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EtherChannel will not bundle — ports stay independent

QuestionSwitching@admin1 min read

EtherChannel will not bundle — ports stay independent

Three links between two switches, configured as an LACP channel on both sides. The port-channel interface exists but never comes up:

SW1# show etherchannel summary
Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------
1      Po1(SD)       LACP        Gi0/1(I) Gi0/2(I) Gi0/3(D)

Two ports are (I) and one is (D).

etherchannellacpswitchingccnp

1 answer

@admin · 2026-10-09

The flags are the answer. (I) means independent — the port is up but is not in the bundle — and (D) means down.

For a port to join, every one of these must match on both ends and across all member ports:

  • speed and duplex
  • switchport mode (all access, or all trunk)
  • the allowed VLAN list and the native VLAN, if they are trunks
  • the access VLAN, if they are access ports
  • spanning-tree cost and port priority

Check them side by side rather than one at a time:

SW1# show interfaces Gi0/1 switchport | include Mode|Native|Trunking VLANs
SW1# show interfaces Gi0/2 switchport | include Mode|Native|Trunking VLANs

A single mismatched allowed-VLAN list on one member is enough to leave it (I) while the others bundle.

The (D) port is a separate problem — that one is physically down or administratively shut, so start with show interfaces Gi0/3 and work up from layer one.

One more thing worth checking: LACP mode. active/active and active/passive both work; passive/passive never does, because neither end starts the negotiation. And if one side is running PAgP (desirable) and the other LACP (active), they will never form — the protocols do not interoperate.

Can you answer this?

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