Debugging EtherChannel

The basic debug command options for EtherChannel are listed here. As always with the debug command in a Cisco network, you can use specific options if you have an idea about where the issues are or can enable all of the debug options for the component — if doing so does not generate too much information.

Switch2> enable
Switch2#debug etherchannel ?
  all       All debugging
  detail    Step below all
  error     Displaying error messages
  event     Major events
  idb       Agport idb related events
  linecard  SCP messages to linecard
  <cr>
Switch2> enable
Switch2#debug pagp ?
  all     PAgP all debugging
  event   PAgP events
  fsm     PAgP Finite State Machine
  misc    PAgP Miscellaneous
  packet  PAgP activity
  <cr>
Switch2> enable
Switch2#debug lacp ?
  all     LACP all debugging
  event   LACP events
  fsm     LACP Finite State Machine
  misc    LACP Miscellaneous
  packet  LACP activity
  <cr>

In this case, both the EtherChannel and PAgP debug commands are enabled, but not LACP because you do not expect to see any LACP information on the network. Previously in this chapter, only PAgP was enabled, so if you see LACP data, something is seriously wrong.

In the production network, where someone else may be configuring the remote end of the connection, it may not hurt to turn on the LACP option as well. Notice in the output that the interface is brought up.

Switch2> enable
Switch2# debug EtherChannel
Switch2# debug PAgP
3d01h: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
3d01h: FEC: pagp_switch_agc_compatable: comparing GC values of Fa0/1 Po5 flag = 1 1
3d01h: FEC: pagp_switch_port_attrib_diff: Fa0/1 Po5 same
3d01h: FEC: pagp_switch_agc_compatable: GC values are compatable
3d01h: PAgP - Fa0/1 failed - not my device_id. 0000.0000.0000 0006.d6ac.46c0
3d01h: FEC: add port (Fa0/1) to agport (Po5)
3d01h: FEC: pagp_switch_add_port_to_agport_internal: msg to PM to bundle port Fa0/1 with Po5
3d01h: FEC: pagp_switch_want_to_bundle: Bndl msg to PM for port Fa0/1 to Agport Po5
3d01h: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
3d01h: %LINK-3-UPDOWN: Interface Port-channel5, changed state to up
3d01h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel5, changed state to up

dummies

Source:http://www.dummies.com/how-to/content/debugging-etherchannel.html