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Catalyst switch running CatOS accepts EtherChannel configuration commands but does not form a channel

Core issue

EtherChannel configuration errors usually occur because of mismatched parameters on the ports involved. This includes different speeds, different duplexes, and different Spanning Tree Protocol (STP) port values. It is possible that no error message is displayed. This is because mismatched parameters can lead to a loop. To prevent major network issues, spanning tree automatically shuts down the link. Watch for these results when creating the channel to make sure it does what it is intended to do.

Resolution

To resolve mismatched port channel configurations, perform these steps:

  1. To ensure that the requirements to implement EtherChannel are met on your Catalyst switch, refer to System Requirements to Implement EtherChannel on Catalyst Switches.
  2. Ensure that the ports intended to be channeled do not have a status of errDisable in the output of the show port command.
  3. If channeling is manually set to the on mode, verify the status on both  the sides. Compare the output of the show port channel command on the two switches across the EtherChannels, as shown:

Switch A: 

Switch-A> (enable) show port channel
No ports channelling

Switch B:

Switch-B> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- -----------
2/1 connected on channel WS-C5505 066507453(SW 2/1
2/2 connected on channel WS-C5505 066507453(SW 2/2
2/3 connected on channel WS-C5505 066507453(SW 2/3
2/4 connected on channel WS-C5505 066507453(SW 2/4
----- ---------- --------- ----------- ------------

  • Try configuring the desirable mode on both sides to see if the ports form an EtherChannel.
  • Issue the show port command to verify that the ports in the EtherChannel belong to the same VLAN. If the ports are not on the same VLAN, change accordingly.

Switch A:

Switch-A> (enable) show port

Port Name Status Vlan Level Duplex Speed Type

----- ------------------ ---------- ----------

2/1 connected 1 normal a-full a-100 10/100BaseTX

2/2 connected 1 normal a-full a-100 10/100BaseTX

2/3 connected 1 normal a-full a-100 10/100BaseTX

2/4 connected 2 normal a-full a-100 10/100BaseTX

Switch B:

Switch-B> (enable) show port channel

No ports channeling

Switch-B> (enable) show port

Port Name Status Vlan Level Duplex Speed Type

----- ------------------ ---------- ----------

2/1 connected 1 normal a-full a-100 10/100BaseTX

2/2 connected 1 normal a-full a-100 10/100BaseTX

2/3 connected 1 normal a-full a-100 10/100BaseTX

2/4 connected 1 normal a-full a-100 10/100BaseTX

For more information, refer to EtherChannel Technical Support.

Show port status

Errdisable

Inactive

Disable

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