A switch shows the following partial 'show etherchannel summary' output for Port-channel1 using LACP: Po1(SU) LACP Gi0/1(P) Gi0/2(P) Gi0/3(D) Gi0/1 and Gi0/2 are actively passing traffic in the bundle, but Gi0/3 shows flag 'D' and is not forwarding as part of the channel. What most likely explains Gi0/3's status?
- AGi0/3 has a mismatched configuration (such as LACP mode, speed, or duplex) preventing it from bundling
- BGi0/3 is administratively shut down with 'shutdown' configured
- CGi0/3 has no physical cable connected to it
- DGi0/3 is operating as the standby link for the port-channel
Show answer & explanationAnswer & explanation
Correct answer: A. Gi0/3 has a mismatched configuration (such as LACP mode, speed, or duplex) preventing it from bundling
The 'D' flag in 'show etherchannel summary' indicates the port is down/not bundled into the channel, commonly due to a configuration mismatch (LACP mode, allowed VLANs, trunk encapsulation, speed/duplex) that prevents LACP from successfully forming the bundle on that link, even though the interface itself may be up. A shut-down or disconnected port typically would not even appear listed as part of the group with a link-layer status.
Why the other options are wrong
- B. An administratively shut interface usually would not be listed as an active channel member candidate this way.
- C. A fully disconnected port would usually show as link-down rather than simply failing to bundle with flag D.
- D. LACP standby/hot-standby links are shown with an 's' flag in some platforms, not simply D, and this isn't typical PAgP-style standby behavior.
EtherChannel Summary Flags
The 'show etherchannel summary' command uses letter flags to indicate the state of each port-channel and its member interfaces.
- P = bundled in port-channel
- D = down, not bundled
- S/U in Po flags = Layer2/in-use
- Common causes of D: mismatched mode, speed/duplex, trunk settings
Memory trick: P for Party (bundled), D for Ditched (not bundled).