Friday, May 6, 2011

Fun with Port-Channels

This week I did what I've done hundreds of times before.  I configured a new port-channel on a Cisco switch for a server.  In doing so I ended up with two new scenarios that I had never seen before.

The first issue was more of a head scratcher than a production problem, but nonetheless it caused me to stop and wonder why.

PAHA-1A-6509E-SW1#show etherchannel 403 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: 34
Number of aggregators:           35

Group  Port-channel  Protocol    Ports
403    Po403(SD)       LACP
403    Po403A(SU)      LACP      Gi1/3/45(P)    Gi1/4/14(P)    Gi2/3/45(P)

Last applied Hash Distribution Algorithm: Fixed
Obviously it's not exactly normal to see a port-channel identifier listed twice with one of them having an alphabetic character on the end.  Digging around on the Internet I finally found a document on Cisco's support community that explained the issue. What I had done was create the port-channel with Gi1/3/45 and Gi2/3/45.  Later when the server guys had asked me to add Gi1/4/14 I added it to the port-channel before making the configuration identical.  The document's resolution of shutting down the ports and defaulting the configurations and then recreating them did remove the crazy A from my show commands.

My second issue was that a server connected to a port-channel was disabling one of the NICs saying that it was faulted.  Again defaulting the configurations and recreating the port-channel cleared up that issue.  

The moral of my story is that even though your configuration may be 100% correct, you may have confused IOS so try starting over.

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