EtherChannel Confusion

[PrimeYeti]

Does a switch only check the switch at the other end of the EtherChannel to ensure it has the correct settings (Speed, Duplex, Trunk/Access etc.) when the EtherChannel is first enabled? Or does it check everytime a new interface is added to the EtherChannel by the other switch? I know it checks each new port added to its own side.

Also does anyone know if there is a Packet Tracer limitation which means that Speed and Duplex don't have to match at each end or even on the same switch for that matter? Because I've had two interfaces added into a portchannel that were different speeds and duplex without an issue on PT.

[Martin L · Accepted solution]

Yes, it;s likely Packet Tracer limitation since PT is just a software simulator based on IOS. Long time ago we had discussion about EtherChannel on CLN; not sure if I can find link; search https://learningnetwork.cisco.com/s/discussions

PAgP or LACP dynamic EtherChannel protocols will check for new link compatibility or link failure and perform action; I think those run every 30 seconds. If u set up EtherChannel manually; then u must change (add/remove) config manually.

Yes, Speed, Duplex, Trunk/Access, plus VLans and some STP characteristics. Note that LACP does not support half-duplex ports. Maybe this is why u see discrepancy in your PT lab. Also, Speed mismatch will bring link down but not duplex;

Some good info on switch is at https://www.cisco.com/c/en/us/support/docs/switches/catalyst-4500-series-switches/13414-103.html

Regards, ML
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