show etherchannel port can display detailed information on the local configuration and information from the packets received. This in some cases can provide too much information and slow down the network administrators troubleshooting efforts. Commands exist to be more specific in troubleshooting efforts.
show lacp neighbor with the optional suffix
detail provides additional information about the LACP neighbour and includes their system ID, priority, and whether it is using fast or slow LACP packets.
The system identifier is used to ensure that all member links connect to the same remote device, and not split between different devices. The local system ID can be viewed with the command
show lacp system-id.
show pagp neighbor will display information regarding the PAgP neighbour and includes the system ID, remote port number, and if it is using fast or slow PAgP packet intervals.
Verifying Etherchannel Packets
An additional helpful tool in troubleshooting the establishment of etherchannels is checking the LACP or PAgP packets that are transmitted across the links.
LACP counters can be viewed with the command
show lacp counters. The output will include a list of Etherchannel interfaces, their member interfaces, and counters for LACP packets that are sent or received plus any errors.
A working LACP link should see the counters increase over an interval of time, with no increments in counters indicating towards a possible issue.
PAgP counters can be viewed with the command
show pagp counters. Similar to LACP, it will show Etherchannel interfaces, their member interfaces and counters for PAgP packets sent or received.