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Core issue

An EtherChannel misconfiguration results in a spanning tree loop, which causes the port status to become errdisable.


The port status may become errdisable because of an EtherChannel misconfiguration.

The errdisable status indicates that the port was automatically disabled by the switch operating system software because of an error condition encountered on the port.

To determine if a port is in errdisable status, issue the show port command. For example, to check the status on port 3/2, issue the show port 3/2 command.

This is a sample:

Cat5500> (enable) show port 3/2
Port  Name               Status     Vlan       Level  Duplex Speed Type
----- ------------------ ---------- ---------- ------ ------ ----- ------------
3/2                      errdisable 1          normal   auto  auto 10/100BaseTX

The switch will send a message to the console describing why the port was disabled when it puts a port in the errdisable state. If syslog is configured, the message will be available on the syslog server as well.

Another way to determine the reason for the errdisable status is to issue the show errdisable-timeout command. This command is available in CatOS 5.4(1) or later. Sample command output is below.

Cat5500> (enable) show errdisable-timeout
ErrDisable Reason   Timeout Status
------------------- --------------
bpdu-guard          disable
channel-misconfig   enable
duplex-mismatch     disable
udld                disable
other               disable

Interval: 30 seconds

Port    ErrDisable Reason
----    -----------------
3/2     channel-misconfig
3/3     channel-misconfig

If EtherChannel is misconfigured between two switches, ports may become errdisable.

Check the EtherChannel configuration on both switches. If one side is configured for EtherChannel in the On mode, the peer ports must also be in On mode or they will go to errdisable.

The On mode of EtherChannel does not send Port Aggregation Protocol (PAgP) packets to negotiate with the other side before channeling. It assumes the other side is channeling. If the other side is not channeling, the Spanning-Tree Protocol (STP) detects a loop and places the channeling ports into errdisable status.

These are valid settings for Etherchannel to work properly:

  • on-on
  • desirable-desirable
  • desirable-auto
  • If both sides are set to auto the channel will not come up.    
  • Verify that all ports in the channel have the same speed and duplex settings

For additional information regarding EtherChannel configuration, refer to EtherChannel Configuration Guidelines and Restrictions.

Once the cause of the errdisable status is found and corrected, re-enable the port by issuing the set port enable command.

For example, to re-enable ports 3/2-3, issue the set port enable 3/2-3 command. If the set port enable command is issued without the cause of the errdisable status being corrected, the port eventually goes back to the errdisable status.

For more information on the errdisable port status, refer to Recovering From errDisable Port State on the CatOS Platforms.

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