Etherchannel – suspended port state

I’ve seen a few suspended ports in etherchannels lately. Not everyone is familiar with this port status. So let’s take a minute to talk about this:

There is one important rule when configuring etherchannels: All interfaces in the etherchannel need the same speed and duplex settings, trunking encapsulation (dot1q/isl) or the same access VLAN in case of an access port, same STP cost and last but not least: no etherchannel port can be configured in a monitor session (SPAN port).

When the switchports in a etherchannel meet all the requirements, the output of a “sh etherchannel summ” looks like:

Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
62     Po62(SU)         -        Gi2/5(P)    Gi2/6(P)

All switchports in the etherchannel (Gi2/5 and Gi2/6) do have a ‘P’ flag which means: life is good :)

In case of some port mismatch, lets say: encapsulation mismatch, the output of “sh etherchannel summ” will look like:

Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
62     Po62(SU)         -        Gi2/5(P)    Gi2/6(s)

You will also get a syslog message:

EC-5-CANNOT_BUNDLE2: Gi2/5 is not compatible with Gi2/6 and will be suspended (trunk encap of Gi2/5 is dot1q, Gi2/6 is isl)

The switchport Gi2/6 is flagged with a ‘s’. This ‘s’ shows us that there is a mismatch in some of the described requirements. When you check the “sh int status” output, the port state will be suspended:

Port      Name               Status       Vlan       Duplex  Speed Type
Gi2/6     Trunk              suspended    trunk        full   1000 1000BaseSX