Change the allowed VLANs on one member interface of the EtherChannel and check show etherchannel summary to see how the switch reacts.