Ccna 00-301, Volume Official

Example 10-6

  Local Interfaces Fail in EtherChannel Because of Mismatched STP Cost

*Mar 1 23:18:56.132: %PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on

 Po1, putting Gi0/1 in err-disable state

*Mar 1 23:18:56.132: %PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on

 Po1, putting Gi0/2 in err-disable state

*Mar 1 23:18:56.132: %PM-4-ERR_DISABLE: channel-misconfig (STP) error detected on Po1, 

putting Po1 in err-disable state

*Mar 1 23:18:58.120: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to  

  down

*Mar 1 23:18:58.137: %LINK-3-UPDOWN: Interface Port-channel1, changed state to down

*Mar 1 23:18:58.137: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to  

  down

SW1# show etherchannel summary

Flags:  D - down        P - bundled in port-channel

        I - stand-alone s - suspended

        H - Hot-standby (LACP only)

        R - Layer3      S - Layer2

        U - in use      N - not in use, no aggregation

        f - failed to allocate aggregator

        M - not in use, minimum links not met

        m - not in use, port not aggregated due to minimum links not met

        u - unsuitable for bundling

        w - waiting to be aggregated

Technet24

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10

Chapter 10: RSTP and EtherChannel Configuration    253

        d - default port

        A - formed by Auto LAG

Number of channel-groups in use: 1

Number of aggregators: 1

Group  Port-channel  Protocol    Ports

------+-------------+-----------+-----------------------------------------------

1      Po1(SD)          -        Gi0/1(D) Gi0/2(D)

The messages at the top of the example specifically state what the switch does when 

determining whether the interface settings match. In this case, SW1 detects the different 

STP costs. SW1 does not use G0/1, does not use G0/2, and even places them into an err-

disabled state. The switch also puts the PortChannel into err-disabled state. As a result, the 

PortChannel is not operational, and the physical interfaces are also not operational.

To solve this problem, you must reconfigure the physical interfaces to use the same STP 

settings. In addition, the PortChannel and physical interfaces must be shutdown, and then