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User cannot form an EtherChannel port bundle due to misconfiguration or port capability

Core issue

A misconfiguration results in the inability to create an EtherChannel bundle.

Resolution

In Catalyst OS (CatOS), issue the show port capabilities [mod [port]] command to verify that the port supports EtherChannel .

This is a sample command output:


cat5k> (enable) sh port cap 4/1

Model                          WS-X5234

Port                           4/1

Type                           10/100BaseTX

Speed                          auto,10,100

Duplex                         half,full

Trunk encap type               802.1Q,ISL

Trunk mode                     on,off,desirable,auto,nonegotiate

Channel                        4/1-2,4/1-4

Issue the show port, show port channel, or show trunk commands to check the configuration.

Verify that all the ports in the bundle belong to the same VLAN or are all trunk ports.

Verify that the same trunk mode, encapsulation, and allowed VLAN list are on all ports in the bundle.

Verify that all ports in the bundle have the same speed and duplex settings.

Verify the port channel mode on both ends of the link. Only ports in desirable and auto mode negotiate a channel. Valid settings are desirable-auto or desirable-desirable. The auto-auto setting does not negotiate a channel.

Ports in on mode only form a functional channel with other ports in on mode. They do not negotiate a channel with ports in desirable or auto mode.

On certain Catalyst 5000 family modules (WS-X5201 and WS-X5203), you cannot form an EtherChannel with the last two ports in a port group unless the first two ports in the group already form an EtherChannel. For example, if you create separate EtherChannels with only two ports in a channel, you cannot assign ports 3-4 to a channel until you have first configured ports 1-2 to a channel (or 7-8 until first done for ports 5-6; 11-12 until done for ports 9-10). This is an exception and only for the Catalyst 5000 family.

For guidelines to avoid EtherChannel Configuration problems, refer the EtherChannel Configuration Guidelines and Restrictions section of the document Configuring Fast EtherChannel and Gigabit EtherChannel.

For more information on EtherChannel configuration on Catalyst switches running CatOS, refer to Configuring EtherChannel section of the document Configuring Fast EtherChannel and Gigabit EtherChannel.

To Configure EtherChannel on Catalyst switches running Cisco IOS Software, refer the document Configuring Layer 3 and Layer 2 EtherChannel.

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