Port channel inconsistency/Secondary Port channel group created with LACP channel protocol


Thu, 06/03/2010 - 02:03
Jun 2nd, 2010
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Issue Description: Creation of a Secondary portchannel "PortChannel 1 and 1A" with LACP channel protocol

Switch#sh etherchannel 1 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, no aggregation due to minimum links not met

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

        u - unsuitable for bundling

        d - default port

        w - waiting to be aggregated

Number of channel-groups in use: 1

Number of aggregators:           2

Group  Port-channel  Protocol    Ports


1      Po1(SU)         LACP      Gi2/1(P)      

1      Po1A(SU)        LACP      Gi5/2(P)      

Last applied Hash Distribution Algorithm: Fixed


Probable causes which trigger such issues with LACP port channels:

1. Adding a new port to an existing port channel. If any configuration mismatch is seen on the newly added port, it will be added to Secondary port-channel as you can see (Here, Po1A)

2. Configuration mismatch on the ports bundled in the port channel.

3. Configuration mismatch on the interfaces of the far end device can also create inconsistency between the ports bundled in the port channel.

'mls qos channel-consistency' is one of the reason which will  put the port in to secondary port-channel.

The first step to resolve this issue is to look for the command "mls qos channel-consistency" in the interface configuration or to recreate the port channel following the best practices mentioned below

The best practices in resolving port channel issues are:

1.         Manually shut the bundled interfaces and the port channel interface down on both the end.

2.         Then reset the interface configuration to default.

3.         Reconfigure the interfaces to be bundled and assign them to the port channel.

4.         Verify the configuration of the interfaces.

5.         Bring up the interfaces after the configuration has been verified.

This is a known and an expected behavior with LACP. If LACP is not a mandatory requirement, you may recreate the port channel with the channel mode "ON".



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